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Date 04" 30 " 0/

0-7 639

This is to certify that the

thesis entitled
Integrated Management Strategies

for Control of Apple Maggot
and Blueberry Maggot Flies
presented by

LUKASZ LECH STELINSKI

has been accepted towards fulfillment
of the requirements for

Master of Scieaégeein Entomology

  

Major professor

MS U is an Affirmative Action/Equal Opportunity Institution

  

 

 

 

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8/01 cJCIFiCIDateDuepes-p 15

 

INTEGRATED MANAGEMENT STRATEGIES FOR CONTROL OF APPLE
MAGGOT AND BLUEBERRY MAGGOT FLIES

By

Lukasz Lech Stelinski

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Entomology

2001

ABSTRACT

INTEGRATED MANAGEMENT STRATEGIES FOR CONTROL OF APPLE
MAGGOT AND BLUEBERRY MAGGOT F LIES

By

Lukasz Lech Stelinski

The apple maggot, Rhagoletis pomonella (Walsh), and the blueberry maggot,
Rhagoletis mendax Curran are the two most important late-season pests of apples and
blueberries, respectively. In an attempt to develop integrated management strategies for
control of these two key Rhagoletis species, insecticide-treated biodegradable spheres,
sphere deployment tactics, and synthetic host-volatile compounds were evaluated over
three field seasons in commercial apple orchards and blueberry plantings. Spheres treated
with imidacloprid killed significantly more apple maggot and blueberry maggot flies
compared to spheres treated with thiamethoxam, thiocloprid and untreated spheres. In
sphere deployment experiments, there were no significant differences in fruit injury
between the three tactics tested. Also, fruit injury in plots that received azinphos-methyl
spray applications did not differ significantly from plots containing insecticide-treated
spheres. In the host volatile studies, a mix blend of apple volatiles attracted significantly
more apple maggot flies than other lures and baits evaluated. In blueberries, ammonium
acetate was significantly more attractive to female blueberry maggot flies in both early-
and mid-season cultivars compared with other compounds. In addition, green sphere traps
baited with the synthetic fruit-volitiles, cis-3-hexen-1-ol and geraniol, captured
statistically equal numbers of blueberry maggot flies compared with ammonium-baited

traps when deployed within an early ripening blueberry cultivar (Earliblue).

ACKNOWLEDGEMENTS

I give my sincere thanks to my close friend and invaluable assistant Daniel
Young. With his insight, enthusiasm, and never ending quest for efficiency, Dan
contributed greatly to the realization of the various projects discussed within this thesis.
In addition to his expert technical assistance in both the laboratory and in the field, Dan
offered his sense of humor in times of distress, advice in times of perplexity, and
criticism always.

I give special thanks to Dr. John Wise, Janice Howard and the entire staff of the
Trevor Nichols Research Complex (TNRC) for their valuable assistance on this project.
Based on their vast knowledge and experience, John and Janice offered crucial advice
and also graciously provided me with materials and work space on virtually every
summer’s day I spent working in Fennville. I will always have fond memories of the
various experiences and adventures I encountered during the summers I spent working
and living on the TNRC.

I thank my fi‘iend and major professor, Dr. Oscar Liburd, for the teaching and
supervision he has offered me throughout the duration of my thesis work. Oscar’s close
guidance and ever present drive and inspiration allowed me to thrive and truly enjoy my
graduate research experience. By offering close attention, through his constant teaching
and criticism, in addition to providing me with autonomy, Oscar created a comfortable,
valuable, and challenging learning and work environment. I also thank my committee
members, Drs. Larry Gut, Jim Miller, and Randolph Beaudry for their direction, advice,

and helpful contributions during various crucial steps of this project.

iii

I recognize Ryan Vander Poppen, Lori Johnson, Brian Dixon, Chad Pastor, and
Kyle Coleman for technical assistance with experiments; thanks for “getting sticky with
me” and braving the ammonia fumes. I express my gratitude to Katherine Pettit, Erin
F inn, and Caitlin Clements for assistance in fieldwork and fruit collection. I also
sincerely thank Drs. Michael McGuire and Robert Behle of the United States Department
of Agriculture (USDA) laboratory in Peoria, IL for their involvement in the
biodegradable sphere studies. In addition, I would like to acknowledge David Bloomberg
of F ruitspheres Inc., Macomb, Illinois, for providing me with biodegradable spheres to
conduct my research in 1999 and 2000.

Finally, I would like to thank the many growers that allowed me to conduct my
research on their orchards, farms and plantings. I thank Fox and Tapper’s Apple
Orchards, Dan’s blueberry plantation, John Vanvoorheis, and Sally Walter for allowing
me to invade their property throughout the summers and for entrusting me with their
fruit. The research reported here was supported by USDA Special Fruit Grant No. 61-

4058 and the North Central IPM Grant No. 61-4081 .

iv

TABLE OF CONTENTS

LIST OF TABLES .............................................................................. x
LIST OF FIGURES ............................................................................ xii
INTRODUCTION ............................................................................... 1
Michigan apple and blueberry industry ....................................................... 1
Michigan fruit fly integrated pest management (IPM) program ............................ 2
Life-history of temperate Rhagoletis species ................................................. 3
Biogeographic range distribution ............................................................... 5
Morphology, ovipositional preference, and genetic isolation ............................... 6
Speciation between R. pomonella and R. mendax ........................................... 9
Research objectives ............................................................................. 11

CHAPTER ONE: EVALUATION OF BIODEGRADABLE, INSECTICIDE-
TREATED SPHERES FOR CONTROL OF RHAGOLE T IS

SIBLING SPECIES.
Introduction ...................................................................................... 13
Materials and Methods ........................................................................ 16
Biodegradable spheres (Apple and blueberry maggot) ........................... l6
Apples .................................................................................... 16
Blueberries ............................................................................... 17
Sampling ................................................................................. 18
Statistical Analysis ..................................................................... 18
Results ............................................................................................ 1 9
Apple maggot (biodegradable spheres). Experiment 1 (Fennville) ............. 19

Experiment 2 (Fox Orchard) .......................................................... 19
Blueberry maggot (biodegradable spheres) Experiment 3 (Fennville). . . . . ....20
Experiment 4 (Fennville) .............................................................. 20

Discussion ....................................................................................... 2 1

CHAPTER TWO: COMPARISON OF NEONICOTINOID INSECTICIDES
FOR USE WITH BIODEGRADABLE SPHERES FOR
CONTROL OF KEY RHAGOLETIS SPECIES

Introduction ...................................................................................... 26
Materials and Methods ........................................................................ 28
Field evaluation of neonicotinoid-treated spheres ................................. 28
Apple Maggot (1999) .................................................................. 29
(2000) .................................................................................... 29
Blueberry Maggot (1999) ............................................................. 30
(2000) .................................................................................... 30
Laboratory bioassays .................................................................. 31
Statistical Analysis ..................................................................... 32
Results ............................................................................................ 33
Field-based evaluation of neonicotinoid-treated spheres ......................... 33
Laboratory bioassays .................................................................. 41
Discussion ....................................................................................... 43

vi

CHAPTER THREE: EVALUATION OF VARIOUS DEPLOYMENT
STRATEGIES OF IMIDACLOPRID-TREATED
SPHERES IN HIGHBUSH BLUEBERRIES FOR
CONTROL OF RHAGOLE T IS MENDAX CURRAN

Introduction ...................................................................................... 49
Materials and Methods ........................................................................ 52
(1999) .................................................................................... 52
Fruit evaluation ........................................................................ 53
(2000) .................................................................................... 55
Fruit evaluation ........................................................................ 55
Monitoring .............................................................................. 55
Statistical Analysis ..................................................................... 56
Results ............................................................................................ 57
(1999) .................................................................................... 57
(2000) .................................................................................... 59
Discussion ....................................................................................... 62

CHAPTER FOUR: ATTRACTION OF APPLE MAGGOT FLIES,
RHA GOLETIS POMONELLA (WALSH)
(DIPTERA: TEPHRITIDAE), TO SYNTHETIC
FRUIT VOLATILE COMPOUNDS AND
FOOD ATTRACTANTS IN MICHIGAN APPLE

ORCHARDS.
Introduction ...................................................................................... 67
Materials and Methods ......................................................................... 70
(1998). Experiment 1 .................................................................. 70
(1998). Experiment 2 .................................................................. 71
(1999) .................................................................................... 71

vii

(2000) .................................................................................... 71

Statistical analysis ..................................................................... 72
Results ............................................................................................ 73
(1998). Experiment 1 .................................................................. 73
(1998). Experiment 2 .................................................................. 75
(1999) .................................................................................... 78
(2000) .................................................................................... 79
Discussion ....................................................................................... 82

CHAPTER FIVE: RESPONSE OF BLUEBERRY MAGGOT FLIES,
RHA GOLE T IS MENDAX, (DIPTERA: TEPHRITIDAE)
TO SYNTHETIC VOLATILE COMPOUNDS IN

BLUEBERRY PLANTIN GS.
Introduction ...................................................................................... 88
Materials and Methods ........................................................................ 91
(1999). Experiment 1. (Earliblue) ................................................... 91
Experiment 2. (Bluecrop) ............................................................. 92
(2000) .................................................................................... 92
Experiment 3. (Earliblue) ............................................................. 94
Experiment 4. (Bluecrop) ............................................................. 94
Sampling ................................................................................. 95
Statistical Analysis ..................................................................... 95
Results ............................................................................................ 96
(1999). Experiment 1. (Earliblue) ................................................... 96
Experiment 2. (Bluecrop) ............................................................. 99
(2000) .................................................................................. 101

viii

Discussion ...................................................................................... 1 06

SUMMARY AND CONCLUSIONS ...................................................... 111
LITERATURE CITED ....................................................................... 114
APPEDIX ....................................................................................... 123

ix

LIST OF TABLES

Table 1. Effect of neonicotinoid-treated spheres on apple maggot fly, Michigan
(1999) ................................................................................................. 34

Table 2. Comparison of neonicotinoid insecticides at 2 % AI using biodegradable spheres
for control of apple maggot and blueberry maggot flies, Michigan (2000) .................. 36

Table 3. Effect of neonicotinoid-treated spheres on blueberry maggot fly, Michigan
(1999) ................................................................................................. 38

Table 4. Comparison of neonicotinoid insecticides at 2 % AI using biodegradable spheres
for control of apple maggot and blueberry maggot flies, Michigan (2000) .................. 40

Table 5. Percent mortality of blueberry maggot flies that fed upon neonicotinoid—treated
spheres with and without piperonyl butoxide (PBO) ........................................... 42

Table 6. Percentage of fruit injury and infestation due to R. mendax oviposition,
Michigan (1999) .................................................................................... 58

Table 7. Percentage of fruit injury and infestation due to R. mendax oviposition,
Michigan (2000) .................................................................................... 60

Table 8. Mean number of R. mendax captured on unbaited Pherocon AM boards within
treatment plots, Michigan, (2000) ................................................................. 61

Table 9. Attraction of apple maggot flies to synthetic fruit volatiles with and without
ammonium-odor and protenaceous baits, Michigan, (1998) .................................. 74

Table 10. Attraction of apple maggot flies to synthetic fruit volatiles and baits, Michigan,
(1998) ................................................................................................. 76

Table 11. Attraction of apple maggot flies to synthetic fruit volatiles and baits, Michigan,
(1999) ................................................................................................. 78

Table 12. Attraction of apple maggot flies to synthetic fruit volatiles and baits, Michigan,
(2000) ................................................................................................. 80

Table 13. Attraction of blueberry maggot flies to synthetic fruit volatiles and baits within
an early—season blueberry cultivar (Earliblue), Michigan, (1999) ............................ 98

Table 14. Attraction of blueberry maggot flies to synthetic fruit volatiles and baits within
a mid-season blueberry cultivar (Bluecrop), Michigan, (1999) .............................. 100

Table 15. Attraction of blueberry maggot flies to synthetic fruit volatiles and baits within
an early-season blueberry cultivar (Earliblue), Michigan, (2000) ........................... 103

Table 16. Attraction of blueberry maggot flies to synthetic fruit volatiles and baits within
a mid-season blueberry cultivar (Bluecrop), Michigan, (2000) .............................. 105

xi

LIST OF FIGURES

Figure 1. Imidacloprid—treated sphere deployment strategies within highbush
blueberries ............................................................................................. 54
Figure 2. Attraction of adult R. pomonella to baited red spheres, 1998 ...................... 77

Figure 3. Attraction of adult R. pomonella to baited red spheres,
2000 ................................................................................................... 80

xii

INTRODUCTION

Michigan apple and bluebefl indust_ry. Michigan ranks second or third,
depending on annual yield and production, in the US. apple industry. Apples are grown

commercially on more than 58,000 acres and more apples are produced by volume than
all other Michigan fruits combined (Michigan Apple Committee). The state also
maintains the lead in highbush blueberry ( Vaccinium corymbosum L.) production,
generating 45 percent of U. S. blueberries on more than 17,000 acres (Michigan
Blueberry Growers Association).

In Michigan, apple orchards and blueberry plantings experience high infestations
of apple maggot and blueberry maggot flies, respectively. Adults, responding to visual
and olfactory cues, migrate into commercial orchards and plantings where mating and
oviposition occurs on host fruit (Liburd and Stelinski 1999). Economically, the apple
maggot fly, Rhagoletis pomonella (Walsh) and the blueberry maggot fly, Rhagoletis
mendax Curran are the most important late season pests of commercially grown apples,
Malus domestica Borkhausen and blueberries, Vaccinium spp. L., respectively in the
northeastern and midwestem United States (Bush 1966). Each fly species restricts its
attack to host plants within a few closely related genera and larval development within
host fi'uit renders it commercially unmarketable.

Federal (USDA) regulations, phytosanitary restrictions, and consumer demands
have resulted in a zero tolerance to maggot infested fruits such as apples and blueberries.
In order to ensure the absence of maggot injury due to Rhagoletis species, growers

generally apply three to five insecticide treatments regardless of whether flies are present

in their orchards or plantings (Stanley et a1. 1987, Liburd et al. 1998 a). Registered
insecticides for fruit fly control include malathion, carbaryl (Sevin), phosmet (Imidan),
dimethoate (Cygon) and azinphosmethyl (Guthion). These insecticides are highly toxic
and kill both pest and beneficial insects indiscriminately. The presence of insecticide
residues on food and their impact on human health has also created widespread
apprehension among the general public regarding the use of insecticides. Future
management practices for protecting apples and blueberries from apple maggot and
blueberry maggot flies with insecticides, particularly organophosphates, are subject to
restriction by the regulations being implemented under the Food Quality Protection Act
(F QPA)-

Miphigap f_rpit fly integgated pest mgagemept (IPM) program. For almost three
decades, integrated fruit fly management programs in Michigan have relied on the use of
visual and olfactory traps to make control decisions. The strategies adopted by most
growers involve the deployment of baited Pherocon AM yellow sticky boards and
colored spheres in apple orchards and blueberry plantings (Reissig 1976, Prokopy and
Hauschild 1979, Liburd et a1. 1998 b). Ground and aerial applications of insecticide
sprays usually follow the detection of one fly per trap (Liburd et al. 2001).

The use of visual and olfactory monitoring traps can be a valuable IPM strategy.
However, the monitoring traps currently used by most growers and scouts become
inundated with a wide variety of non-target insects after only two weeks of deployment,
which drastically reduces their effectiveness (Liburd et a1. 1999). In addition, the odor of
decomposing insects on the sticky surface of these traps overpowers the insect attractant

(bait) used with them, which further reduces trap effectiveness. Under these

circumstances, traps need to be cleaned and replaced frequently in the field to maintain
accurate monitoring. Trap preparation, replacement, and maintenance is a time
consuming and labor-intensive operation (Prokopy er al. 1990). Trap monitoring efficacy
could be improved by increasing selectivity to apple maggot and blueberry maggot flies.
This could be accomplished by identifying appropriate synthetic fruit volatiles that
selectively attract each fruit fly species. The development of traps baited with selective
lures may extend the longevity of trap effectiveness, possibly allowing growers to make
more informed and precise management decisions.

In addition, the development of insecticide-treated sphere technology (attract-and-
kill devices) as part of an IPM strategy could potentially reduce broad-spectrum
insecticides for the control of key Rhagoletis species. Laboratory and field studies have
shown that insecticide-treated spheres are effective in attracting and killing both apple
maggot and blueberry maggot flies (Hu et a]. 1998, Liburd et a1. 1999). However, there
have been no published studies on optimization of sphere deployment strategies in the
field and little work has been done on determining performance, longevity, and
compatibility of various novel insecticides for use with this technology.

Life-histog of temperate Rhagoletis species. The majority of temperate
Rhagoletis species are univoltine (Fletcher 1989). Puparial diapause is followed by
emergence of adults beneath host plants that yielded fruit the previous year; emergence
nearly coincides with appearance of suitable host fruit for egg laying in the current year
(Lathrop and Nickels 1932). Sexual maturity is reached within 1-2 weeks of fly
emergence and is followed by mating on fruiting host plants, which culminates in

oviposition by the females into ripe or ripening host fruits (Smith and Prokopy 1981 and

1982, Liburd et a1. 1998 b, Lathrop and Nickels 1932). Prior to sexual maturity, the
females exhibit an attraction to ammonia (Liburd et al. 1998a), apparently seeking a
protein source that may be important for egg maturation (Prokopy and Roitberg 1989,
Prokopy 1993, and Prokopy et al. 1994). Odor emitted by ripening fruit, which is
attractive to both sexes at distances of at least 20 m may serve as a long-range attractant
to Rhagoletis flies (Prokopy et a1. 1973). In addition, R. pomonella have been reported to
detect the visual stimuli of host trees at distances of at least 3 In (Green et a1. 1994). After
locating an appropriate mating site (species-specific host fruit), males defend their
territory by various displays including wing waving, foreleg kicking, and boxing
(Messina and Subler 1995). Observations by Prokopy and Bush (1973) and Smith and
Prokopy (1981,1982) suggest that R. pomonella and R. mendax males force copulation
upon the females. The female fly usually visits several fruits prior to oviposition. After
identifying an appropriate site, she inserts her ovipositor into the fruit and deposits a
single egg just below the surface of the fruit. Immediately afier the egg is deposited, the
female walks around the fruit dragging her extended ovipositor on the fruit surface and
laying down an epidictic pheromone, which deters other females from ovipositing into
the same fi'uit (Prokopy 1972 b). Interestingly, studies have shown that flies from
different species do not recognize each others host-marking pheromones, while different
populations of the same species show marked recognition of each others’ pheromones
(Prokopy 1976, Prokopy et a1. 1982).

Rhagoletis larvae feed and develop inside the fruit, which results in destruction of
the internal fruit tissues (Liburd et a1 1998 b). During the third or fourth instar, the larvae

bore a hole in the skin of the decaying fruit and drop or crawl to the ground. Emergence

from the fruit takes place in the early morning hours and is stimulated by the onset of
light and an increase in surrounding temperature (Goeden and Ricker 1971, Boller and
Porkopy 1976). Larvae usually burrow 3 to 5 cm below the surface of the soil where they
pupariate and overwinter in diapause, with 20 % of the puparia remaining in the soil for
more than two seasons (Lathrop and Nickels 1932).

Biogeoggaphic range distribution. Species of the genus Rhagoletis are widely
distributed over the Holarctic and Neotropical regions (Bush 1966). More than 60 species
with their related host plants have been described (Smith and Bush 1996), and it is likely
that Speciation within the genus Rhagoletis is associated with the ecological separation of
populations, resulting from flies shifting to new host plants (Bush 1992). Bush (1969)
argued that the use of different hosts by these syrnpatrically speciating forms would
generate immediate and complete reproductive isolation. A prominent characteristic of
the genus is the frequent occurrence of morphologically indistinguishable sibling species
that are ecologically independent.

The apple maggot fly is native to North America and its original host is believed
to be hawthorn, Crataegus spp., which is a close botanical relative of apples (Dean and
Chapman 1973). Although the apple maggot fly appears to be most common in the
northeastern United States and southeastern Canada, it is widely distributed and present
in all of the Atlantic States to northern Florida (Bush 1966). Its distribution also includes
the central states as far south as Arkansas and states west to the Dakotas and southern
Manitoba (Bush 1966). The apple maggot fly also occurs in the Pacific Northwest in

Oregon, Washington and northern California (Larry J. Gut, personal communication).

The blueberry maggot fly is a sibling species of the apple maggot fly. The three
primary ericaceOus host plants used by R. mendax in the northeastern United States
include blueberries, (Vaccinium corymbosum L. and V. angustifolium Aiton), and
huckleberries, (Gaylussacia Humboldt, Bonpland, and Kunth spp.) (Bush 1966). In the
south, V. stamineum L. (deerberry) is the primary host (Payne and Berlocher 1995 a, b).
The blueberry maggot fly’s distribution extends northward into Canada. The fly is known
to occur in Nova Scotia, Prince Edward Island and New Brunswick (Wood 1965, Neilson
and Wood 1985). In the northern United States, high populations occur in Maine, New
Hampshire, Vermont, New Jersey, and Michigan. (Bush 1969). The blueberry maggot fly
is also widely distributed within the southern United States into northern Florida and as
far to the west as the Ozark Plateau (Bush 1969).

Morphology, ovipositional preference, and genetic isolation.

Considerable work has been carried out to determine the taxonomic placement of
the apple maggot and blueberry maggot (Bush 1966, 1969, Feder 1998). Distinction
based on morphological features has been difficult, while few structural characteristics
can be discerned with which to separate the species. The blueberry maggot form is
smaller than apple maggot, in every stage of the life cycle, yet the processes of
oviposition, pupariation, as well as larval habits appear identical (Lathrop and Nickels
1932). In western Michigan, blueberry maggot flies of both sexes captured on sticky
yellow pane traps and sticky sphere traps are consistently smaller than apple maggot flies
captured on the same manner (personal observation). Bush (1966) concluded that R.
pomonella and R. mendax are separate species based on the morphological differences of

ovipositor length, femur coloration, and wing band ratios.

Divergent host-fruit preferences exist between the apple maggot and blueberry
maggot. The literature documenting the apple maggot’s attraction to its particular larval
host-fruit volatiles is voluminous. Prokopy et a1. (1973) and later Reisig (1974) provided
evidence that apple maggot flies positively respond to apple odor in the field. Later, Fein
et a1. (1982) isolated apple volatiles from two apple varieties (Red Delicious and Red
Astrachan) and found that a mix blend consisting of a series of short chain carbon esters,
including butyl hexanoate was attractive to apple maggot flies. Also, Reissig et a1. (1985)
showed that sticky red spheres (8.5 cm diam) baited with synthetic apple volatiles were
four times more effective than unbaited red spheres. Recently, Averill et a1. (1998)
determined that apple maggot flies exhibits a high degree of olfactory specificity,
showing a minimum behavioral response to straight chain esters, 10-11 carbons in length
and having an acid portion of six to eight carbons and an alcohol portion of three to five
carbons. Finally, a recent study has shown that a lure consisting of a mix blend of
synthetic apple volatiles combined in specific proportions and including butyl butanoate,
propyl hexanoate, butyl hexanoate, hexyl butanoate, and pentyl hexanoate was
significantly more attractive to adult apple maggot flies than lures containing butyl
hexanoate alone (Zhang et al. 1999).

Blueberry maggot flies are relatively more sensitive to the odor of blueberries,
their specific host, than of apples and vice versa with apple maggot flies, indicating that
antenna] sensitivity may be adapted to the species-specific host (Frey and Bush 1990).
Furthermore, hybrids of apple maggot and blueberry maggot flies exhibit significantly
weaker peripheral responses to host odor compounds as measured by

electroantennograms, (Frey and Bush 1996). In addition, the two species have evolved

divergent egg-laying responses to chemical stimuli on the fruits of their respective hosts
(Bierbaum and Bush 1990). Specifically, apple maggot flies lay more eggs compared
with blueberry maggot flies when stimulated by extract from apples, while bluebeny
maggot flies lay more eggs when stimulated by blueberry extract.

Sibling species within the genus Rhagoletis also exhibit differential behavioral
responses based on host-fruit size and color. Fruit size may be a particularly important
influence on Rhagoletis fly orientation and response, while females of several species
prefer a limited range of sizes of fruit hosts in which to oviposit (Weisman 1937, Reissig
et a1. 1990, Messina and Jones 1990). In studies using inanimate fruit-mimicking objects,
it has been found that blueberry maggot flies (natural host fruit size ranges fi'om 5 to 15
mm in diameter) deposited eggs in equal numbers in 10 and 20 mm models, with fewer
eggs laid in 40 and 70 mm models (Prokopy and Bush 1973). The same study showed a
contrasting result in the response of apple maggot flies (natural host fruit sizes range from
15 to 70 mm in diameter), which deposited eggs in equal numbers in of 20 and 40 mm
models, with fewer eggs laid in 10 mm or 70 mm models. In other studies involving the
closely related western cherry fruit fly, Rhagoletis indeflerens Curran, and R. pomonella,
females flies were found to preferentially bore into fruit models of similar or slightly
larger size to that of native host fruit and they had a lesser inclination to oviposit into
models smaller than or much larger than native host fruit (Prokopy and Boller 1971 ,
Papaj and Prokopy 1986, Messina 1989). Given these observations, it was concluded that
in Rhagoletz's species whose native host fruits are small (5 to 15 mm in diameter) and
which have not expanded their host range to host fruit of larger size (15 to 70 mm in

diameter), oviposition is limited to a restricted range of host fruit sizes within close range

of native host fruit diameter. On the other hand, in Rhagoletis species that have expanded
their host range to fruit of a larger size, such as apples, the range of host fruit size
acceptable for oviposition is more expansive and characterized by less selectivity.
Evidence for genetic divergence among R. pomonella and R. mendax has also
been compiled. Feder et al. (1989) found species-specific alleles for 11 different
allozymes. Further experiments by Bierbaum and Bush (1989) corroborate the genetic
evidence for Speciation, and provide support for the theory that sympatric Speciation
occurred as a result of a divergence in host preference and acceptance behaviors. To test
the hypothesis that these two species have evolved viability differences on different
hosts, Bierbaum and Bush (1989) measured the larval-to-adult viability of R. mendax, R.
pomonella, and F1 interspecific hybrid progeny reared on naturally growing hi ghbush
blueberries and apple (Malus pumila Miller). Fewer interspecific hybrids survived to
adulthood than either R. pomonella reared in apples or R. mendax reared in blueberries.
Thus, reduced hybrid viability compared with that of conspecific crosses provides a
mechanism for restriction of gene flow among the two species.
Speciation between R. pomonella and R. mendax.

Allopatric Speciation within various Rhagoletis sibling-species complexes may
have occurred as a result of geographic separation among populations, resulting from
changes in environmental conditions in particular localities (Bush 1966). Bush (1969)
notes Mayr’s (1963) proposal that populations may become adapted to a secondary host
within an isolated locality when climatic or other changes lead to the extinction of the

primary host. Such a host shift among temporally isolated peripheral populations could

lead to rapid adaptation to the new host and explain the sympatric existence of sibling
species within the genus Rhagoletis.

Bush (1969) proposed a mechanism for the evolution of Rhagoletis sibling-
species complexes via sympatric Speciation based on the correlation between mate and
host selection within the genus, which involves courtship and mating on larval host-
plants. Sympatric Speciation may have occurred as follows: 1) Diapause and emergence
times are under genetic control. 2). Orientation to and selection of hosts is in response to
chemical cues. 3) Host selection has a genetic basis, ei. AA and Aa orient preferentially
toward apples, while aa orient toward blueberries. 4) A mutates to a in a location where
blueberries are available and a few homozygous individuals are eventually produced as a
result of recombination. 5) Host plant and mate selections are positively correlated and
thus individuals orient preferentially to their respective host plants (AA-apples or aa-
blueberries), depending on genotype. Mating occurs on each sibling species’ respective
host plant. The result of this process would be the establishment of two ecologically
separated sibling species.

Speciation within the genus Rhagoletis may have also taken place as a result of a
temporal separation of host races, resulting in allochronic divergence. The emergence
patterns of Rhagoletis species occur within a relatively short period and are tightly
synchronized with the phenology of host plants (Lathrop and Nickels 1932). However,
within naturally occurring populations of both R. pomonella and R. mendax, there are
individuals that will emerge up to a month earlier or later than the peak emergence period
(personal observation, Bush 1966). These early or late individuals are at a distinct

selective disadvantage since host fruit are usually not readily available for oviposition

10

during these time periods (Bush 1966). However, such genetic diversity within a
population prevents extinction during years when peak emergence does not coincide with
fruit maturation. In this case, the few early or late emerging flies could possibly
propagate the population and save it from extinction.

Rpsearph objeptives. As federal mandates on the use of organophosphates become
more stringent, there is a growing need to develop effective and environmentally safe
pest management tactics. The main objective of this study was to determine the
effectiveness of biodegradable spheres treated with neonicotinoid insecticides for control
apple maggot and blueberry maggot flies. The second research objective was to evaluate
potential sphere deployment strategies within blueberry plantings and to determine their
relationship to fruit injury. The final objective was to evaluate synthetic host-plant
volatile compounds and determine appropriate load rates and blends to be used as
attractants for effective monitoring and control of apple maggot and blueberry maggot
flies. The overall goal of this project was to develop novel management tactics and
improve existing monitoring and control techniques for apple maggot and blueberry

maggot flies, thereby reducing fruit growers’ reliance on organophosphate insecticides.

11

CHAPTER ONE

EVALUATION OF BIODEGRADABLE, INSECTICIDE-TREATED SPHERES FOR

CONTROL OF RHA GOLE T [S SIBLING SPECIES.

12

INTRODUCTION

In Michigan and the eastern regions of the United States, there is a zero tolerance
policy on the part of the fruit industry to maggot infestation in fruit, including apples and
blueberries. In order to avoid significant losses, growers must implement effective
monitoring programs to detect the presence of fruit-parasitic Rhagoletis flies. Currently,
most growers administer three to five applications of insecticides irrespective of whether
or not Rhagoletis flies are present (Liburd et al. 1998 a). This type of management
strategy increases the potential for environmental contamination, evolution of insecticide
resistance, and poisoning of humans.

Yellow sticky boards and colored spheres (baited and unbaited) have been shown
to be effective monitoring traps for Rhagoletis species (Johnson 1983, Liburd et al. 1998
a). However, after two weeks of deployment both sticky boards and spheres frequently
become inundated with insects, which reduces their effectiveness. Replacing, coating,
and hanging sticky boards and spheres is time consuming (Liburd et al. 2000) and labor
intensive (Prokopy et al. 1990). Duan and Prokopy (1993) indicated that the reliance on
sticky Tangle-Trap® for killing and monitoring Rhagoletis species in large—scale
operations is a major impediment due to the previously mentioned labor intensity
involved. The disadvantages associated with use of sticky boards and spheres necessitate
seeking alternative management tactics for Rhagoletis species. One possible alternative is
to develop a chemically and visually attractive biodegradable sphere that is coated with

insecticide.

13

Although several researchers (Prokopy and Coli 1978, Prokopy and Hauschild
1979, Johnson 1983, Neilson et al. 1984) have reported on the use of sticky traps for the
management of Rhagoletis species, only a few investigations have explored the potential
of using combinations of traps, lures, and an insecticide (Duan and Prokopy 1993, Duan
and Prokopy 1995 a, Duan and Prokopy 1995b, Hu et al. 1997). To date, mortality data
on Rhagoletis species using insecticide-treated spheres have been based on visual
observations and data collected from variation in fruit injuries. Currently, there are no
field studies illustrating mortality of any Rhagoletis species using insecticide-treated
spheres and tracking flies visually after they have visited a sphere has been a difficult
operation (Duan and Prokopy 1995 b). Growers who may wish to adopt the use
insecticide-treated spheres need information on mortality of Rhagoletis flies encountering
these devices in their commercial orchards in order to evaluate the effectiveness of this
tactic.

In laboratory studies using spheres treated with a combination of a pesticide,
feeding stimulant, and a residue-extending agent, it was discovered that several
insecticides (except dimethoate and malathion) reduced apple maggot fly visitation and
feeding (Duan and Prokopy 1995 a). Spheres treated with combinations of an insecticide,
corn syrup, and latex paint were effective in killing > 50 % of alighting flies. In a related
laboratory study, Duan and Prokopy (1995 h) compared the effectiveness of insecticide-
treated spheres with conventional sticky, baited spheres for control of apple maggot flies.
They found that freshly baited insecticide—treated spheres were just as effective as freshly

baited sticky spheres in killing released flies, as well as reducing oviposition. Similarly,

l4

under field conditions they sighted equal numbers of R. pomonella flies visiting apple
trees containing insecticide-treated spheres and red sticky spheres.

The objective of this study was to document the mortality of Rhagoletis flies in
the field using insecticide-treated spheres. The hypothesis was that insecticide-treated
spheres baited with an appropriate lure and feeding stimulant would attract and kill
Rhagoletis flies. Furthermore, we hypothesized that killed flies could be documented and

counted on sticky coated plexiglas panes hung directly underneath the spheres.

15

MATERIALS AND METHODS

Research in 1998 was conducted at two sites near Fennville, Michigan: the
Michigan State University Trevor Nichols Research Station and an organic grower’s
commercial bluebeny farm. Additional experiments were conducted at Hood’s Farm and
Fox orchard located near Paw Paw, Michigan.

Biodegradable spheres (Apple and blugbem maggot). Biodegradable spheres (9-
cm diameter) obtained from the United States Department of Agriculture (USDA)
laboratory in Peoria, IL were used in the apple and blueberry experiments. These spheres
were made from sugar (20%), water (15%), syrup (isosweet 100) (20%), and
pregelatinized corn flour (45%) and produced mechanically by the process of extrusion.
Spheres were hard and durable (resulting from extrusion process) which allowed them to
withstand adverse weather conditions during the summer. Spheres were painted with red
(Glidden Red Latex Gloss) and green (Shamrock green 197A111) enamel paint,
respectively. The red spheres were used in both apple and blueberry experiments; green
spheres (Liburd et. al 1998 a) were only used in blueberry experiments. Prior to field
deployment, spheres treated with insecticide were brush-painted with a mixture
containing 2% (AI) imidacloprid, 20% sucrose solution, 8% water, and 70% paint.
Control spheres, lacking insecticide, were painted with the same mixture without
imidacloprid. The decision to use of imidacloprid was based on the positive results from
laboratory assays with R. pomonella (Hu and Prokopy 1998). All spheres were allowed to
dry for 48 hours after brush painting prior to deployment in the field.

Apple; Two experiments were conducted to evaluate the effectiveness of 9-cm

diameter, biodegradable, red spheres treated with insecticide for the control of apple

16

maggot flies. Experiment 1 was located at the Trevor Nichols Research Station in
Fennville and was designed to establish data on apple maggot mortality using insecticide-
treated spheres. We also wanted to monitor the apple maggot population within a 2-5 m
radius of the biodegradable spheres. Experiment 2 was established at Fox orchard to
reevaluate the potential for controlling apple maggot flies in a different location.

The experimental designs were randomized complete blocks (blocked by apple
variety) with 5 replications. Spheres were hung approximately 25 m apart and 30 m
between one-acre blocks of Red Delicious in experiment 1, and Red and Golden
Delicious in experiment 2. An apple maggot BioLure® dispenser (Consep. Inc. Bend,
Oregon) containing 1.8 g (load rate) butyl hexanoate was affixed (using a staple gun) to
the branch adjacent to each insecticide-treated sphere. A 60 x 45 cm plexiglas pane was
placed approximately 30 cm below each sphere. Each plexiglas pane was lightly coated
with insect Tangle-Trap® aerosol formula (Great Lakes IPM). In experiment 1, unbaited
(9-cm diameter) red spheres (Great Lakes IPM) coated with 13 g of insect Tangle-Trap®
(Great Lakes IPM) were placed within a 2 m radius of the biodegradable spheres to
monitor the apple maggot population. Sphere positions were rotated every 5 days in
experiment 1, and every 3 days in experiment 2.

Blpeberries. Green and red spheres were used in blueberry experiments (Liburd
et al. 1998 a and b) targeting the blueberry maggot fly. Experiment 3 was located in an
area with a moderate blueberry maggot population (z 10 flies / trap over 2 weeks catch)
based on trap data from previous years. Experiment 4 was located in a different area

within the same plantation known to have a low population of R. mendax flies.

17

The experimental designs were randomized complete blocks arranged within
Jersey and Earliblue cultivars and blocked by cultivar with 4 replications. Insecticide-
treated and control spheres were used in both experiments. Spheres were hung within
blueberry bushes approximately 15 m apart (20 m between blocks) in plantings of
Jerseys, Rube] and Bluecrop. A 60 x 45 cm plexiglas pane was placed approximately 30
cm below each sphere. Each plexiglas pane was lightly coated with insect Tangle-Trap®
(aerosol formula). A scintillation vial (National Diagnostics, Atlanta, GA) containing 1 g
of ammonium acetate (Aldrich Chemical Co., Milwaukee, WI) dissolved in 5 ml of water
was affixed (using a masking tape) to the branch adjacent to each insecticide-treated
sphere. Each vial was plugged with cotton wool, which became damp whenever branch
movement occurred. Sphere positions were rotated every 4 days.

Sampling. Both spheres and plexiglas panes were checked twice per week and
the number of R. pomonella and R. mendax flies found on plexiglas panes in apples or
blueberries were counted. Both R. pomonella and R. mendax flies captured were counted
by sex on a weekly basis.

Statistical analysis. Data from biodegradable sphere experiments (except the red
spheres used in the blueberry experiment) were analyzed by ANOVA followed by mean
separation using the least significant difference (LSD) test (SAS Institute 1989). Data
from red spheres in the blueberry experiment was square root transformed (x + 0.5)

before subjecting to ANOVA. The means were separated by the LSD test.

18

RESULTS

Apple maggot (biodeggadable spheres). Experiment 1 (Fennville The mean

number of R. pomonella caught on plexiglas panes placed below insecticide-treated
spheres (20.0 i 3.0) was significantly greater (F = 52.4; df = 1,4; P < 0.01) than the
number of flies that were caught on plexiglas panes placed under biodegradable spheres
without insecticide (0.8 i 0.6). Flies spent significantly (F = 12.7; df = 1,4; P < 0.02)
more time alighting on spheres treated with imidacloprid (8.8 i 1.9 min) than they did on
untreated spheres (2.0 i 0.6 min).

Experiment 2 (on Orchard). We observed more R. pomonella flies on sticky
plexiglas panes under insecticide-treated spheres than on panes placed under spheres
without insecticide. The mean number of R. pomonella caught on plexiglas panes under
insecticide-treated spheres (17.4 i 2.6) was significantly greater (F = 34.2; df = 1,4; P <
0.01) than the number of flies caught on panes placed under untreated spheres (1.0 i 0.5).
There was no significant difference in the number of females and males (R. pomonella
flies) caught on plexiglas panes under insecticide-treated or untreated spheres. We caught
an average of 10.8 i 1.6 female and 6.8 i 2.2 male R. pomonella flies on plexiglas panes
placed below insecticide-treated spheres. However, we caught only an average of 0.8 i
0.2 and 0.4 i 2.2 females and males respectively, beneath untreated spheres.

The mean number of flies caught on unbaited sticky spheres placed within a 2 m
radius of insecticide-treated spheres (33.4 i 5.0) was significantly less (F = 7.2; df = 1,4;
P < 0.05) than the number of flies caught on sticky spheres placed at the same distance

from untreated spheres (103.2 i 26.7).

19

Blupbem maggot (biodegradable spheres) Experiment 3 (Fennville). In a

naturally infested area with a moderate population, the mean number of flies captured
(10.8 i 2.9) on sticky plexiglas panes placed under red insecticide-treated spheres was
significantly (F = 10.4; (if = 1,3; P < 0.05) more than the number of flies caught on
panes placed under untreated spheres (3.0 i 0.7). There were no significant differences in
the ratio of male and female flies caught on plexiglas panes below insecticide-treated
spheres. The mean numbers of female and male flies caught were 7.0 i 1.6 and 5.8 i 0.9
respectively, for plexiglas panes below insecticide-treated spheres. Plexiglas panes below
untreated spheres captured an average of 1.5 i 0.6 and 1.8 i 0.3 female and male flies,
respectively.

Experiment 4 (Fennville). In another area where the population of R. mendax
flies was much lower, highly significant (P < 0.001) differences in mortality data
occurred between sticky plexiglas panes placed under green, insecticide-treated spheres
and sticky plexiglas panes positioned under untreated spheres. Sticky plexiglas panes
placed under green, insecticide-treated spheres captured an average of 4.0 i 0.4 flies
versus 0.8 i 0.5 for non insecticide-treated spheres. The amount of time flies spent
alighting on spheres treated with insecticide (7.4 i 1.9 min) was significantly (F = 7.0; df
= 1,3; P < 0.02) less than the amount of time flies spent on untreated spheres (1.9 i 0.6
min). More than 60 % of the flies caught on plexiglas panes were positioned directly
under insecticide-treated spheres. The few flies caught on plexiglas panes under untreated

spheres were randomly distributed throughout the panes.

20

DISCUSSION

Our findings showed that Plexiglas panes lightly coated with a sticky trapping
material and hung 30 cm below baited, insecticide-treated spheres can be used to monitor
populations and record the mortality of apple maggot and blueberry maggot flies in
commercial orchards and plantings. These studies have also indicated that insecticide-
treated spheres can be used effectively to suppress populations of Rhagoletis flies. Duan
and Prokopy (1995 b) indicated that a nearly acceptable level of control (based on fruit
injury) was achieved using insecticide-treated spheres in commercial orchards that
contained the Liberty apple variety. In their study, repeated applications of sucrose were
necessary after each rainfall to maintain sphere effectiveness, and spheres were retreated
with an insecticide as the season progressed. Our spheres appeared to be more effective
after each rainfall or heavy dew. This difference may have been due to the composition of
our spheres. Biodegradable spheres used in this study were partially composed of
sucrose, which progressively exuded from the spheres over the coarse of the season and
continuously provided a fly feeding stimulus.

Insecticide-treated spheres killed 25 and 17 times as many flies respectively, as
untreated spheres in our apple maggot studies (experiments 1 and 2). The observed
mortality rate could have been significantly higher because in many situations flies were
observed feeding on insecticide-treated spheres and then flying away. However, it was
impossible to tell whether these flies were killed later. It is possible that flies feeding for
an average of 8.8 i 1.9 min ingest a lethal amount of insecticide. Moderate consumption
of imidacloprid causes R. pomonella flies to regurgitate and cease feeding (Hu and

Prokopy 1998). The small number of flies killed in the control was probably the result of

21

accidental injuries and captures or the result of a lethal ingestion of the paint. Preliminary
laboratory tests on enamel paints indicated that they are toxic to R. pomonella flies.

An equal ratio of captured male and female flies was observed. Both sexes may
have been attracted to the apple maggot BioLure®, which releases butyl hexanoate at a
constant rate (16 mg /d) (Edie Christensen, Consep, personal communication). Butyl
hexanoate is a fruit odor that is attractive to R. pomonella flies seeking fruit resources for
mating and ovipositing (Carle et al. 1987), which may have accounted for the observed
nonsignificant differences in capture between males and females.

The results from our blueberry experiments were similar to those involving
apples. A fairly equal number of both sexes were attracted to ammonia baits. Immature R.
mendax females are attracted to ammonia (Liburd et al. 1998 a), which provides a protein
source for reproductive development (Hendrichs et al. 1990). As flies mature, there is a
change in the physiological state from feeding to ovipositing (Hendrichs et al. 1990).
This results in a shift of female activities from leaves onto fruits (Smith and Prokopy
1981, 1982). Males usually respond by moving onto the fruit for mating purposes.
Therefore, approximately equal numbers of both sexes are usually found on the fruit later
in the season (Liburd 1997). This may account for the lack of a significant difference in
capture between R. mendax males and females during our experiments.

Imidacloprid is a new systemic neonicotinoid insecticide with relatively low
mammalian toxicity (Fleischer et al. 1998), that has been shown effective in controlling
R. pomonella flies (Hu and Prokopy 1998). Flies appeared to be disoriented after feeding
on insecticide-treated spheres for a short period of time. This was probably due to the

imidacloprid since it has rapid lethal and sublethal effects when ingested orally (Hu and

22

Prokopy 1998). This may also account for the significantly longer feeding duration on
insecticide-treated spheres compared to untreated spheres. The higher percentage (60% of
total capture) of flies found on plexiglas panes directly under insecticide-treated spheres
was probably due to the rapid effects of imidacloprid, which prevented the flies that had
consumed it from flying away. The application rate for imidacloprid used in our
experiment was higher than field application rates. However, since fruit was not sprayed,
the potential risk due to insecticide residues was greatly reduced. In addition, due to its
target specificity, the use of insecticide-treated spheres could also protect beneficial
insects and prevent the potential for resistance development (Prokopy et al. 1990, Duan
and Prokopy 1995 b).

Sticky spheres placed within a 2 m radius of insecticide-treated spheres captured
significantly fewer R. pomonella flies than sticky spheres placed at the same distance
from untreated spheres. This indicates that there is some level of suppression within the
area where insecticide-treated spheres were deployed. However, population suppression
could not be confirmed since the apple maggot BioLure® contained butyl hexanoate,
which is known to draw flies from neighboring sites. Also, R. pomonella can move from
infested areas to noninfested areas when the orchard perimeter is not protected to
intercept immigrating flies (Prokopy et al. 1990).

This was the first study to document that biodegradable spheres treated with
imidacloprid are effective in attracting and killing both R. pomonella and R. mendax in
commercial orchards and plantings. Growers who employ the use of insecticide-treated
spheres can monitor fly populations with sticky plexiglas panes placed directly beneath

the spheres. This study documented that mortality data from these panes can also be used

23

to evaluate the effectiveness of the insecticide on the treated spheres. Insecticide-treated
spheres in combination with lures have potential for use in commercial orchards for the
control of Rhagoletis sibling species. Their use could reduce the need for insecticide
sprays that kill natural enemies, contaminate the environment, and pose a danger to

humans.

24

CHAPTER TWQ

COMPARISON OF NEONICOTINOID INSECTICIDES FOR USE WITH

BIODEGRADABLE SPHERES FOR CONTROL OF KEY RHA GOLE T IS SPECIES

25

INTRODUCTION

Recent studies have shown that non-sticky, imidacloprid-treated, biodegradable
spheres are effective in killing apple maggot (Hu et al. 1998, Liburd et a1. 1999) and
blueberry maggot flies (Liburd et al. 1999). Rhagoletis flies foraging for suitable host
plants are attracted to baited, insecticide-treated spheres for mating and oviposition
(Liburd et al. 1999). Flies landing on these spheres die after consuming a lethal dose of
insecticide. As discussed in Liburd et al. (1999), the use of biodegradable spheres offers
several advantages over conventional trapping using sticky traps or insecticide spray
applications, including the potential for season-long control of fruit flies by a single
deployment of spheres at the onset of the season, a possible reduction of insecticide
residues on the fruit, and a reduction in labor costs.

In field studies, Liburd et al. (1999) caught 25 times as many apple maggot and 4
times as many blueberry maggot flies on Plexiglas panes placed beneath imidacloprid-
treated spheres compared with untreated (control) spheres. Further studies showed that
the mean time that flies spent on imidacloprid-treated spheres was significantly longer
than on untreated spheres. Most recently, Hu et al. (2000) achieved season long residual
activity with 80 % fly kill in laboratory assays after weathering spheres treated with
imidacloprid (Merit® 75 WP) at 1.5 % (AI) in an orchard for 3 months. However, there is
no published research documenting the effectiveness of the insecticides thiamethoxam
(Actara®) or thiocloprid (Calypso®) on apple maggot flies and only one recent paper
(Ayyappath et al. 2000) has discussed the effects of thiomethoxam but not thiocloprid on

blueberry maggot flies using insecticide-treated sphere technology.

26

As Food Quality Protection Act (F QPA) regulations lead to reduction in the use
of organophosphate insecticides and public pressure against the use of broad-spectrum
insecticides increases, it becomes necessary to identify effective non-organophosphate
insecticides for inclusion into novel pest management tactics. The objective of this study
was to investigate the duration of activity and performance of biodegradable spheres
treated with the neonicotinoid insecticides imidacloprid (Provado® 1.6 F and Merit® 75
WP), thiamethoxam (Actara®), and thiocloprid (Calypso®) on apple maggot and
blueberry maggot flies. A second objective was to evaluate whether the commonly used
synergist, piperonyl butoxide (PBO), would increase the toxicity of biodegradable
spheres treated with either imidacloprid (Provado®) or thiamethoxam, (Actara®) to

alighting blueberry maggot flies.

27

MATERIALS AND METHODS

Field experiments to determine the effectiveness of biodegradable, neonicotinoid-
treated spheres in killing apple maggot and blueberry maggot flies were conducted in
commercial apple orchards and blueberry plantings in southwestern Michigan during the
1999 and 2000 field seasons. Biodegradable spheres (9-cm diameter) made fi'om a
combination of sugar, starch, and flour were obtained from the United States Department
of Agriculture (USDA) laboratory in Peoria, IL. Specifications for sphere preparation
were described in Liburd et al. (1999).

Field evaluation of neonicotinoid-treated spheres. The experimental designs were
randomized complete blocks (blocked by apple varieties and blueberry cultivars) with 4
replications. In apples, spheres were spaced 20 m apart within blocks (25 In between
blocks) and were hung 1.5 m above ground within the canopy of Red and Golden
Delicious trees. Spheres were positioned 0.25-0.5 m from fruit and foliage according to
the guidelines suggested by Drummond et a1. (1984). All biodegradable spheres used in
apple maggot experiments were baited with polyethylene vials (Isreal Andler and Sons,
Evrett, MA) containing 4 ml of butyl hexanoate (Penta international Corporation, West
Caldwell, NJ).

In blueberries, biodegradable spheres were hung within the canopy of ‘Bluecrop’
and ‘Jersey’ blueberries at a height 15 cm below the tops of blueberry bushes according
to the recommendations of Liburd et a1. (2000). Biodegradable spheres used in blueberry
maggot experiments were baited with polycon dispensers (Great Lakes IPM, Vestaburg,

MI) containing 5 g of ammonium acetate (Liburd et al.1998a).

28

Apple Maggot (1999). Three treatments were evaluated that included (1) spheres
treated with imidacloprid (Provado® 1.6 F) [Bayer, Kansas City, MO], (2) spheres treated
with thiamethoxam (Actara®) [Novartis, Greensboro, NC], and (3) untreated control
spheres. A sample of apple maggot flies killed was collected using Plexiglas panes (60 x
45 cm) coated with sticky, aerosol-formula Tangle-Trap® (Tanglefoot, Grand Rapids,
MI) and placed horizontally ~ 30 cm below each sphere (Liburd et al.1999). Killed apple
maggot flies were counted by sex and removed from panes twice per week. Data on the
number of apple maggot flies killed were separated into four monitoring periods to reflect
the seasonal abundance of apple maggot flies in Michigan (Howitt, 1993) and to provide
even comparisons with laboratory assays conducted at the University of Massachusetts,
Amherst, MA. During the first monitoring period (8 July-19 July), flies were beginning to
emerge. The second (22 J uly-2 August) and third (5 August-16 August) monitoring
periods constituted peak fly activity, depending on the predominant apple varieties within
the area. During the final monitoring period (19 August-9 September), fly populations
were in decline.

(2090), During our 2000 field season, the three treatments from our 1999 apple
maggot study were selected for further investigation. These treatments were (1)
imidacloprid (Provado®), (2) thiamethoxam (Actara®), and (3) untreated spheres. Two
additional neonicotinoid treatments, thiocloprid (Calypso®) [Bayer, Kansas City, MO]
and another formulation of imidacloprid (Merit® WP 75) were included in our 2000
evaluation of spheres. Spheres were prepared according to the previously described

protocol and all insecticide concentrations were prepared at 2% AI . The Merit® WP 75

29

formulation was prepared as a slurry by mixing the wettable powder with distilled water
prior to mixing this insecticide with paint. The number of apple maggot flies killed was
assessed in the same manner as described for 1999. Field data collected in 2000 were not
compared with laboratory assays. Therefore, data in 2000 were not divided into separate
monitoring periods. The numbers of apple maggot flies killed over the course of the
entire season were compared to determine the most effective insecticide treatment.

Blpebepy Maggot (1992). Field experiments to compare the effectiveness of
imidacloprid and thiamethoxam in blueberry plantings paralleled our apple maggot
studies. The three treatments evaluated included (1) spheres treated with imidacloprid
(Provado® 1.6 F), (2) spheres treated with thiamethoxam (Actara®), and (3) untreated
control spheres. The number of blueberry maggot flies killed was assessed twice per wk
using the Plexiglas pane monitoring system described in our apple maggot experiments.
Blueberry maggot fly data were separated into two distinct monitoring periods to
coincide with the seasonal abundance of blueberry maggot flies in Michigan (Liburd and
Stelinski 1999).

(M0), Our blueberry maggot fly experiment in 2000 likewise paralleled 2000
apple maggot study. Five treatments were evaluated, including (1) imidacloprid
(Provado®), (2) imidacloprid (Merit® WP 75) (3) thiamethoxam (Actara®), (4) thiocloprid
(Calypso®), and (5) untreated control spheres. All insecticide treatments were prepared at
2 % Al. The number of blueberry maggot flies killed was assessed using Plexiglas panes
as described for the 1999 apple experiment. Treatments were compared by using total

numbers of blueberry maggot flies found killed over the course of the entire season.

30

Laboratory bioassays. In 1999, we conducted a laboratory bioassay to determine
the effectiveness of biodegradable spheres treated with imidacloprid (Provado® 1.6 F)
and thiamethoxam (Actara®) in killing blueberry maggot flies. The second objective of
this assay was to evaluate whether the commonly used synergist, piperonyl butoxide
(PBO), would increase the toxicity of biodegradable spheres treated with either
imidacloprid (Provado®) or thiamethoxam, (Actara®) to alighting blueberry maggot flies.

Bioassays were conducted with 5 flies per replicate and each treatment was
replicated 6 times. Blueberry maggot flies were reared from larvae that were collected
from blueberries of unsprayed bushes in Fennville, MI. Flies were maintained in
aluminum screen cages (30 x 30 x 30 cm) and supplied with water and food strips
consisting of 5 x 7 cm sheets of filter paper dipped in a solution of enzymatic yeast
hydrolysate and sucrose [1:3] and dried 24 h prior to use. All flies used in bioassays were
sexually mature (14-20 (1 of age) and deprived of food, but not water, 10 h before testing
(Hu et al. 2000). Different sets of spheres were used for each replicate. Prior to laboratory
bioassays, biodegradable spheres were brush-painted with a mixture containing 2% (A1)
of the neoticotinoid insecticide tested with or without PBO, 20% sucrose solution, 8%
water, and 70% latex paint. Control spheres were painted with the same mixture, lacking
both insecticide and PBO. The sphere treatments were as follows: (1) Irnidacloprid alone
(Provado® 1.6 F), (2) Thiamethoxam alone (Actara®), (3) Irnidacloprid plus PBO in 1:1
ratio, (4) Thiamethoxam plus PBO in 1:1 ratio, (5) Irnidacloprid plus PBO in 1:5 ratio,
(6) Tiomethoxam plus PBO in 1:5 ratio, (7) Control spheres lacking insecticide and PBO.
Spheres were hung from the inner, top surface of cubical wire mesh cages in a central

position. Spheres were lightly moistened 24 h prior to the start of bioassays to simulate

31

natural dew accumulation in the field. Blueberry maggot flies were released into cages
and allowed to feed on all sphere treatments. Feeding duration was defined as time
blueberry maggot fly spent alighting on sphere while exhibiting proboscis extension in a
continuous ‘lapping’ manner. Afler time of exposure to sphere treatments elapsed (10
minutes), flies that had not yet died were removed from cages and placed individually
into plastic cups with food and water. Observations to determine mortality were made
during the lO-minute feeding bout, as well as 1 and 24 hours after feeding.

Statistical Analysis. Data from all experiments were square — root transformed (x
+ 0.5) and then subjected to an analysis of variance (ANOVA). Means were separated by
least significant difference (LSD) (P = 0.05) (SAS Institute 1989). The untransformed

means and standard errors are presented in tables and figures.

32

RESULTS

F ield-pased evaluation of neonicotinoid-treated spheres. During our 1999 apple
maggot study, significantly (F = 35.8; df = 2,6; P < 0.01) more apple maggot flies were
found killed on Plexiglas panes hung beneath biodegradable spheres treated with
imidacloprid (Provado® 1.6 F) compared with spheres treated with thiamethoxam
(Actara®) for data embracing the entire growing season (Table 1). Both imidacloprid and
thiamethoxam-treated spheres killed significantly more apple maggot flies compared with
control (untreated) spheres (Table l). The number of apple maggot flies killed by
imidacloprid-treated and thiamethoxam-treated spheres averaged ~18 and ~8 times more,
respectively, than the number killed by untreated spheres (Table 1).

As the growing season progressed, we noticed changes in the effectiveness of
imidacloprid and thiamethoxam-treated spheres based on Plexiglas trap data. During the
first monitoring period (8 July- 19 July), we recorded significantly (F = 26.4; df = 2,6; P
< 0.01) more apple maggot flies on Plexiglas panes hung beneath imidacloprid-treated
spheres compared with thiamethoxam-treated spheres (Table 1). During the second and
third monitoring periods, there were no significant differences in the number of killed
apple maggot fly beneath spheres treated with either insecticide (imidacloprid or
thiamethoxam) (Table 1). During the fourth monitoring period, again significantly (P <
0.01) more apple maggot flies were killed by imidacloprid-treated spheres compared with

thiamethoxam-treated spheres (Table l).

33

Table 1. Effect of neonicotinoid-treated spheres on apple maggot fly, Michigan (1999).

 

 

 

Sphere 18‘ 2nd 3rd 4th Total Season
Treatments Monitoring Monitoring Monitoring Monitoring
period Period Period Period
7/8-7/19 7/22-8/2 8/5-8/16 8/19-9/9 7/8-9/9
Mean :5 SEM no. flies found killed on Plexiglas
Provado®- 98.8 i 21.1 a 63.3 i 16.1 a 48.0 i 9.0 a 36.8 i 4.8 a 280 i 52.8 a
treated
Actara® - 31.0 i 6.1 b 33.3 i 3.0 a 42.5 32 9.6a 12.5 i 0.9 b 119.3 i 10.6b
treated
Untreated

4.0i3.0c 8.3i7.0b 2.0il.4b l.0i0.0c 15.3 i11.3c

 

Means within the same column followed by the same letter are not significantly different,

(P = 0.05, LSD test).

34

The results of our second year’s apple maggot study showed no significant
differences in the number of killed apple maggot flies beneath spheres treated with either
formulation of imidacloprid (Provado® 1.6 F or Merit® 75 WP) (Table 2). However,
biodegradable spheres treated with either formulation of imidacloprid (Provado® 1.6 F
and Merit® 75 WP) killed significantly (F = 54.9; df = 4,12; P < 0.001) more apple
maggot flies than any other insecticide treatment tested (Table 2). There was no
significant difference in the number of dead apple maggot flies beneath spheres treated

with thiocloprid (Calypso®) and our untreated (control) spheres (Table 2).

35

Table 2. Comparison of neonicotinoid insecticides at 2 % AI using biodegradable sphere

for control of apple maggot, Michigan (2000).

 

 

Sphere treatments Mean i SEM no. killed apple maggot flies
6/26 — 8/11
Imidacloprid-treated (Provado® 1.6 F) 182.8 i 13.6 a
Imidacloprid-treated (Merit® 75 WP) 190.0 i 35.7 a
Thiomethoxam-treated (Actara®) 76.3 i 8.6 b
Thiocloprid-treated (C alypso®) 10.8 i 2.8 C
Untreated (control) 9.8 21‘. 1.5 C

 

Means within the same column followed by the same letter are not significantly different,

(P = 0.05, LSD test).

36

The results from our 1999 blueberry field experiments were different from those
observed for apples. There were no significant differences between the number of killed
blueberry maggot flies found on Plexiglas panes hung beneath spheres treated with either
imidacloprid or thiamethoxam over the course of the season (Table 3). Also, there was no
significant difference in the number of flies killed between imidacloprid and
thiamethoxam-treated spheres in either first or second monitoring periods. However, we
recorded significantly (F = 32.4; df = 2,6; P < 0.01) more killed blueberry maggot flies
on Plexiglas panes placed beneath treated spheres compared to untreated spheres (Table

3).

37

Table 3. Effect of neonicotinoid-treated spheres on blueberry maggot fly, Michigan

 

 

 

(1999)
Sphere treatments 1St Monitoring 2“Wonitoring Total Season
‘ period Period
7/16-7/22 7/28-8/6 7/8-9/9
Mean i SEM no. flies found killed on Plexiglas

Provado®- 99.8 i 17.2 a 52.3 i 9.9 a 133.5 i 30.4 a
treated

Actara® -treated 71.3 i 34.0 a 27.5 i 11.9 a 127.3 i 43.5 a
Untreated 12.3 i 3.8 b 3.5 i1.8 b 15.8 i 5.0 b

 

Means within the same column followed by the same letter are not significantly different,

(P = 0.05, LSD test).

38

Our second year’s blueberry maggot results were similar to those observed in our
apple maggot 2000 field studies. There were no significant differences in the number of
blueberry maggot flies killed by either Provado® 1.6 F or Merit® 75 WP (Table 4).
However, both imidacloprid treatments killed significantly (F = 53.2; df = 4,12; P <
0.001) more blueberry maggot flies compared with spheres treated with thiamethoxam
(Actara®) (Table 4). On average, imidacloprid-treated spheres killed 2.3 times as many
flies compared with spheres treated with thiamethoxam (Table 4). Finally, spheres treated
with thiocloprid (Calypso®) did not kill significantly more blueberry maggot flies

compared with control spheres (Table 4).

39

Table 4. Comparison of neonicotinoid insecticides at 2 % AI using biodegradable sphere

for control of blueberry maggot, Michigan (2000).

 

 

Sphere treatments Mean i SEM no. killed blueberry maggot
flies
6/26 — 8/11
Imidacloprid-treated (Provado® 1.6 F) 512.0 i 78.5 a
Imidacloprid-treated (Merit® 75 WP) 449.3 i 72.0 a
Thiomethoxam-treated (Actara®) 216.3 2% 47.7 b
Thiocloprid-treated (Calypso®) 121.5 i 8.6 c
Untreated (control) 93.8 i 19.9 c

 

Means within the same column followed by the same letter are not significantly different,

(P = 0.05, LSD test).

40

Laboratog bioassays. After the 10 minutes of feeding, significantly (F = 13.4; df
= 11,41; P < 0.001) more blueberry maggot flies were killed by spheres treated with
imidacloprid (Provado®), thiamethoxam (Actara®), imidacloprid + PBO (1 : 5 ratio), and
thiamethoxam + PBO (1 : 5 ratio) compared with spheres treated with imidacloprid +
PBO (1 : 1 ratio) (Table 5). Twenty-four hours after the allowed lO-minute feeding bout,
100 % mortality was achieved among all sphere treatments (Table 5). There was no
mortality observed in the flies that alighted and fed upon the untreated control spheres 24

hours after exposure to spheres (Table 5).

41

Table 5. Percent mortality of blueberry maggot flies that fed upon neonicotinoid—treated

spheres with and without piperonyl butoxide (PBO).

 

 

Sphere treatments Percent of Percent of Percent of
cumulative cumulative cumulative
mortality after 10 mortality 1 hour mortality 24 hours
minutes of feeding after exposure after exposure
Mean i SEM no. dead flies

Provado® 73.4 i 4.3 a 100 i 0.0 a 100 i 0.0 a

Actara® 63.4 i 6.2 a 90 i 6.4 ab 100 i 0.0 a

Provado® : PBO 36.6 i 8.0 c 76.6 i: 12.0 bc 100 i 0.0 a

(1:1)

Actara® : PBO (1 :1) 40.0 i 10.4 bc 60 .+_ 7.4 c 100 i 0.0 a

Provado® : PBO 56.6 i 8.0 ab 80 :1: 12.6 abc 100 1r 0.0 a

(1 :5)

Actara® : PBO (1:5) 63.4 i 8.0 a 73.4 i 4.3 bc 100 i 0.0 a

Untreated (control) 0.0 :t 0.0 d 0.0 i 0.0 d 0.0 :1: 0.0 b

 

 

Means within the same column followed by the same letter are not significantly different,

(P = 0.05, LSD test).

42

DISCUSSION

The study demonstrated that baited, biodegradable spheres treated with the
insecticide imidacloprid, irrespective of formulation (Provado® 1.6 F or Merit® 75 WP),
were more effective in killing apple maggot flies than identical spheres treated with
thiamethoxam or thiocloprid. Upon initial field deployment, imidacloprid-treated spheres
killed high numbers of apple maggot flies, but there was a gradual decrease in the number
of flies killed as the season progressed. Alternatively, thiamethoxam-treated spheres
killed fewer apple maggot flies initially and the numbers of flies killed also gradually
decreased as the season progressed. The decreased numbers of dead flies over time may
be due to a number of factors, including loss of insecticide from sphere coating, aging
effects on spheres, decreasing fly populations in late season, or a combination of these
factors.

During our second (2000) field season, spheres treated with either formulation of
imidacloprid showed equal effectiveness in killing apple maggot flies. Thiamethoxam-
treated spheres again killed fewer apple maggot flies than imidacloprid-treated spheres.
Laboratory bioassays conducted in 1999 at the University of Massachusetts, Amherst,
MA supported our field data by indicating that field-aged imidacloprid-treated spheres
were more effective in killing apple maggot flies compared with similarly weathered
thiamethoxam-treated spheres (Stelinski et al. in press). Spheres treated with thiocloprid
(Calypso®), however, were no more effective than control spheres in the field. We
believe that treating spheres with imidacloprid rather than thiamethoxam or thioclOprid
may result in more effective control of apple maggot flies in commercial orchards.

The results from our blueberry studies were slightly different from those observed

43

in apples. In 1999, imidacloprid— and thiamethoxam-treated spheres showed statistically
equal effectiveness in killing blueberry maggot flies throughout the blueberry-growing
season. By contrast, in 2000 imidacloprid-treated spheres performed better than
thiamethoxam-treated spheres over the course of the season. In 2000, we captured our
first blueberry maggot fly on monitoring traps two weeks earlier than in 1999. Therefore,
all biodegradable sphere treatments were deployed in the field two weeks earlier in 2000
(26 June) compared with than the July 16 deployment date in 1999. However, during
both years blueberry maggot fly mortality was monitored until the end of berry harvest (6
August in 1999 and 11 August in 2000). The longer period field exposure of
thiamethoxam-treated spheres in 2000 may have resulted in the greater observed decline
in efficacy near the end of that field season, while such a decline was not observed for
imidacloprid-treated spheres. These results imply that thiamethoxam may have been lost
from biodegradable spheres at a greater rate than imidacloprid. As observed for the apple
maggot fly, spheres treated with thiocloprid were no more effective in killing blueberry
maggot flies than control spheres in the field.

Laboratory bioassays conducted at the University of Massachusetts in Amherst
using biodegradable and wooden spheres provided us with data similar to those obtained
in the field and helped explain some of the differences and changes in effectiveness that
were observed over the course of the growing season in Michigan (Stelinski et al. in
press). The assays also showed that the effectiveness and period of activity of
imidacloprid- and thiamethoxam-treated spheres could be lengthened by increasing the
percentage of A1 of insecticide in the spheres above 2 %. Such a change in formulation

needs further research before it can be implemented in commercial apple orchards.

44

However, increasing the concentration of AI above 2 % may not be necessary for
blueberry maggot fly management.

The Massachusetts bioassays also indicated that fungal infestation acquired by
both biodegradable and wooden spheres over the course of the growing season does not
significantly decrease the spheres’ effectiveness in killing apple maggot flies (Stelinski et
al. in press). Such fungal growth was observed in the field during the 4th monitoring
period in apple orchards in Michigan. The problem of flmgal growth was less apparent in
our blueberry field experiments. The shorter sphere deployment period necessary for
control of blueberry maggot flies may account for the observed differences in fimgal
growth on the spheres.

In addition to fimgal growth, rodent feeding has been observed to be a problem
with using biodegradable spheres. Assays showed that biodegradable spheres that were
previously fed upon by rodents had a decreased effectiveness (Stelinski et al. in press).
Also, the complete loss of spheres in the field due to animal feeding is a significant
problem. In Michigan, rodent feeding appeared to be insignificant in 1999 when ~ 95 %
of spheres deployed in field studies were retrieved at the end of the season. In 2000,
however, ~ 20 % of spheres deployed in an abandoned apple orchard required
replacement one month after initial deployment because of rodent feeding.

Our findings with respect to feeding stimulants were consistent with the earlier
studies of Hu et al. (1998). The use of a feeding stimulant (sucrose) encourages
prolonged feeding and increases the potential for Rhagoletis flies to ingest a greater
dosage of insecticide. Although aged wooden spheres performed equally well or better

than aged biodegradable spheres in the Massachusetts laboratory studies, previous field

45

studies have shown that the use of wooden spheres requires the periodical reapplication
of feeding stimulant, because the externally applied sucrose is washed off due to rain
(Stelinski et al. in press). Therefore, we still support filrther development and future use
of biodegradable spheres or the development of a constant release sucrose dispenser to be
used with wooden spheres as a control tactic for key Rhagoletis species.

The laboratory bioassays conducted in Michigan showed that imidac10prid- and
thiamethoxam-treated spheres that were not exposed to outdoor environmental conditions
were equally effective in killing blueberry maggot flies. The fact that thiamethoxam-
treated sphere are less effective than imidacloprid-treated spheres in the field provides
further evidence that thiamethoxam is either broken down or washed off of spheres at a
higher rate than imidacloprid. The addition of PBO in both 1 : 1 and 1 : 5 ratios to
imidacloprid and thiamethoxam applied to biodegradable spheres did not increase their
effectiveness in killing blueberry maggot flies. However, it was also observed that
spheres containing PBO appeared to deter alighting blueberry maggot flies. Flies exposed
to this treatment required periodic recapture and replacement, while flies placed on
spheres treated only with the insecticide (imidacloprid or thiamethoxam) remained on
spheres for the duration of the allowed 10 minute feeding interval.

Overall, both field and laboratory experiments confirmed several crucial
requirements that must be met in order for insecticide-treated spheres to be effective
throughout the growing season. First, they must deliver a lethal dose of insecticide over
the course of the entire growing season in order to provide adequate fruit protection.
Second, they must be able to withstand adverse weather conditions and present a feeding

deterrent for rodents. Future prototypes of biodegradable spheres should include

46

appropriate anti-fungal agents and rodent-feeding deterrents.

Recent studies have shown that insecticide-treated spheres can achieve
comparable control of the apple maggot fly (Prokopy et al. in press) and the blueberry
maggot fly (Stelinski and Liburd in press) to the use of organophosphate insecticides.
This study demonstrated that field-deployed imidacloprid-treated spheres are more
effective in killing apple maggot and blueberry maggot flies than similar spheres treated
with thiamethoxam or thiocloprid. The study also provided initial evidence that the use of
the neonicotinoid insecticide thiocloprid at 2 % A1 with biodegradable spheres may be an
ineffective tactic. Thus, we provide fiirther evidence that imidacloprid is currently the
most effective neonicotinoid insecticide tested for use with biodegradable spheres against

both apple maggot and blueberry maggot flies.

47

HAPTER THREE

EVALUATION OF VARIOUS DEPLOYMENT STRATEGIES OF IIVIIDACLOPRID-

TREATED SPHERES IN HIGHBUSH BLUEBERRIES FOR CONTROL OF

RHA GOLE T IS MENDAX CURRAN

48

INTRODUCTION

Given their status as insect pests of economic significance, species within the
genus Rhagoletis have been the subject of a vast number of studies focusing on the
development of integrated management strategies (Boller and Prokopy 1976, AliNiazee
1978, Prokopy et al. 1990, Liburd et al. 1999). Many of these studies have concentrated
on the development and optimization of monitoring techniques (Kring 1970, Prokopy and
Hauschild 1979, Drummond et al. 1984, Liburd et al. 2000) for early season detection of
adult flies. Effective monitoring techniques for fruit parasitic tephritids are of great
importance given the strict tolerance levels imposed on maggot infested fruit (Liburd et
a1. 2000). Additionally, sensitive monitoring of adult flies in commercial settings can
potentially reduce unnecessary, prophylactic pesticide applications.

In addition to the optimization of monitoring techniques for key Rhagoletis
species, a considerable amount of research has dealt with the development of behavioral
control methods designed to complement existing management techniques, such as
pesticide spray applications (Prokopy and Mason 1996). Many of the behavioral control
tactics involve the exploitation of fly response to visual and olfactory stimuli using fruit
or foliage mimicking sticky traps baited with food or host-fruit mimicking synthetic
attractants (Russ et al. 1973, Neilson et. al. 1981, Stanley et a1. 1987, Duan and Prokopy
1992). In addition to their effectiveness as monitoring devices, Prokopy et a1. (1990)
showed that appropriately baited and visually attractive traps had the potential of
reducing fruit injury when deployed within orchards to intercept immigrating adult apple
maggot flies, Rhagoletis pomonella (Walsh). Furthermore, Reynolds et a1. (1998) found

that both perimeter and within-orchard deployment patterns of odor-baited red sticky

49

spheres reduced oviposition by apple maggot flies compared with control blocks without
such traps.

The use of odor-baited sticky traps (Neilson et al. 1984, Liburd et al. 1998b) and
biodegradable attract-and-kill devices (Liburd et al. 1999, Ayyappath et al. 2000) have
been evaluated against Rhagoletis mendax Curran and have potential for implementation
as behavioral control tactics. Liburd et al. (1999) reported that biodegradable, fruit-
rnirnicking spheres treated with the neonicotinoid insecticide imidacloprid effectively
killed both blueberry maggot and apple maggot flies in field studies. In a later study,
Ayyappath et al. (2000) demonstrated that biodegradable spheres treated with the
neonicotinoid insecticide Actara® (thiomethoxam) were also effective in killing blueberry
maggot flies in blueberry plantings. The results of this same study revealed that
increasing the dosage of thiomethoxam used with biodegradable spheres prolonged their
effectiveness when deployed in the field. Most recently, Prokopy et al. (in press) showed
that both wooden and biodegradable insecticide-treated spheres were only slightly less
effective than the use of organophosphate sprays or sticky red spheres in preventing fruit
injury by R. pomonella.

The potential benefits of using insecticide-treated spheres instead of
organophosphate applications or odor-baited sticky traps for control of R. mendax has
been cited in recent studies (Liburd et al.1999, Ayyappath at al. 2000). However, there
are no detailed studies demonstrating how insecticide-treated sphere deployment tactics
within highbush blueberries (Vaccinium corymbosum, L.) affect the status of resident or
immigrant populations of blueberry maggot flies. Also, no direct comparisons of

conventional organophosphate sprays versus deployment of insecticide-treated spheres

50

have been made with respect to controlling R. mendax. Consequently, there has been no
documentation of preventing fruit injury caused by blueberry maggot fly oviposition with
the use of insecticide-treated spheres.

The objective of this study was to evaluate three potential insecticide-treated
sphere deployment patterns in highbush blueberry plantings to determine how they may
impact fi'uit injury and infestation levels of R. mendax. Furthermore, the study aimed to
compare insecticide-treated spheres, as a behavioral control tactic for blueberry maggot

flies, with conventional spray applications of an organophosphate.

51

MATERIALS AND METHODS

Field experiments to determine the effectiveness of biodegradable spheres treated
with the neonicotinoid insecticide Provado® (Irnidacloprid) [Bayer, Kansas City, M0],
for the control of blueberry maggot flies were conducted at an experimental blueberry
farm in Douglas, Michigan in 1999 and 2000. Biodegradable spheres (9-cm diameter),
made with the specifications outlined in Liburd et al. (1999), were obtained from the
United States Department of Agriculture (USDA) laboratory in Peoria, IL. Spheres were
brush-painted with two coats of a mixture containing DevFlex latex green paint (ICI
Paints) (70 %), sucrose feeding stimulant (20 %), water (8 %) and Provado®
(Irnidacloprid) at 2 % AI (Liburd et al. 1999). Spheres were allowed to dry for 72 hours
prior to field deployment. Biodegradable spheres were hung within the canopy of
blueberry bushes within the cultivar Jersey at a height approximately 15 cm below the
tops of the uppermost bush according to the recommendations of Liburd et al. (2000).
Biodegradable spheres used in blueberry maggot experiments were baited with polycon
dispensers (Great Lakes IPM, Vestaburg, MI). The dispensers were attached to the strings
used for hanging spheres and contained 5 g of ammonium acetate (Liburd et al. 1998b).
The experimental designs were completely randomized blocks with 4 replications.

& The experiment was designed to determine the most effective strategy for
deploying (arrangement and interval distance) imidacloprid-treated spheres to control R.
mendax and consequently reduce maggot injury and infestation. The experimental plots
were 10 x 40 m rectangles, containing 3 rows of 12 highbush blueberries. Treatments
were randomly assigned to the experimental plots contained within larger blueberry

plantings. All treatment plots were spaced at least 20 m apart and treatments were

52

assigned randomly with respect to field borders. Twelve biodegradable, imidacloprid-
treated spheres were used in each treatment / replicate (Figure 1). The 4 treatments
evaluated were: (1) perimeter deployment in which spheres were hung individually and
spaced equally around the perimeter of experimental plots (Figure 1); (2) cluster
deployment in which 4 groups of 3 spheres were hung in equally spaced perimeter
locations of experimental plots (Figure 1); (3) uniform deployment in which spheres were
placed 10 m apart (in a grid-like pattern) within experimental plots (Figure 1); (4)
untreated experimental plots containing no spheres (Figure 1). All spheres were deployed
on 30 June afier the detection of the first adult blueberry maggot on Pherocon AM yellow
sticky boards (Great Lakes IPM, Vestaburg, Michigan).

Fruit evaluation. At the end of the growing season (5 August), three hundred ripe
blueberries (majority of berries turned blue around stem) were picked at random from
each experimental plot and kept separate according to treatment. From each batch of 300
berries, 50 were randomly selected and examined under a magnifying lens for blueberry
maggot fly oviposition scars. The numbers of berries with oviposition scars were used to
calculate percent fruit injury. All 300 berries from each replicate were then placed over
0.5 cm mesh hardware cloth to allow larvae to exit the fruit and drop into containers
filled with vermiculite (Liburd et a1 1998 b). The vermiculite was sif’ted and blueberry

maggot fly puparia were collected and counted in order to quantify fruit infestation.

53

@011

O O G @

Perimeter G E Cluster

Q@®

 

O

O 0 O O

Internal-grid

Q Q Q Untreated
9 3 6 G

 

Figure 1. Irnidacloprid-treated sphere deployment strategies within highbush
blueberries.

fl - 9 cm diam, green imidacloprid-treated sphere

 

- 10 x 40 m Highbush blueberry plot

 

 

 

54

m During our second field season, we evaluated the same three imidacloprid-
treated sphere deployment strategies as described for 1999 and compared deployment
tactics with standard treatment of Guthion 50 W (azinphos-methyl) [Bayer, Kansas City,
MO] sprays. Azinphos-methyl sprays were made on lS-June, 6- and 25-July with a
tractor air-blast sprayer (Air-O-F an, Reedley, CA). Plot sizes and experimental designs in
2000 were identical to those described for 1999; plots receiving azinphos-methyl sprays
were spaced 50 m or further away from sphere-treated plots. The 5 treatments evaluated
were: (1) perimeter sphere deployment; (2) cluster sphere deployment; (3) uniform
sphere deployment; (4) Two applications of Guthion 50 W at a rate of 1.7 kg/hectare; (5)
untreated experimental plots containing no spheres or azinphos-methyl sprays. All
spheres were deployed on 20 June.

Fruit evaluation. Twelve hundred ripe blueberries were picked (August 8) at
random from each experimental block and fruit was kept separate according to treatment.
Similar to our procedure in 1999, we randomly selected 50 from each batch of 1200 and
examined them under a magnifying lens for R. mendax oviposition scars. The numbers of
berries with oviposition scars were again used to calculate percent fruit injury. All 1200
berries from each replicate were then placed over 0.5 cm mesh hardware cloth as
described for 1999 and blueberry maggot fly puparia were later collected and counted in
order to quantify fruit infestation.

Monitoring. During the second year of our study (2000), two unbaited Pherocon
AM yellow sticky boards (Great Lakes IPM, Vestaburg, Michigan) were hung 20 m apart

in the center of each treatment plot to monitor R. mendax activity within treatments.

55

Traps were positioned in the V shaped orientation (folded into a 45°- degree angle with
apex downward and sticky surface outwards) (Prokopy and Coli 1978). Flies were
counted and removed from traps two times per week and traps were replaced in the field
every two weeks.

Statistipal Analysis. Percentage data from fruit injury analysis were arcsine
transformed and fly monitoring data were square - root transformed (x + 0.5) to stabilize
variances and then subjected to an analysis of variance (ANOVA). Least significant
difference (LSD) tests were used to show treatment mean differences (P = 0.05) (SAS

Institute 1989). The untransformed means and standard errors are presented in tables.

56

RESULTS

(£22), Significantly (F = 29.1; df = 3,9; P < 0.01) more oviposition scars and
puparia (F = 71.1; df = 3,9; P < 0.01) were recorded from blueberries that were collected
from the untreated plots (not containing spheres) compared with berries from plots that
contained imidacloprid-treated spheres, regardless of their deployment pattern (Table 6).
The numbers of oviposition scars in untreated blocks were 3 times higher than sphere-
treated blocks. Likewise, the numbers of puparia in untreated blocks were 11.6 times
higher than in sphere-treated blocks. We recorded no significant differences in the
numbers of R. mendax oviposition scars and puparia from blueberries collected from
plots containing imidacloprid-treated spheres in the three deployment strategies tested.
(Table 6). Finally, the percentages of fruit injury based on oviposition scars and puparia
recorded were below 1 and 2 %, respectively, in all plots containing imidacloprid-treated

spheres (Table 6).

57

Table 6. Percentage of fruit injury and infestation due to R. mendax oviposition,

Michigan (1999).

 

 

 

Mean i SEM
Control Strategy Oviposition scars Puparia

Perimeter deployment of 0.3 i 0.3 b 1.3 i 0.6 b
spheres

Internal-grid deployment of 0.3 i 0.3 b 1.0 i 1.0 b
spheres

Cluster deployment of 0.0 i 0.0 b 1.8 i 0.5 b
spheres

Untreated plots (Control) 3.7 i 0.2 a 21.0 i 2.4 a

 

Means within columns followed by the same letter are not significantly different, (P =

0.05, LSD test).

58

(20(1)), The results of our second year’s study were similar to those observed in
1999. Significantly (F = 21.3; df = 4,12; P < 0.01) more oviposition scars and puparia (F
= 10.1; (if = 4,12; P < 0.01) were found on berries picked from untreated control plots
compared with plots containing imidacloprid-treated spheres or plots sprayed with
Guthion (Table 7). Untreated (control) plots had more than 2.5 times as many oviposition
scars and/or puparia compared with any of our plots treated with imidacloprid-treated
spheres or Guthion sprays. We did not record any significant differences in the numbers
of R. mendax oviposition scars or puparia from berries collected from plots containing
imidacloprid-treated spheres in the three deployment strategies tested (Table 7). An
important finding was that there were no significant differences in fruit injury, based on
oviposition scar data, between plots containing imidacloprid-treated spheres and those
sprayed with Guthion (Table 7). However, plots treated with Guthion had significantly (F
= 10.1; df = 4,12; P < 0.01) fewer puparia compared with plots containing imidacloprid-
treated spheres (Table 7).

In our monitoring program, significantly (F = 9.3; df = 4,12; P < 0.01) more R.
mendax flies were captured on Pherocon AM boards placed within control plots
compared with fly captures in plots containing imidacloprid-treated spheres in perimeter,
uniform, and cluster orientations and plots sprayed with Guthion (Table 8). There were
no significant differences in the numbers of blueberry maggot flies captured on unbaited
Pherocon AM boards within plots containing imidacloprid-treated spheres, regardless of

deployment pattern, and plots sprayed with Guthion (Table 8).

59

Table 7. Percentage of fruit injury and infestation due to R. mendax oviposition,

Michigan (2000).

 

 

 

Mean i SEM
Control Strategy Oviposition scars Puparia

Perimeter deployment of 4.0 i 1.8 b 1.3 i 0.3 b
spheres

Internal-grid deployment of 4.0 i 0.8 b 0.8 i 0.1 b
spheres

Cluster deployment of 4.6 i1.0 b 1.0 i 0.2 b
spheres

Guthion (azin-phosmethyl) 2.0 i 0.8 b 0.1 i 0.1 c

spray
Untreated plots (Control) 11.6 i 1.0 a 3.9 i 0.7 a

 

Means within columns followed by the same letter are not significantly different, (P =

0.05, LSD test).

60

Table 8. Mean number of R. mendax captured on unbaited Pherocon AM boards within

treatment plots, Michigan, (2000).

 

Mean i SEM no. R. mendax

 

 

Control Strategy 25 June-8 August
Perimeter deployment of spheres 20.0 i 4.4 b
Internal-grid deployment of spheres 19.3 i 2.8 b
Cluster deployment of spheres 16.5 d: 2.1 b
Guthion (Azinphosmethyl) spray 14.5 d: 2.8 b
Untreated plots (Control) 47.0 i 5.3 a

 

Means within each experiment followed by the same letter are not significantly different,

(P = 0.05, LSD test).

61

DISCUSSION

Our results showed that deployment of imidacloprid-treated, biodegradable
spheres decreased blueberry infestation levels to 1 % in 1999 and 0.8 % in 2000 (with
internal-grid deployment patterns), while untreated (control) plots had maggot infestation
levels > 20 % and > 3.2 % in 1999 and 2000, respectively. In both years, there were no
differences in fi'uit injury levels obtained using the three different strategies for sphere
deployment. Several factors may have contributed to the observed non-significant
differences, including the fact that the blueberry planting used in our experiments had a
residential population of R. mendax flies (emerging from within the planting), as well as
immigrating populations invading from the surrounding areas and natural bogs. Perimeter
trapping tactics could be effective in intercepting immigrants (Prokopy et al. 1990) into
the planting, but the degree of fruit protection from fly oviposition is dependent on trap
spacing, the pressure of immigrating flies, and field status with respect to the presence or
absence of residential blueberry maggot fly populations. By contrast, the internal-grid
pattern of sphere deployment may hold more potential in suppressing adult blueberry
maggot flies and preventing fruit infestation in plantings harboring residential fly
populations. Again, the effectiveness of the intemal-grid pattern is dependent on the
degree of sphere spacing and fly population densities within the planting. Also, factors
such as fruit-load, degree of fruit maturity, and the physiological status of R. mendax
(Liburd and Stelinski 1999), may influence the effectiveness of the intemal-grid
deployment pattern. Overall, our experiments have implied that specific sphere placement
patterns (perimeter versus intemal-grid) may be less important in blueberry plantings that

are exposed to both residential and immigrating R. mendax populations.

62

The observed non-significant differences among the deployment strategies tested
may have been also due to equal levels of visual and olfactory stimuli provided by the
odor-baited, fruit-mimicking spheres in each treatment plot. Given the strong attraction of
R. mendax to 9 cm diam green spheres baited with ammonium acetate (Liburd et al.
1998a, 2000), it is possible that flies foraging within each of our plots had approximately
equal probabilities of encountering the bait-odor or visual stimulus provided by the
imidacloprid-treated spheres, irrespective of sphere deployment patterns. This may have
been due to our relatively small plot sizes and comparatively small differences between
baited sphere spacing in the perimeter treatments versus the uniform or cluster
treatments. Future studies comparing the effectiveness of imidacloprid-treated sphere
deployment strategies should be conducted within plantings known to harbor resident
populations of R. mendax, as well as in plantings that are only infested seasonally by
immigrant blueberry maggot flies. By conducting a comparison of residentially infested
plots versus those that receive immigrants only, it may be possible to gain filrther insight
into the importance of sphere deployment patterns for effective fruit protection. Also,
future studies must include larger scale treatment plots before this technology can be
recommended to growers as a possible substitute to conventional pesticide applications.

During the second field season (2000), we found that field-deployed,
imidacloprid-treated spheres were only slightly less effective than conventional
applications of a sprayed organophosphate (Guthion 50 W at 1.7 kg/hectare) insecticide
in providing fruit protection against R. mendax oviposition. We observed no difference in
fruit injury (oviposition scars) and only a 0.9 % difference in fruit infestation between

plots sprayed with Guthion and plots protected by imidacloprid-treated spheres. These

63

results indicate that it is possible to achieve fruit protection against R. mendax oviposition
equivalent to the level obtained with broad-spectrum, organophosphate sprays in
highbush blueberries. However, the sphere density used in our experiments to compare
the various deployment patterns was relatively high. At an estimated cost of a $1.00 per
sphere, commercial use of this technology would necessitate a smaller number of
deployed spheres in order for this technology to be commercially viable and comparable
to insecticide treatments. Future research must also focus on optimizing sphere
deployment densities and determining whether effective and economically viable
densities can be achieved.

Our monitoring program confirmed that blueberry maggot fly activity in plots
containing imidacloprid-treated spheres was suppressed to a level similar to that observed
in plots that were treated with Guthion. Similar suppression of fly activity has been
recorded with the apple maggot fly foraging in areas where imidacloprid-treated spheres
were deployed (Liburd et al. 1999, Prokopy et al. in press). In a separate study, Stelinski
et al. (in press) showed that imidacloprid-treated spheres at 2 % AI did not lose their
effectiveness in killing R. mendax throughout the duration of the 9 wk period when
sexually mature flies are ovipositing (Liburd and Stelinski 1999). We therefore believe
that a single deployment of ammonium-baited, imidacloprid-treated spheres could
potentially provide effective, season-long control of blueberry maggot flies in a
commercial setting.

Despite their effectiveness, the current version of biodegradable spheres is
susceptible to rodent feeding. We encountered this problem in 2000 and replaced ~ 10 %

of our spheres two weeks after initial deployment. Future prototypes of insecticide-

treated spheres must be more resistant to rodent feeding if this technology is to be
effectively implemented as a control tactic for blueberry maggot flies.

To our knowledge, this is the first study that documents deployment of
biodegradable, imidacloprid-treated spheres as a form of behavioral control reduces R.
mendax infestation levels below 1 %. Although this is still above the currently mandated
zero tolerance, we believe that even greater control can be achieved by making spheres
more attractive with more effective and selective baiting systems, further optimizing
sphere deployment and density strategies, and perhaps making fruit less attractive by
coating it with visual or olfactory deterrents. Due to their target-specificity and reduced
impact on the surrounding environment, imidacloprid-treated spheres have potential for
integration into a second level IPM program (Prokopy 1990) by involving methods of
cultural (Liburd et al. 1998b) and biological controls. Our study provides direct evidence
for the potential of using biodegradable spheres treated with imidacloprid for control of

blueberry maggot fly.

65

CHAPTER EQUR

ATTRACTION OF APPLE MAGGOT F LIES, RHA GOLE T IS POMONELLA (WALSH)
(DIPTERA: TEPHRITIDAE), TO SYNTHETIC FRUIT VOLATILE COMPOUNDS

AND FOOD ATTRACTANTS IN MICHIGAN APPLE ORCHARDS.

66

INTRODUCTION

Michigan ranks second or third (depending on annual production) in crop value in the
US. apple industry. Apples are grown commercially on more than 23,400 ha and more
apples are produced by volume than all other Michigan fruits combined (Michigan Apple
Committee, 2000). The apple maggot, Rhagloletis pomonella (Walsh), is an important
fruit pest infesting commercially grown apples in Michigan and throughout the eastern
United States. There is a zero tolerance for maggot infestation in apples bound for
commercial sales. High numbers of apple maggot flies migrate into commercial orchards
in Michigan, responding to visual and olfactory cues of host fi'uit, where mating and
oviposition occurs (Liburd and Stelinski 1999). Sensitive and reliable monitoring
techniques for the apple maggot fly are of extreme importance for making accurate and
responsible control decisions.

Apple maggot flies are attracted to apple odors in the field (Prokopy et al.1973,
Reisig 1974). Location of appropriate mating and oviposition sites by apple maggot flies
is mediated in part by odors, which serve as primary cues for host site location and
acceptance in fruit parasitic insects (Frey and Bush 1990). Among apple volatiles isolated
from two apple varieties (Red Delicious and Red Astrachan), a blend consisting of a
series of short chain carbon esters, including butyl hexanoate, is attractive to apple
maggot flies (Fein et al. 1982). A comparison of visual stimuli showed that unbaited, 8
cm diam. red spheres captured significantly more apple maggot flies than unbaited, 10
cm diam. red spheres (Duan and Prokopy 1992). Furthermore, sticky spheres baited with

vials of butyl hexanoate captured significantly more apple maggot flies than unbaited

67

spheres, although there was no difference in catch with one, two, or four vials/sphere. A
combination treatment containing one vial of ammonium carbonate and one vial of butyl
hexanoate also significantly increased the capture of apple maggot flies compared to
capture on unbaited spheres.

More recently, Reynolds and Prokopy (1997) evaluated synthetic odor lures
(butyl hexanoate, ammonium carbonate, or butyl hexanoate plus ammonium carbonate on
red sticky spheres) for their attractiveness to apple maggot flies. Butyl hexanoate plus
ammonium carbonate was more attractive than either odor alone. Finally, a recent study
has shown that a lure consisting of a mix blend of synthetic apple volatiles, including
butyl butanoate, propyl hexanoate, butyl hexanoate, hexyl butanoate, and pentyl
hexanoate combined in specific proportions, is significantly more attractive to adult apple
maggot flies than lures containing butyl hexanoate alone.

In addition to synthetic fruit volatiles, other odor baits are used in tephritid
monitoring programs. Attraction of the Queensland fruit fly, Dacus tryom' F roggatt, to
several hydrolysed proteinaceous baits is mainly due to the ammonia they release
(Bateman and Morton 1981). Ammonium acetate is also commonly used as an attractant
in tephritid monitoring programs in Michigan (Liburd and Stelinski 1999). Ammonia is a
by-product of the bacterial decay of several adult tephritid food sources (Prokopy and
Roitberg 1984). Ammonia-producing baits may be attractive because flies are seeking a
protein source important for egg maturation (Prokopy and Roitberg 1989, Prokopy 1993,
and Prokopy et al. 1994).

The goal of this research was to establish a sensitive, reliable, and selective

monitoring device for the apple maggot fly that can be implemented by apple growers in

68

Michigan and other apple producing regions. The objective of this study was to evaluate
the attractiveness to of several synthetic fruit volatile lures, as well as ammonium-odor
and protenacious baits, to the apple maggot fly using sticky-coated red sphere monitoring

traps.

69

MATERIALS AND METHODS

Research on potential baits for apple maggot flies was conducted in apple
orchards in Van Buren Co., Michigan during the 1998, 1999, and 2000 field seasons.
Each treatment consisted of a 9 cm diam., red sphere coated with 13 g of Tangle Trap®
(Great Lakes IPM Vestaburg, MI). Spheres were hung approximately 25 m apart and 30
m between one-acre blocks of Red Delicious and Golden Delicious. The experimental
designs were randomized blocks (blocked by apple variety) with four replications. Traps
were replaced every three weeks in the field and re-randomized weekly. Apple maggot
flies caught in traps were counted and removed twice per week. They were counted by
sex once per week. Visual estimates of beneficial and non-beneficial insects captured on
spheres were made in the field in 1998 and 2000.

(1998 ). Experiment 1. The purpose of this experiment was to evaluate the
importance of protein hydrolysate and ammonium baits for capture of apple maggot flies.
Depending on the treatment, varying amounts of ammonium acetate, ammonium
carbonate, and protein hydrolysate were mixed thoroughly into the 13 g of Tangle Trap®
before it was applied to the spheres. Apple maggot BioLure® (contained in a plastic
dispenser) was used in some treatments. The plastic dispenser with BioLure® contained
1.8 g (load rate) butyl hexanoate. The experiment evaluated nine treatments that included
a red sphere coated with (1) 2 g of ammonium acetate (Aldrich Chemical Co.,
Milwaukee, WI) plus 0.5 g protein hydrolysate (Pfaltz & Bauer Chemicals Co.,
Waterbury, CT) and apple maggot BioLure®, (2) 2 g ammonium acetate plus 0.5 g
protein hydrolysate, (3) 2 g ammonium acetate, (4)2 g of ammonium carbonate plus 0.5

g protein hydrolysate and apple maggot BioLure®, (5) 2 g ammonium carbonate plus 0.5

70

g protein hydrolysate, (6) 2 g ammonium carbonate, (7) 2 g protein hydrolysate, (8) apple
maggot BioLure®, (9) and untreated control.

(1998). Experiment 2. The second experiment examined the attractiveness of
different types of volatile blends with and without ammonium acetate. In some
treatments, polyethylene vials [5 ml] (Great Lakes IPM, Vestaburg, MI) containing 1.8
ml of butyl hexanoate or 1.8 ml of a mix volatile blend were used. The mix volatile blend
contained butyl butanoate (10%), propyl hexanoate (4%), butyl hexanoate (37%), hexyl
butanoate (44%), and pentyl hexanoate (5%). Six treatments were evaluated that included
a red sphere baited with (1) apple maggot BioLure®, (2) apple maggot BioLure® plus 2 g
of ammonium acetate, (3) mix blend of apple volatiles, (4) a mix blend of apple volatiles
plus ammonium acetate, (5) butyl hexanoate, (6) butyl hexanoate plus 2 g of ammonium
acetate

M), In 1999, we chose 4 of the treatments evaluated in 1998 and compared
them with unbaited (control) spheres. The location of our study, experimental design, and
sampling regime were the same as described for 1999. The five treatments evaluated
were red spheres baited with (1) apple maggot BioLure®; (2) polyethylene vial containing
1.8 ml butyl hexanoate; (3) polyethylene vial containing 1.8 ml of the mix volatile blend;
(4) 2 g of ammonium acetate impregnated into the Tangle-Trap® coating the spheres, (5)
untreated spheres (control) covered in Tangle-Trap® alone.

(2% During the 2000 field season, we carried out an exact replicate of our
1999 study, using the same treatments, experimental design, location, and sampling

regime.

71

Statistical analysis. In order to stabilize the variances, the data fiom both
experiments were square root transformed (x + 0.5) before subjecting it to ANOVA. This
was followed by mean separation using the least significant difference (LSD) test (SAS

Institute 1989).

72

RESULTS

(1998 ). Experiment 1. Spheres baited with protein hydrolysate captured
significantly (F = 4.1; df = 8,24; P < 0.05) fewer R. pomonella flies in comparison to
spheres baited with other lures (Table 9). With the exception of protein hydrolysate, there
were no significant differences among the other baits and lures evaluated in this
experiment. We noticed that spheres baited with BioLure® (n = 15) only were highly
selective and captured an average of 70 i 8.6 % of apple maggot flies in relation to other
beneficial and non-beneficial insects. Alternatively, spheres baited with ammonium
carbonate and ammonium acetate were non-selective capturing on average 38 i 3.6 %

apple maggot flies, as well as many beneficial and non-beneficial insects.

73

Table 9. Attraction of apple maggot flies to synthetic fruit volatiles with and without

ammonium-odor and protenaceous baits, Michigan, (1998).

 

Treatment Mean :1: SEM flies per trap
3 July—19 August

 

Ammonium acetate + protein hydrolysate + 175.3 :t 39.6 a

Biolure® dispenser

Ammonium acetate + protein hydrolysate 143.8 d: 29.3 a
Ammonium acetate 215.5 i 54.2 a
Ammonium carbonate + protein 174.3 :1: 43.8 a
hydrolysate + Biolure® dispenser

Ammonium carbonate + protein 156.3 d: 23.3 a
hydrolysate

Ammonium carbonate 171.8 d: 35.9 a
Protein hydrolysate 34.3 :t 9.6 b
Biolure® dispenser 200.5 :t 53.5 a
Unbaited (control) 133.0 :t 26.1 a

 

Means followed by the same letter are not significantly different (P = 0.05, LSD test).

74

(1998) Experiment 2. Significantly (F = 4.8; df= 5,15; P < 0.01) more R.
pomonella flies were captured on spheres baited with the mix volatile blend compared
with all other treatments tested (Table 10). Total counts throughout the season indicated
that there were no significant differences between spheres baited with a combination of
butyl hexanoate and ammonium acetate, or spheres baited with either compound alone
(Table 10). However, with the exception of spheres baited with butyl hexanoate (in

polyethylene vials), ammonium baits captured significantly more females than males

early in the season (Figure 2).

75

Table 10. Attraction of apple maggot flies to synthetic fruit volatiles and baits, Michigan,

 

 

(1998).

Treatment Mean :h SEM flies per trap

25 June—9 August

Volatile mix blend polyethylene vial 175.0 d: 35.5 a
Volatile mix blend polyethylene vial + 60.5 i 25.4 b
ammonium acetate
Biolure® dispenser 48.0 d: 2.9 b
Biolure® dispenser + ammonium acetate 55.8 i 16.8 b
Butyl hexanoate polyethylene vial 75.3 i: 10.7 b
Butyl hexanoate polyethylene vial + 71.3 i 22.1 b

ammonium acetate

 

Means followed by the same letter are not significantly different (P = 0.05, LSD test).

76

Mean No. of Flies I Trap

Mean No. of Flies I Trap

Mean No. of Files I Trap

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

50 50
Biolure dispenser Biolure dispenser +
40 4 4o 4 Ammonium Acetate
30 - ao~
20 i 20 .
10 r ''''' 1o 4
.................... Mi .................... 1..
0 4‘ J 0 . % .................. ,
50 so
Mix blend Nix blend
40 4 polyethylene vial 40 « polyethylene vial
+ Ammonium acetate
30 q ................... i- ,0 ,
20 4 i 20 -
lo ‘ ‘0 ‘ _..._].
._ ’ _. ' ' ........................................... i
0 i 0 J i r
50 so
B hexanoate
4o 4 Butyl hexanoate 40 - UM .
. polyethylene Vial
polyethylene v1al + Ammonium acetate
30 « 30 .
20 ‘l 20 .
10 q ...... 10 .................... i---- ......
0 i a i 0 i L g ’

Figure 2. Attraction of adult R. pomonella to baited red spheres,

Female]

 

1998, [ ------- Male;

77

LE2), As observed in 1998, significantly (F = 3.2; df = 7,12; P < 0.05) more R.
pomonella flies were captured on spheres baited with the mix volatile blend compared
with all other treatments evaluated (Table 11). In fact, spheres baited with the mix blend
captured approximately twice as many apple maggot flies as spheres baited with the
standard ammonium acetate bait and approximately three times as many apple maggot
flies as unbaited (control) spheres (Table 11). There were no differences observed among

the other treatments evaluated.

Table 11. Attraction of apple maggot flies to synthetic fruit volatiles and baits, Michigan,

 

 

(1999).

Treatment Mean :1: SEM flies per trap
Volatile mix blend polyethylene dispenser 326.5 d: 67.2 a
Biolure® dispenser (Butyl hexanoate) 111.5 i 13.8 b
Ammonium Acetate 164.3 :t 51.7 b
Butyl hexanoate polyethylene vial 150.3 d: 23.7 b
Unbaited (control) 105.5 :1: 9.0 b

 

Means followed by the same letter are not significantly different (P = 0.05, LSD test).

78

(1099), During our third field trial, we once again observed that spheres baited
with the mix blend captured significantly (F = 13.5; (if = 7,12; P < 0.01) more apple
maggot flies compared with spheres baited with any of the other lures evaluated (Table
12). Furthermore, in 2000, we recorded significantly (F = 13.5 ; df = 7,12; P < 0.01) more
R. pomonella flies captured on spheres baited with butyl hexanoate placed in
polyethylene vials compared with spheres baited with the Biolure® dispenser and
unbaited (control) spheres (Table 12). We observed high selectivity to apple maggot
capture on spheres baited with the mix blend (polyethylene vial), butyl hexanoate
(polyethylene vial), and the Biolure® dispenser, which captured 74.7 i 5.3 %, 84.2 i 7.5
%, and 79.5 i 7.1 %, respectively, of apple maggot flies in relation to other beneficial
and non-beneficial insects. We observed a moderate degree of selectivity for the unbaited
(control) spheres, which captured 60.3 i 12.9 % of apple maggot flies relative to non-
target captures. The lowest degree of selectivity was observed on spheres baited with
ammonium acetate, which captured 19.8 i 2.0 % apple maggot flies. Throughout the
season, spheres baited with ammonium acetate captured significantly (F = 17.5; df = 3,4;
F < 0.05) more R. pomonella females than males, while such a difference was not

observed with the other treatments evaluated (Figure 3).

79

Table 12. Attraction of apple maggot flies to synthetic fruit volatiles and baits, Michigan,

 

 

(2000)

Treatment Mean i SEM flies per trap
Volatile mix blend polyethylene dispenser 983.8 i 203.5 a
Biolure® dispenser (Butyl hexanoate) 421.0 i 32.1 cd
Ammonium Acetate 580.0 :h 60.8 bc
Butyl hexanoate polyethylene vial 610.5 :1: 143.4 b
Unbaited (control) 336.3 :2 49.1 d

 

Means followed by the same letter are not significantly different (P = 0.05, LSD test).

80

 

250-
200.
150-
100-

50-4

 

Mix blend in polyethylene vial

 

or"

 

250-

150‘
100‘
50-1

Butyl Hexanoate in polyethylene vial

. --------- I .....................

 

o 1 -

 

2501

1501

Biolure dispenser

 

 

 

 

Ammonium Acetate

 

----- I”... ------ I .......... i .......... {Nun-v”

 

 

150~

 

Unbaited (Control)

..u

A'.
m1

 

 

4 Jul

14 Jul~
17 Jul« j
20 Jul«
26 Jul“
7 Aug-

Figure 3. Attraction of adult R. pomonella to baited red spheres,

2000, [ ------- Male; Female]

 

81

21 Aug

DISCUSSION

Red spheres (9 cm diam) baited with the mix volatile blend were the most
effective traps tested for attracting the apple maggot fly. R. pomonella use chemical and
visual stimuli in long range orientation to their host plants and use chemical cues alone to
discriminate between host and non-host fruit (Prokopy and Roitberg 1984). When adult
R. pomonella detect an appropriate blend of odors, such as a synthetic fruit volatile lure,
they move upwind in a series of flights that eventually culminate in the arrival at the odor
source (Aluja and Prokopy 1992). Over the course of three field seasons, we observed
that the mix volatile blend was the most effective synthetic lure for attracting apple
maggot flies to red sphere monitoring traps. In addition, the mix volatile blend, as a fruit
oddr source, was significantly more attractive to R. pomonella than butyl hexanoate
alone. It is possible that the mix may produce a distinct, attractive odor due to a
synergistic relationship existing between the individual compounds that elicits a greater
response than either compound alone. More research is needed to investigate this
hypothesis properly.

The results from our first experiment in 1998 indicate that spheres baited with
protein hydrolysate alone are not an effective means of monitoring R. pomonella
populations. Spheres baited in this fashion were less effective than spheres baited with
various other treatments tested, as well as unbaited spheres. Gow (1954) also evaluated
various protein hydrolysates and found that although they were initially very attractive to
the oriental fruit fly, D. dorsalis Hendel, their attractiveness decreased when the protein

hydrolysates experienced bacterial decay. We noticed that when protein hydrolysate was

82

mixed into the Tangle-Trap and applied to a red sphere, the sphere became discolored,
assuming a whitish appearance. Spheres baited in this fashion were possibly visually
unattractive to R. pomonella flies. When spheres baited with protein hydrolysate were left
in the field for 2 weeks, they began to lose their initial whitish color as the bait
progressively dissipated (a possible reaction from bacterial decomposition). During the
course of the season, we observed that spheres baited with protein hydrolysate alone
gradually caught a greater number of flies compared to earlier catches. Based on this
observation, we hypothesize that as the spheres began to regain their original red (dark)
color, their effectiveness in catching R. pomonella increased.

The development of monitoring traps for R. pomonella has been based on the
identification of synthetic visual and olfactory stimuli that are naturally attractive to
Rhagoletis flies. Rhagoletis sibling species are strongly attracted to yellow color, which
may be due to the visual stimulus exuded by yellow foliage, locations which may be
associated with honeydew producing insects such as aphids (Kring 1970). Hodson (1943)
was the first to show that ammonium baits are highly attractive to R. pomonella. Since
that time, a plethora of published studies have described the effectiveness of ammonium
baits for monitoring Rhagoletis species (Liburd et al. 1998, Liburd et al. 1999, Liburd et
al. 2000). However, a study conducted by Drummond et al. (1984) found that spheres
baited with ammonium compounds do not attract R. pomonella selectively. Instead, the
traps used in their study attracted and captured a wide variety of Dipteran (beneficial)
insects. This decreased the effectiveness of the traps for detecting R. pomonella due to the
reduced trapping area caused by the inundation of non-target insects. We recorded similar

results in our study; spheres baited with ammonium compounds became saturated with

83

insects after 7-10 (1 in the field during all three field trials. We observed that the average
life span of a sphere baited with ammonia was at most 3 wk, depending on fly pressure.
Afier 3-4 wk, the decomposing insects caused a blunt odor that may have competed with
the odor given off by the ammonia baits. This may have decreased the effectiveness of
ammonia-baited spheres. Bateman and Morton (1981) studied the role of ammonium
compounds and concluded that both ammonia and amino acids were essential to attract
Rhagoletis species, the former for olfactory stimulation and the latter for feeding
response. Additional studies revealed that although ammonia is the major attractant, an
accompanying increase in the pH level of the bait compound further increases its
attractiveness. They assumed that at this increased pH level, additional unidentified
volatiles maybe produced, resulting in increased attractiveness to Rhagoletis flies. These
variables may have effected the results of our study; however, we did not measure these
factors.

The addition of protein hydrolysate or ammonium compounds to spheres baited
with BioLure did not significantly increase the attractiveness of these spheres to R.
pomonella flies. In fact, the only difference that was recorded by combining an
ammonium bait with an apple volatile lure in comparison to using the fruit volatile alone
was an increased capture of female R. pomonella relative to males in early season.
However, unbaited spheres and spheres baited only with BioLure, butyl hexanoate, or the
mix volatile blend, were far more selective in capturing R. pomonella flies than lures
containing ammonium compounds. Such spheres, containing no ammonia or protein bait
impregnated in the Tangle-Trap maintained the original deep red color of the plastic.

Spheres that were treated with baits impregnated into the Tangle-Trap tended to become

84

discolored (lighter in color, whitish appearance). The attractiveness of unbaited spheres
observed in both 1998 and 2000 may be indicative of the visual stimulus, which closely
mimics apples in both size and color (Prokopy 1968). The addition of apple volatiles to
such a spheres increased their attractiveness to R. pomonella flies, while at the same time
preserving the selectivity of the spheres. The principal component of BioLure is butyl
hexanoate, a fruit odor that attracts sexually mature R. pomonella flies for mating and
oviposition (Reynolds and Prokopy 1997). The possible reason why we did not observe
an increased total trap capture by combining ammonium baits with BioLure may be the
decreased selectivity associated with this type of trap baiting system in comparison to
using the synthetic apple volatile alone. Also, apple maggot flies immigrating into
commercial orchards are sexually mature and therefore exhibit a greater response to host-
fruit volatiles than food-odor attractants (Rull and Prokopy 2000). Therefore, we feel that
using synthetic apple volatiles without ammonium baits may produce more accurate and
sensitive monitoring of R. pomonella flies in commercial apple orchards.

We found that by using synthetic apple volatiles (mix blend, butyl hexanoate,
BioLure), the effectiveness of red-sticky sphere traps could be extended beyond the 3-
week life span of spherical monitoring traps baited with ammonium attractants. This may
be due in part by an extended available surface area on spheres baited with apple volatile
lures, as well as a decrease in odors associated with insect decomposition found on
spheres heavily inundated with non-target captures. The combination of attractiveness
and selectivity associated with using the mix volatile blend may provide the highest
degree of effectiveness for monitoring both sexes of R. pomonella populations in

commercial apple orchards. Furthermore, the use of the mix volatile blend may produce

85

the best possible results for controlling R. pomonella with mass trapping (Prokopy et al.

1990) or through the use of baited insecticide-treated spheres (Stelinski et al. in press).

86

HAP ER FIVE
RESPONSE OF BLUEBERRY MAGGOT FLIES, RHA GOLE T IS MENDAX,
(DIPTERA: TEPHRITIDAE) TO SYNTHETIC VOLATILE COMPOUNDS IN

BLUEBERRY PLANT INGS.

87

INTRODUCTION

The bluebeny maggot fly, Rhagoletis mendax Curran, is a widely distributed pest
of low- and highbush blueberries (Vaccinium angustzfolium Aiton and Vaccinium
corymbosum L., respectively) within the northeastern and midwestem United States, as
well as Canada. High infestations have been found in several states including Maine,
New Hampshire, Vermont, New Jersey, and Michigan (Bush 1968). Its range extends as
far south as northern Florida, where its primary host is the deerberry, Vaccim'um
stamineum L. (Payne and Berlocher 1995). The distribution of the blueberry maggot fly
also extends northward into Canada. R. mendax is known to occur in Nova Scotia, Prince
Edward Island and New Brunswick (Wood 1965, Neilson and Wood 1985). Additionally,
there have been sightings of blueberry maggot flies in areas previously thought to be
uninfested in Canada as for example in Saint-Bruno, Quebec (Jobin 1965).

The behavior of R. mendax has been the studied extensively for the purpose of
developing effective integrated control programs (Prokopy and Coli, 1978, Liburd et a1.
1998 a,b, 2000). Several attempts have been made to develop and refine blueberry
maggot fly monitoring programs in order to forecast the presence of R. mendax in
commercial blueberry plantings (Liburd et al. 1998a, 2000). The current monitoring
practices employed by commercial growers of low- and highbush blueberries involve the
deployment of ammonium-baited Pherocon AM yellow sticky panels or green and red
sticky spheres. (Prokopy and Coli 1978, Liburd et al. 1998 a). Such practices allow
growers to detect fly emergence for more accurate timing of spray regimes. One of the
primary problems with current monitoring techniques is that ammonium/protein

hydrolysate baits attract non-target insects and other arthropods, including beneficials.

88

Inundation of monitoring traps with non-target captures significantly reduces their
effectiveness (Liburd et a]. 1999, 2000). Due to the blueberry maggot fly’s status as a
major economic pest of commercially grown blueberries, (Liburd et al. 1998b) and the
fact that consumer demands have resulted in a zero tolerance for maggots in
commercially sold berries, growers in the eastern and mid-westem United States seek
further improvements for monitoring and integrated control practices. Refined monitoring
programs with a high degree of trap selectivity may alleviate some of the problems
encountered with non-target insect captures discussed in Liburd et a1. (2000) and improve
growers’ capabilities of accurately detecting the presence of adult R. mendax.

Host-plant volatiles are important behavior-modifying stimulants for Rhagoletis
sibling species (Liburd et al. 2000). Odor emitted by ripening fruit, which is attractive to
both sexes of Rhagoletis flies, (Prokopy et a]. 1973), may serve as a long-range attractant
since flies detect host fruit odor at a distance of at least 20 m. R. pomonella and R.
mendax exhibit preferential ovipositional responses to their respective host fruit volatiles.
Specifically, R. pomonella are more sensitive to the odor of ripe apples, their specific
host, compared with blueberries and vice versa for R. mendax, indicating that antenna]
sensitivity may be adapted to the species specific host (Frey and Bush 1990). In addition,
hybrids of R. mendax and R. pomonella display a significantly weaker peripheral
responses to host odor compounds as measured by electroantennograrns than either
parental species (Frey and Bush 1996).

Parliament and Kolor (1975) identified twenty-one volatile compounds emitted by
hi ghbush blueberries and found that the compounds trans-Z-hex-enal, transZ-hex--enol

and linalool were associated with the human sensory characteristic flavor of fresh

89

blueberries. Later, Horvat and Senter ( 1985) extracted fifty-one volatile compounds from
blueberries and found that the compounds cis—3-hexen-l-ol and geraniol also had the
characteristic fruity aromas of fresh blueberries.

Although R. mendax has been shown to be responsive to host-specific chemical
cues as measured by electroantennograms (Frey and Bush 1990) and volatile compounds
from blueberries have been collected and characterized, an effective synthetic volatile
lure, load rate, and release rate have not been determined for effective monitoring of the
blueberry maggot fly. In addition, there have been no published reports on the attraction
of R. mendax to synthetic fruit volatiles in commercially grown blueberry plantings.
Identifying synthetic volatiles attractive to the blueberry maggot fly could potentially
make monitoring devices more selective to this species, allowing growers to make more
informed and precise management decisions. The purpose of this study was to evaluate
the behavioral responses of R. mendax to spherical monitoring traps baited with synthetic
host-plant volatiles in early— and mid-season blueberry cultivars. We also wanted to
document how the responses of R. mendax to synthetic host-plant volatile lures change

over the course of the season.

90

MATERIALS AND METHODS

Two experiments to evaluate synthetic bluebeny volatiles were carried out during
the 1999 blueberry field season. Both experiments were located in southwestern
Michigan. Experiments 1 and 3 were located at a large commercial organic blueberry
planting within an early-season blueberry cultivar (Earliblue), where blueberry maggot
fly emergence occurred in early June. Experiments 2 and 4 were located at a smaller
organic blueberry farm within a mid-season blueberry cultivar (Bluecrop), where
blueberry maggot fly infestation took place in late June and early July. Based on previous
monitoring data, it was known that both sites contained large residential populations of R.
mendax. In 1999, volatile treatments were selected based on preliminary experiments
conducted by Liburd et al. 1997 (unpublished data). During 2000, volatile treatments that
demonstrated potential for attraction in 1999 were included for further evaluation. In both
years, experiments were conducted at the same Michigan sites. All treatments were
arranged in a randomized complete block design. The treatments were blocked by
location and replicated four times.

(1999), Experiment 1. (Earliblue). Our inaugural experiments in 1999 focused on
evaluating previously identified synthetic blueberry volatile compounds and attractants at
very high load-rates (Liburd et al. unpublished data). In treatments consisting of synthetic
volatiles, 3 ml of each volatile was pipetted into 5 ml polyethylene vials (Great Lakes
IPM, Vestaburg, MI). Treatments consisting of ammonium acetate had 2 g of solid
ammonium acetate dissolved in 4 ml of water and placed into 5 ml polyethylene vials.
Four pinholes were bored into the caps of each vial in the field to facilitate a high release

rate of the volatile compounds and ammonium baits. Nine volatile compounds

91

(treatments) were evaluated. Polyethylene vials containing the nine treatments were
affixed to 9-cm diam green, spheres coated with 13 g of Tangle Trap® (Liburd et al.
1998a). All synthetic blueberry volatiles and ammonium acetate were obtained from
Aldrich Chemical Co., Milwaukee, WI while protein hydrolysate was purchased from
Pfaltz & Bauer Chemicals Co., Milwaukee, WI. The treatments included spheres baited
with (1) 2.0 g of ammonium acetate, (2) cis-3-hexen-1-ol, (3) geraniol, (4) alpha-
terpiniol, (5) trans-Z-hexen-l-ol, (6) 6-methyl-5-hepten—2-one, (7) linalool, and (8) trans-
2-hexen-al. Spheres were hung within blueberry bushes approximately 15 m apart (20 In
between blocks) in plantings of Earliblue (cultivar) blueberries. Spheres were placed
within the canopy of blueberries ~ 15 cm from the top of the highest bush (Liburd et al.
2000).

Experiment 2. (Bluecrop), Our second experiment was placed within a mid-
season bluebeny cultivar (Bluecrop). It was similar in design and served as a replicate for
our first experiment and as a comparison among phenologically differing blueberry
cultivars. The six treatments that were evaluated included spheres baited with (1) 2.0 g of
ammonium acetate, (2) cis-3-hexen-l -ol, (3) geraniol, (4) alpha-terpiniol, (5) beta-
caryophyllene and (6) unbaited spheres.

(2099), Our objective during the 2000 field trials was to evaluate different
release-rates of blueberry volatile compounds. We also wanted to continue the evaluation
of volatile compounds in blueberry cultivars with different phonologies by, once again,
comparing volatile treatments within both early- and mid-season blueberry cultivars.
Four of synthetic blueberry volatile compounds that were evaluated in 1999 were chosen

for further study in 2000. These compounds were geraniol, cis-3-hexen-1-ol, trans-2-

92

hexen-l-ol, linalool. Volatile treatments were compared against the standard ammonium
acetate bait used in current blueberry maggot fly monitoring programs as well as an
untreated control.

All volatile-treatments were placed in BEEM® embedding (polyethylene)
capsules (Ted Pella, Inc., Redding, CA). We loaded 0.3 ml of each volatile-treatment via
pipette into the polyethylene capsules for field release. Release rates of all pure
compounds from sealed BEEM® capsules were approximated by gas chromotography
(HP-6980, Hewlett-Packard Co.) and time-of-flight mass spectrometry (Pegasus 11,
LECO Corp., St. Joseph, M1); the GC was fitted with a column of length 15 m and
internal diam. 100 u. The GC temperature program was 30°C/ 1 min, 10-250°C and held
for 5 min; the carrier gas was He. BEEM® capsules containing volatile compounds were
aerated in Teflon collection systems with an airflow z33 ml/min. Volatiles were sampled
with solid-phase microextraction (SPME) using 1 cm long fibers coated with a 100 pm
thick layer of poly(dimethylsiloxane) (Supelco Co., Bellefonte, PA); the absorption time
was 5 min. Volatiles were sampled from aerating chambers 1, 3, 6, 9, and 12 d post
loading at ~ 22° C. Each volatile released from BEEM® capsules and collected by SPME
was compared with a previously prepared standard of known concentration. Steady
emission from BEEM® capsules was observed for all compounds after 9 d; 12 (1 data
were used to estimate release rates. All compounds were identified by comparison of
collected mass spectra with the reference standards and spectra of the National Institute
for Standards and Technology (NIST) mass spectra library, search version 1.5 (Mir and

Beaudry 1999).

93

During the 2000 field season, BEEM® capsules containing treatments were
affixed to 9 cm diam, green spheres coated with 13 g of Tangle Trap®. Volatile release
rates were varied by placing treatments in one capsule (lowest release rate), five capsules
(mid-range release rate), or single capsules with a single hole bored into its lid (highest
release rate). Spheres containing treatments were hung within the canopies of blueberry
bushes approximately 15 m apart within rows and 20 m between blocks in plantings of
either Earliblue or Bluecrop blueberry cultivars.

Experiment 3. (Earliblue). In our first experiment of the 2000 field season
conducted in the early-season blueberry cultivar (Earliblue), we evaluated treatments of
geraniol, cis-3-hexen-l -o], and ammonium acetate. Overall, a total of six treatments were
tested. The compounds geraniol and cis-3-hexen-1-ol were deployed at two different
release rates based on the number of BEEM® capsules attached. Each trap (sphere) had
either one or five capsules containing each volatile, totaling 4 treatments for geraniol and
cis-3-Hexen-l-ol. The fifth treatment of ammonium acetate was evaluated at a very high
release rate. This was accomplished by boring a hole into the cover of the BEEM® ‘
capsule. The sixth treatment was a control that consisted of traps left unbaited (without
volatile or bait compounds).

Experiment 4. (Bluecrop). In our second study carried out during the 2000 field
season, we investigated the performance of synthetic volatiles within the mid-season
blueberry cultivar (Bluecrop). A total of 8 treatments were evaluated including the two
volatiles, trans-2-hexen-1-ol and linalool at the two load rates previously discussed
(treatments 1-4). In addition, a new mixed blend consisting of 0.1 ml of geraniol, 0.1 ml

of trans-2-hexen-1-ol, and 0.1 ml aqueous ammonium acetate was tested at the two load

94

rates discussed (treatments 5,6). Our seventh treatment consisted of the standard
ammonium acetate at a very high release rate (hole punctured in polyethylene capsule).
Treatment 8 was an unbaited sphere.

Sampling. R. mendax flies caught on traps were counted by sex and removed
from spheres twice per week. Traps were re-randomized on a weekly basis and replaced
every three weeks.

Statistical Analysis. Data from all experiments were square - root transformed (x
+ 0.5) and then subjected to an analysis of variance (ANOVA). Means were separated by
least significant difference (LSD) (P = 0.05) (SAS Institute 1989). The untransformed

means and standard errors are presented in tables and figures.

95

RESULTS

(1999). Expprimpnt ]. (Earliblue). Our 1999 study conducted within the early
blueberry cultivars showed that during the first monitoring period (26 J une-02 July)
spheres baited with ammonium acetate captured significantly (F = 3.0; (if = 8,24; P =
0.02) more blueberry maggot flies than spheres baited with Alpha-Terpiniol, Trans-2-
Hexen-l-ol, 6-Methyl-5-hepten-2-one, Linalool, and Trans-2-Hexen-al (Table 13). The
response of R. mendax to the conventional ammonium acetate bait during the first
monitoring period was not statistically different from the response to Cis-3-Hexen-l -01
and Geraniol volatiles (Table 13). During our second monitoring period (06-13 July)
spheres baited with the standard ammonium acetate attracted significantly (F = 17.5; df =
7,21; P < 0.01) more blueberry maggot flies than all of the synthetic fruit volatiles
evaluated (Table 13). Spheres baited with ammonium acetate captured 2.4 times as many
flies as all other treatments evaluated during this period. During the second period, Cis-3-
Hexen-l-ol was the second most effective treatment, attracting significantly (F = 17.5; df
= 7,21; P < 0.01) more R. mendax than all other synthetic volatile treatments, apart from
Alpha-Terpineol. During the final monitoring period (July 16-23) spheres baited with
ammonium acetate captured significantly (F = 12.1; df = 7,21; P < 0.01) more flies
compared with all of the synthetic fruit volatiles evaluated (Table 13). The compound
Cis—3-Hexen-l ~01, which performed well during our second monitoring period, attracted
significantly (F = 12.1; df = 7,21; P < 0.01) more flies than Trans-Z-Hexen-l-ol and
Linalool volatile compounds during the final monitoring period (Table 13).

The mean number of females caught on spheres baited with ammonium acetate

(255.5 i 10.0) was significantly greater (F = 11.8; df = 4,3; P < 0.05) than the mean

96

number of males (146.8 d: 18.3). There were no significant differences between male and

female captures on any of the other treatments evaluated.

97

Table 13. Attraction of blueberry maggot flies to synthetic fruit volatiles and baits within

an early-season blueberry cultivar (Earliblue), Michigan, (1999).

 

 

 

Sphere treatments 1St Monitoring 2"3 Monitoring 3rd Monitoring
period Period Period
6/26-7/2 7/6-7/13 7/16-7/23
Mean i SEM no. flies found killed on Plexiglas

Ammonium Acetate 43.0 d: 14.8 a 172.3 i 23.2 a 235.8 :t 37.6 a
Cis-3-Hexen-l-ol 24.8 :1: 1.5 ab 71.8 :t 11.4 b 111.8 i 12.2 b
Geraniol 21.5 i 9.9 ab 42.0 :l: 4.6 cd 94.3 :t 11.6 bc
Alpha-terpineol 16.5 i 5.6 b 69.0 i 18.2 bc 88.5 :1: 13.7 bc
Trans-2-Hexen-1-ol 11.3 i 4.0 b 38.5 a: 12.3 d 72.0 d: 6.2 c
6-Methyl-5-hepten- 10.8 i 1.9 b 34.3 i 5.5 d 78.0 :1: 11.7 bc
2-one

Linalool 13.8 i 5.0 b 30.0 :1: 5.4 d 74.5 d: 4.9 c
Trans-2-Hexen-al 13.5 i 3.8 b 41.8 :1: 11.2 d 86.8 :t 10.3 bc

 

Means within the same column followed by the same letter are not significantly

different, (P = 0.05, LSD test).

98

Experiment 2. (Bluecrop). In 1999, the response of R. mendax to our synthetic
fruit volatiles within mid-season blueberry cultivars was different from that observed in
our trials conducted in the early-season varieties. During the first monitoring period (1 6-
23 July), spheres baited with ammonium acetate captured significantly (F = 7.35; df =
5,15; P < 0.01) more flies than all of the fruit volatile treatments evaluated and unbaited
spheres (Table 14). Ammonium baited spheres captured 2.8 times as many flies as any
volatiles compound and 2.4 times as many R. mendax flies as the unbaited spheres.
(Table 14). There were no differences observed among captures of flies on spheres baited
with any of the synthetic blueberry volatiles. Also, there were no differences between
captures on spheres baited with any volatile compound and the unbaited spheres. This
same trend continued throughout the second (07 J uly-02 August) and third (05-12

August) monitoring periods (Tables 14).

99

Table 14. Attraction of blueberry maggot flies to synthetic fruit volatiles and baits within

a mid-season blueberry cultivar (Bluecrop), Michigan, (1999).

 

Sphere treatments

1St Monitoring
period
7/ 1 6-7/23

2nd Monitoring

Period
7/26-8/2

3rd Monitoring

Period
8/5-8/ 12

 

Ammonium Acetate

Cis-3-Hexen-1 -ol
Geraniol
Alpha-terpineol
Beta-Caryophyllene

Control

Mean i SEM no. flies found killed on Plexiglas

 

230.3 :t 42.1 a

52.3 :t 15.9 b

81.5 i 33.7 b

65.3 i 16.9 b

48.0 i 7.1 b

96.5 :1: 23.3 b

142.8 :1: 44.2 a

44.8 d: 12.8 b

73.3 i 30.7 b

46.02]: 14.5 b

53.8 :1: 13.3 b

59.0 :t 17.5 b

65.3 :1: 10.3 a

158i46b

28.8i11.6b

31.3 i11.2b

275i41b

18.8 i 4.9 b

 

Means within the same column followed by the same letter are not significantly

different, (P = 0.05 , LSD test).

100

M The approximate release rates for 0.3 ml of Geraniol, Cis-3-Hexen-1-ol,
Trans-Z-Hexen-l-ol, and Linalool from single, closed BEEM® capsules at 22 ° C were
0.034, 0.051, 0.041, and 0.0047 111 / h, respectively.

During the second field trial, we observed a slightly different response of R.
mendax in our early-season blueberry cultivar trials, possibly due to the lowered volatile
release rates. During the first monitoring period (22-29 June) when blueberry maggot
flies were beginning to emerge, there were no differences in fly response to all of the
treatments evaluated, including the control (Table 15). During the second monitoring
period (3-10 July), we recorded our highest trap captures on spheres baited with Cis-3-
Hexen—l-ol with a release rate of 5 capsules. Cis-3-Hexen-l-o] attracted significantly (F =
3.63; df = 5,15; P = 0.03) more flies than spheres baited with Geraniol (1 and 5 capsules)
and unbaited spheres (Table 15). During the third monitoring period (13-21 July), during
which peak blueberry maggot fly activity was observed, there was no significant
difference in the performance of spheres baited with Cis-3-Hexen—l-ol at both release
rates tested and the standard ammonium acetate bait (Table 15). During the final two
weeks of monitoring (24 July-l August and 3-10 August), as R. mendax populations were
in decline, ammonium acetate attracted significantly (F = 6.9; df = 5,15; P < 0.01) and
(F = 3.48; df = 5,15 ; P < 0.05) more blueberry maggot flies than all of the other
treatments (Table 15).

There were no significant differences among male and female captures on spheres
baited with any of the synthetic volatile compounds and unbaited (control) spheres.

However, the mean number of females (123.8 i 20.3) caught on spheres baited with

10]

ammonium acetate was significantly (F = 15.8; df = 4,3; F < 0.05) greater than the mean

number (52.3 i 5.6) of males.

102

Table 15. Attraction of blueberry maggot flies to synthetic fruit volatiles and baits within

an early-season blueberry cultivar (Earliblue), Michigan, (2000).

 

Treatments 1St Monitoring 2nd Monitoring 3rd Monitoring 4th Monitoring
period Period Period Period
6/22-6/29 7/3-7/ 10 7/13-7/21 7/24—8/1

 

Mean i SEM no. flies found killed on Plexiglas

Geraniol 2.5 :t 2.5 a 20.8 d: 9.0 bc 28.5 :t 7.0 b 11.5 a: 1.9 b
(1 capsule)

Geraniol 1.3 i 0.5 a 25.0 :1: 7.0 bc 26.5 a: 9.3 b 12.0 :t 4.2 b
(5 capsules)

Cis-3-Hexen-l- 1.5 at 0.7 a 35.0 i: 8.0 abc 46.8 :t 9.4 ab 7.3 i: 1.7 b
o] (1 capsule)

Cis—3-Hexen-l- 1.3 d: 0.5 a 57.0 :t 10.1 a 48.5 :l: 15.3 ab 13.0 :1: 3.5 b
o] (5 capsules)

Ammonium 7.3 i 3.1 a 37.5 d: 7.2 ab 88.3 :t 21.5 a 30.0 i 7.5 a

acetate

Unbaited 2.3 :t 2.3 a 16.8 d: 5.2 c 42.8 i 5.3 b 8.5 d: 0.9 b
iControl)

 

Means within the same column followed by the same letter are not significantly

different, (P = 0.05, LSD test).

103

In our second study of the 2000 field season, carried out in the mid-season
blueberry cultivar, we observed no significant differences in trap captures among the

volatile and bait treatments evaluated during all four monitoring periods (Table 16).

104

Table 16. Attraction of blueberry maggot flies to synthetic fruit volatiles and baits within

a mid-season blueberry cultivar (Bluecrop), Michigan, (2000).

 

 

 

Treatments 1St Monitoring 2nd Monitoring 3rd Monitoring 4th Monitoring
period Period Period Period
6/29-7/6 7/10-7/17 7/21-7/27 8/1-8/8
Mean i SEM no. flies found killed on Plexiglas
Linalool 2.5 i 1.0 a 17.8 i 1.9 a 7.3 i 1.5 a 27.5 i 6.0 ab
(1 capsule)
Linalool (5 6.0 i 3.8 a 18.8 i 8.4 a 9.5 i 2.4 a 14.5 i 1.7 b
capsules)
Trans-2- 2.8 i 0.5 a 11.0 i 3.5 a 5.8 i 1.6 a 32.5 i 15.7 ab
Hexen-l-ol
(1 capsule)
Trans-2- 2.8 d: 0.8 a 19.8 3: 7.9 a 11.3 :1: 4.3 a 13.0 a: 3.2 b
Hexen—l-ol
(5 capsules)
Mixed blend (1 6.3 i 5.3 a 18.3 i 5.5 a 13.3 i 5.9 a 39.8 i 9.5 a
vial)
Mixed blend (5 10.5 i 3.1 a 20.8 :t 6.7 a 12.5 i 4.8 a 25.8 i 13.1 ab
vials)
Ammonium 12.0 a: 7.3 a 26.8 i 8.0 a 10.5 i 2.0 a 28.3 i 5.2 ab
acetate
Unbaited 7.3i 2.8 a 22.5 :1: 10.4 a 8.8 i 3.3 a 24.8 i 6.2 ab
(Control)

 

Means within the same column followed by the same letter are not significantly

different, (P = 0.05, LSD test).

105

DISCUSSION

This study confirmed that ammonium acetate can be highly attractive food-odor
bait to blueberry maggot flies and that its use with sticky, green sphere monitoring traps
produces high captures of adult flies in both early- and mid-season ripening blueberry
cultivars. These results are in concordance with many previous studies, which have
shown that synthetic ammonium baits are highly attractive to Rhagoletis species
(Prokopy 1969, Reissig 1974, Liburd et a1. 1998 a, Liburd et al. 2000). In addition, we
found that the synthetic blueberry volatiles, cis-3-hexen—1-ol and geraniol, can be
attractive to blueberry maggot flies during the first half of the season, when deployed
within an early ripening blueberry cultivar.

Numerous studies have shown successful use of synthetic host-odor lures for
attracting Rhagoletis flies, such as the apple maggot Rhagoletis pomonella (Walsh), in
the field (Riessig 1985, Duan and Prokopy 1992, Zhang et al. 1999). Evidence for a
similar attraction of blueberry maggot flies to synthetic fruit-odor lures in the field was
observed during this study. However, the effectiveness of the synthetic volatiles
evaluated here was dependent on several factors including host-plant phenology, fruit
maturity, and volatile release rates.

During both field seasons, we observed a significant change in the response of
blueberry maggot flies to synthetic host-fruit volatiles within the early ripening blueberry
cultivar (Earliblue) over the course of season. In both years, traps baited with cis-3-
hexen-l-ol and geraniol were equally attractive to blueberry maggot flies as traps baited
with ammonium acetate in early season cultivars (26 June—10 July). However, the

attractiveness of traps baited with these two synthetic host-fruit compounds decreased

106

over the course of the season as host-fruit ripening occurred (after July 13). Such a
decrease in fly captures was not observed on spheres baited with ammonium acetate,
which remained highly effective in attracting blueberry maggot flies throughout the
course of the blueberry growing season (26 June-1 August). We believe that early in the
season, there is a lower concentration of blueberry volatiles being released from
immature green fruit. Therefore, blueberry maggot flies immigrating into the early
cultivar plantings may be responding to the point source traps that are emitting attractive
synthetic blueberry volatiles, such as cis-3-hexen-1-ol and geraniol. Later in the season,
as fruit begins to ripen, a greater overall concentration of blueberry volatiles may be
emitted from the maturing fruit. The effect is a greater level of competition between with
synthetic fruit-volatile lures and the volatiles being released from berries as fruit
maturation progresses. This results in a decline in bluebeny maggot captures on fruit-
volatile baited traps later in the season.

During both seasons, both female and male blueberry maggot flies were equally
responsive to synthetic blueberry volatiles because females were foraging for both mating
and oviposition sites and males were searching for sites harboring females for mating
(Prokopy et a1. 1973). However, ammonium-baited traps captured approximately twice as
many females as males. Recently, a study conducted by Liburd et al. (1998 a) showed
that the olfactory stimulus provided by ammonium baits was more important than trap
shape and color for attracting adult blueberry maggot flies. The greater captures of
females over males on ammonium-baited traps occurred because female flies were

seeking a protein source required for sexual maturation (Liburd et a]. 1998 a).

107

In 2000, we reduced the release rates of our synthetic fruit-volatiles by decreasing
the load rate from 3 ml to 0.3 m1 and by using smaller 1 ml, sealed polyethylene vials
compared with the 5 ml polyethylene vials containing holes in the lids used in 1999.
Therefore, in 2000, the fruit volatiles were only allowed to escape through the matrix of
the polyethylene and over a smaller surface area, which likely reduced the rate at which
volatiles were released. The decrease in release rates caused a change in the response of
blueberry maggot flies to cis-3-hexen-1-o] in the early-season blueberry cultivar.
Specifically, the attractiveness of traps baited with this compound at the lower release
rates remained high throughout the end of mid-season (until 21-July) in 2000, while it
declined significantly at the high release rate before the onset of mid-season (2-July) in
1999. High volatile release rates may depict mature fruit that is no longer suitable for
oviposition and generally not preferred by gravid females (Liburd et a]. 1998 a). The
lowered release rates in 2000 may have mimicked susceptible, ripening fruit, which are
used preferentially by blueberry maggot flies for mating and oviposition (Liburd et al.
1998 a). Therefore, effectiveness of cis-3-hexen-1-ol may have been extended at the
lower release rate because sexually mature females found it more attractive during mid-
season, compared with fully mature (ripe) berries.

There was a substantial difference in the response of blueberry maggot flies to
synthetic fruit-volatiles in the early-season blueberry cultivar (Earliblue) versus the mid-
season cultivar (Bluecrop). Specifically, baiting traps with synthetic fruit-volatiles did not
increase capture of blueberry maggot flies over unbaited spheres in the mid-season
cultivar. Spheres baited with ammonium acetate, however, captured significantly more

flies compared with the other treatments throughout the entire season. These results

108

provide further evidence that later in the season (7-17 July), when fruit has ripened in
early blueberry cultivars and is ripening in mid-season cultivars, there is a greater
competition between fruit-volatile lures and the concentration of volatiles released from
maturing berries. This may render traps baited with synthetic fruit-volatile lures less
effective in capturing blueberry maggot flies.

In 2000, we recorded no differences in blueberry maggot fly captures between
spheres baited with synthetic fruit-volatiles, ammonium acetate, or unbaited spheres
within the mid-season cultivar. Furthermore, we observed decreased overall fly captures
in comparison to 1999. However, in 2000, the planting of Bluecrop in which this study
was conducted experienced unusually low pollination, as well as severe flooding with
standing water accumulated from 25 June — 4 July (John Vanvoorheis personnel
communication, personal observation). Factors such as decreased fruit load and flooding
may have influenced our fly captures due to decreased emergence of resident flies and
decreased immigration from surrounding populations.

Our study showed that ammonium acetate is an attractive lure for R. mendax
throughout the season. In addition, the results provide evidence that blueberry volatiles
may serve as important stimuli for host-plant location by foraging blueberry maggot flies
infesting blueberry plantings early in the season. The effectiveness of traps baited with
synthetic blueberry volatiles in capturing bluebeny maggot flies decreases as blueberries
mature and therefore such traps are less effective in monitoring flies during mid-season
compared with early-season. Our results provide evidence that the synthetic blueberry-
odor volatiles cis-3-hexen-1-ol and geraniol have potential as components of a lure

attractant for blueberry maggot fly IPM monitoring programs, possibly replacing the non-

109

selective ammonium acetate baits that are currently used. Future development of such a
lure should focus on identifying other important blueberry volatiles, which may, in the
correct proportions, act synergistically with cis-3-hexen-l -01 and geraniol to produce

greater and extended attractiveness to bluebeny maggot flies.

110

SUMMARY AND CONCLUSIONS

During our 2000 field season, spheres treated with either formulation of
imidacloprid (Provado® 1.6 F or Merit‘ID 75 WP) showed equal effectiveness in killing
apple maggot and blueberry maggot flies. Thiamethoxam-treated spheres killed fewer
apple maggot and blueberry maggot flies than imidacloprid-treated spheres. Spheres
treated with thiocloprid (Calypso®) were ineffective, killing no more apple maggot or
blueberry maggot flies than control spheres in the field. We therefore feel that treating
spheres with imidacloprid rather than thiamethoxam or thiocloprid may produce better
results for possible control othagoletis sibling species.

The results we obtained from our 2000 deployment strategy experiment were
similar to those that were obtained in 1999. The three deployment strategies that were
tested in both years worked equally well in protecting hit from R. mendax infestation.
Based on the number of puparia reared from fruit collected fi'om treated plots, we found
that fruit infestation using insecticide-treated spheres was reduced from > 20 % in control
plots to < 2 % in plots containing insecticide-treated spheres in 1999 and from 3.8 % to
0.8 % in 2000. The control offered by insecticide-treated spheres was comparable to
organophosphate sprays, which produced fruit injury levels below 0.2 %, on average.
Although our experimental replicate plots were only 10 x 40 m rectangles, we believe
that similar fruit protection could be achieved on a larger scale, if adequate numbers of
spheres were deployed in a commercial setting.

Our volatile work in 2000 with the apple maggot clearly showed that the mixed

apple volatile blend is the most effective attractant when compared with the other

111

treatments evaluated. We obtained similar data in both the 1998 and 1999 field seasons.
We therefore recommend that the mixed apple volatile blend should be used in current
monitoring and control programs for this species.

In blueberries, the most widely used attractant for the blueberry maggot fly has
been ammonium acetate. This compound is very effective in attracting R. mendax,
especially when maggots are seeking a protein source for ovarian development.
Ammonium acetate, however, also attracts a wide range of Diptera and other beneficial
insects, causing monitoring traps to become inundated with non-target arthropods, thus
decreasing their effectiveness. In 1999 and 2000, we evaluated synthetic blueberry
volatiles that can potentially replace ammonium acetate in future monitoring regimes.
The blueberry volatile compounds cis-3-hexen-1-ol and geraniol were highly attractive to
blueberry maggot flies early in the growing season. Early in the season, cis-3-hexen-1-ol
and geraniol performed equally to ammonium acetate in attracting blueberry maggot flies
to 9 cm diam. spherical monitoring traps. The use of synthetic blueberry volatiles that are
equally attractive to the blueberry maggot flies as ammonium acetate may improve
current IMP tactics by making traps more selective to blueberry maggot flies and
reducing the capture rate of non-target insects on monitoring traps.

Overall, our research showed good potential for use of biodegradable, insecticide-
treated spheres baited with a mix blend of apple volatiles for management of apple
maggot flies. Other key Rhagoletis species, including R. mendax can also be suppressed
using insecticide-treated spheres baited with ammonium acetate stored in plastic
dispensers. In addition, growers who adopt this management tactic can use Plexiglas

panes coated with sticky Tangle-Trap® to monitor Rhagoletis populations.

112

During the course of this study, we confirmed that imidacloprid is the best
neonicotinoid available for use with insecticide-treated spheres. We were also able to
demonstrate a significant reduction in fruit injury using insecticide-treated spheres in
replicated blueberry plots. However, we encountered the problems of fungal growth on
biodegradable spheres and the loss of spheres in the field due to rodent feeding. Future
prototypes of these spheres should include more advanced anti-fungal agents and rodent
deterrents before this technology can be recommended to growers for commercial
application. Still, based on our data from 1998, 1999, and 2000, we feel that the use of
biodegradable spheres treated with imidacloprid and baited with appropriate attractants
has good potential as an alternative to conventional organophosphate sprays for control of
Rhagoletis sibling species.

The use of imidacloprid-treated, biodegradable spheres may be implemented
commercially in the near future. The USDA has currentlysubrrritted this technology to
the Environmental Protection Agency (EPA) for registration. The final prototype will be
black, green, or yellow in color and treated with imidacloprid at 4 % AI (Stelinski et al. in
press). In addition, a company has been formed (Fruit Spheres Inc.) to produce these
spheres and market them nationally. The USDA is also in the process of developing more
effective rodent feeding deterrents to help prevent the occurrence of such damage in the
field. Preliminary trials of this technology in commercial apple orchards in Michigan
have produced satisfactory fruit protection as demanded by Gerber Corporation (Stelisnki

and Liburd, unpublished data).

113

LITERATURE CITED

114

LITERATURE CITED

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122

 

APPENDIX

123

Appendix 1

Record of Deposition of Voucher Specimens‘
The specimens listed on the following sheet(s) have been deposited in the named museum(s) as
samples of those species or other taxa, which were used in this research. Voucher recognition
labels bearing the Voucher No. have been attached or included in fluid-preserved specimens.
Voucher No.: 2000-06

Title of thesis or dissertation (or other research projects):

Integrated Management Strategies for Control of Apple Maggot and Blueberry Maggot Flies

Museum(s) where deposited and abbreviations for table on following sheets:

Entomology Museum, Michigan State University (MSU)

Other Museums:

lnvestigator’s Name(s) (typed)
LEM”

 

 

Date QZQQZQl

*Reference: Yoshimoto, C. M. 1978. Voucher Specimens for Entomology in North America.
Bull. Entomol. Soc. Amer. 24: 141-42.

Deposit as follows:
Original: Include as Appendix 1 in ribbon copy of thesis or dissertation.

Copies: Include as Appendix 1 in copies of thesis or dissertation.
Museum(s) files.
Research project files.

This form is available from and the Voucher No. is assigned by the Curator, Michigan State
University Entomology Museum.

124

Appendix 1.1

Voucher Specimen Data

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