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Comparison of Monitoring Strategies and Evaluation of
Spinosad Formulations for Management of Key
Rhagoletis Species

presented by

Kirsten Suzanne Pelz

has been accepted towards fulfillment
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6/01 crlCIRC/DateDuepGS-pts

COMPARISON OF MONITORING STRATEGIES AND EVALUATION OF
SPINOSAD FORMULATIONS FOR MANAGEMENT OF KEY RHAGOLETIS
SPECIES
By

Kirsten Suzanne Pelz

A THESIS

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

MASTER OF SCIENCE
Department of Entomology

2004

ABSTRACT
COMPARISON OF MONITORING STRATEGIES AND EVALUATION OF
SPINOSAD FORMULATIONS FOR MANAGEMENT OF KEY RHAGOLETIS
SPECIES
By
Kirsten Suzanne Pelz
In the eastern and midwestem United States, the cherry fruit fly, Rhagoletis
cingulata (Loew), the blueberry maggot, R. mendax Curran, and the apple maggot, R.
pomonella (Walsh) are important late—season pest of cherries, blueberries, and apples,
respectively. Two insecticide formulations containing the naturalyte insecticide
Spinosad, GF-120 Fruit Fly Bait and SpinTor 28C, were compared for control of, R.
pomonella and R. mendax. Larval infestation in blueberries and apples was
Si gnificantly lower in plots treated with GF-120 or SpinTor than in untreated control
plots. Observations of wild R. mendax flies revealed that similar numbers of flies
landed on blueberry foliage treated with Spinosad bait, bait, or water droplets.
However, flies on Spinosad bait and bait treated plants spent significantly more time
within 5 cm of the treatment droplets compared with control (water) droplets. Several
monitoring strategies for R. mendax and R. cingulata were compared in abandoned
blueberry plantings and cherry orchards. Significantly more R. cingulata were
captured on Pherocon AM traps hung at the uppermost portion of cherry tree canopies
(4.6 m) than in traps hung at the standard height for monitoring traps (2.1 m) or at 1.2
m. In comparisons of traps and lures, significantly more R. cingulata and R. mendax
were captured on traps baited with ammonium acetate lures than unbaited traps or

traps baited with concentrated fruit lures.

ACKNOWLEDGEMENTS

I am very appreciative of the contributions made by individuals, many whose
names I do not know, for allowing me to utilize their orchards and plantings for my
research. In particular, I thank Ron Brouwer for volunteering to spray his blueberry
planting for my experiments.

I am deeply thankful to my dear friend Rob Oakleaf, who has given up his
summer vacation to be at my Side every field season. His insights, cunning use of duct
tape, and Magiver-like abilities were integral contributions to the experiments within this
thesis. Even more important than his abilities as a field assistant was the unrelenting wit
he exhibited in the face of long days, no flies, and bad weather.

I am sincerely grateful to my major professors, Dr. Larry Gut and Dr. Rufus
Isaacs, for the guidance, time, insights, and understanding they have provided me
throughout the course of my work. I have been fortunate to have the mentorship of two
exceptional individuals and have enjoyed my time as a member of both of their labs.

I thank Dr. John Wise for his sharing not only his valuable insights, but his office
as well. John’s kindness and good humor never failed to brighten my days.

I thank Mike Haas, Kevin, and the Trevor Nichols Research Complex (TNRC)
staff. I will truly miss my days Spent at Trevor Nichols and the people who not only
helped facilitate my work there, but also made the experience enjoyable. I am also
grateful to the undergraduates who have assisted me with my fieldwork, particularly
Katie Bosch and Betsy “Maggie” Muellen.

More than anyone, I thank my husband, Lukasz Stelinski for encouraging me to

keep going when things were not going well, for believing in my abilities, and for

iii

teaching me what it means to be a great scientist. He has been my favorite (and toughest)
critic and my greatest inspiration. I also thank my parents, whose love and support have
allowed me to pursue and reach my goals.

Finally, thank you to the research vehicles we have used throughout the summers:
Faustus (2002), Major Tom (2003), and Manni (2004). Their dedication to us in the

many, many hours of driving are much appreciated.

TABLE OF CONTENTS

LIST OF TABLES ........................................................................................................... viii
LIST OF FIGURES ............................................................................................................ ix
CHAPTER ONE:

INTRODUCTION ............................................................................................................... 1
Michigan cherry, blueberry, and apple production ................................................. 1
Ecology and management of fruit fly pests of apple, blueberry and cherry ........... 1
Distribution, host specificity and life history .......................................................... 2
Management of Rhagoletis ...................................................................................... 6
History of trap development .................................................................................... 8
Development of attracticidal spheres .................................................................... 10
Baited insecticide formulations ............................................................................. 11
Research objectives ............................................................................................... 14

CHAPTER TWO:

PROTECTION OF FRUIT AGAINST INFESTATION BY APPLE MAGGOT AND
BLUEBERRY MAGGOT FLIES (DIPTERA: TEPHRITIDAE) USING COMPOUNDS
CONTAINING SPINOSAD.

Introduction ........................................................................................................... 16
Materials and Methods .......................................................................................... 19
Experimental Sites ..................................................................................... 19
Spinosad Sprays in Apples ........................................................................ 19
Spinosad Sprays in Blueberries ................................................................. 21
Field Observations of R. mendax .............................................................. 22
Results ................................................................................................................... 23
Spinosad Sprays in Apples ........................................................................ 23
Spinosad Sprays in Blueberries ................................................................. 23
Field Observations of R. mendax .............................................................. 24
Discussion ............................................................................................................. 27
CHAPTER THREE:

VERTICAL POSITIONING OF TRAPS AND HOST FRUIT PRESENCE INFLUENCE
CAPTURES OF EASTERN CHERRY FRUIT FLY (DIPTERA: TEPHRITIDAE).

Introduction ........................................................................................................... 3 1
Materials and Methods .......................................................................................... 34
Experimental sites ..................................................................................... 34
Trap Height ............................................................................................... 34
Response to Cherries ................................................................................. 34
Results ................................................................................................................... 36
2002 Vertical Trap Placement ................................................................... 36
2003 Vertical Trap Placement ................................................................... 36

2002 Fruit Lure Trials ............................................................................... 36
Discussion ............................................................................................................. 39

CHAPTER FOUR:
INFLUENCE OF SYNTHETIC LURES AND TRAP TYPES ON CATCHES OF
BLUEBERRY MAGGOT AND EASTERN CHERRY FRUIT FLY (DIPTERA:

TEPHRITIDAE).
Introduction ........................................................................................................... 43
Materials and Methods .......................................................................................... 46
Field Sites .................................................................................................. 46
Lures .......................................................................................................... 46
R. mendax Lure Comparisons ................................................................... 47
R. cingulata Lure Comparisons ................................................................. 47
Statistical Analysis .................................................................................... 48
Results ................................................................................................................... 49
R. mendax .................................................................................................. 49
R. cingulata ............................................................................................... 49
Discussion ............................................................................................................. 55
SUMMARY AND CONLUSIONS .................................................................................. 58
APPENDIX
Appendix 1. Record of Deposition of Voucher Specimens .................................. 61
Appendix 1.1. Voucher Specimen Data ................................................................ 62
LITERATURE CITED ..................................................................................................... 64

vi

LIST OF TABLES

Table 1.1. Emergence dates (Accumulated Growing Degree Days) for Rhagoleris Spp.
(Michigan 2002, 2003) ............................................................................... 5

Table 2.1. Effect of different spinosad formulations on mean (i SEM) apple and
blueberry infestation by the apple maggot, R. pomonella and the blueberry maggot, R.
mendax, ............................................................................................... 25

Table 2.2. Number (mean i SEM) of R. mendax flies observed per weekly sample on
blueberry plants treated with Spinosad bait, protein bait, or water droplets and the
duration (mean :2: SEM) spent within 5 cm of the droplets. Data collected 14 July — 08
Aug. 2003 ............................................................................................... 26

Table 3.1. Seasonal captures of adult R. cingulata on Pherocon AM boards hung adjacent
to enclosures containing ripe or unripe sweet or sour cherries in Michigan cherry

orchards ............................................................................................... 38

Table 4.1. Effect of different lures on seasonal captures of adult R. mendax on Pherocon
AM traps .............................................................................................. 51

Table 4.2. Effect of different lures on seasonal captures of adult R. cingulara captured on
Pherocon AM traps ................................................................................. 52

Table 4.3. Effect of different lures on seasonal captures of adult R. cingulata captured on
Rebel] traps .......................................................................................... 53

vii

LIST OF FIGURES

Figure 3.1. Number of adult R. cingulata captured per season on Pherocon AM boards
placed at high (4.6 m), standard (2.1 m), and low (1.2 m) heights within cherry trees. The
experiment was conducted in 2002 (A) and 2003 (B). Means with the same letter within

years are not significantly different (Fisher’s LSD Test, P < 0.05). Untransforrned means
are shown ............................................................................................. 37

Figure 4.1. Seasonal captures of adult R. cingulata on traps with different surface areas
(214, 428, and 642 cmz). ........................................................................... 54

viii

CHAPTER ONE: INTRODUCTION

Michigan cherry, blueberry, and apple production. Michigan is the leading
producer of cherries and blueberries in the United States. Tart cherries, Prunus cerasus
L., are grown on 30,800 acres that produced an average of 234 million pounds of fruit
from 1997 to 2001, or 75% of the national total (Anon. 2004a). An average of 53 million
sweet cherries, P. avium (L.), were harvested in Michigan from 1997 to 2001, accounting
for 12% of the US. production. Highbush blueberries, Vaccinium corymbosum L., are
grown on ca. 18,000 acres in Michigan, with the 64 million pounds harvested in 2002
accounting for 33.4% of the national blueberry production (Anon. 2004a). Michigan has
also historically ranked among the top three states in the US. for apple, Malus domestica
Borkhausen, production with an average of 976 million pounds produced annually from
1997 to 2001 on 47,500 acres (Anon. 2004b). Apples represent 62% of the 1.4 billion
pounds of fruit annually produced in Michigan.

Ecology and management of fruit fly pests of apple, blueberry and cherry.
The eastern cherry fruit fly, Rhagoletis cingulara (Loew), the blueberry maggot, R.
mendax Curran, and the apple maggot fly, R. pomonella (Walsh) are economically
important late-season pests of commercial cherry, blueberry, and apple crops,
respectively. Migration of flies into commercial plantings can result in severe economic
losses if their activity leads to detection of larvae within host fruits. Indeed, detection of a
Single larva in harvested fruit can lead to rejection of all fruit from an infested field or

from an infested load of fruit. This zero tolerance for infestation has driven the

widespread use of broad-Spectrum insecticides against fruit flies to attempt their complete
control.

Distribution, host specificity and life history. Olfactory and visual cues
produced by host plants mediate selection of hosts by Rhagoletis Species for foraging,
mating, and oviposition by fruit flies (Prokopy 1968a Moericke et al. 1975, Aluja and
Prokopy 1993). The specificity of these stimuli limits the distribution of Rhagoletis
Species to a few associated plant genera (Prokopy et al. 1987, Bush and Smith 1998). In
addition, host choice for a given species can be influenced by odor cues. For example,
Linn et a1. (2003) found that resident R. pomonella in hawthorn copses were more
attracted to synthetic hawthorn fruit volatiles than to synthetic apple volatiles, while
populations of R. pomonella resident in apple orchards were more attracted to apple
volatiles than hawthorn volatiles. This difference in odor preference between races of R.
pomonella underscores the strong host fidelity exhibited by members of the Rhagoletis
genus.

Approximately 60 species of Rhagoletis flies have been described, dispersed
broadly throughout the Holarctic and Neotropical regions (Bush 1966). The distributions
of R. cingulata, R. mendax and R. pomonella extend throughout the northeastern and
Midwestern U.S. (Bush 1966). Each of these economically important species feed only
on one or a few fruit crops. Lowbush blueberry, V. angustifolium Aiton, and highbush
blueberry are hosts of R. mendax, while R. cingulata infests sweet and tart cherries.
Apple is the preferred host of R. pomonella, but this species is also a pest of cherries in

Utah (Jorgensen et al. 1986, Jones and Davis 1989).

Most temperate species of Rhagoletis, including R. mendax, R. cingulata and R.
pomonella, are typically univoltine (Fletcher 1989). Adults become sexually mature
approximately one week after emergence and mate on the fruit or foliage of host plants.
Virgin females forage on host foliage and are generally receptive to mating. As the
season progresses, females that have mated previously are found more frequently on the
fruit of host plants and copulation is often forced by males (Prokopy and Bush, 1973,
Smith and Prokopy 1981, 1982). Females are gravid for one week, after which they
oviposit into developing host fruit (Smith and Prokopy 1981). After inserting an egg just
beneath the fruit skin, the female marks the site with an epideictic pheromone by
dragging her ovipositor around the perimeter of the fruit, thereby deterring other females
from ovipositing into the same fruit (Prokopy et al. 1972, Boller and Prokopy 1976).
While each Rhagoletis female can lay up to 400 eggs, usually only one egg is deposited
at a time.

Larvae hatch and develop within the host fruit for 2-4 weeks, depending on the
softness, sugar content, and acidity of the fruit (Boller 1966, Dean and Chapman 1973,
Boller and Prokopy 1976). Upon reaching the third instar, larvae tunnel out of the fruit
and drop to the soil where they form a puparium (Lathrop and Nickels 1932, Boller and
Prokopy 1976). Rhagoletis Spp. spend the winter in diapause ca. 3-5 cm below the soil
surface and emerge the following summer, although some individuals may not emerge
for as long as four years (Lathrop and Nickels 1932). Diapause has been studied more
extensively in R. pomonella and R. mendax than in R. cingulata. The onset of diapause in
R. pomonella is brought about by decreased photoperiod and low temperature during the

larval stage (Filchak et al. 2001). Adult emergence coincides with the phenology of their

hosts, typically around the fruit ripening Stage (see Table 1.1 for a list of fly emergence
dates for each species in 2002 and 2003). Increases in light, moisture, and surrounding
soil temperature foster adult emergence (Neilson 1962, 1964, Prokopy 1968b, Feder et al.
1997, Teixeira and Polavarapu 2002). Degree-day models for predicting adult emergence
are helpful but not as accurate as those described for Lepidoptera, presumably due to the
interaction of moisture and temperature driving Rhagoletis emergence. Teixeira and
Polavarapu (2002) found that postdiapause development rates of R. mendax influence
adult emergence and that these rates are probably determined by exposure to high

temperature during prepupal development.

Table 1.1. Emergence dates (Accumulated Growing Degree Days) for Rhagoleris spp.

(Michigan 2002, 2003).

 

Species Location 2002 2003
R. cingulata Sutton's Bay 7/17 (1473) 7/ 14 (1374)
Benton Harbor 6/28 (1300) --
Fennville (2003) -- 7/7 (1291)
R. mendax West Olive 7/8 (1469) 7/ 12 (1470)
R. pomonella Fennville 7/15 (1405) 7/14 (1445)

 

Growing degree days (DD45) were calculated using Baskenville E. from a start date of

March 01 and obtained from www.agyeather.geo.msu.edu.

Management history of Rhagoletis. In the past century, control of Rhagoletis
species has followed the general trends in crop protection, progressing from cultural
control methods, to extensive pesticide sprays, to the current integrated methods that
combine a monitoring program with behavioral controls and a pesticide regime.
Management of these species in fruit crops once relied on the destruction of infested fruit
underneath hosts to prevent the emergence of flies the following year (Boller and
Prokopy 1976). During the 19508 and 19603, arsenics and DDT applications were
employed to control adult fly populations prior to oviposition (Dean 1947, Boller and
Prokopy 1976). As these chemicals fell into disuse due to environmental concerns and
lack of efficacy, new classes of broad-spectrum insecticides, such as the
organophosphates, targeting adult stages were registered and became the standard options
for Rhagoletis control (Boller and Prokopy 1976, Wise et al. 2004). Increasingly stringent
consumer demands, phytosanitary restrictions and federal (USDA) regulations have
resulted in a zero tolerance for the presence of Rhagoletis larvae in fruit. This standard of
larva-free fruit has necessitated the use of contact insecticides aimed at adults prior to egg
laying, to obtain the desired level of control. Organophosphate and carbamate

insecticides are typically used for control of Rhagoletis flies, and those registered for use

in Michigan fruit crops include dimethoate (Cygon®), carbaryl (Sevin®), azinphosmethyl

(Guthion®), phosmet (Imidan®), thiacloprid (Calypso®), and methomyl (Lannate®). In

addition to having deleterious effects on beneficial insects, these products are also
characterized by their acute toxicity to mammals. The high toxicity of broad—spectrum
insecticides has caused concerns regarding environmental quality, worker safety, food

safety and human health. In 1996, the Food Quality Protection Act (FQPA) was passed,

wherein the US. Environmental Protection Agency (EPA) was required to review the
registrations of all pesticides over a 10-year period. Considering the most toxic pesticides
first, the EPA has begun to restrict the use and availability of organophosphates for non-
agricultural and agricultural uses. Because of the more stringent review process after
FQPA, reduced risk insecticides such as neonicotinoids, insect growth regulators, and
naturalytes have been registered for use in fruit crops. Recently registered reduced risk

products for use against fruit flies in apple, cherry, or blueberry include the

. . . . . . ® . ® .
neonrcotrnords rmrdaclopnd (Provado ) and thramethoxam (Actara ), and formulations

of the naturalyte Spinosad (SpinTor®, GF-120®, Entrust®).

In addition to insecticides, cultural practices, trapping, and behavioral
manipulation are important tactics and strategies for Rhagoletis management when used
as part of an integrated program. Behavioral control methods employed against R.
pomonella show promise as alternatives to insecticides in Integrated Pest Management
(IPM) programs. Flies immi grating from nearby unmanaged orchards pose the greatest
threat to commercial orchards; therefore, interceptive trapping with spheres may offer an
alternative to broadcast sprays for preventing fruit infestation by R. pomonella. Red
spheres baited with a five-component fruit volatile lure (Fein et a1. 1982) or butyl
hexanoate and deployed in perimeter row trees provided Similar levels of control to
traditional insecticide sprays (Reynolds et a1. 1998, Prokopy et al. 2003a). To date, mass
trapping with baited spheres as an alternative to pesticides has not been described for use
against R. mendax or R. cingulata.

Recent work has Shown the potential of the parasitic wasp Diachasma alloeum

for control of R. mendax (Liburd and Firm 2003a, Stelinski et al. 2004). Parasitism of R.

mendax larvae in unmanaged blueberry fields can reach as high as 30-50% (Liburd and
Finn 2003a). However, parasitic wasps do not provide the high level of fly control
required in managed fields so the use of parasitic wasps as a management tactic must be
supplemented by additional control measures. Availability of reduced-risk insecticides
for fruit fly control may offer new opportunities for integrated control of Rhagoletis
Species combining these more selective products with conservation of natural enemies.

History of trap development. Trapping of Rhagoletis species is an important
component of IPM programs as a method for determining fly emergence and population
densities. In addition to detecting adult females during their pre-oviposition period,
accurate trapping allows growers to appropriately time pesticide sprays, thereby
preventing unnecessary sprays and reducing the possibility of resistance development. An
insecticide is typically applied within seven days of capturing a single fly on traps
deployed in apple and cherry orchards and blueberry plantings, targeting adult flies
during the 8-10 day pre-oviposition period (Stanley et al. 1987, Howitt 1993, Liburd et al.
2001).

Research has focused on determining the optimal combination of trap shape,
color, lure, and position in the crop for capturing Rhagoletis Species. Trap color is an
important factor mediating attraction of flies, as it provides a short-range (ca. 3 m) visual
cue similar to that of the host foliage or host fruit (Green et al. 1994). The Pherocon AM
yellow panel trap is most commonly used for monitoring Rhagoleris pests of temperate
fruit crops (Prokopy and Coli 1978, Liburd et al. 1998a), however red or green sticky
spheres are also used for R. pomonella and R. mendax, respectively (Reissi g 1976,

Prokopy and Hauschild 1979, Liburd et al. 1998a). Colored spheres are more attractive to

flies than yellow traps later in the season, when mature female flies oviposit into fruit
(Liburd et al. 1998b). Rebell traps are more effective in capturing R. cingulata than
Pherocon AM traps or colored spheres (Liburd et al. 2001). It is likely that trap color and
dimension (three dimensional versus two dimensional) play a role in the effectiveness of
the Rebell trap, however to date the source of this heightened effectiveness compared to
other traps has not been explored.

Ammonia-based attractants mimic volatiles produced by natural food sources of
adult Rhagoletis, namely avian fecal material, and these volatiles are often used in
combination with monitoring traps. The addition of an ammonia lure significantly
increases the attractiveness of traps to flies, and ammonium acetate has been shown to be
a more effective lure for attracting R. mendax than ammonium carbonate (Liburd et al.
1998a). In addition, lures releasing fruit volatiles can increase captures of R. pomonella
on red sphere traps. A blend of synthetic apple volatiles (Reissig 1982, Fein et al. 1982,
Zhang et al. 1999) mimics the odor emitted by host fruits, selectively attracting flies over
a range of 20 m or more (Prokopy et. al. 1973, Stelinski and Liburd 2002). As a result,
this trap and lure combination may be used to monitor R. pomonella, and has potential for
control of populations via mass trapping (Reynolds et al. 1998, Rull and Prokopy 2001).
Similar fruit—based volatile lures have not been described for use in capturing R. mendax
or R. cingulata, however in recent studies significantly more R. mendax were captured on
traps placed next to cages holding fresh blueberries than traps placed next to cages
containing marbles, suggesting that blueberries release an odor attractive to R. mendax

(L. Stelinski unpublished data).

Trap position also appears to have a substantial impact on the number of flies
captured in monitoring traps. Liburd et al. (2000) showed that Pherocon AM traps folded
in a V orientation (Prokopy and Coli 1978, Geddes 1989, Gaul 1995) and placed in the
top one-third of blueberry bushes were the most effective at capturing R. mendax
compared to other positions. In small (1.2 m or less) bushes, traps hung in the top and
bottom of the bush canopy captured similar numbers of flies (Teixeira and Polavarapu
2001). In contrast, significantly more R. pomonella were captured on sticky yellow cards
impregnated with ammonium acetate when traps were placed at 2.1 min the canopy of
apple trees compared to traps hung at 1.2 or 3.0 m (Reissig 1975). Drummond et al.
(1984) found that placement of traps within 025-05 In of host fruit also significantly
enhanced the number of apple maggot flies captured. To date there have been no
published studies determining the effect of trap position on captures of R. cingulata.

Development of attracticidal spheres. Pesticide-treated spheres have shown
promise as an alternative to sprays for control of R. pomonella and R. mendax (Hu and
Prokopy 1998, Liburd et al. 1999, Prokopy et al. 2001, Stelinski and Liburd 2001, Liburd
et al. 2003b). Colored spheres impregnated with the neonicotinoid insecticide
imidacloprid and deployed in apple orchards or blueberry plantings achieved similar
reduction (79%) in larval infestation compared to azinphosmethyl (Guthion) sprays
(97%) (Stelinski and Liburd 2001). Pesticide treated spheres with sugar/wax discs affixed
to the top of spheres have also shown promise for R. pomonella control (Prokopy et al.
2001). These discs are designed to provide a continuous film of sugar on the sphere for
ca. 6 weeks or 6 in. of rainfall and, therefore, a constant food source for foraging

Rhagoletis flies. Although sphere technology is promising as an alternative to broadcast

10

pesticide applications, there are drawbacks that may hamper the adoption of this
approach for control of Rhagoletis fruit pests. Labor costs associated with deployment of
high numbers of spheres per acre and the cost of the spheres are prohibitive and may
provide an explanation for their failure to gain popular usage in commercial agriculture
(Prokopy et al. 2000, Prokopy et al. 2003c).

Baited insecticide formulations. Combining insecticides with an attractive
phagostimulatory bait is a potential alternative control tactic to broadcast Sprays or
pesticide-treated spheres. The use of baited insecticide formulations against tephritid
species has been practiced for nearly a century (Severin et al. 1914, Back and Pemberton
1917, Steiner 1952, 1955, Nishida et al. 1957, Roessler 1989, Peck and McQuate 2000,
Burns et al. 2001, Moreno et al. 2001, Vargas et a1. 2001, Prokopy et al. 2003b).
Reproduction and longevity in tephritids are tightly linked to the intake of nutrients,
particularly carbohydrates and amino acids and/or proteins (Hagen 1953, Drew and
Yuval 2000). Thus, female Rhagoleris flies, like most tephritids, require a protein meal
following eclosion for successful egg development, while carbohydrates, in the form of
sugar, act as phagostimulants to both male and female flies (Prokopy 1993, Prokopy et al.
1994, Prokopy and Papaj 2000). The baits used in attract-and-kill pesticide formulations
employ food-based attractants designed to mimic natural food sources, typically a yeast-
derived enzymatic protein hydrolysate and a sugar (Steiner 1952, Prokopy et al. 1992,
King and Hennessey 1996, Peck and McQuate 2000). Ammonia emitted from
proteinaceous baits serves as the primary component that attracts flies (Bateman and
Morton 1981, Mazor et al. 1987). Compared to conventional insecticide sprays, baited

toxicants can be applied to a smaller area of the crop surface, as flies will move to

11

interact with the droplets, reducing the amount of insecticide released into the crop
ecosystem, and provide control targeted only at insects that feed on the bait (Prokopy et
al. 1992). The behavioral response of Rhagoletis to these baits is poorly understood,
although recent work by Barry and Polavarapu (2004) has shown that 8% sucrose is

effective in stimulating R. mendax feeding. In addition, feeding assays comparing

NuLure insect bait® (Miller Chemical and Fertilizer Co., Hanover, PA), SolBait®

(USDA-ARS, Weslaco, TX), and AY50% (Mauri Yeast Australia) indicate that R.
mendax spend significantly more time feeding on Solbait than on the other treatments
(Barry and Polavarapu 2004).

Due to relatively low toxicity to mammals, malathion was originally incorporated
into bait sprays for use against the oriental fruit fly, Bactrocera dorsalis (Hendel) (Steiner
1952, Steiner et al. 1961, Roessler 1989). Malathion bait sprays for the Mediterranean
fruit fly, Ceratitis capitara (Wiedmann) and the Caribbean fruit fly, Anastrepha suspensa
(Loew) have been used in eradication programs since the 1950’s (Steiner 1952, Vargas et
al. 2002)). These sprays consist of 20-25% malathion, a contact and stomach poison,
combined with Stanley’sProtein Insect Bait (PIB-7), now known as N uLure Insect Bait

(Miller Chemical and Fertilizer Co., Hanover, PA) (Buttery et al. 1983, Roessler 1989,

King and Hennessey 1996, Vargas et al. 2002). NuLure® is used routinely in bait sprays

due to its attractiveness to flies, low cost, and relative availability (Roessler 1989).
Malathion bait sprays have been criticized for their adverse effects on biocontrol agents,
pollinators, and other beneficial insects, as well as the destruction they cause to the paint
on cars near aerial application sites (Gary and Musson 1984). In addition, concerns for

environmental and human health have prompted the need for alternative bait spray

12

formulations. Photoactive dyes and Spinosad have been the latest subjects in the search
for a replacement toxicant.

Photoactive dyes have been suggested as potential malathion alternatives in bait
formulations due to their lack of contact activity and low vertebrate toxicity (McQuate et
al. 1999, Peck and McQuate 2000, Moreno et al. 2001). The toxic activity of these dyes
functions only when adult flies ingest the material, and light exposure then oxidizes the
dye, causing mortality (Peck and McQuate 2000). Phloxine B (2’,4’,5’,7’-tetrabromo-

4,5,6,7-tetrachloro-flourecein, disodium salt) is formulated with protein bait for fruit fly

control under the name SureDye® (Phytodye International, Baltimore, MD). However,

use of phloxine B as an aerial Spray is limited due to potential damage the dye may
render to property (Peck and McQuate 2000).

Another alternative to the organophosphate malathion in baited insecticides is the
naturalyte insecticide spinosad. Spinosad is derived from metabolites (spinosyns A and
D) produced by the actinomycete Saccharopolyspora spinosa (Mertz and Yao 1990).
Spinosad is a neurotoxin that acts directly on ganglia of the insect central nervous system,
targeting nicotinic acetylcholine and GABA receptors (Salgado et al. 1997). Ingestion of
spinosad results in periods of prolonged nervous system excitation and muscle
contractions, culminating in paralysis and death after 24 h (Salgado 1998). It has low
vertebrate toxicity (LDso > 3500 mg/kg) and minimal impact on bees (DowElanco 1994,
Thompson and Hutchins 1999) and is classified by the EPA as a reduced risk pesticide
(Saunders and Bret 1997). Bee mortality following bait Sprays results from contact with
the wet toxic spray residue rather than direct feeding on the bait (Gary and Mussen

1984); therefore, spinosad represents a relatively safe alternative when bees are present as

13

it has minimal contact activity in comparison to malathion (Cisneros 2002, Mazor 2003).
However, Cisneros et a1. (2002) found that spinosad may have deleterious effects on
beneficial insects, in contrast to the findings of Bret et al. (1997).

Spinosad is the active ingredient in several insecticides produced by Dow

Agrosciences: SpinTor®, Success®, Tracer®, Conserve®, Entrust®' and GF-120 Fruit Fly

Bait®. SpinTor (EPA Reg. No. 62719-294), a non-baited sprayable formulation, was

registered for use in the US. in 1998 and GF-l20 Fruit Fly Bait, a baited sprayable
formulation, was registered for use in apples, blueberries and cherries in 2002. The bait
component of GF-120, described in Peck and McQuate (2000), consists of 70% com
protein (Mazoferm E802, Corn Products, Argo, IL). Like phloxine B bait sprays, Peck
and McQuate (2000) found that Spinosad bait Sprays provided significant reduction in
fruit infestation by Mediterranean fruit fly compared to untreated controls, although it
was not as effective as malathion bait sprays. This study and others (King and Hennessey
1996, Peck and McQuate 2000, Prokopy et a1. 2000, Burns 2001, Vargas et al. 2001,
Vargas et al. 2002, Prokopy et al. 2003b) have indicated that GF—120 is effective for
control of several tropical tephritid species, but its efficacy against Rhagoletis pests of
temperate fruit crops has not been demonstrated.

Research objectives. The changes currently underway in the fruit industries as a
result of federal regulations on pesticides have prompted the need for increased
evaluation of reduced-risk insecticides and integrated approaches to fruit fly control.
This requires a better understanding of fly behavior and the control tactics and
management strategies currently available. The overall aim of the research presented

herein was to advance current management programs for Rhagoletis pests of blueberrry,

14

cherry and apple by improving monitoring techniques and by evaluating the potential of
new insecticide formulations for their control. The first objective was to determine the
effectiveness of unbaited and baited spinosad formulations for control of R. pomonella,
R. mendax, and R. cingulata under field conditions. Included within this objective was a
goal to describe R. mendax interactions with the baited insecticide formulation, GF-120.
The second objective was to determine the most effective trap position for capturing R.
cingulata and R. pomonella within the canopy of their respective host trees. The final
objective was to evaluate the response of R. mendax and R. cingulata to several trap and
lure combinations, including fresh fruit. The approach taken in the first objective
provides a unique multi-species comparison of the complex of Rhagoletis flies infesting
Midwestem fruit crops. Although the latter two objectives do not encompass all three
Rhagoletis species, the data included therein supplement previously published work, from

which comparisons across the species can be made.

15

CHAPTER TWO. PROTECTION OF FRUIT AGAINST INFESTATION BY APPLE
MAGGOT AND BLUEBERRY MAGGOT FLIES (DIPTERA: TEPHRITIDAE)

USING COMPOUNDS CONTAINING SPINOSAD.

INTRODUCTION

The apple maggot, Rhagoletis pomonella (Walsh), and the blueberry maggot,
Rhagoletis mendax Curran, are among the most important late-season pests of apples,
Malus domestica L., and highbush blueberries, Vaccim'um corymbosum L., respectively,
in the eastern and northwestern United States (Bush 1966, Howitt 1993). Infestation of
the crop by these frugivores renders it unmarketable in regions with quarantine
restrictions for R. mendax and R. pomonella. Fruit destined for regions certified as being
free of these pests is inspected and detection of one infested fruit leads to rejection of the
entire load. Currently, organophosphates such as phosmet, malathion and azinphosmethyl
are the most widely used insecticides in apples and blueberries for control of Rhagoletis
fruit flies (Wise et a1. 2003). However, increased restrictions on the use of these broad-
spectrum insecticides imposed by the US. Environmental Protection Agency in response
to the 1996 Food Quality Protection Act (FQPA) will create a challenge for successful
pest management in these crops. In particular, extensions of the re-entry and preharvest
intervals for the most efficacious insecticides against fruit flies will restrict their utility

for the critical period of control just prior to harvest.

Some new insecticide chernistries have recently been registered that show

promise as alternative controls for fruit flies, and others are being developed that should

l6

be registered over the next few years (Wise and Gut 2002, Wise et al. 2002). Spinosad is
a naturalyte insecticide consisting of two compounds derived from the actinomycete
Saccharopolyspora spinosa, spinosyns A and D (Mertz and Yao 1990). Baited
formulations of this naturally-derived insecticide have been effective in controlling
populations of several tropical fruit fly species, including Caribbean fruit fly, Anastrepha
suspensa (Loew) (King and Hennessey 1996, Burns et al. 2001), Mexican fruit fly,
Anastrepha ludens (Loew) (Moreno and Mangan 2003) and Mediterranean fruit fly,
Ceratitis capitata (Wiedemann) (Peck and McQuate 2000, Vargas et al. 2001, Vargas et
al. 2002). Bait sprays at concentrations as low as 1 ppm Spinosad have provided
significant fruit fly control (King and Hennessey 1996, Peck and McQuate 2000).

Spinosad used alone or in combination with bait has received much less attention
as a possible control for temperate species of fruit flies. Smith (1999, 2000) reported
control of R. indifierens in small-plot trials using spinosad (Success, Dow AgroScienceS,
Indianapolis, IN) alone or with horticultural mineral oil (Kuhlmann and Jacques 2000).
Two formulations of spinosad have recently been registered for use in blueberry and
apple against R. mendax and R. pomonella, respectively, despite relatively little efficacy
data against Rhagoletis fruit pests (Liburd et a1. 2003, Reissi g 2003). Spinosad was
registered for use in apples and blueberries in 2002 as a foliar spray formulation (Success
or SpinTor, Dow AgroScienceS, Indianapolis, IN). GF-120 Fruit Fly Bait (Dow
AgroSciences) is a baited formulation of spinosad that was first available for commercial
use in apples and blueberries during 2003.

The lethal action of spinosad against Rhagoletis fruit flies occurs primarily

through ingestion; there is little or no contact activity (Mangan and Moreno 1995, Vargas

l7

 

'et al. 2002). Feeding by adult R. pomonella is greatest during the first week following
emergence and decreases thereafter (Webster et al. 1979), so preventing larval infestation
using spinosad is likely to require novel approaches that entice the fly to consume a lethal
dose of the toxicant. Optimizing the use of baited insecticides will require a better
understanding of how Rhagolen’s flies respond to various formulations under natural field
conditions. Specifically, parameters such as duration of efficacy and attractiveness to
flies will need to be investigated. Although efficacy of baited spinosad has been
demonstrated in many systems (see above), in greenhouse assays, Prokopy et al. (2003)
showed attractiveness of GF-120 decreased 50% by 5 hrs post-application, suggesting the
need for frequent reapplication.

The specific objectives of the current study were to: 1) determine the
effectiveness of GF-120 Fruit Fly Bait in controlling two temperate fruit fly Species, R.
pomonella and R. mendax and 2) quantify the behavioral response of R. mendax flies to

GF—120 under field conditions.

18

MATERIALS AND METHODS

Experimental Sites. Research was conducted in the summers of 2002 and 2003
in apple orchards at Michigan State University’s Trevor Nichols Research Complex
(Fennville, MI) and in a non-commercial highbush blueberry planting (Holland, MI).
Field sites were chosen because of known histories of moderate to high infestations of R.
pomonella or R. mendax and the lack of insecticide applications for at least two years.

Spinosad Sprays in Apples. In 2002, experiments were conducted in a 1.0 ha
apple (var. ‘Red Delicious’) orchard planted on a 3.0 m within-row by 5.5 m between-row
tree spacing, with treatments applied to 12.4 x 22 m (0.03 ha) plots. Experiments in 2003
were conducted in 39.2 x 55.8 m (0.08 ha) plots in the same orchard and in an adjacent
1.3 ha orchard (var. ‘Rome’) planted on a 2.4 m x 5.5 m tree spacing. The 2002
experiment consisted of the following four treatments: 1) GF-l20 Fruit Fly Bait (Spinosad
bait), 2) SpinTor 2 SC (unbaited Spinosad), 3) bait (which includes all compounds in GF-
120 except spinosad) and 4) untreated (control). Protein-bait without the insecticide
incorporated could not be obtained from the manufacturer in sufficient quantity during
2003; therefore only three treatments were compared. Experiments in both years were
arranged in a randomized complete block design with four replicates and at least a one-
row buffer between plots.

Initial applications of all treatments were made one week after the first R.
pomonella fly was captured on Pherocon AM traps (Great Lakes IPM, Vestaburg, M1),
on 11 July in 2002 and 15 July in 2003. An 80 ppm aqueous mixture of spinosad bait or
bait (1:1.5 vzv) was applied at 2.4 liters/ha using a MeterJet spray gun (Model No. 23624-

3OL, Spraying Systems Co., Wheaton, IL). The handgun produced droplets with ca. 4-6

19

mm diameter. SpinTor was applied at 21.4 g [AI]/378 liters (8 oz in 100 gall acre) using
an airblast sprayer (Model No. CP3000, John Bean Sprayers, LaGrange, GA, in 2002;
Model No. 1029, FMC Corp., Lakeland, FL, in 2003). Spinosad bait and bait were
applied weekly until harvest for a total of Six applications and unbaited spinosad was
applied every two weeks for a total of three applications.

The relative abundance of flies in each plot was estimated by captures on unbaited
red sphere traps (Great Lakes IPM) placed at the center of each plot. One trap per plot
was hung approximately 2.0 m above the ground and all foliage within 0.5 m the trap was
cleared away (Drummond et al. 1984). Once per week, captured flies were counted and
removed from monitoring traps.

Fruit infestation evaluations were conducted at the end of each growing season to
determine the effectiveness of control for each treatment (12 September in 2002 and 02
September in 2003). A total of 100 apples per plot were randomly picked from the
innermost four trees in 2002. In 2003, 250 apples were randomly picked from the
innermost 10 trees. Fruit samples from each plot were kept separate and placed on wire
hardware mesh suspended above trays containing fine vermiculite, allowing mature
larvae exiting fruit to drop into the vermiculite medium and pupariate. After four weeks,
the vermiculite was sifted for fly puparia, which were counted to determine the level of
infestation per plot.

Effects of treatments on mean fly catches in traps throughout the season and mean
larval infestation in fruit were determined by analysis of variance (AN OVA) followed by

means separation using Fisher’s protected least significant difference (LSD) procedure (P

20

= 0.05) (PROC GLM, SAS Institute 1998). Prior to analysis, fly capture data were
normalized by square-root transformation [(x + 0.5)”2].

Spinosad Sprays in Blueberries. Experiments were conducted in a 1.8 ha
highbush blueberry field (var. ‘J ersey’) planted at 2.7 m x 3.7 m spacing, with treatments
applied to 16.2 x 37 m (0.06 ha) plots in 2002 and 16.2 x 37.4 m (0.08 ha) plots in 2003.
Treatments in 2002 and 2003 were the same as those tested in apple with the exception of
SpinTor, which was applied at the lower registered blueberry rate of 14.2 g [AI]/ 378
liters (6 oz in 100 gal/acre). As in apples, bait was not available for the 2003 experiment.
Four and five replicates of each treatment were used in 2002 and 2003, respectively, with
treatments arranged in a randomized block design and plots separated by at least one row
of bushes. All treatments were applied following the first fly caught on monitoring traps
(08 July in 2002 and 12 July in 2003). Spinosad bait and bait were applied each week
until harvest for a total of six applications as previously described. Unbaited spinosad
was applied every two weeks for a total of three applications.

Monitoring of R. mendax adults was conducted using Pherocon AM traps hung in
a V-orientation ca. 15 cm below the uppermost portion of the bush, the optimal position
for capturing sexually mature R. mendax (Liburd et al. 2000). Each week, monitoring
traps (one per plot) were checked for R. mendax flies, which were counted and removed.

Assessment of larval infestation was conducted using methods similar to those
described for apples. Samples of 1000 blueberries per plot were harvested on 24 August
in 2002 and 28 August in 2003. Fruit were held for one month before puparia were
counted. Numbers of adult blueberry maggot flies captured on traps and larval infestation

within treatments were compared by the analysis described above for R. pomonella.

21

Field Observations of R. mendax. The first objective of the behavioral
component of the study was to compare the number and duration of R. mendax visits to
plants treated with (1) spinosad bait, (2) bait only, or (3) untreated (control). The second
objective was to quantify the behavioral interactions of R. mendax with the GF-120 Fruit
Fly Bait formulated with or without insecticide. All observations were conducted in a 1.8
ha unsprayed V. corymbosum (cv. ‘Jersey’) field in Douglas, MI. This planting was
chosen because it historically harbors a high population of R. mendax (Stelinski and
Liburd 2001). The experiment was conducted using a randomized complete block design
with three replicates of three treatments: 1) Spinosad bait, 2) bait, and 3) water as a
control, with each replicate consisting of one treated plant. Treatments were applied at
the beginning of each week for four weeks. Five IO-ul droplets (2-3 mm in diameter,
according to label recommendation) of each treatment were applied to each plant on the
top surface of leaves spaced at least 30 cm apart. Observations of wild flies were
conducted daily for five days post-treatment between 0800 and 1300 hours. During the
observations, air temperature was ca. 21- 27°C. Investigators stood ca. 0.5 m away from
a treated bush and observed the plant for 20 minutes or until an observed fly left the
plant. Data were collected by recording observations of R. mendax into handheld micro-
cassette audio recorders (Model No. 3-5375A, GE, Westminster, CO). The behaviors
recorded were: 1) number and duration of fly visits to blueberry plants, 2) number and
duration (3) of feeding events on treatment droplets, and 3) proximity of a fly (cm) to the
nearest treatment droplet. The effects of treatments on mean numbers of R. mendax
observed visiting blueberry bushes were determined using ANOVA followed by means

separation using Fisher’s protected least significant difference (LSD) procedure (P =

22

0.05) (PROC GLM, SAS Institute 1998). Prior to analysis, data were normalized by
square-root transformation [(x + 0.5)1/2]. A two-sided Sign test (BIOMDIST, Microsoft
Excel 2000) was used to determine whether the number of flies observed on blueberry
bushes varied over time following treatments, where Y = (flies observed on days 0-2) -
(flies observed on days 3-4) (Sokal and Rohlf 1981). The probability (P = 0.05) of no
difference in response to treatment over time (mean Y = 0) versus a change in response

(mean Y i 0) was determined.
RESULTS

Spinosad Sprays in Apples. In 2002, mean captures of adult apple maggot flies
on sphere traps in spinosad bait (1.9 i 0.5), SpinTor (2.7 i: 0.6), and bait treated plots (2.9
i 0.6) were not significantly different (F = 1.44; df = 3,9; P > 0.05) than captures on
sphere traps in untreated plots (3.7 i 0.8). Similarly, the number of flies captured in 2003
on sphere traps in spinosad bait (11.6 i 2.5), SpinTor (11.5 .1: 3.0), and untreated (19.3 i

3.6) plots were not Si gnificantly different (F = 0.44; df = 2,6; P > 0.05).

In 2002, larval infestation of apples was Significantly lower (F = 3.4; df = 3,9; P =
0.049) in the untreated, SpinTor and spinosad bait plots compared with plots treated with
bait (Table 2.1). There were no Si gnificant differences in mean apple infestation levels
among the untreated, SpinTor and spinosad bait plots. In 2003, the percentage of apple
infestation by R. pomonella was significantly lower in spinosad bait and SpinTor plots
compared with untreated plots (Table 1) (F = 7.16; df = 2,8; P = 0.02).

Spinosad Sprays in Blueberries. In 2002, captures of adult flies on Pherocon
AM traps hung in spinosad bait (0.68 i 0.26), bait (1.46 i 0.38), SpinTor (1.43 i 0.43),

and untreated (1.68 i 0.29) plots were not Significantly different (F = 2.74, df = 3,9, P >

23

0.05). Similarly, in 2003 there were no significant differences in the numbers of flies
captured on traps among any treatments (F = 2.71; df = 2,8; P = 0.3).

In 2002, infestation of blueberries in plots treated with bait was not Significantly
different from that in untreated plots (Table 2.1). In both 2002 and 2003, blueberry plots
treated with spinosad bait or SpinTor had significantly lower fruit infestation compared
with untreated plots (2002: F = 4.43; df = 3,9; P = 0.02; 2003: F = 7.14; df = 2,8; P =
0.007) (Table 2.1).

Field Observations of R. mendax. There were no significant differences in the
mean numbers of adult R. mendax observed visiting spinosad bait, bait or untreated
blueberry bushes (Table 2.2). For all treatments, the mean numbers of flies visiting
bushes did not differ between days 0-2 and days 3-4 (two-sided Sign test P = 0.286, n =
22). The mean duration (5) of fly presence within 5 cm of spinosad bait and bait treatment
droplets was significantly greater than the mean duration spent within the same distance
of control (water) droplets (F = 3.9; df = 2,22; P = 0.03) (Table 2). Flies spent ca. 10-fold
more time, on average, within 5 cm of GF-12O droplets than near water droplets.
Although flies were observed feeding on droplets, the sample Size observed was too small

for analysis.

24

Table 2.1. Effect of different spinosad formulations on mean (i SEM) apple and

blueberry infestation by the apple maggot, R. pomonella and the blueberry maggot, R.

mendax, respectively.

 

 

Treatment % Infested apples % Infested blueberries
2002 2003 2002 2003
Spinosad bait 0.9 : 0.3b 0.4 i 0.1b 0.5 i 0.3b 0.1 i 0.03b
SpinTor 0.6 i 0.2b 0.2 i 0. lb 0.6 i 0.2b 0.3 :I: 0.1b
Bait 2.9 : 0.0a -- 2.5 i 0.6a --
Untreated
1.0 : 0.4b 1.2 i 0.1a 3.3 i 0.53 4.4 i 0.9a

(control)

 

Means within each column followed by the same letter are not Significantly different, (P

< 0.05, Fisher’s Protected LSD Test). Data were subjected to arcsine transformation prior

to analysis. Untransforrned values are shown.

25

Table 2.2. Number (mean i SEM) of R. mendax flies observed per weekly sample on
blueberry plants treated with spinosad bait, protein bait, or water droplets and the

duration (mean i SEM) spent within 5 cm of the droplets. Data collected 14 July — 08

 

Aug. 2003.
—
Treatment Number of flies observed Duration within 5 cm of droplet (S)
Spinosad bait 8.8 : 1.8a 598.0 i 175.8a
Protein bait 11.8 i 0.93 381.3 $141.13
Water (control) 8.0 i 1.2a 53.6 :1: 38.0b

 

Means within each column followed by the same letter are not significantly different (P <

0.05, Fisher’s Protected LSD Test).

26

DISCUSSION

In light of the reduction in fruit infestation Observed in apples (2002) and
blueberries (2002 and 2003), unbaited and baited formulations of Spinosad Show promise
for control of two of the most commercially important temperate fruit fly species, R.
pomonella and R. mendax. Substantial levels of control were achieved for both
Rhagoletis species when their respective host plants were treated with Spinosad bait or
SpinTor at recommended rates. In apples, spinosad bait provided 67% reduction in fruit
fly infestation in 2003, while in blueberries there were 85% (2002) and 98% (2003)
reductions in fly infestations compared with controls. GF-120 did not outperform the
unbaited formulation of spinosad, but did provide equivalent control using only 0.5—1.5%
as much active ingredient.

Although Spinosad bait caused a reduction in fruit infestation, it did not eliminate
infestation by Rhagoleris flies. In order for an insecticide-bait to be commercially viable
for fruit fly control, it must provide extremely high fruit protection to allow growers to
meet the stringent quality standards of the market. At least one infested blueberry or
apple was collected in plots treated with GF-120 or SpinTor in 2002 and 2003. Complete
suppression of fly infestation did not occur in earlier experiments conducted with
spinosad formulations on Mediterranean fruit fly (Peck and McQuate 2000, Vargas et al.
2002) or the melon fly (Prokopy et al. 2003), yet these products are used commercially
for fly control. Similarly, SpinTor did not prevent larval infestation of apples in small
(single tree) plots with large apple maggot populations (Reissi g 2003). In the current
Study, infestation of fruit in the relatively small test plots may have been due to

immigration of flies from nearby untreated areas; therefore, future tests of SpinTor or

spinosad bait should be conducted at a larger scale. Coverage of larger areas with these
products may provide the high level of control required to meet the zero tolerance for
infested fruit.

Observations of R. mendax in blueberry plantings revealed that similar numbers
of flies visited blueberry plants treated with spinosad bait, bait, or water. Flies were
observed within close proximity (5 cm) of spinosad bait and bait droplets. Mediterranean
fruit flies exhibit attraction to GF-120 droplets on coffee plant leaves only when they are
within several centimeters of the droplet (Barry et al. 2003). In the present study, R.
mendax remained close to the droplet (within 5 cm) for Significantly longer durations
than near control water droplets (Table 2.2). As defined by Kennedy (1978), an arrestant
chemical is that which causes orthokinetic movement (the insect alters its rate of
movement) or klinokinetic movement (the insect alters its rate of turning). Alternatively,
an attractive chemical is that which causes non-random movement, orientational
movement of the insect toward the stimulus. The observational findings reported in Table
2.2 support the hypothesis that arrestment behavior in response to cues from the bait
component of GF—120, rather than attraction, is the underlying mechanism for the
efficacy of this product.

Prokopy et al. (2003) demonstrated that significantly fewer melon flies contacted
GF-120 applied to sorghum (Sorghum Sp.) (non-host) plants surrounding host cucumbers
(Cucumis sativus L.) 1-4 days following application compared with freshly applied GF—
120. In addition, GF-120 aged for 4 days under dry conditions retained half of its initial
toxicity to melon flies despite the finding that a complete loss in attractiveness occurs

after only one day under dry greenhouse conditions. In that study, stochastic (accidental)

28

interactions between flies and the phagostimulants in GF-120 were the suggested

mechanism by which ingestion of spinosad occurred.

The bait component of GF-120 contains only 1% (wt:vol) of the attractant
ammonium acetate (Moreno and Mangan 2003). Field studies have shown that ammonia
in Polycon dispensers or incorporated into Pherocon AM traps dissipates after
approximately 2 weeks in the field, resulting in an almost complete loss of attractiveness
(Liburd et a1. 1998, K. S. Pelz unpublished data). Rapid volatilization of ammonia from
spinosad bait may explain the lack of attraction reported here. Several studies indicate
that increasing the amount of ammonium acetate or ammonium bicarbonate has a
repellant effect on tropical fruit flies (Heath et al. 1994, Robacker 1995). In contrast, a
recent study indicates that captures of R. pomonella increase with increasing percentages
of ammonia (Yee and Landolt 2004). Future studies Should test the effects of increasing
the percentage of ammonia in spinosad bait on temperate fruit flies. If higher rates of
ammonium acetate enhance the duration of arrestment on spinosad bait, it would be
expected to increase the interaction of flies with the toxicant and the likelihood of

preventing larval infestation.

Some technical challenges must be addressed in order to make the use of Spinosad
bait practical on a commercial scale. The current formulation must be applied frequently
and requires reapplication following moderate to heavy rainfall. Modifications of the
formulation to increase rain-fastness would greatly enhance its suitability for control of
fruit flies in both temperate and tropical climates. Furthermore, the efficacy of spinosad
bait could be improved by incorporation of host fruit volatiles, similar to the use of apple

volatiles to enhance R. pomonella captures on spheres (Zhang et al. 1999). In addition,

29

increasing the amount of ammonium acetate in the GF-120 formulation from 1% could
potentially enhance its capacity to attract flies for a greater duration after application, and

over a greater distance.

Pesticide-treated Sphere traps that mimic host fruit have been the recent focus of
bait-and-kill technology against Rhagoletis fruit flies, and these have provided substantial
control of apple and blueberry maggot flies (Liburd et al. 1999, Stelinski and Liburd
2001, Stelinski et al. 2001). However, commercial use of attracticidal sphere traps has
been limited due to the high rate of sphere deployment and cost of this approach
(Stelinski et al. 2001). Baited insecticide formulations fit into the current system of pest
control based on the use of Sprayable pesticides, whereas employing pesticide-treated
spheres for large-scale control requires a shift in convention. Sprayable formulations of
spinosad and protein bait offer several other advantages, including ease of application,
lower dosage of active ingredient, and reduced impact of insecticide load on the
environment and non-target insects (Vargas et al. 2001, Vargas et a1. 2002, Mazor et al.
2003). Due to their less restrictive pre-harvest intervals, compared with conventional
insecticides, bait-and-kill formulations of spinosad may provide fruit protection close to

harvest when growers have fewer control options available.

30

CHAPTER THREE. VERTICAL POSITIONING OF TRAPS AND HOST FRUIT
PRESENCE INFLUENCE CAPT URES OF EASTERN CHERRY FRUIT FLY

(DIPTERA: TEPHRITIDAE).

INTRODUCTION

The eastern cherry fruit fly, Rhagoletis cingulata (Loew), is an important late-
season pest of cherries in the eastern and Midwestern United States (Frick et al. 1954).
Adults emerge from overwintering puparia in mid-June, mate on the host fruit, and lay
eggs into cherries (Pettit and Tolles 1930, Prokopy 1976). A sibling species, the black
cherry fruit fly, R. fausta (Osten Sacken), has a Similar biology and geographical range,
but is only occasionally a pest in commercial orchards. Additionally, R. cingulata adults
are more frequently found on host fruit than foliage (Smith 1984).

Michigan produces ca. 75% of the total US. tart cherries, Prunus cerasus L., and
12% of the U. S. sweet cherries, P. avium (L.) (Anon. 2004a). Zero tolerance standards
for fly larvae in fruit require sensitive fly monitoring systems early in the growing season
as part of integrated pest management (IPM) programs to prevent fruit infestation. To
monitor R. cingulata, Pherocon AM boards are placed ca. 2.1 m from the ground within
the tree canopy. The yellow traps are typically baited with an ammonia and protein
hydrolysate lure (Bateman and Morton 1981), providing both visual and olfactory cues to
attract flies. The first insecticide is applied after a single fly is captured on a monitoring
trap. Three-dimensional Rebell traps, also yellow, are highly selective for both R. fausta
and R. cingulata and are more effective for capturing R. fausta than baited Pherocon AM
boards or red sphere traps (Liburd et al. 2001). However, Rebell traps are expensive and

have not been widely adopted by Michigan cherry growers for monitoring.

31

Steady progress has been made in developing effective trapping systems for some
important Rhagoletis pests of temperate fruit crops. Ammonium acetate is a highly
effective olfactory lure for attracting Rhagoletis flies to monitoring traps (Reissig 1976,
Liburd et al. 2001). Trap placement has been optimized for monitoring the apple maggot
fly, R. pomonella (Walsh), (Reissig 1975, Drummond 1984) and the blueberry maggot, R.
mendax Curran (Liburd et al. 2000, Teixeira and Polavarapu 2001). The optimal position
for traps to monitor R. pomonella is approximately 2.1 m from the ground within the tree
canopy (Reissi g 1975, Drummond 1984) and 0.25-0.5 m from fruit, while traps for R.
mendax are most effective when placed within the top of hi ghbush blueberry, Vaccinium
corymbosum L., plants when the bushes are 1.5 to 2.0 m high (Liburd et al. 2000,
Teixeira and Polavarapu 2001). To date, the optimum positioning of traps for monitoring
R. cingulata has not been reported.

Host volatile lures have been developed for trapping R. pomonella that provide a
more accurate indication of fly presence than ammonium-based lures (Prokopy 2001,
Stelinski and Liburd 2002) and Show promise for development of attract-and-kill
approaches to control this pest. A seven-component blend of apple volatiles was
determined via field, wind tunnel, and olfactometer bioassays to attract R. pomonella
(Fein et al. 1982, Reissi g et al. 1982, Averill et al. 1988). Further experiments indicated
that a five-component blend (Zhang et al. 1999) combined with a red sphere is the
optimal trap for attracting the maximum number of R. pomonella (Stelinski and Liburd
2002). The capacity of spheres to capture more flies provides a viable method for mass-
trapping, thus offering an alternative control tactic to pesticides. Recently, the Food

Quality Protection Act (FQPA) called for the review of registrations for some of the most

32

important insecticides traditionally used for fruit fly control. Thus, tactics using attractive
lures for behavioral modification, such as mass trapping and novel attract-and-kill tactics
(Foster and Harris 1997, Stelinski and Liburd 2001, Prokopy et a1. 2004) may feature
more prominently as valuable alternatives or supplements to insecticides. Prior to the
development of an attractive synthetic apple volatile lure, Prokopy et al. (1973) showed
that R. pomonella flies were attracted to the odor of apples. To date, it has not been
determined whether R. cingulata are attracted to volatiles specific to their host fruit,
cherries.

Based on studies of related fruit fly Species, I hypothesized that trap placement
within the cherry tree canopy and cherry volatiles would affect captures of R. cingulata
on monitoring traps. My first objective was to compare high (4.6 m), standard (2.1 m),
and low (1.2 m) trap heights to determine the response of R. cingulata. My second
objective was to compare captures of R. cingulata on Pherocon AM traps hung adjacent

to unripe sweet, unripe tart, ripe sweet, ripe tart cherries, or no cherries.

33

MATERIALS AND METHODS

Experimental Sites. In 2002, trap heights were compared in a mature,
unmanaged tart cherry orchard located in southwestern Michigan (Van Buren Co.). Trap
position and host-fruit attraction experiments were carried out in 2003 in separate
unmanaged tart cherry orchards in southwestern Michigan (Van Buren Co. and Allegan
Co.). All orchards used in these experiments were unsprayed, mature trees ca. 4.6 m in
height.

Trap Height. The effect of trap height on captures of R. cingulata was
determined by placing unbaited Pherocon AM traps (Trécé Inc, Adair, OK) at three
positions within in cherry trees (ca. 4.6 m high): (1) below the tree canopy (ca. 1.2 m
above ground), (2) at the standard trap height (ca. 2.1 m), or (3) in the top portion of the
tree canopy ca. (4.6 m). Traps hung at 4.6 m were attached to a PVC pipe (6 mm diam.)
and attached to trees. A tree was selected randomly and a Single trap was placed at one of
the three positions. Treatments were arranged with a distance of at least 20 m between
trees (one trap/tree) and 30 m between blocks. Foliage surrounding all traps was removed
in a 0.5 m radius (Reissi g 1975). Five replicates of each treatment were arranged in a
randomized complete block design. Flies were counted and removed from traps weekly
for six weeks. To minimize position effects, all treatments were rotated one position
clockwise after each weekly inspection.

Response to Cherries.

Fruit lure construction. For each treatment, 1.0 kg of fruit (described below) was
washed and placed in 0.5 cm cheesecloth bags. These bags were placed in cylindrical

enclosures (30.5 cm length X 15.2 cm diam.) constructed of 1 mm mesh aluminum

34

window screening. Enclosures were designed to prevent flies from contacting fruit, yet
allow the emission of olfactory stimuli. Cheesecloth fruit bags were suspended from a
wire hanger in the enclosures with a twist tie such that fruit was ca. 3 cm from the cage
walls. Enclosures were hung at 2.1 m above ground with surrounding foliage removed in
a 0.5 m radius around the enclosures. Two Pherocon AM traps were hung on opposite
sides of the enclosures 3 cm from the edge of the enclosure. All cherries within a radius
of ca. 2 m were removed to prevent competition with the caged fruit.

Treatments. The following treatments were tested: 1) unripe tart cherries, 2)
unripe sweet cherries, 3) ripe tart cherries, 4) ripe sweet chenies, and 5) no fruit (control).
Ripe fruit was obtained from a local fruit market while unripe fruit was obtained from
research orchards at Michigan State University’s Trevor Nichols Research Complex
(Fennville, MI). Five replicates of each treatment were arranged in a randomized block
design. R. cingulata flies captured on the two traps adjacent to the fruit lures were
counted and removed every 3 d. Following each trap check, all fruit was replaced with
fresh fruit and treatment positions were rotated clockwise within blocks.

Statistical Analysis. Total fly captures on each trap across the seasons in both the

vertical trap placement and fruit attraction experiments were subjected to analysis of

variance (ANOVA). All data were square root-transformed (x + 0.5)“2 prior to analysis.

Fisher’s Least Significant Difference test (LSD, SAS Institute 1999) was used to separate

mean differences among treatments (P = 0.05).

35

RESULTS

2002 Vertical Trap Placement. Captures of R. cingulata were significantly
affected by trap height (F = 79.2; df = 2,8; P < 0.05), with more R. cingulata flies caught
at 4.6 m within canopies of cherry trees than on traps placed at 2.1 m (standard trap
height) or 1.2 m at the Van Buren Co. site (Figure 3.1A). Overall, more than three times
the number of flies was captured on traps placed at 4.6 m than on traps hung at lower
positions.

2003 Vertical Trap Placement. As in 2002, captures of R. cingulata flies were
significantly affected by trap height (F =27.0; df = 2,8; P < 0.05). Significantly more flies
were caught on traps hung at 4.6 m than on traps placed at a 2.1 m or 1.2 m height
(Figure. 3.1B). Traps in the highest canopy position caught more than three times as
many flies as those hung in either of the two lower canopy positions.

2003 Fruit Lure Trials. Captures of R. cingulata were not significantly affected
by the type of fruit treatments placed near to traps at the Allegan Co. site (F = 2.26; df =
4,12; P = 0.1) (Table 3.1). However, at the Van Buren Co. site, significantly higher
numbers of R. cingulata were captured on traps next to cages containing ripe tart cherries

compared with the other treatments (F = 5.25, df = 4,8, P < 0.05).

36

    

      

 

 

 

 

 

 

00000000
999999999

and. \

00000
22222

moan mo .02 532

4.6

2.1

1.2

tured per season on P

(2.1 m), and low

Trap Height (m)

at high (4.6 111), standard

experiment was conducted in

02 (A) and 2003

(Fisher’

years are not significantly different
are shown.

Table 3.1. Seasonal captures of adult R. cingulata on Pherocon AM boards hung adjacent

to enclosures containing ripe or unripe sweet or sour cherries in Michigan cherry

orchards.

   

o. flies caudpte (mena :

 

 

Treatment (cherry type) at the indicated experimental Site
Allegan Co. Van Buren Co.
Ripe tart 9.5 i 3.0 a 216.0 i 32.5 a
Ripe sweet 4.0 i 1.7 a 129.3 1 31.1 b
Unripe tart 4.0 i 1.1 a 97.0 t 46.9 b
Unripe sweet 2.5 i 0.9 a 78.0 i: 8.7 b
No fruit (control) 2.3 i 0.8 a 94.7 i 21.7 b

 

Untransformed means within each column followed by the same letter are not

significantly different, (P < 0.05).

38

DISCUSSION

Captures of R. cingulata were substantially greater on traps placed at the highest
position (4.6 m from the ground) compared with those hung at 2.1 m or 1.2 m. Flies may
spend more time foraging in the uppermost portion of the host tree canopy, or traps
placed higher in the tree may be more visible than those placed within the tree canopy.
Similar results were obtained with R. mendax captures within blueberry bushes, where
traps placed in the upper third of bushes captured the greatest number of flies (Liburd et
al. 2001). In contrast, more R. pomonella are captured on Pherocon AM traps placed at
2.1 m within the canopy of apple trees than on traps at 1.2 or 3.0 m (Reissig 1975, Pelz et
al. unpublished). We propose that monitoring traps for R. cingulata should be placed high
in the tree canopy, to improve the sensitivity and accuracy of R. cingulata monitoring,
allowing cherry growers to more effectively time insecticide applications. Additionally,
the improved trap performance may provide growers with a higher level of confidence in
monitoring, allowing decisions to treat a Specific orchard to be delayed until a fly is
captured.

At the Van Buren Co. site, the increased response of flies to Pherocon AM boards
placed next to ripe tart cherries compared to unripe tart cherry, sweet cherry, and no fruit
treatments suggests that the odors specific to ripe tart cherries are attractive to R.
cingulata. Ripe tart cherries are present later in the season, a time when a greater
proportion of the population of R. cingulata has reached sexual maturity. Female
Rhagoletis flies spend more time on fruit compared to foliage searching for oviposition
Sites, while males spend more time on fruit waiting for females with which to copulate

(Prokopy et al.1972, Prokopy and Bush 1973, AliNiazee, 1974, Boller and Prokopy

39

1976). In addition, the tough texture of unripe cherries may be a sub-optimal substrate for
successful oviposition or larval development. Therefore, it is possible that R. cingulata
have developed a preference for ripe tart cherry fruit due to the optimal combination of
odor and developmental stage these fruit provide. Choice tests should be performed to
determine the age, sex, and maturity of flies attracted to ripe tart cherries.

Although the results of the fruit lure trial at the Allegan Co. site did not indicate
Significant differences in fly responses to treatments, numerically higher numbers of flies
were captured on traps placed next to ripe tart cherries. The lack of significant differences
was possibly due to the low population of flies present at the site.

That fewer flies were caught on traps placed next to ripe sweet cherries than traps
placed next to ripe tart chenies suggests a possible preference for the latter. Apple
cultivar preferences are exhibited by R. pomonella (Dean and Chapman 1973, Rull and
Prokopy 2001). Rull and Prokopy (2001 a) reported that traps in the ‘Gala’ cultivar
amassed higher numbers of flies throughout the season and were more susceptible to
oviposition than other cultivars. This cultivar represents a more attractive oviposition site
for R. pomonella, possibly due to the odor and ripeness of fruit when females are
searching for egg laying sites (Rull and Prokopy 2001a, b). A similar mechanism is
possible for R. cingulata. Sweet cherry varieties ripen around two weeks after fly
emergence. During this time, the majority of females are not sexually mature and
therefore not searching for oviposition sites. Tart cherries continue to ripen after sweet
cherry varieties have been harvested, leaving them available to flies during the peak
oviposition period. Fruit firmness may also be a factor in selection of oviposition site,

thus ripe fruit is likely a more appealing resource compared to unripe fruit. Future studies

40

should be done to determine whether R. cingulata females preferentially oviposit into
ripe tart cherries.

Our field results suggest that R. cingulata may be attracted to some volatile
component(s) of tart cherry fruit. Further studies are needed to determine specific
composition of fruit volatiles attractive to flies. A volatile lure for R. cingulata that
incorporates attractive, host specific odors, similar to the five-component blend described
for R. pomonella (Zhang et a1. 1999), could enhance the current trapping capabilities of
pest management programs. A recent study (Nojima et al. 2003a) has shown that a blend
of host-specific volatiles from flowering dogwood fruit resulted in a greater flight
response from dogwood—derived R. pomonella compared to blends originating from apple
or hawthorn fruits. Similarly, R. pomonella originating in hawthorn fruit exhibited a
greater response to a hawthorn volatile blend than to the apple volatile blend (Feder et al.
2003, Nojima et al. 2003b). Subjecting wild and commercial cherry fruits to these
techniques will be necessary to determine the feasibility of developing a volatile lure for
R. cingulata.

Ammonium acetate or ammonium carbonate lures are currently used in
combination with traps for R. cingulata; however these lures are not selective for this
species and capture many non-target insects (Stelinski and Liburd 2003). Traps lose
effectiveness over time due to a decreased trapping surface and a reduction in visual
attractiveness to flies, resulting in increased labor costs associated with trap replacement.
Combining the knowledge of R. cingulata behavior obtained from these studies, we may
be better able to approximate population levels within orchards through the use of

species-specific trapping methods. These methods could eventually be incorporated into a

41

system of mass-trapping, providing an alternative to conventional spraying as a system

for fly control.

42

CHAPTER FOUR. INFLUENCE OF SYNTHETIC LURES AND TRAP TYPES ON
CATCHES OF BLUEBERRY MAGGOT AND EASTERN CHERRY FRUIT FLY

(DIPTERA: TEPI-RITIDAE).

INTRODUCTION

Monitoring traps are used by blueberry and cherry growers to detect the presence
and determine the seasonal activity pattern of the blueberry maggot, Rhagoletis mendax
Curran, and the eastern cherry fruit fly, R. cingulata (Loew). The initial insecticide sprays
targeting these pests are timed in response to the first fly captured on monitoring traps
(Stanley 1987, Howitt 1993, Liburd et al. 2001). Optimizing trap design and lure type
used for monitoring these pests may improve detection of fly emergence and activity,
thereby optimizing and perhaps reducing insecticide applications (Kring 1970, Prokopy
and Hauschild 1979, Neilson et al. 1981, Liburd et al. 1998, Liburd et al. 2000). Precise
tinting is especially critical for the more selective and less toxic insecticide chemistries
being adopted as a result of the Food Quality Protection Act (1996) regulations. Unlike
older insecticides, such as organophosphorous compounds, the efficacy of these new
chemistries often requires their ingestion by the target pest; therefore, it is increasingly
important that pesticides be applied immediately following fly emergence. Additionally,
properly timed sprays should improve the likelihood that fly larvae will not be detected in
harvested fruit, for which there is a zero tolerance.

Monitoring of Rhagoletis flies typically relies on the manipulation of behaviorally
relevant visual and olfactory stimuli. These stimuli may mimic host foliage, host odor, or

natural food sources (Prokopy and Coli 1978, Prokopy and Hauschild 1979, Neilson et al.

43

1981, Duan and Prokopy 1992, Liburd et al. 1998, 2001). Pherocon AM boards baited
with release devices containing ammonium acetate are highly effective monitoring tools
for both R. mendax and R. cingulata (Prokopy and Coli 1978, Liburd et al. 1998, 2001),
as well as other Rhagoletis species (Prokopy and Hauschild 1979). Current commercially
available lures for these Species consist of plastic dispensers containing 2.0 g ammonium
acetate, which are affixed to traps. Researchers using ammonium acetate for field studies
have relied on plastic chargers, or polyethylene vials, affixed to traps for deployment of
the volatile (Liburd et al. 1998, 2001). However, in Michigan the majority of cherry and
blueberry growers typically deploy the ‘prebaited’ Pherocon AM boards, containing
ammonium acetate and protein hydrolysate impregnated within the T angle-Foot sticky
coating covering the traps, rather than deploying the dual system of an unbaited Pherocon
AM board with manually attached ammonia dispenser.

Recent studies have shown that apple volatiles used in combination with red
sphere traps attract and capture high numbers of apple maggot flies (Prokopy et al. 1973,
Stelinski and Liburd 2002). In contrast, attractive and effective host fruit volatiles for use
with monitoring traps for R. mendax and R. cingulata have not been identified, although
some blueberry volatiles have Shown promise for R. mendax (Liburd 2004).

Green spheres and Rebell traps are more effective than Pherocon AM boards for
R. mendax and R. cingulata, respectively, in that they capture the maximum number of
flies (Liburd et al. 1998, 2001). Compared to Pherocon AM boards, however, these traps
are more expensive. The higher cost can be somewhat offset by reusing them, but this
requires an additional expenditure to replace the adhesive. Rebell traps and Pherocon AM

boards are yellow, reflecting light across similar wavelengths as host foliage. These traps

44

differ primarily in shape; therefore it is suggested that the three dimensional structure of
the Rebel] trap is more attractive to flies than the two-dimensional structure of Pherocon
AM traps (Liburd et al. 2001). Alternatively, trap size may be responsible for the superior
performance of Rebell traps. Rebell traps have a total surface area of 642 cm2, whereas
Pherocon AM boards have a total surface area of only 214 cm2. The greater surface area
of Rebell traps could increase the probability of fly captures compared to Pherocon
boards,

The objectives for this study were to: 1) compare the attractiveness of host fruit
concentrates on Pherocon AM boards with and without ammonium acetate for R. mendax
and R. cingulata, 2) determine the optimal method of ammonium acetate deployment
(plastic dispenser versus pre-baited Pherocon AM boards) for R. mendax, and 3)
determine the relative effects of trap dimension and trap surface area on captures of R.

cingulata.

45

MATERIALS AND METHODS

Field sites. Field experiments with fruit and ammonium acetate attractants were
conducted during the 2002 field season in a non-commercial blueberry planting located in
southwest Michigan (Allegan Co.) and non—commercial cherry orchards in northwest
(Leelanau Co.) and southwestern (Van Buren Co.) Michigan. The blueberry Site was a ca.
2 ha ‘Jersey’ planting used in past field studies (Stelinski and Liburd 2001) due to the
presence of a resident R. mendax population. The southwestern cherry site was a recently
abandoned ca. 2 ha planting of ‘Montmorency’ tart cherries. The northwestern cherry site
was a ca. 5 ha planting of ‘Montmorency’ tart cherries that had not been commercially
managed for at least five years.

Lures. Cherry and blueberry concentrates were obtained from Milne Fruit
Products, Inc (Prosser, WA). For the cherry concentrate 5% tart cherry concentrate (Brix
68 g sugar/ 100 ml; lot # TEL-02-092-MI), 5% sweet cherry concentrate (Brix 68 g
sugar/ 100 ml; lot # MFP-92-074-M3), and 85% water were blended. Because of the high
sugar content, ethanol (5% v:v) was also added to preserve freshness under field
conditions. Milne Fruit Products removed all non-soluble components, including sugars,
from the blueberry concentrate; therefore it was not necessary to add ethanol to this
purified essence. Five ml of each concentrate was dispensed into 2.5 cm x 5.0 cm plastic
bags and heat-sealed. A 6.4 cm long cotton wick was inserted into the dispenser prior to
scaling to draw the concentrate out for release. Fruit concentrate dispensers were then
attached to the top of traps with 0.6 cm binder clips.

Ammonium acetate lures consisted of plastic yellow dispensers (Great Lakes

IPM, Vestaburg, MI) that were filled with 2 g of solid ammonium acetate (Sigma

46

Aldrich, St. Louis, MO) immediately before deployment. A single dispenser was attached
to the upper corner of the Pherocon AM trap with a yellow twist tie.

R. mendax lure comparisons. Five treatments were compared in a randomized
complete block design with six replicates. Treatments consisted of Pherocon AM yellow
boards prebaited with ammonium acetate (2 g) and protein hydrolysate (0.5 g) (Great
Lakes IPM), and Pherocon AM yellow boards baited with the following lures: 1)
blueberry concentrate, 2) ammonium acetate, 3) blueberry concentrate and ammonium
acetate, 4) nothing (control). Traps were hung at the optimum height within blueberry
bushes ca. 15 cm below the uppermost canopy and in a vertical orientation on the south
side of the blueberry bushes with foliage and fruit cleared in a ca. 0.5 m radius (Liburd et
al. 2000). Traps were separated by at least 15 m, with 10 m between blocks. Each week
R. mendax were removed and counted by sex, and treatments rotated within each block to
account for positional bias. Treatments and traps were replaced biweekly for an 8 wk
period.

R. cingulata lure comparisons. Two trapping experiments were conducted
during the 2002 field season. In the first experiment, conducted at the northwest site, the
trapping systems evaluated were yellow Rebell traps (Great Lakes IPM, Vestaburg, MI)
baited with: 1) cherry concentrate, 2) solid ammonium acetate, 3) cherry concentrate and
ammonium acetate, and 4) nothing (control). In the second experiment, conducted at the
southwest site, the same lures compared at the northwest site were evaluated in
combination with yellow Pherocon AM boards rather than Rebell traps. The experimental

design was a randomized complete block with five replicates for the Rebell systems and

47

Six replicates for the Pherocon AM systems. Traps were separated by at least 20 m, with
30 m between blocks.

Traps were hung vertically on the south Side of trees with foliage cleared in a 0.5
m radius from the traps. No fruit was present on trees at either site during the 2002 field
season due to spring frosts. Traps were separated by at least 20 m and maintained as
described above in blueberries.

To determine the effects of trap Size and dimension on captures of R. cingulata
flies, three trap designs were compared in a randomized complete block experiments at
the southwest site. There were six replicates of each of three treatments: 1) a Pherocon
AM board hung vertically, 2) two Pherocon AM boards unfolded and attached back to
back such that sticky sides faced out, and 3) a Rebell trap. The total surface areas coated
with Tanglefoot for each trap design were ca. 214 cm2, 428 cm2, and 642 cm2,
respectively.

Statistical Analysis. For each experiment, data were square root-transformed (x +

0.5)“2 prior to analysis with ANOVA followed by means separation using Fisher’s least

significant difference (LSD) test (SAS Institute 1998). Treatment means were considered

different at P = 0.05.

48

RESULTS

R. mendax. Analysis of the blueberry trapping experiment results indicated a
significant effect due to treatment (F = 10.69; df = 4, 20; P < 0.05). Pherocon AM boards
pre-baited with ammonium acetate and protein hydrolysate, unbaited Pherocon AM
boards with ammonium acetate chargers, and unbaited Pherocon AM boards with
ammonium acetate chargers and blueberry essence captured significantly more R.
mendax flies compared to boards baited with other lures, but were not Significantly
different from each other (Table 4.1). Fly captures on traps baited with blueberry essence
did not differ significantly from those on unbaited traps.

R. cingulata. Direct comparisons of four trapping systems based on the Pherocon
AM board revealed that the treatment effect was significant (F = 9.7; df = 3, 15; P <
0.05). Significantly more R. cingulata flies were captured on traps baited with
ammonium acetate, cherry concentrate or a combination of the two compared to an
unbaited trap (Table 4.2). The mean number of flies captured on boards baited with either
ammonium acetate or cherry concentrate was not Si gnificantl y different. However, the
use of ammonium acetate in combination with cherry concentrate increased fly captures;
significantly more flies were captured on traps baited with this dual system than on those
baited only with the cherry concentrate. Although there was not a significant difference
between the mean number of flies captured on the Pherocon AM boards baited with the
combination of lures or only with ammonium acetate, the former captured ca. 30% more
flies than the latter. The number flies captured on boards baited with cherry concentrate

was also significantly higher than those captured on unbaited (control) boards, which

49

suggests that cherry concentrate may have an additive effect when used with ammonium
acetate to attract flies.

The response of R. cingulata to ammonium acetate and cherry concentrate lures in
combination with Rebell traps differed from that observed on Pherocon AM boards,
although there was a significant treatment effect (F = 9.79; df = 3, 12; P < 0.005).
Significantly fewer flies were captured on unbaited Rebell traps or traps baited with
cherry concentrate in comparison to traps baited with ammonium acetate (Table 4.3). The
addition of a cherry concentrate lure did not increase fly captures on the Rebell traps.
Similarly, there was no significant difference between the mean number of flies captured
on ammonium acetate and ammonium acetate plus cherry concentrate-baited traps.
Approximately twice as many flies were captured on traps baited with either ammonium
acetate treatment compared to other treatments.

In comparisons of trap types for capture of R. cingulata, the mean number of flies
on Rebell traps (108.5 i 9.9) was significantly greater than the mean number of flies
captured on a Single Pherocon AM board (23.5 i 5.5) or two Pherocon AM boards (25.8
i 6.8) joined together to form a trap of similar size and shape as the Rebel] trap (F =

91.5; df= 2, 10; P < 0.05).

50

Table 4.1. Effect of different lures on seasonal captures of adult R. mendax on Pherocon

AM traps.

Lure type Mean 1: SEM flies per trap

 

Ammonium acetate (dispenser) +

blueberry concentrate 66'3 i 12.2a
Ammonium acetate + protein hydrolysate

(impregnated in adhesive) 63.0 : 11.8a
Ammonium acetate 58.2 i 15.0a
Blueberry concentrate 18.8 :t 4.9b
None 15.5 i 2%

 

Means within each column followed by the same letter are not Significantly different, (P

> 0.05, Fisher’s Protected LSD Test). Untransformed values are Shown.

51

Table 4.2. Effect of different lures on weekly captures of adult R. cingulata captured on

 

Pherocon AM traps.
—
Lure type Mean 3 SEM. flies per trap
Ammonium acetate + cherry concentrate 51.7 i 9.4a
Ammonium acetate 37.2 i 9.9ab
Cherry concentrate 28.7 i 5.1b
None 15.8 i 4.5c

 

Means within each column followed by the same letter are not Significantly different, (P

> 0.05, Fisher’s Protected LSD Test). Untransformed values are shown.

52

Table 4.3. Effect of different lures on weekly captures of adult R. cingulata captured on

Rebell traps.

 

Lure type Mean 1 SEM no. flies per trap
Ammonium acetate 43.6 i 9.2a
Ammonium acetate + cherry concentrate 32.8 : 9.9a
Cherry concentrate 16.0 i 3.4b
None 17.4 :t 4.8b

 

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

different, (P > 0.05, Fisher’s Protected LSD Test). Untransformed values are shown.

53

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54

DISCUSSION

Ammonium acetate significantly increased fly catches in all three experiments, in
agreement with the findings of a previous study (Liburd et al. 2001). This indicates that
an attractive olfactory lure is an important component of any trapping system for
maximizing Rhagoletis capture. Rhagoletis flies, like most Tephritids, require a protein
meal following emergence. Ammonium acetate represents an attractive food source
because ammonium is an important component of the flies’ natural protein source, avian
fecal matter. However as the season progresses, flies spend a decreasing proportion of
time feeding and more time searching for mates and, in the case of females, oviposition
sites (Smith 1984). If volatiles emitted by cherries or blueberries are acting to attract R.
cingulata and R. mendax, respectively, to their hosts, as shown for other Rhagoletis flies
(Linn et al. 2003, Fein et al. 1982, Reissig 1982), then fruit volatile lures may be more
important during the latter half of the growing season to accurately monitor population
levels.

The addition of cherry concentrate to Pherocon AM boards or Rebell traps
increases their attractiveness to R. cingulata. This result was slight and not significantly
different from control (no lure) Pherocon AM boards. However, when used in
combination with an ammonium acetate lure, an additive effect of the concentrate did
increase fly captures. A similar effect was not seen in the captures of flies on ammonium
acetate baited Rebell traps when cherry concentrate was added. Other studies with the
Rebel] trap have Shown its high efficacy in capturing the black cherry fruit fly, R. fausta
(Liburd et a1. 2001), and the European cherry fruit fly, R. cerasi (Russ et al. 1973),

compared to Pherocon AM boards. Liburd et al. (2001) speculated that the three-

55

dimensional structure of the Rebell trap visually stimulates flies over a larger field as they
move through the host canopy because the trap is visible from all angles of fly approach.
Although a direct comparison between Rebell traps and Pherocon AM boards was not
made, the results indicate that the addition of ammonium acetate and/or cherry
concentrate to Pherocon AM boards makes the attractiveness of this trap equivalent to the
Rebel] trap. Similar results for ammonia-baited Pherocon AM boards were obtained by
Liburd et al. (2001).

Cherry and blueberry concentrates did not consistently increase fly captures when
used alone, suggesting that the volatile composition, concentration, or release rate of the
concentrate lures are either insufficient host fruit mimic or that flies do not rely on cherry
fruit odor for locating host fruits. However, cherry concentrate did numerically increase
captures of R. cingulata on Pherocon AM boards. This suggests that there is potential for
identifying attractive cherry fruit volatiles and that some level of an attractive volatile or
volatiles are present in the lure used in this study. This finding is significant because
growers and pest management consultants are unlikely to adopt Rebell traps due to the
constraints of cost, labor-intensive deployment, and maintenance. Augmentation of
Pherocon AM boards currently in use with attractive volatile lures or fruit concentrates
would be a feasible economic means of enhancing traps catches. Further studies on the
volatile components fruits, particularly host fruits remaining on the tree after harvest, are
necessary to determine whether a blend such as described for apple maggot (Fein et al.
1982, Reissig 1982) could exist for R. cingulata before such a lure can be developed to
improve trap attractiveness. To this end, laboratory and field choice assays should

investigate fly response to fruit odors. If flies are attracted by an olfactory cue emitted by

56

their host, they should exhibit higher levels of visitation to these fruit. Additionally, the
specific individual volatiles and fly responses to these individual components need to be
evaluated via GC-EAD to identify specific behaviorally-active chemical components, as
described for apple and hawthorn fruits for R. pomonella (Fein et al. 1982, Linn at e1.
2003).

R. mendax responded similarly to Pherocon AM boards baited with ammonium
acetate dispensers or with ammonium acetate and protein hydrolysate incorporated into
the Tangle-trap. Pre-baited traps are a therefore a better choice for monitoring this species
because although the cost of the pre-baited traps is higher compared to unbaited traps and
ammonia dispensers, the labor requirements are lower because lure deployment and
maintenance are not needed initially.

My data indicate that the surface area of Rebell traps is not entirely responsible
for the effectiveness of Rebell traps, as the relationship between increasing surface area is
non-linear (Figure 4.1). It is likely that the three-dimensional structure of the Rebell trap
is the source of its superior performance over Pherocon AM boards. Future studies should
be done to evaluate the effect of trap shape by directly comparing the response of flies to

Pherocon boards arranged in the Rebell formation and Rebell traps.

57

SUMMARY AND CONCLUSIONS

This research indicates that there is potential for the adoption of baited spinosad
(GP-120) for control of Rhagoletis flies. The results obtained from 2002 and 2003
experiments demonstrate that spinosad bait is effective at controlling larval infestation of
fruit, but less effective than unbaited spinosad (SpinTor) at controlling populations of
adult Rhagoletis flies. Commercial implementation of spinosad bait will require
improvements in the formulation of the product. Specifically, enhancements in
attractiveness and rain fastness should improve its efficacy and practicality as an
alternative to conventional insecticide sprays.

With the registration of selective insecticide chemistries for control of Rhagoletis
pests of fruit crops, it is necessary to reevaluate the timing of insecticide applications.
Specifically, targeting the 8-10 day pre-oviposition period was adequate for contact
insecticides. However, as these insecticides are replaced by selective cherrristries reliant
on behavior of flies, particularly those related to feeding, spray guidelines will need to
require initial sprays immediately after the first capture of a fly within the target crop
when flies are spending the greatest amount of time feeding. Therefore, the deployment
of highly attractive traps is critical to ensure the earliest possible capture of flies
following emergence.

Position, design and attractiveness are key components of an effective trapping
system. Optimal trapping of adult flies is particularly important for capturing flies early
in their emergence, as a more effective trap will be more likely to detect fly presence at

lower population levels. The results of the 2002 and 2003 cherry trapping studies showed

58

the importance of placing traps high in the canopy for maximum capture of R. cingulata.
Furthermore, it appears that the three-dimensional structure of Rebell traps, rather than
surface area are responsible for their efficacy, although future studies must be done to
evaluate this directly. The results of the 2002 experiment indicate that the attractiveness
of Rebell traps is not enhanced by the addition of ammonium acetate or fruit concentrate
lures. However, these traps are economically less feasible than Pherocon AM boards and
are therefore less abundantly used among growers and pest management consultants. The
utility of the more preferable Pherocon boards can be enhanced through the addition of
ammonium acetate alone or with a fruit concentrate lure.

Enhancement of trap attractiveness to R. mendax was not observed for Pherocon
boards baited with blueberry essence or blueberry essence and ammonium acetate. Fruit
lures that emit an attractive bouquet of host volatiles may have potential for use to
enhance trap captures, as described by work done on other Rhagoletis species (Linn et al.
2003, Fein et al. 1982, Reissig 1982). However, the results obtained in the cherry and
blueberry studies do not strongly indicate this possibility. It is likely that the fruit lures
used did not release the correct volatiles or proportion of volatiles necessary to elicit fly
responses. Thorough analyses of volatile emissions from ripe and unripe fruits must be
completed and the resulting volatiles individually tested for olfactory receptor and
behavioral responses from flies before trapping studies can be used as an efficient

assessment fruit-based attractive lures.

59

APPENDIX

60

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.: 2004-9
Title of thesis or dissertation (or other research projects):
Comparison of Monitoring Strategies and Evaluation of Spinosad Formulations for
Management of Key Rhagoletis Species

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

Entomology Museum, Michigan State University (MSU)

Other Museums:

Investigator’s Name(s) (typed)

 

Kirsten S. Pelz

 

Date December 06, 2004

*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.

61

Appendix 1.1

Voucher Specimen Data

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62

LITERATURE CITED

63

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