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THESIS

’ZDOI

This is to certify that the

thesis entitled

TRAP DESIGNS AND ATTRACTANTS FOR MONITORING
PLUM CURCULIO CONOTRA CHEL US NENUPHAR (HERBST)

presented by

Andrea B. Coombs

has been accepted towards fulﬁllment
of the requirements for

Masters degree in Entomology

 

4}”

 

Major professor

Date I [010/

0-7639 MS U is an Afﬁrmative Action/Equal Opportunity Institution

 

 

LIBRARY
Michigan State
Unlvorslty

 

 

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE I DATE DUE DATE DUE

 

 

OCTC 7 E083 I

 

 

 

 

 

 

 

 

 

 

 

 

 

6’01 c:/C|RC/DateDuo.p65—p. 15

TRAP DESIGNS AND ATTRACTAN TS FOR MONITORING PLUM
CURCULIO, CONOT RACHEL US NENUPHAR (HERBST)

By

Andrea Biasi Coombs

A THESIS

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

MASTER OF SCIENCE
Department of Entomology

2001

ABSTRACT

TRAP DESIGNS AND ATTRACTANTS FOR MONITORING PLUM
CURCULIO, CONOT RACHEL US NENUPHAR (HERBST)

By

Andrea Biasi Coombs

Research on monitoring traps and attractants for plum curculio, C onotrachelus nenuphar
(Herbst) in Michigan apple and cherry orchards was conducted during the 1997 and 1998
ﬁeld seasons at Clarksville Horticultural Research and Experiment Station, Trevor
Nichols Research Complex, and Douglas Farm. The objective of the ﬁrst study was to
determine the relative efﬁcacy of pyramid traps baited with and without synthetic
pheromone lures. In this study, baited pyramid traps captured a total of 4.14 :I: 1.75 more
plum curculio on average than their nonbaited pairs and performed well just before fruit
set when plum curculio begin to damage fruit. In the second study, pyramid traps were
compared to a new trap design, a modiﬁed circle trap, and the ability of attractant lures,
including synthetic pheromone and plum essence, a natural host-plant kairomone blend,
to enhance beetle capture was also investigated. Plum essence combined with
pheromone captured signiﬁcantly more plum curculio when data was grouped by each
day and over the season in both trap types although the combination of attractants was
not synergistic. At fruit set, circle traps captured signiﬁcantly more beetles than pyramid
traps when averaged over attractant lure and circle traps baited with plum essence and
pheromone captured signiﬁcantly more beetles than all pyramid traps except those baited
with plum essence. At the end of June, pyramid traps baited with plum essence and

pheromone performed best.

To my Grandmother, Jeanette Giron, who comforted a very
young entomologist confronted with a move to new state by
assuring her that Michigan would have insects too.

iii

ACKNOWLEDGEMENTS

I have had the great privilege of interacting with an outstanding guidance committee
and I am honored to acknowledge their contributions to my Thesis research and scientiﬁc
training. Dr. Larry Gut, my co-advisor, has been crucial in developing, supporting, and
advancing plum curculio monitoring techniques. Dr.Rufus Isaacs was indispensable in
providing insight and honing methods on insect behavior assays and analytical
techniques. I have also had the opportunity to work closely with Dr. Randy Beaudry in
the Department of Horticulture during which time I learned several techniques including
gas chromatography-mass spectrometry.

I would especially like to thank my major professor, Dr. Mark E. Whalon for his
guidance throughout my degree program who has been and will continue to be an
extraordinary mentor. Dr. Whalon has made signiﬁcant contributions to developing my
research skills and has lead me to understand and appreciate applied science from
identifying research ideas, conducting experiments, and understanding its importance not
only in the scientiﬁc community but also to the tree fruit industry. I am fortunate to work
with an amazing visionary who continues to inspire me.

I have to thank Pat Bills for hiring me into Dr. Whalon’s lab when I was an
undergraduate and Dr. Michael R. Bush for introducing me to the beauty and complexity
of apple, cherry, and peach orchards. I would also like to acknowledge the dedicated
assistance of Kevin Youngs, Erin Vidmar, and Matt Bennet.

I am grateful for the love and support of friends and family, especially my parents,

Karl and Mary Giron Biasi, and my husband, Joseph Coombs, whom I love and respect.

iv

TABLE OF CONTENTS

List of Tables ......................................................................................................................... vii
List of Figures ........................................................................................................................ viii
Chapter 1
Literature Review ................................................................................................................... 1
Hosts ........................................................................................................... 1
Pest status .................................................................................................... 3
Life cycle ..................................................................................................... 5
Adult biology ....................................................................................... 5
Sound production .......................................................................... 6
Spring activity ............................................................................... 12
Feeding .......................................................................................... 12
Mating ........................................................................................... 13
Oviposition .................................................................................... 16
Egg and larval stages ........................................................................... l6
Pupation ............................................................................................... 18
Fall activity .......................................................................................... 19
Two strains .................................................................................................. 24
Control of plum curculio ............................................................................. 25
Cultural, mechanical, and genetic control ........................................... 25
Biological control ................................................................................ 27
Chemical control ................................................................................. 29
Monitoring plum curculio ........................................................................... 30
Visual monitoring ................................................................................ 31
Limb jars .............................................................................................. 3 1
Interception traps ................................................................................. 32
Pyramid traps ....................................................................................... 33
Cylinder traps ...................................................................................... 35
Comparing traps ................................................. I ................................ 36
PC Attractants ............................................................................................. 37
Thesis Research .......................................................................................... 41
Chapter 2
Pyramid traps baited with pheromone lures for monitoring plum curculio, Conotrachelus
nenuphar (Herbst) .................................................................................................................. 42
Introduction .................................................................................................. 42
Materials and Methods ................................................................................. 44
Results .......................................................................................................... 48
Discussion .................................................................................................... 50

Chapter 3
Pyramid and circle traps baited with pheromone and plum essence for monitoring plum

curculio, Conotrachelus nenphar (Herbst) ............................................................................ 59

Introduction .................................................................................................. 59
Materials and Methods ................................................................................. 62
Research sites ............................................................................................ 62
Trap types .................................................................................................. 62
Attractant lures .......................................................................................... 63
Trap deployment and data collection ......................................................... 64
Statistical analysis ..................................................................................... 64
Total trap catch analysis ..................................................................... 64
Synergy analysis ................................................................................. 66
Repeated measures analysis ............................................................... 66
Results .......................................................................................................... 67
Total trap catch analysis ..... 67
Synergy analysis ........................................................................................ 69
Repeated measures analysis ....................................................................... 71
Discussion .................................................................................................... 81

Appendix 1 .......................................................................................................................... 86

References ........................................................................................................................... 89

vi

LIST OF TABLES

Table 1.1. Native and exotic rosaceous hosts of plum curculio in the northeastern
United States (from Maier 1990). .................................................................................... 2

Table 1.2. Climatic factors related to behavior associated with emergence and dispersal
from overwintering sites (from Racette et al. 1992). ....................................................... 22

Table 1.3. Important natural enemies of the plum curculio (from Racette et al. 1992). ....... 28

Table 2.1. Plum curculio trap catch data for all trap location groupings summed over
time. ................................................................................................................................. 49

Table 2.2. Mean differences in trap catches at TNRC, DF, and TNRC + DF for
different time intervals. .................................................................................................... 52

Table 3.1. Total trap catch X2 test of likelihood main effects for trap type and attractant
lure, and their interaction (on = 0.05). ............................................................................... 67

Table 3.2. Synergy X2 test of likelihood analysis of main effects for plum essence,
pheromone, and their interaction for all traps combined, pyramid traps only, and
circle traps only (CL = 0.05) ............................................................................................... 71

Table 3.3. Repeated measures univariate ANOVA analysis of main effects for trap
type, attractant lure, time, and two and three component interactions (on = 0.05). .......... 72

Table 3.4. Weevil species (Coleoptera: Curculiondae) with male-produced aggregation
pheromone (from Landolt 1997). ..................................................................................... 83

vii

LIST OF FIGURES

Figure 1.1. Schematic drawing of pyramid trap developed by Tedders and Wood

(1995). .............................................................................................................................. 33

Figure 1.2. Naturally-occurring component of the plum curculio pheromone (a), (+)-

(1R,2S)-1-Methyl-2-(l-methylethenyl)-cyclobutaneacetic acid, and its racemer (b),
(-)-(1R,ZS)-l-Methyl-2-(l-methylethenyl)-cyclobutaneacetic acid, that is present in
the synthetic formulation. ................................................................................................ 40

Figure 1.3. Major component of the cotton boll weevil (a), (+)-cis-2-isopropenyl-l-

methylcyclobutaneethanol, and its racemer (b), (-)-trans-2-isopropenyl-l-
methylcyclobutaneethanol, present in synthetic formulation and the three minor
components of pheromone (c), cis-3,3-dimethyl-A"B-cyclohexaneethanol; (d) cis-
3,3-dimethyl-A"“-cyclohexaneacetaldehyde; and (e), trans-3,3-dimethyl-Al’a-
cyclohexaneacetaldehyde. ................................................................................................ 40

Figure 2.1. Plot map of the Clarksville Horticultural Research and Experiment Station

(Clarksville, MI) with locations of baited and nonbaited pyramid traps. ........................ 44

Figure 2.2. Plot map of Trevor Nichols Research Center (Fennville, MI) with locations

of baited and nonbaited pyramid traps. ............................................................................ 46

Figure 2.3. Plot map of Dougals Farm (Fennville, Michigan) with locations of baited

and nonbaited pyramid traps. ........................................................................................... 47

Figure 2.4. Trend in the number of plum curculio caught in baited and nonbaited

pyramid traps at Trevor Nichols Research Center and Douglas Farm. ............................ 53

Figure 2.5. Total number of plum curculio captured for each location and crop (top

graph) and mean differences between number of plum curculio captured baited and
unbaited traps (baited - unbaited) for each location and crop (bottom graph). ................ 54

Figure 3.1. Schematic drawing of modiﬁed circle trap. ........................................................ 63

Figure 3.2. Main effects of adjusted marginal means :t SE of total trap catch analysis

for. factors (a) traptype and (b) attractant. Means, within a factor, followed by the
same letter are not signiﬁcantly different (Wald X2 test, on = 0.05). ................................ 68

Figure 3.3. Simple effects of adjusted cell means of total trap catch analysis for trap

type * attract lure interaction for (a) circle traps and (b) pyramid traps. Means for

viii

attractant lures, within each trap type, followed by the same letter are not
signiﬁcantly different (Wald X2 test, on = 0.05). .............................................................. 70

Figure 3.4. Main effects of adjusted marginal mean number of plum curculio for time.

Means followed by the same letter are not signiﬁcantly different (t test, on = 0.05). ....... 73

Figure 3.5. Adjusted mean number of plum curculio captured over time for circle and

pyramid traps summed over attractant lure. (a) Trends of means over time for each
trap type. Asterisk denotes a signiﬁcant marginal main effect for trap type
(univariate AN OVA F test, a = 0.05). (b) Simple effects of adjusted cell means for
signiﬁcant main effects. Means for trap type, within each date, followed by the
same letter are not signiﬁcantly different (t test, (1 = 0.05) .............................................. 74

Figure 3.6. Adjusted mean number of plum curculio captured over time for attractant

lures summed over trap type. (a) Trends of means over time for each attractant lure.
Asterisk denotes a signiﬁcant marginal main effect for attractant type (univariate

ANOVA F test, or = 0.05). (b) Simple effects of adjusted cell means for signiﬁcant
main effects. Means for attractant lures, within each date, followed by the same
letter are not signiﬁcantly different (t test, a = 0.05). ...................................................... 76

Figure 3.7. Adjusted mean number of plum curculio captured over time for attractant

lures for circle trap data only. (a) Trends of means over time for each attractant lure.
Asterisk denotes a signiﬁcant marginal main effect for the trap type * attractant lure
main effect (univariate ANOVA F test, on = 0.05). (b) Simple effects of adjusted
cell means for signiﬁcant main effects. Means for attractant lures, within each date,
followed by the same letter are not signiﬁcantly different (t test, CL = 0.05) .................... 78

Figure 3.8. Adjusted mean number of plum curculio captured over time for attractant

lures for pyramid trap data only. (a) Trends of means over time for each attractant
lure. Asterisk denotes a signiﬁcant marginal main effect for the trap type *
attractant lure interaction (univariate ANOVA F test, or = 0.05). (b) Simple effects
of adjusted cell means for signiﬁcant main effects. Means for attractant lures,
within each date, followed by the same letter are not signiﬁcantly different (t test, CL
= 0.05).me letter are not signiﬁcantly different (t test, a = 0.05). ................................... 79

Figure 3.9. Adjusted mean number of plum curculio captured over time for each trap

type and attractant lurecombination. (a) Trends of means over time for each
attractant lure. Asterisk denotes a signiﬁcant marginal main effect of trap type *
attractant lure interaction (univariate ANOVA F test, a = 0.05). (b) Simple effects
of adjusted cell means for signiﬁcant main effects. Means for attractant lures,

within each date, followed by the same letter are not signiﬁcantly different (t test, on
= 0.05). ............................................................................................................................. 8O

ix

CHAPTER 1

LITERATURE REVIEW

Hosts

The plum curculio is a native North American weevil whose hosts include shrubs
and trees in the Amygdaloideae (Prunoideae) and Maloideae (Pomoideae) subfamilies in
the family Rosaceae. Distribution of the plum curculio generally conforms to, but is not
limited to, the clumped distribution of native host plants such as Canada plum, Prunus
nigra Aiton; wild plum, P. americana Marsh; and P. mexicana Wats. (Chapman 1938).
Stedman (1904) includes plum, peach, nectarine, prune, apricot, cherry, apple, pear,
quince, wild plum, wild crabapple, and hawthorn as native and exotic hosts of plum
curculio. Maier (1990) determined whether native and exotic rosaceous plants harbored
plum curculio. Of the 24 plants sampled, plum curculio was found in 19 of the 24
species sampled. Table 1.1 lists the species tested and includes plants in the genera
Amelanchier sp., Crategus sp., Prunus sp., and Malus sp. among others. Plum curculio
was also found in wild blueberries but in very low numbers, however it is known to infest
cultivated blueberries (Beckwith 1943). Maier (1990) suggests that wild blueberries are
extremely small and may not allow curculio larvae to develop adequately.

It is generally understood that plum curculio shifted from native to exotic hosts,

predominantly exploiting apple monoculture (Maier 1980). Nonetheless, pest status of

Table 1.1. Native and exotic rosaceous hosts of plum curculio in the northeastern
United States (from Maier 1990).

 

 

Fruiting Species Common Name Ilihltairtridznce'
Native
Amelanchier arborea (Michaux f. ) Fenald Downy juneberry 0.50
A. canadensis (L.) Medicus Common juneberry 1.39
Amelanchier sp.2 Shadbush 8.75
Crateagus sp. Hawthorn 0.14
Prunus alleghaniensis Porter Allegheny plum 400
P. americana Marshall Wild plum 27.50
P. maritima Marshall Beach plum 26.18
P. pensylvanica L. Pin cherry 1.26
P. pumila L. Sand cherry 24.00
P. serotina Ehrhart Black cherry 0.28
P. virginiana L. Choke cherry 0.09
Exotic
Cydonia oblonga Miller Quince 20.00
Malus domestica Borkhausen Apple 56.64
Malus sp. Crabapple 8.50
Prunus avium L. Sweet cherry 30.00
P. cerasus L. Sour cherry 230
P. domestica L. European plum 320
P. persica (L.) Batch Peach 650
P. salicina Lindley Japanese plum 1000
Pyrus communis L. Pear 3.53

 

' Density = (number of adults * 10'3)/number of fruits
2 In discussion of weevil hosts, this Shadbush though near A. canadensis is not considered
to be distinct from A. canadensis.

plum curculio on cultivated tree fruits varies among regions depending on a number of
factors. For example, in Delaware, apple infestation is comparatively light compared to
peach except in years when a short peach crop results from low winter temperatures or
severe frosts during early spring (Steams et al. 1935). In Connecticut, peaches are not
severely attacked by plum curculio, while apples can be seriously damaged (Garman and
Zappe 1929). This may reﬂect the importance of the apple crop in the state and the
difﬁculty of controlling plum curculio under normal conditions rather than the amount of
feeding or egg laying on apple compared to peach (Garman and Zappe 1929). In
Missouri, plum curculio is not a serious pest of apple which has been attributed to is
inability to readily multiply in apple at this location but can be found regularly in plums
and peaches (Stedman 1904). Alm and Hall (1986b) found a greater range of

susceptibility to plum curculio on crabapple cultivars than on commercial apple cultivars.

Pest status

Plum curculio causes economical damage to tree fruit crops by two means. First,
plum curculio render fruit unmarketable by 1) creating catfacing scars as a result of both
feeding and oviposition and 2) larval presence and/or feeding in the fruit at harvest.
Second, plum curculio larvae can cause added fruit abscission after fruit set above and
beyond natural abscission, as will be discussed in greater detail below. There is a
decided concentration of the adult population in the ﬁve marginal rows of the orchard
adjacent to overwintering sites, while the distribution throughout the remainder of the
orchard is apparently somewhat uniform (Steams et al. 1935). Damage can be found on
both pome and stone fruits throughout most of its geographical range often ranking ﬁrst

or second of insect pests in terms of potential economic damage if left unchecked (Hoyt

et al 1983). Vincent and Roy (1992) report that harvest damage between 1977 and 1989
was usually below 1% in Quebéc commercial apple orchards, compared to from 6 to 85%
in unsprayed orchards. Many have reported plum curculio populations returning to levels
of economic importance within 3 years after pesticide use has been discontinued (Glass
and Lienk 1971, Hagley et al. 1977, Hall 1974). In one case in Michigan when apples
were controlled exclusively by biological means, damage by plum curculio showed
biennial ﬂuctuation and a positive correlation with yield which ranged from 24 to 83%
and averaged 56% (Clark and Gage 1997). In another case in Geneva, NY, plum curculio
oviposition represented 70 to 80% of all injuries in McIntosh fruit (Reissig et al. 1998).
Despite its key pest status, plum curculio has remained the least known of the key

North American fruit pest species (Hoyt et a1. 1983, Whalon and Croﬁ 1984). Field
research of the plum curculio is encumbered by (1) its cryptic coloration and
morphology, which mimics apple bark and bud scales, and (2) a defensive behavior
called thanatosis (Wiggelsworth 1953). Thanotosis, often referred to as dropping
behavior, consists of feigning death by pulling the legs into the body and consequently

falling off the trees. These two short comings have undoubtedly limited the
understanding of the behavior and ecology of the plum curculio particularly its
community and host plant relationships, dispersal behavior, factors inﬂuencing its mode
of locomotion, choice of food sources, overwintering sites, micro-habitat selection,

orientation, and action thresholds (Racette et al. 1992).

Life cycle
Several components of the life cycle of plum curculio have been featured in a

scattering of papers throughout the years. Quaintance and J enne’s (1912) seminal paper

is an invaluable source of information on plum curculio synonymy, distribution,
developmental stages, life history, habits, host plants, natural enemies, and control
measures. Plum curculio in New York apple orchards were described by Chapman

(193 8). Smith and Flessel (1968) reported thorough studies of hibernation and winter
mortality, duration of diapause, emergence from hibernation, and time of arrival in host
trees. Finally, Racette et al. (1992) wrote the consummate review of the life history,
behavior, and ecology of plum curculio as it pertains to control measures with speciﬁc
reference to Quebec orchards. The basis of the following discussion was primarily taken

from these four articles.
Adult biology

Sound production

Both adult males and females produce sounds (Carylsle et al. 1975, Mampe and
Neunzig 1966) which may play a communication role in the early spring as beetles
aggregate at the base of host trees (Racette et al. 1992). The morphology of sound
production was described by Carlysle et al. (1975). A stridulitrum extending along the
medial line of the posterior third of the left eleytron works in unison with a plectrum
located on the dorsal surface of the 6th abdominal tergite. Sound is produced as abdomen
muscles are contracted and extended, elevating and moving the plectrum along the
stridulitrum. Males and females have a diversion in morphology that results in different
sounds produced. The stridulitrum is composed of ridged rows in males and rows of
overlapping microteeth in females. The plectrum in males is larger but both are ellipsoid
with a tapered seta that points posteriorly, the morphology of which suggests a sensory

function.

Spring activity

Some early investigators were convinced that plum curculios move little from tree to
tree (Rings 1952, Snapp 1940, Steiner and Worthley 1941). However, curculios are
reported to be more active than previously assumed (Calkins et al. 1976, Smith and
Flessel 1968). In fact, Chapman (193 8) found that curculios are capable of exploring
most trees in an orchard. Plum curculios can be located in trees not bearing any fruit
(Chapman 193 8, Laﬂeur and Hill 1987, Smith and Flessel 1968) but are able to quickly
detect that fruit are not on the tree and leave the tree (Chapman 1938). Before much
movement is detected in the tree, adults may congregate in equal ratios of males and
females within the ground cover at the base of the tree in the orchard perimeter rows
when the they arrive in the orchard in early spring (Chounard 1991, Racette et al. 1991).
Plum curculios gradually invade trees between pink and petal fall, (Chouinard et al.
1994) after spending several days on the ground (Racette et al. 1991). When beetles are
marked and released, gradual recovery of marked beetles in limb jarring suggests that
beetles are not continuously in the trees (Smith and Flessel 1968).

It was generally believed that plum curculios vacate the trees under adverse weather
conditions and at night (Smith and Flessel 1968), dropping to the ground in response to
changes in humidity and temperature (Chouinard 1991, Laﬂeur and Hill 1987, Racette et
al. 1991 , Smith and Flessel 1968). Chouinard et al. (1994) investigated plum curculio
movement between trees and the ground and found that presence on the ground was
highly related to less favorable weather conditions. Curculios were found on the ground
at pink protected by tufts of grass and 30% resting at the base of tree trunks at bloom

prior to their invasion into trees. From the beginning of bloom until full bloom, plum

curculio were still found resting on the ground at the base of the tree. Between full
bloom and fruit set, 54% were found on the ground with constant movement between
trees and the ground. Occurrence in the tree was positively related to temperature and
humidity during this time. Incidentally, at petal fall, plum curculios were mostly in the
trees which is also supported by the fact that limb jarring results in highest catches at
petal fall (Chapman 193 8, Chouinard et al. 1994, Garman and Zappe 1929, Quaintance
and Jenne 1912, Smith and Flessel 1968, Snapp 1930, Whitcomb 1929).

Plum curculios move to other protective areas during the morning besides the ground
(i.e. branch crotches or spurs) irrespective of the temperature and humidity conditions
(Racette et al. 1991). Spurs are the most common structures harboring plum curculios
during the day (Chouinard et al. 1994). Females use spurs more than males as daytime
protective resting sites (Racette et al. 1992). Curculios are detected most frequently on
host structures (except spurs) at the end of the day and in the ﬁrst part of the night (1800
to 0300 h) than before or after this time (Chouinard et al. 1994). Evening also
corresponds to the period of greatest activity (Chouinard et al. 1993). Females spend
signiﬁcantly more time on spurs, but less time on ﬂowers and fruits than males.
Curculios can be found in fruit clusters various times of the day (Chouinard et al. 1992b)
but are most likely be located on fruit between 2100 and 2300 h (Chouinard et al. 1994).

In general, nocturnal activity of the plum curculio has been observed when
temperature and humidity are favorable (Smith and Flessel 1968), but daily activity
rhythms shift as the growing season progresses. During full bloom, curculios remain
relatively inactive but are most active in the late afternoon and night (Racette et al. 1991).

Dropping behavior is observed most frequently before sunrise and the early morning

during bloom but is observed over the entire 24 hour period during fruit set and June drop
(Racette et al. 1990). Beetles are mainly nocturnal before fruit set and as fruits become
available for oviposition, adults extend their activity to the daytime (Racette et a1. 1992).
Racette et al. (1990, 1992) also found that as the season progressed plum curculio move
into trees for increasingly longer time intervals and begin to extend their activity period
to daytime. A few days after fruit set, within host tree movement decreases (Laﬂeur and
Hill 1987, Racette et al. 1991) while overall diurnal activity decreases and nocturnal
activity increases (Racette et al. 1991). During late summer curculio activity subsides
remaining highest during the night, even on cold nights (Racette et al. 1990).

Curculios enter the tree canopy most frequently for a 3 to 6 h period beginning at
1800 h (Chouinard et al. 1994, Dixon et al. 1999, Racette et al. 1991). Curculios also
have daily patterns in activity, rate of movement, and movement from the center of the
tree to the peripheral canopy (Chouinard et al. 1992b). However, diel periodicity of
within tree movement is not the general consensus. Chouinard et al. (1993) observed that
distribution within host structures between full bloom and three weeks after fruit set is
not strongly related to photoperiod but more dependent on weather conditions. Little or
no periodicity is apparent for plum curculio presence on fruit, height in trees, or
movement along directional axes (Chouinard et al. 1992b). Racette et al. (1990) suggest
that falling behavior is related to temperature, therefore canopy reentry patterns appear to
follow a periodic pattern.

Although curculios enter the tree between 1800 and 0000 h, curculio movement rates
are at their highest between 2100 and 0400 h (Chouinard et al. 1992b) with activity

peaking at 24 cm/h (Chouinard et al. 1993). Rate of movement is positively related to

mean daily air temperature, but some activity persists at temperatures as low as 1° C
(Racette et al. 1990, 1991). Rate of movement follows a diel periodicity (lower during
the day than night) and is positively related to an increase in relative humidity and
temperature (Chouinard et al. 1994). Speed of crawling increases with increasing
temperature between 1500 and 2100 h at which time the average height of beetles in trees
increases form 65 cm to 85 cm then gradually declines (Chouinard et al. 1994). Average
height above the ground is also positively related to an increase in relative humidity and
temperature (Chouinard et al. 1994) and to a decrease in air saturation (Chouinard et a1.
1993). Of all curculio collected during the season, 40% were males and the proportion of
males to females declined as the season advanced with females occurring higher in the
trees than males (Smith and Flessel 1968). Females move greater distances from the tree
trunks and higher in the trees probably due to a need for suitable oviposition sites
(Chouinard et al. 1994).

Stedman (1904) observed plum curculio frequently dropping to the ground during
the middle of the aftemoon, hiding until late afternoon, then ﬂying up into the trees.
More recently, Chouinard et al. (1993) found that dropping to the ground precedes
dispersal to adjacent trees (Chouinard et al 1993). Curculio beneath host trees exhibit an
increasing propensity to ﬂy and increasing propensity to cause fruit injury with increasing
ambient temperature above 20° C (Prokopy et al. 1999). Prokopy and Wright (1997a)
investigated the means of entry into the canopy by comparing limb jar data from a tree
with an impassable band of Tangletrap around the trunk of an apple tree. The total
number of curculios collected by tapping from a tree having a band of Tangletrap was

nearly equal to that of trees without a band of Tangletrap and there was a signiﬁcant

positive correlation between daily numbers tapped from either tree type and daily high
temperature. This suggests that those curculios which crawl up tree trunks are unable to
pass beyond a sticky barrier and subsequently ﬂy into the tree canopy provided the
temperature is warm enough to permit ﬂight. Not only was the number of curculios high
in trees on warm days but it was also equally low on cool days. In another study of
curculio entry into trees, Prokopy and Wright (1998) found that when curculios are
tapped out of trees onto white sheets 35% rest in place, 31% leave the cloth by ﬂight,
16% leave by crawling, and 18% hide beneath foliage on the sheet. Signiﬁcantly higher
numbers of ﬂying or crawling curculio disperse toward the tree canopy than in other
directions.

Whitcomb (1929) reported that plum curculio was a strong ﬂyer, but more recently,
plum curculio has been described as a poor ﬂyer (Le Blanc 1982) or that they rarely ﬂy
(Owens et al. 1982). This discrepancy in understanding curculio ﬂying behavior may be
substantiated by the complex of environmental factors affecting curculio ﬂight. Dixon et
al. (1999) recently found that ﬂights directly into the tree canopies are facilitated by high
temperature and calm air and ﬂights onto tree trunks are facilitated by low barometric
pressure, calm air, and high humidity (Dixon et al. 1999). Generally speaking, curculio
ﬂight is positively correlated to temperature, with a lower thermal limit of 67° F
(Prokopy and Wirth 1998)

Individuals have been observed to move 146 m in 10 d and 205 m in 40 (1 (Rings
1952, Snapp 1940). However, in a study conducted by Laﬂeur and Hill (1987) 42% of
marked beetles remained on the same standard apple tree over a 65 (1 period starting at

bloom. Curculios that reach the orchard ﬁrst from overwintering sites tend to move the

10

farthest over the season (Laﬂeur and Hill 1987). Curculios are most active before tight
cluster and June drop and display greatest activity at fruit set (Laﬂeur and Hill 1987,
Racette et al. 1991). Highest population densities have been recorded 1-2 weeks after
petal fall (Chapman 1938, Cox 1951, Garman and Zappe 1929, Quaintance and Jenne
1912, Smith and Flessel 1968, Snapp 1930, Whitcomb 1929) but highest rates of
movement occur at full bloom (Chouinard et al. 1993). Racette et al. (1991) found that
plum curculios move more and increase diurnal activity at fruit set. A few days before
June drop, within-host movements and diurnal activity decreases (Laﬂeur and Hill 1987,
Racette et al. 1991) reaching its lowest level in early August (Armstrong 1958, Laﬂeur
1985) probably as the need for food and oviposition sites is met (Racette et al. 1992).
Dispersal within host trees and within the orchard probably occurs in response to the
associated within-tree decrease in air movement and increase in humidity (Racette et al.
1991) due to a critical need for humid conditions at this time (Garman and Zappe 1929,
Smith and Flessel 1968). Laﬂeur and Hill (1987) observed that curculios exhibit a
preference for early cultivars with dense foliage, even before fruit set. Further evidence
includes observations of increased activity on warm damp cloudy days compared to clear
ones and inhibited activity as a result of air movement within vegetation (Garman and
Zappe 1929). As foliage develops, air movement in apple trees decreases and humidity
increases (Laﬂeur and Hill 1987). Coinciding with these changes, curculios move higher

in the trees and remain there for longer periods (Racette et al. 1991).

11

Feeding

The feeding behavior of plum curculio is best described by Stedman (1904):

...in making the feeding punctures the beetle eats a small round
hole through the skin by means of its mandibles or jaws, which are
situated on the extreme end of its long beak or snout. This hole is
about one-tenth of an inch in diameter. It then eats the pulp about one-
tenth of an inch in depth, thus leaving a small cylindrical hole in the
apple... During July and August the beetles have the habit of also

eating the pulp back under the skin as far as they can reach.

Mating

Reproductive habits were studied in the 19603 and 1970S as a combined effort to
mimic successful eradication of the screw-worm, Cochliomyia hominivorax (Coquerel)
and to understand diapause (Johnson and Hayes 1969). In laboratory experiments
curculio were found to mate as young as 5 d at which time males are sexually mature but
females are unable to successively produce viable eggs at this age until 8 (1 (Johnson and
Hays 1969). Females mate by the 11th and males by the 12th day of adult life (Yonce and
Jacklin 1978). Males frequently mate with 3 females in one day (Yonce and J acklin
1978). Johnson and Hays (1969) found males to mate with as many as 16 females in a 30
day period with an average of 10.4. Their study also found that males, both virgin and
non-virgin, mate with at least one female in a 24 h period resulting in the production of
viable eggs. There is no preference in time of day for mating in both LL and LD (12:12)

photoperiods (Yonce and Jacklin 1978). Mating has been observed in the ﬁeld as beetles

12

congregate in host trees (Smith and Salkeld 1964), in apple blossoms (Le Blanc 1982),
and on the ground under the canopy (Racette et al. 1992).
Oviposition

Lack of a signiﬁcant correlation between numbers tapped from the canopy and
occurrence of fruit injury suggests that most curculio in the canopy of an apple tree at any
given time are engaged in behaviors other than egg laying, such as feeding, mating,
crawling, or resting (Dixon et al. 1999). Females lay eggs singly in young apples and cut
a distinctive crescent-shaped ﬂap that will prevent the emerging larva from being crushed

by the growing apple (Armstrong 1958, Chapman 1938, Quaintance and Jenne 1912).

Stedman (1904) gives the following description of oviposition:

...a female eats a small hole through the skin and then eats pulp
back about 1/16 inch, she then turns around and deposits an egg in the
hole which is usually just large enough to receive the egg, she then eats
the tissue while cutting a small crescent shaped hole through the skin
and into the pulp, since females actually eat tissues of the apple while
depositing eggs, this is probably the reason why during the egg-laying
season they do not make as many purely feeding punctures as the do

later in the season.

Females do not deposit an egg in more than half the egg punctures, even though they
make the crescent structure (Stedman 1904). A female can make as many as 616 egg
punctures (Quaintance and Jenne 1912) but lays an average of 73 eggs (Paradis 1956) and

is capable of laying anywhere up to 250 to 400 eggs (Stedman 1904). Field experiments

13

have shown that curculios are capable of responding with increased oviposition in years
with greater fruit yield (Clark and Gage 1997). Laboratory studies have shown that time
between mating and oviposition was greater for young females and became shorter as
females became older (Yonce and Jacklin 1978).

In May, females make four to ﬁve times as many feeding punctures as egg
punctures. In June, females make almost as many egg punctures as feeding punctures
(Stedman 1904). Overall, there are about twelve times as many feeding punctures as egg
punctures as a result of the both male and female beetles. Average number of feeding
punctures is much higher than the number of egg punctures; however, average number of
egg punctures per female is 79 while average number of feeding punctures per female is
46 (Garman and Zappe 1929)

Under choice and no choice tests conducted by Yonce et al. (1972) in the laboratory,
females prefer to oviposit in apples whose peel is intact as opposed to an apple whose
peel has been removed. In this case, the female will oviposit in the portion of an apple
where the peel is intact. Incidentally, it was also found that when apples are coated with
a thin layer of paraﬁlm, beetles do not probe through the paraﬁlrn layers and deposit eggs
beneath the apple peel. Females also prefer a curved surface to a ﬂat surface for
oviposition. Fruit size is one factor in the ovipositional preference of curculio on
crabapple where curculio preferred ovipositing in larger fruit (Alm and Hall 1986b). It
may not be possible for larvae to develop in small fruits and it may be more efﬁcient to
oviposit multiple times in one fruit rather than multiple times in multiple fruit.

Damaged fruit are most abundant in rows adjacent to woodlots (Chapman 1938,

Garman and Zappe 1929, Le Blane et al. 1984, Quaintance and Jenne 1912). Fruit in the

14

upper part of the tree tend to be attacked more than those in the lower part (Calkins et al.
1976, Le Blanc et al. 1984); however Chouinard et al. (1994) found that egglaying is
most frequent at mid-level of the tree. There is no difference in level of attack with
respect to compass direction (Le Blane et al. 1984).

The greatest damage results from early feeding punctures which deform the fruit
(Garman and Zappe 1929). Oviposition begins at fruit set (Armstrong 1958, Paradis
1956) when the fruit is as small as 6 mm in diameter (Garman and Zappe 1929). Egg
laying continues for three weeks until early July (Paradis 1956b) and then declines
abruptly with relatively few eggs being laid until the termination of oviposition in early
August (Armstrong 195 8, Paradis 1956). Onset of oviposition is affected by temperature,
size and rate of growth of the young apples, and possibly the physiological state of the
curculio but oviposition rate is directly related to temperature (Lathrop 1949).
Oviposition is most likely to occur on days having high temperature and low barometric
pressure and especially on days following a high temperature day (Dixon et al. 1999).

Daily oviposition patterns are apparently unaffected by temperature ﬂuctuations
(Owens et al. 1982, Whitcomb 1929). Yonce et al. (1972) found that in LL oviposition is
least from 1200 to 1600 h and greatest from 2000 to 2400 h. In LD (12: 12) oviposition
tends to occur more during darkness, however others have observed that females deposit
an equal number of eggs at night and during the daytime (Crandall 1905, Quaintance and
Jenne 1912).

There is lag time between plum curculio entry into the tree canopy and injury which
may be due to a physiological need to feed and mate before commencing egg laying

(McGiffen and Meyer 1986). In an unsprayed orchard, ﬂight directly into apple tree

15

canopies is followed the next day by dropping to the ground and then crawling or ﬂying
onto tree trunks with subsequent crawling up tree trunks into the tree canopies to
oviposit, on the other hand after insecticide sprays, curculios do not crawl up tree trunks

before ovipositing (Prokopy et al. 1999).

Egg and larval stages

There is a low survival rate during the egg stage (15%) (Stedman 1904). The egg
stage lasts from 3 — 12 days at mean daily temperatures of 25 to 18° C, respectively
(Paradis 1956). The egg and larval period in fruit averages 22.9 days, varying from 17 to
39 (Garman and Zappe 1929). The main part of the brood leave the fruit less than a
month after the peak of egg laying (Garman and Zappe 1929). Larvae spend anywhere
from 15 to 21 din the fruit (Armstrong 1958, Paradis 1956, Steams et a1. 1935, Stedman
1904) where they eat out irregular cavities in the apple and, in extreme cases, reduce the
fruit to a frass ﬁlled shell (Chapman 193 8).

When larvae ﬁrst hatch they eat their way straight into the pulp of the apple from 6 —
12 mm and then begin to mine in a zigzag direction, often doubling over on their course
(Stedman 1904). The tissue where the larvae has traversed is bitter in taste, becomes
dense, and does not enlarge with the surrounding tissue, hence the depression increases as
the apple becomes larger (Stedman 1904).

Larvae produce ﬁve pectic enzymes (pectin methyl-esterase, endo-
polymethylgalacturonase, endo-polygalacturonase, pectin methyl-trans-eliminase, and
polygalacturonate-trans-eliminase) and cellulase which are released as larvae feed and
are capable of causing fruit tissue maceration (Levine and Hall 1978a). In controlled

studies, 45% more plums receiving active commercial pectinase and cellulase abscised

16

than fruit receiving inactive enzymes (Levine and Hall 1978b). These pectic enzymes
and cellulase are released by the larvae as they feed on the fruit result in premature
dropping of infested fruit (Whitcomb 1932) before it reaches 3 cm in diameter (Levine
and Hall 1977). Fruit will fall 10 - 13 d after curculios are introduction into bagged
apples (Levine and Hall 1977). Seed damage was not necessary and adult feeding and
egg cavity preparation do not cause abscission (Levine and Hall 1977).

Plum curculio induced abscission was similar to the process of mature fruit drop
(Levine and Hall 1977). There are three primary means of abscission in plums and
apples: (1) structurally or functionally abnormal ﬂowers, (2) unpollinated and unfertilized
ﬂowers, and (3) aborted embryos in fertilized ﬂowers; fruits that develop beyond this
point are considered 'set' (Gardner et al. 1952). Since only a small percentage of ﬂowers
of most deciduous fruit trees must set in order to produce full commercial crops, curculio
damage prior to fruit set is not likely to result in reduced yields; however, once fruits
have set, additional fruit abscission probably will result in some economical loss (Hall
1974). It is difﬁcult to assess the true impact of plum curculio on June drop because this
phenomenon overlaps with natural fruit abscission (Racette et al. 1992).

Apples must abscise before the larva is much more than half grown or it will not live
longer (Stedman 1904). Larvae in fruit that did not fall prematurely do not complete
development (Levine and Hall 1977, Gannan and Zappe 1929) and some believe they are
crushed by the growing fruit (Paradis 1957, Quaintance and Jenne 1912). Stedman
(1904) believed that apple growth does not kill the larvae but that larvae become

weakened for some other reason and cannot emerge from the apple. Heat from direct

17

sunlight may also result in larval death in the apple (Racette et al. 1992). Apples that
remain on the tree become more deformed as they mature (Chapman 1938).

Time of larval emergence from apples is not significantly different between LL and
LD light regimes although under LD conditions larvae tended to emerge more during the
scotophase (Yonce and J acklin 1978). Fourth instar larvae remain in the fallen fruit for a
few days, make an exit hole, and then leave the fruit to burrow into the soil to pupate
(Quaintance and J enne 1912). Larval emergence from apples increases after rainfall, at
which time temperature has no effect (Lathrop 1949). Emerged larvae move around from

30 to 50 min as if searching for a suitable place to enter the soil (Racette et al. 1992).

Pupation

Although plum curculios burrow in the soil to pupate, some may attain full grth in
fallen apples (Stedman 1904). Curculios pupate at a depth of 1 - 8 cm but will most
likely be found in the 3 — 5 cm range (Garman and Zappe 1929, Quaintance and Jenne
1912, Stedman 1904). Development from egg to adult takes 50 to 55 d (Armstrong 1958,
Garman and Zappe 1929, Paradis 1956) of which 15 to 20 d are apportioned to pupation
(Garman and Zappe 1929, Stedman 1904). The adult will spend varying durations of
time in the soil emerging at various stages of maturity (Garman and Zappe 1929).
Moisture is necessary for both the larvae to enter and the adults to emerge from the soil
(Chandler 1932). Adult emergence increases aﬁer rainfall (Armstrong, 195 8,
Neiswander 1948, Quaintance and Jenne 1912) and also after a few days of high
temperature (26 - 29° C) (Lathrop 1949). On average, only two percent of the eggs
deposited in apples reach the adult beetle stage, this means that each female can normally

produce 5 - 8 beetles (Stedman 1904).

18

Fall activity

Newly emerged adults feed on apples both on the trees and ground by digging out
cavities under the skin (Racette et al. 1992). Fall feeding punctures on sprayed fruit is
disregarded as far as preventive measures are concerned (Garman and Zappe 1929). At
the approach of fall, old beetles die and young beetles ﬂy about in search of suitable
places in which to overwinter (Stedman 1904). When adults have stored sufficient fat
they cease feeding and seek suitable overwintering sites (Smith and Salkeld 1964).
Curculio populations in the orchard begin to diminish numbers in August with most
curculios leaving for overwintering sites in September (Steams et al. 1935). Migration
out of the orchard occurs from early September to the end of October (Laﬂeur and Hill
1984, Laﬂeur et al. 1987). The farthest fall migration distance recorded is 142 m (Laﬂeur
and Hill 1987). The average fall dispersal rate is around 3.3 m/d (Laﬂeur et al. 1987).

At a distance, some insects visually detect the silhouette of host trees against the sky
(Prokopy and Owens 1983). Plum curculio adults migrate toward tall non-host tree
silhouettes at woodlot edges when seeking overwintering sites in autumn (Laﬂeur et al.
1987). Upon reaching the edge of a woodlot, curculio search for an area with a thick
layer of dead leaves about 3 — 5 m inside the woodlot (Laﬂeur et al. 1987). Plum
curculios are not gregarious in the fall and winter (Laﬂeur et al. 1987, Smith and F lessel
1968). In an 8 year ﬁeld study, crop failure did not reduce the number of beetles
collected that year or the following year suggesting that redistribution of beetle
populations occur when seeking overwintering sites or when emerging the following year

(Smith and Flessel 1968).

19

Plum curculios have been reported to overwinter under leaves, grass roots, dried
grass, trash, honey suckle growth, or pruning piles; along ditch banks; and near or in
orchards, woodlots, brush land, fence rows, stone walls, and rubbish (Bobb 1949,
Chapman 1938, Driggers 1935, Laﬂeur et a1. 1987, Quaintance and Jenne 1912, Steams
et al. 1935, Stedman 1904, Whitcomb 1929). These sites are generally high in relative
humidity and low in air movement thus minimizing the risk of desiccation particularly in
the spring (Garman and Zappe 1929, Smith and F lessel 1968). When leaf litter
approximates the normal cover in undisturbed deciduous woods or when 1 - 5 cm thick
straw is available, plum curculios remain between the ground and the leaf cover
(Armstrong 1958, Laﬂeur et al. 1987, Smith and Flessel 1968, Snapp 1930). When the
litter layer is thin or absent some penetrate as deep as 5 to 8 cm (Armstrong 1958, Bobb
1949, Smith and Flessel 1968). Some adults enter loose soil even when litter is thick
(Laﬂeur et al. 1987).

If substrate along woodlots is unsuitable for overwintering, curculios may returned to
the orchard to overwinter under orchard turf beneath apple trees, however higher winter
mortality is associated with orchard turf (Laﬂeur et al. 1987), grass liter (Bobb 1949), and
bare soil (Smith and Flessel 1968). Winter mortality in orchard turf is comparable to bare
soil, usually in excess of 90%, whereas in thick litter it ranged from around 25 to 50%
(Laﬂeur et a1. 1987, Smith and F lessel 1968). McGiffen and Meyer (1986) found that
high temperatures can induce mortality up to 90%. Winter mortality is slightly higher in
males than in females (Smith and Flessel 1968).

Under choice tests, plum curculios do not have a preference between light sandy soil

or heavy clay with ground cover (Smith and F lessel 1968). When provided with a ground

20

cover, a majority of the curculios occurred between the ground cover and the soil and less
than 5% hibemated in the soil (Smith and F lessel 1968). Insects that hibernate in bare
soil are conspicuously marked by soil particles upon emergence (Smith and Flessel

1968). Although a majority of beetles should not have soil particles on their elytra, limb
jarred beetles have been found with clay particles on the elytra (Garman and Zappe 1929,
Smith and F lessel 1968). The curculio must then be entering the soil for protection once
in the orchard.

Reproductive diapause is terminated after long exposures to low temperatures
(McGiffen and Meyer 1986, Smith and Flessel 1968). Smith and Flessel (1968)
hypothesized that it is likely that the low temperature requirements differ among beetles
at different localities over the species range (Smith and Flessel 1968). Some climatic
factors affecting emergence from overwintering sites are outlined in Table 1.2. Rain does
seem to play a role in spring emergence from overwintering (Bobb 1949, Garman and
Zappe 1929, Lathrop 1949 Smith and Flessel 1968, Smith 1954) but temperature patterns
have been associated most with emergence.

Both Quaintance and J enne (1912) and Snapp (1930) found that a mean temperature
between 13 and 15° C for 3 - 4 days induces emergence. Whitcomb (1932) also found the
activity threshold to be 13° C and migration to trees was induced by temperatures of 24°
C or above for several consecutive days. Correlations between emergence and
temperature over 4 years resulted in emergence from overwintering occurring with a
mean daily temperature of 13 to 15° C degrees and with maximum daily temperature
from 21 to 27° C (Steams et al. 1935). Bobb (1949) concluded that none of these

relationships applied precisely in studies in Maine. Smith and Flessel (1968) established

21

 

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22

that in one year, all the days of heavy emergence were characterized by several hours or
more above 21° C and RH above 50%; however, there are days where this criterion was
met and emergence did not take place. Long days are not required for termination of
diapause (McGiffen and Meyer 1986). Spring emergence has been reported to last from
3 - 4 weeks (Laﬂeur and Hill 1987) to 6 weeks (Stearns et al. 1935). Garman and Zappe
(1929) stated that the earliest record of emergence was April 25 and adults continued to
emerge from the soil until June 12. Although emergence may extend over several
weeks, up to 60% of all individuals have been observed to emerge on a single day with
males emerging slightly earlier than females (Smith and F lessel 1968). The physiology
of curculio at time of emergence is probably unfavorable for migration. A good food
source is needed to increase lipid levels necessary for dispersal; therefore, it is quite
possible that plum curculios may feed somewhere else before migrating (Smith and
Flessel 1968). Availability of native hosts that bear fruit earlier may favor any
physiological adjustment required for heightened dispersal activity (Racette et al. 1992).
Emerged females must also feed on a suitable host for the maturation of their ovaries
(Smith and Salkeld 1964).

Water loss may also inhibit adult dispersal (Smith and Flessel 1968). Curculios
remain in protected sites even though temperature is favorable rather than to expose
themselves to desiccation (Smith and Flessel 1968). Curculios have been experimentally
shown to avoid conditions conducive to water loss such as low humidity and high air
movements (Garman and Zappe 1929). Up to tight cluster, most curculios can be found
within 1 m of their overwintering site (Laﬂeur and Hill 1987). The greatest speed of

spring dispersal from overwintering site is 4.4 m/d and occurs during fruit set (Laﬂeur

23

and Hill 1987). Mean speed of spring dispersal is characterized by a series of peaks that
coincide with the phenological stages of apple trees (Laﬂeur and Hill 1987).

A delay occurs between emergence of curculio from hibernation and appearance in
host trees (Garman and Zappe 1929, Lathrop 1949, Smith and Flessel 1968). Although
beetles come from hibernation beginning in April (Garman and Zappe 1929), curculio
begin to appear in the orchard sometime between the pink and calyx period and do not
become abundant until later (Garman and Zappe 1929). Paradis (1956) found that arrival
of curculios peaks between 6 d before petal fall and 10 d aﬁer petal fall. First appearance
in the orchard is closely related to temperature and host plant phenology (Chapman 193 8,
Cox 1951, Garman and Zappe 1929, Quaintance and Jenne 1912, Smith and Flessel 1968,
Snapp 1930, Whitcomb 1929). Beetles ﬁrst appear in the orchard following several days
of either a mean temperature of 15° C or above (Quaintance and Jenne 1929) or a
maximum of 24° C or above (Whitcomb 1929). However, before tight cluster, an
increase in mean temperature does not elicit rapid dispersal (Laﬂeur and Hill 1987).
Curculios most likely arrive near hosts via an anemotactic response stimulated by
olfactory host cues that are enhanced when combined with visual cues (Butkewich and
Prokopy 1997). Once in the orchard, curculios will feed on leaves even on petals of the

ﬂower before fruit become available (Garman and Zappe 1929, Stedman 1904).

Two strains

The plum curculio is univoltine north of Virginia and mutlivoltine to the south
(Schoene 1936). In southern Delaware there is evidence of a second brood, whereas in
central and northern Delaware there is only one brood (Stearns et al. 1935). In the north,

reproductive diapause limits the species to a single brood while in the southern area a

24

partial second occurs (Smith 1957, Smith and Flessel 1968). The northern strain is
characterized by a reproductive diapause which is broken during the course of
overwintering (Smith and Flessel 1968). Northern strain curculios survive the winter by
physiological adaptations during diapause and behavioral adaptations involved in leaving
the host trees, seeking an overwintering site, and returning the following year (Smith and
Flessel 1968). Smith (195 7) found that diapause is obligatory in the univoltine strain and
facultative in the multivoltine strain. Oviposition occurs following hibernation in the
northern strain and without regards to hibernation in the southern strain (Smith 1957). In
the laboratory, southern strain females produce over twice as many eggs as the northern
strain due to higher fecundity rates and a longer period of oviposition (Smith 195 7).
Multivoltine females mated with univoltine males resulted in reduced oviposition and egg
hatch. A reduction in oviposition is also associated with early degeneration of
spermatozoa in the spermathecae as a result of a postmating isolating mechanism which
occurs in low frequency in females mated with multivoltine males (Padula and Smith

1971)
Control of plum curculio

Cultural, mechanical, and genetic control

Habitat management, sanitation, and apple cultivar preference were control tactics
used before the advent of synthetic chemicals (Racette et al. 1992). Removing wild hosts
and neglected apple trees (Alm and Hall 1986b, Maier 1990, Prokopy et al. 1990) and
other overwintering materials such as fence rows and stone walls (Bobb 1949, Chapman
193 8, Graham 1938) can help to reduce plum curculio populations. Steams et al. (1935)

recommended to burn over in February or March areas up to 200 to 300 m wide adjoining

25

orchards that serve as overwintering habitats. Habitat management should be of concern
from 160 to 300 m from the orchard (Laﬂeur et al. 1987, Prokopy et al. 1990, Radke
1983). Others have advised that apples should not be planted adjacent to woodlands not
only because it serves as an important role in plum curculio development but also
because it harbors others insect pests of tree fruits (Racette et al. 1992, Stedman 1904).
Early apple cultivars and other ﬂowering alternate hosts can be used as trap trees (Hill
1990). Early cultivars that have dense ﬂowers and fruit sooner are more subjected to
curculio attack because they allow better cover against natural enemies and adverse
climate conditions and provide food at a critical period (Racette et al. 1992).

Cultivating the orchard and surrounding land can disrupt the pupal stage and reduce
plum curculio damage (Garman and Zappe 1929, Steams et a1. 1935, Stedman 1904).
Disking deeper than 5 cm, especially under the tree canopy, for several weeks after petal
fall is recommended (Racette et al. 1992). Removing and subsequently destroying
wormy fruit has also been shown to decrease plum curculio pressure (Chandler 1940,
Chapman 1938, Quaintance and Jenne 1912, Snapp 1931, Stedman 1904). Fallen fruit
can be collected with modiﬁed golf ball machines (Hill 1990). Larvae can be fed upon
by free range foul (Clark and Gage 1997, Qintance and Jenne 1912). Trees can be jarred
to remove adult curculio (Chandler 1940, Chapman 193 8, Wylie 1951), however
reduction in fruit damage is variable, ranging from 1 to 36% (Chapman 193 8), deeming
this control tactic not practical for large orchards.

Curculios were sexually irradiated (Hayes and Chochran 1964) and released in South
Carolina in the early 1960S (Johnson and Hayes 1969). Jacklin et a1. (1970) sterilized

males and females with 8 kRad of 60Co but Huettel et al. (1976) found that sperm from

26

the last mating replaced that from a previous mating so innundative release would be
necessary. Entomologists also believed that the tendency for diapause in the Northern
strain could be eliminated from a population by inter-breeding it with a non-diapausing
strain so it and its offspring could not survive the winter but were not successful

(Featherstone and Hays 1971).

Biological control

A number of predators, parasitoids, and pathogens have been identiﬁed for plum
curculio and are outlined in Table 1.3, however, few of the commercially available
biological control agents have been tested in the ﬁeld. In an orchard where plum curculio
adults were labeled with 65 Zn, released toads (Bufo americanus americanus Holbrook)
were found with high levels of 65 Zn (Chouinard et al. 1992a). Curculio was not
controlled with free-range chickens in a low-input orchard in Michigan (Clark and Gage
1997). The use of nematodes including Steinernema bibionis, S. carpocapsae, and S.
feltiae in vitro and in vivo resulted in inconsistent infection rates (Olthof and Hagley
1993, Tedders et al. 1982). Fungal pathogens (Beauvaria bassiana and Metarhizium
anisophilae (Metschnikoff) Sorokin) have been tested in the laboratory and resulted in
high larval mortality (Tedders et al. 1982). Reissig et al. (1984) found that orchards
treated with Bacillus thuringiensis, a bacterial pathogen, suffer severely from plum
curculio attack. Overwintered beetles have been found to be infected with the fungal
pathogen Beauvaria bassiana (Balsamo) (Laﬂeur et a1. 1987, McGiffen and Meyer 1986)

but its effectiveness as a control has not been tested.

Table 1.3. lrnportant natural enemies of the plum curculio (from Racette et al. 1992).

 

Name Family Stage Reference
Parasitoids
Anaphoidae conotracheli Mymaridae egg Garman & Zappe 1929,
Girault Quaintance & J enne 1912
Aliolus ruﬁts (Riley) Braconidae larva Armstrong 1958
A liolus curculionis Fitch Braconidae larva Armstrong 1958, Garman
& Zappe 1929
T riapsis kurtogaster Martin Braconidae larva Paradis 1956
Microbracon mellitor Say Braconidae larva Quaintance & Jenne 1912
Thersiocholus conotraceli Ichneumonidae larva Armstrong 1958,
(Riley) Quaintance & Jenne 1912
Myophasia aenae Tachinidae larva Armstrong 1958,
Wiedmann Quaintance & Jenne 1912
Cholomyia inaequipes Bigot Muscidae larva Armstrong 1958,
Quaintance & J enne 1912
Predators
Chrysopa spp. Chrysopidae larva Quaintance & J enne 1912
Garmania bulbicola Phytoseiidae larva Smith 1957
Owdms.
Lycosaﬁzlosa Walckenaer Lycosidae adult Laﬂeur et al. 1987
Bufo americanus Bufonidae adult Chouinard et al. 1991
americanus Holb.
thrips Thripidae egg Quaintance and Jenne 1912
ground beetles Carabidae larva Howard 1906, Quaintance
& Jenne 1912
ants Formicidae larva Howard 1906, Snapp 1930
fowls Phasianidae adult Clark and Gage 1997,
larva Quaintance & Jenne 1912,
Pathogens
Beauveria bassiana adult Laﬂeur et al. 1987,
(Balsamo) Vullimen McGiffen & Meyer 1986
Bacillus thuringiensis var. adult Leﬂuer et al. 1987

entomocidus or subtoxicus
Heimpel

 

28

Chemical control

Chemical control of plum curculio has followed the same trend as many agricultural
pests, beginning with lead arsenate (Driggers 1935 , Stearns et al. 1935) and moving onto
other products such as natural compounds (Freedman et al. 1982) and synthetic insect
growth regulators (Calkins et al. 1977). Currently in Michigan, organophosphates,
azinphos methyl (Guthion®, Bayer), phosmet (Imidan®, Gowan); permethrin
(Ambush®, ZENECA Agrochemicals; Pounce®, FMC Corp.) and esfenvalerate
(Asana®, DuPont) are recommended at petal fall and 1St cover for most pome and stone
fruits (Jones et al. 2000).

Susceptibility to insecticides increases with activity of target species, therefore
spraying should be done in the early evening or at night (Chounard et al. 1992, Racette et
al. 1990). Sprays should be directed toward the ground, adjacent wild hosts, and
neglected orchards where plum curculios are likely to occur (Chounard et al. 1992a).
Susceptibility to insecticides varies by compound (Hall 1979, Neiswander 1948),
voltinism, age of the adult (Snapp 1951), and with time of year (Smith 1954). Insecticide
sprays at petal fall should have a long residual since curculio disperse into orchards over
several weeks (Leﬂeur and Hill 1987, Smith and Flessel 1968). It is not necessary to
maintain insecticide residues on fruit and foliage for the duration of the oviposition cycle
to effectively limit damage (Reissig et al. 1998) but is optimal to control the larvae as
they leave the fruit (Stelzer and Fluke 1958). Reissig et al. (1998), using a logistic model
based on the relation of plum curculio feeding and oviposition to cumulative heat units
(degree-days base 10° C) following petal fall, found that maintaining insecticide residues

until the model-predicted the 40th percentile of cumulative damage required the fewest

29

insecticide applications. This timing coincides with declining plum curculio activity
(Chouinard et a1. 1993, Racette et al. 1991). Prokopy (1985) recommended using
monitoring to time the petal fall spray, spraying within hours of the ﬁrst detection of a
fresh oviposition scar then 10 d after if substantial rainfall has occurred, 14 d after if
conditions are relatively dry, or if additional scars are detected (Prokopy 1989).
Insecticides may be applied only to border rows based on monitoring (Chouinard et al.
1992, Racette et al. 1992, Steams et a1. 1935). Chouinard et al. (1992a) attained
economically acceptable control with the combination of a pink spray and a petal fall
border spray.

Commercially available biocontrol agents are not effective, and convenient and
reliable monitoring techniques for the timing of sprays have not been developed (Racette
et al. 1992). However, a better knowledge of the behavior and ecology of plum curculio
can reduce the amount of pesticides used (Racette et al. 1992, Roitberg and Angerilli
1986, Steams et al. 1935). The development of an adequate monitoring tool would

beneﬁt both the scientists, as a research tool, and the grower, as a decision making tool.

Monitoring plum curculio

It is likely that the effectiveness of sprays to control this pest could be improved, and
possibly the number of sprays minimized, by the development of a trap for monitoring
plum curculio activity (Prokopy and Wright 1998, Yonce et al. 1995). To date, an
efﬁcient and reliable monitoring technique or device, and applicable economic thresholds

are lacking (Racette et a1. 1992).

30

Visual monitoring

Curculio pressure can be monitored by the examination of several hundreds to
thousands of apples at fruit set for evidence of fresh feeding or egg laying scars (Hoyt et
al. 1983, LeRoux 1961, Prokopy et al. 1980, Prokopy et a1. 1993), especially on early
cultivars since they are preferentially attacked (Laﬂeur and Hill 1987). On some
cultivars, early plum curculio damage can be detected in the upper portion of the tree
even before ﬁ'uit set (Le Blanc et al. 1984). A speciﬁc monitoring strategy (i.e., number
of fruit per tree and total trees inspected) depends upon previous infestation history and
on the characteristics of the surrounding environment such as proximity to neglected
orchards, natural hosts, and potential overwintering sites (Racette et al. 1992). Detection
of scars usually happens several weeks after the ﬁrst curculio have arrived in the orchards
and may be too late to achieve optimal control (Le Blanc et al. 1984). This monitoring
method is not only insufﬁcient due to the quantity of apples that need to be observed but
also because early season detection needs to be done more than once a day. For example,
Prokopy et al. (1993) found that fruit injury rose from 0 to 14% within a 12 h period
during petal fall. Using this visual observation of oviposition scars as a decision tool for
additional sprays after petal is inadequate due to indiscernible differences between fresh

and older scars (Prokopy et al. 1993).

Limb jars

Another method for monitoring plum curculio populations is limb jarring. This
method exploits curculio thanotosis by laying a white sheet under the tree canopy, jarring
the tree, and counting the number of curculio that fall to the white sheet. In most seasons,

beetles are ﬁrst collected slightly before full bloom (Smith and Flessel 1968). Racette et

31

al. 1990 found that during fruit set, the most beetles collected were between 0900 and
1700 h and between 0900 and 0100 h during June drop; overall, they found the most
productive time for jarring to be between 1800 and 2100 at petal fall. Greater catches are
obtained when the number of dropping events decreases (Racette et al. 1990) as the
beetles are most likely to be located in trees. Curculios do not occupy the tree
continuously so only a proportion of them are present in the trees at the time of jarring
(Smith and F lessel 1968). Therefore, limb jars are inaccurate, inconvenient, and may
also cause tree damage (Racette et al. 1992). Limb jars not only vary with time of day
and time of year (Racette et al. 1990) but also with the skill of the ﬁeld scout (Racette et
al. 1992).

Chapman (193 8) captured no more than 22% of the season’s total on a single day
whereas Smith and F lessel (1968) caught no more than 12% in a three year period. When
beetles are marked and released at petal fall, only about half are recovered in limb jars
over an extended period with no more than 20% of the total recovered captured on a
single day (Smith and Flessel 1968). Smith and Flessel (1968) also marked and released
beetles from overwintering sites before and after petal fall and caught 52 and 35%,
respectively over a two year period. Chapman (193 8) showed that the number of beetles
captured per tree throughout the season was closely related to the size of crop borne by

the tree, with few beetles being taken from nonbearing trees.

Interception traps
Blanchet (1987) intercepted curculio ﬂying from a deciduous forest to an adjacent
apple orchard using large screen traps covered with Tangletrap. There was no signiﬁcant

difference in number captured between the low and high position although there was a

32

signiﬁcant positive correlation between daily numbers captured at each position and daily
high temperature (Prokopy et al. 1998). Dixon et al. 1999 found daily captures by
interception traps to be positively correlated with daily average temperature and

secondarily with wind speed.

Pyramid traps

Tedders and Wood (1994) developed a pyramid trap (Figure 1.1) which is believed

 

Figure 1.1. Schematic drawing of pyramid trap developed by
Tedders and Wood (1995).

to represent a super-normal mimic of a tree trunk for host-seeking pecan weevils,
Curculio caryae (Horn), for which the trap was originally designed and described it as

follows:

The base of each trap was constructed from 0.95 cm thick exterior

plywood and consisted of two triangular pieces, each measuring 55 cm

33

wide base x 122 cm vertical height. One triangular piece was partially
bisected with a 1 cm wide vertical saw-cut from the apex to one-half
way to the base. The second was partially bisected with a 1.0 cm
vertical cut from the center of the base to one-half way to the apex.

The two triangular pieces were then interlocked utilizing the two
vertical cuts to a form a free-standing pyramidal trap base which served
as the main attractant to the weevils. To collect the beetles a trap...
constructed from a 11.5 cm diam. X 20.0 cm deep screen wire inverted
funnel having a 0.79-cm opening apex and a 2 l cylindrical plastic
container. The screen funnel was nestled into and ﬁxed to the mouth of
a plastic container (collecting cylinder) to form the trap... then placed

on top of the pyramid base.

Pyramid traps placed adjacent to tree trunks captured at least ﬁve times more

curculios than pyramid traps in other positions but there are no meaningful correlations

between daily trap captures and daily numbers of sampled fruit injured by plum curculios

(Prokopy and Wright 1997b, Prokopy et al. 1999). Pyramid trap captures correlate

negatively with barometric pressure and secondarily with wind speed for both intact

pyramid traps and pyramid trap with a band of Tangletrap around the base that is

impassible by crawling (Dixon et a1. 1999).

About two-thirds of curculios captured by pyramid traps arrive on the traps by

crawling onto them rather than by ﬂying onto them (Prokopy and Wright 1997a). Adults

in ﬂight are much less likely to orient towards and be captured by pyramid traps than are

crawling adults (Prokopy and Wright 1998). Traps without a Tangletrap band on the

34

base of the trap capture about twice as many curculios from 0500 to 2200 h as from 2200
to 0500b, whereas traps with Tangletrap capture more than 20 times as many curculio
from 0500 to 2200 h as from 2200 to 0500 h; therefore, it can be concluded that about
twice as many curculios arrive on pyramid traps during daylight as during darkness,
about half of those arriving on pyramid traps during daylight do so by ﬂying and half by
crawling, and that most of those arriving on pyramid traps during darkness do so by
crawling (Prokopy and Wright 1997a). There is a signiﬁcant positive correlation
between daily numbers captured by sticky pyramid traps and daily high temperatures
(Prokopy and Wright 1997a). Adults in ﬂight are prone to ﬂy directly into apple tree
canopies hence, when temperatures increase above 20° C the probability of injury to
apple fruit in tree canopies increases as does the probability that adults will bypass tree

trunks and pyramid traps when entering apple tree canopies (Prokopy et al. 1999).

Cylinder traps
Cylinder traps were developed by Prokopy et al. (1998) as an alternative to pyramid

traps and are described below:

Cylinder traps were 8 cm diam by 30 cm tall, constructed of
polyvinylchloride pipe, and painted black... each cylinder was ﬁtted
with a black-painted pyramidal insert between the cylinder and funnel
cap that facilitated movement of adults onto the cap and held the
detachable cap ﬁrmly in place. Each cylinder was attached in upright
position to a horizontal tree limb using a locking plastic cable tie that
was threaded through holes at the base of the cylinder and drawn tight

to the limb (Prokopy et al. 2000).

35

Captures with cylinder traps coincide better with fruit injury than pyramid traps
(Prokopy et al. 1998) and thus are more desirable for understanding curculio activity in
relation to damage. Prokopy et al. (2000) found that pyramid traps caught more curculio
than cylinder traps and neither the amount or timing of trap catches regardless of trap

type did not reﬂect amounts or timing of damage.

Comparing traps

Considerable effort has been put into evaluation of trap types for monitoring plum
curculio populations. Of 15 devices tested by Le Blanc (1982), Le Blanc et al. (1981),
and Radke (1982) none caught enough to be reliable. There were no signiﬁcant
differences in number of plum curculios captured per trap among high interception traps,
low interception traps, and pyramid traps (Prokopy et al. 1998). Increases in captures by
interception traps but not by pyramid traps were signiﬁcantly positively correlated with
increases in fruit damage caused by plum curculios the following day. Captures by
interception traps as well as fruit damage were signiﬁcantly positively correlated with
temperature, while fruit damage was signiﬁcantly negatively correlated with wind speed
(Prokopy et al. 1998).

Dixon et a1 (1999) compared limb jars and visual observation of fruit with three trap
types — pyramid, interception and cylinder. No signiﬁcant differences between trap types
were found, however interception traps caught numerically more curculio at all 4 h time
intervals except for 1400 to 1800 h when pyramid trap caught more. Limb jars caught
numerically more plum curculios than any trap types tested during 4 h intervals except
from 2100 to 0100 h when interception traps caught more. Captures by tapping were

numerically greatest at 1800 to 2100 h while captures by each of the trap types were

36

numerically greatest at 2100 h. Daily pyramid trap captures signiﬁcantly positively
correlated with and increase in fruit injury on the same day and daily interception trap
captures and increase in fruit injury on the following day. Interception trap catches on
one day were strongly correlated with pyramid trap captures the following day. Daily
captures by interception traps and sticky pyramid traps were signiﬁcantly positively
correlated with limb jars on the same day. Correlation with sticky pyramid traps was
slightly lower suggesting that adult appearance in the tree canopy is more by direct ﬂight
into then by ﬂight onto or crawling up the tree trunk. Captures in interception traps
during 4 h intervals were also correlated with numbers tapped from the canopy but not
for other trap types at any time interval. Average daily temperature and wind speed
signiﬁcantly correlated positively with average daily captures by tapping. Tapping
captures grouped by daily time intervals did not signiﬁcantly correlate with any weather

variable measured.

PC Attractants

Since curculio behavior was ﬁrst studied, it was believed that they are sensitive to
odors (Garman and Zappe 1929). Recently, the need for an odor-based monitoring trap
for plum curculio was recognized (Prokopy et al. 1993), because of the overwhelming
inability to capture curculio with nonbaited traps. Plum curculios respond positively to
host olfactory cues in the ﬁeld, being more attracted toward cages containing apple
branches as Opposed to cages containing nonhost branches in no choice tests and also
respond strongest when host visual and olfactory cues are combined (Butkewich and
Prokopy 1997). Plum curculio females have the ability to ﬁnd and oviposit in apples

placed in nonhost thickets although it was not determined if females do this over a

37

limited (1 — 3 m) or long (65 m) range (Calkins et al. 1976). Males and females are
equally attracted to hexane extracts of McIntosh twigs, leaves, and fruit collected at petal
fall as opposed to extracts during other times (Leskey et al. 1999a).

Acetaldehyde, acetaldehyde-sodium bisulphite, and malic acid have been shown to
be attractive in the laboratory, but beetles have not been successfully trapped by these
compounds in the ﬁeld which may be due to the high volatility of these compounds
(Garman and Zappe 1929). Synthetic ethyl isovalerate and limonene, two volatile
compounds of green plum, attracted curculio both in the laboratory and ﬁeld (Leskey et
al. 1999b). Plum curculios are attracted to 50% and 500% more concentrated solutions of
ehtyl isovalerate and limonene, respectively in the ﬁeld compared to the laboratory
(Leskey et al. 1999b).

Alm and Hall (1986a) found sensory structures on the antennae similar to those of
other insects used for pheromone reception. A male-produced aggregation pheromone
was identified and described by Eller and Bartelt (1996). Although the univoltine
northern strain and the multivoltine southern strain are reported to be reproductively
incompatible, both strains were found to produce grandisoic acid, therefore, it is unlikely
that pheromone differences contribute to reproductive isolation of the strains (Eller and
Bartelt 1996). The pheromone compound, (+)-(1R,2S)-1-methyl-2-(1-methylethenyl)
cyclobutaneacetic acid (Figure 1.2), was given the common name (+)-grandisoic acid and
is the carboxylic acid analog of (+)-grandisol, the major pheromone component of cotton
boll weevil, Anthonomis grandis Boheman, (Eller and Bartelt 1996) a key pest of cotton
that is closely related to plum curculio. Synthetic grandisoic acid is synthesized from the

racemic grandisol, thus synthetic grandisoic acid contains both (+) and (-) racemers. The

38

pheromone of cotton boll weevil contains four components (Figure 1.3). Apart from the
major component, (+)-grandisol, there is a cyclohexane alcohol and racemic cyclohexane
acetaldehyde whose presence increases the attraction of the major component
(Tumlinson et al. 1969, Tumlinson et al. 1971).

Synthetic pheromone may increase trap efficacy when combined with host plant
volatiles. To date, there is no published data on using synthetic pheromone in
conjunction with traps, although researchers have attempted to bait traps with
conspeciﬁcs. Prokopy and Leskey (1997) found that pyramid traps baited with males,
females, immature McIntosh, mature Fuji, or ammonium carbonate do not catch more
plum curculio than nonbaited traps. This may occur because conspeciﬁcs emit stress
sounds that repel and the volatile attractants may need to be at higher concentrations in
order to compete with fruit odor sources on adjacent trees. An alternative hypothesis
may be that the volatiles rapidly loose attractiveness due to composition change. In the
laboratory, Leskey et al. (1997) found that males are attracted to females plus plums in
signiﬁcantly greater numbers than to plum alone versus males plus plums, males alone,
or an empty bag. Females are attracted to males plus plums in signiﬁcantly greater
numbers than to males alone or the empty bag with an intermediate attraction to plums

alone (Leskey et al. 1997).

39

(a) CH /(b) CH \
5 do W0
H H
/ \”
Figure 1.2. Naturally-occurring component of the plum curculio pheromone (a),
(+)-(1R,2S)-1-Methy1-2-(1-methylethenyl)-cyclobutaneacetic acid, and its racemer

(b), (-)-(1R,ZS)-1~Methyl-2-(1-methylethenyl)-cyclobutaneacetic acid, that is present
in the synthetic formulation.

(a) CH 6» C“ \

/ k; y

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CH2OH CHO OHC

(C) (d) (6)

Figure 1.3. Major component of the cotton boll weevil (a), (+)-cis-2-isopropenyl-1-
methylcyclobutaneethanol, and its racemer (b), (-)-trans-2-isopropenyl-1-
methylcyclobutaneethanol, present in synthetic formulation and the three minor
components of pheromone (c), cis-3,3-dimethyl-A"B-cyclohexaneethanol; (d) cis-3,3-
dimethyl-A1 ra-cyclohexaneacetaldehyde; and (e), trans-3,3-dimethyl-A ‘ ’0‘-
cyclohexaneacetaldehyde

40

Thesis Research

The goal of the research herein in is to improve the efﬁcacy of plum curuclio
monitoring through the utilization of pheromone- and host plant-based lures in
conjunction with current and newly designed traps. The reliability of these strategies will
be measured not only by the total amount of curuclios that are captured but also in terms
captures during relevant time intervals in relation to the number of curuclios found in the
tree canopy, as determined by limb jars, and the onset, increase in, and harvest damage.
Research was conducted in experimental orchards where plum curuclio populations were
large enough to establish meaningful treatment comparisons. This research is a stepping
stone for implementation of the trap design in commercial orchards as decision-making
tools in order to optimize the timing and frequency of insecticide applications for control
of plum curculio. The next four phases of this research will be to: (1) move the most
effective trap and attractant combination into commercial orchards where plum curculio
populations are smaller and may display altered trends in activity due to insecticide
control and residues, (2) determine if trap lines can accurately predict either peak
migration into the orchard or onset of ﬁ'uit damage, (3) develop an economic threshold
for a trap deployment and monitoring protocol, and (4) maintain plum curculio damage
levels equivalent to or beneath that of calendar-sprayed orchards over time in a variety of

locations and crops.

41

CHAPTER 2

PYRAMID TRAPS BAITED WITH PHEROMONE LURES FOR
MONITORING PLUM CURCULIO, CONOT RACHEL US NENUPHAR (HERBST)

Introduction

Plum curculio, Conotrachelus nenuphar (Herbst) is considered a serious pest of
tree fruits east of the Rocky Mountains. Despite its status as a key pest of peaches,
apples, cherries and plums, plum curculio has remained the least known of the major
North American fruit pest species (Hoyt et al. 1983, Racette et al. 1992, Whalon and
Croﬁ 1984). A reliable method for monitoring plum curculio movement into the orchard
from overwintering sites before signiﬁcant damage occurs or for quantifying the
population density within an orchard currently does not exist. Therefore, fruit injury is
generally prevented by calendar-based application of organophosphate insecticides at
petal fall and ﬁrst cover. Better understanding of plum curculio ecology is needed to
improve management strategies that will optimize timing of insecticide sprays
(Chouinard et al. 1992, Racette et al. 1992, Roitberg and Angerilli 1986).

Various tools and techniques have been developed for monitoring plum curculio,
but all have their limitations and none have been widely adopted. The complexity of
factors involved in jarring trees and collecting fallen plum curculio on white sheets laid
on the ground generates variable results and may cause tree damage (Le Blanc et al.

1984, Racette et al. 1990). Visual observation of young fruit for oviposition scars is

42

more reliable than jarring (Hoyt et al. 1983, LeRoux 1961, Prokopy 1985, Prokopy et al.
1980). However, screening at least 50 fruit twice a day is recommended (Prokopy et al.
1993) making this a labor-intensive practice for control decisions in commercial settings.
Furthermore, this approach detects plum curculio presence after they begin to arrive in
the orchard, which may overlook key control opportunities (Le Blanc et al. 1984). The
most practical method for monitoring plum curculio movement into the orchard to date is
the pyramid trap placed in border-rows adjacent to overwintering sites (Prokopy et al.
1996, Schmitt and Berkett 1995). The pyramid trap consists of a cotton boll weevil trap
set on a pyramid-shaped base constructed of two interlocking panels of dark tempered
pressboard (Tedders and Wood 1995). Plum curculio orient toward the silhouettes of tall,
dark objects (Laﬂeur et al. 1987, Prokopy and Owens 1983) making pyramid traps
effective traps early in the season before tree canopies ﬁll out. Behavior exhibited by
plum curculio when interacting with this trap and other factors inﬂuencing trap efﬁciency
are not fully understood.

One strategy for increasing the efficacy of a monitoring tool is to add a chemical
attractant. Male-produced pheromone has been identiﬁed for 20 Curculionid species
(Landolt 1997). Many of these pheromones are commercially produced for trapping
important pest species including cotton boll weevil, Anthonomus grandis Boheman
(Johnson and Gilreath 1982). Eller and Bartelt (1996) recently identiﬁed a male-
produced aggregation pheromone for plum curculio, grandisoic acid. This has resulted in
the development of a synthetic pheromone lure that could potentially increase the

efficacy of pyramid traps. The following research was performed to determine the

43

efﬁcacy of pyramid traps baited with grandisoic acid lures compared to nonbaited

pyramid traps for monitoring plum curculio in apple and cherry orchards in Michigan.

MATERIALS & METHODS

Research was conducted at Clarksville Horticultural Research and Experiment
Station (CHRES) in Clarksville, MI and Trevor Nichols Research Center (TNRC) and
Douglas Farm (DF) in Fennville, MI. CHRES is a 440 acre diverse agricultural
ecosystem in Ionia Co. with numerous tree fruit plots dedicated to the development and
evaluation of new varieties, fruit thinning and growth regulators, dwarf rootstocks for
fruit trees, weed control, integrated pest management, and pruning and training practices.
Traps were located in apples, cherries, and in wooded areas adjacent to apple plots

(Figure 2.1). Lorsban 50W, an organophosphate, was applied at petal fall and ﬁrst cover

 

LEGEND
® baitedtrap
@ nonbaited trap .

apple 1PM :1 W00“
plot

apple [PM with '2 grass
poplar barrier C] ﬁeld crop

 

 

 

 

 

 

 

 

 

 

 

Figure 2.1. Plot map of the Clarksville Horticultural Research and Experiment Station
(Clarksville, Ml) with locations of baited and nonbaited pyramid traps.

44

to control plum curculio in all tree ﬁ'uit plots except in apple Integrated Pest Management
(IPM) plots where, depending on the treatment, Spinosid® (insect growth regulator),
Provado® (nicotinyl) and Coax® (feeding stimulant) were used on 3 apple cultivars
(Liberty, Ida Red and Empire). TNRC is a 170 acre research station in Allegan Co.
dedicated to fruit research pertaining to the biology of pests and beneﬁcial insects,
strategies for reducing pesticide use in orchards, and evaluation of registered and
experimental pesticides. The research site at TNRC consists of an 8 acre plot of apples
cv. Red Delicious (Figure 2.2). For the previous three years, this plot had not received
any insecticide sprays on border rows, but randomly selected trees within the plot were
utilized in broad-spectrum insecticide spray trials. The two acre sweet cherry plot cv.
Bing at DF (Figure 2.3) utilized in this study has not been sprayed with insecticides since
1993.

Pyramid traps were manufactured by Great Lakes 1PM (V estaburg, MI). The basic
design was a cotton boll weevil trap secured to the top of a pyramid shaped base
constructed of two interlocking panels of black pressboard as described by Tedders and
Wood (1995). Each pyramid trap was paired with another trap that was baited with
pheromone. Pheromone lures consisted of a polyethylene vial loaded with 3 mg of
racemic grandisoic acid (IPM Technologies, West Linn, OR) and were placed inside the
collection cylinder of the cotton boll weevil trap. Traps remained baited with the same
lure throughout the experiment.

Each baited and nonbaited trap pair was placed approximately 100 m apart at the
CHRES site and 2 m apart at TNRC and DF sites. Traps were located in border rows of

orchards adjacent to overwintering sites with a recent history of plum curculio pest

45

 

 

LEGEND

 

apple

cherry
baﬁed
peach O trap

plum ® unbaited
trap

   

pear
grape

blueberry

 

 

hulmnlll

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-
ill-II I .—

 

 

 

 

 

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Figure 2.2. Plot map of Trevor Nichols Research Center (Fennville, MI) with
locations of baited and nonbaited pyramid traps.

46

 

 

  
  
  
   
   
  

 

 

 

 

LEGEND
- apple
cherry Obaited
peach trap
1:] pear ©irrggaited
I:l blueberry
- woods

 

 

 

 

Figure 2.3. Plot map of Dougals Farm (F ennville, Michigan) with locations of
baited and nonbaited pyramid traps.

47

pressure. A total of 14 pairs (28 traps: l4 baited, 14 non-baited) were monitored. Five
pairs were located at CHRES (3 in cherry, 1 in apple, and 1 in a wooded area adjacent to
apple plots), ﬁve in TNRC (all in apple), and four located at DF (all in cherry). CHRES
traps were set-up in late May and checked weekly through July 1. TNRC and DF
traps were set-up in late April and checked every 2 to 3 days through June 23. The
overall experimental design was a paired comparison of plum curculio captures in baited
versus nonbaited traps. The total and mean number of plum curculios captured in baited
and nonbaited traps were calculated for the following locations: CHRES, TNRC, DF, and
TNRC + DF. Plum curculio captures in baited versus nonbaited traps for each location
were analyzed for treatment effects by paired t-test (a=0.05) in JMP (SAS Institute Inc.,
1995). The mean of the difference between the total number of plum curculio captured in
baited traps and nonbaited traps [(l/n)Z(capture in baited trap — capture in its nonbaited
pair)] was also calculated for each location grouping. For each trap location grouping
resulting in a positive mean difference, means differences were partitioned into the
following time intervals that are signiﬁcant to plum curculio activity: before petal fall
(April 28 through June 2), during petal fall (June 2 through June 11), and bloom through
fruit set (May 26 through June 13). A one-sided t-test (a = 0.05) was conducted to
determine if mean differences are signiﬁcantly different than 0 and each mean
combination within each time interval were analyzed by a two-sided two-sample t-tests

(a = 0.05).

RESULTS
A total of 138 plum curculios were captured in traps at all locations (Table 2.1). Over

two-fold were captured in baited than in nonbaited traps. The majority were captured at

48

the TNRC and DF sites. Only 9 plum curculio were caught at the CHRES, 4 in baited
and 5 in nonbaited traps. The total number of plum curculios caught in baited traps was

greater than the total number caught in non-baited trap for all other location groups.

Table 2.1. Plum curculio trap catch data for all trap location groupings
summed over time.

 

 

 

Trap Number of Number of Captures
Location Trap Pairs Baited Non-Baited Total
All traps 14 98 40 138
CHES 5 4 5 9
TNRC 5 36 9 45
DF 4 58 26 84
TNRC + DF 9 94 35 129

 

The temporal trend of captures in baited and nonbaited traps at TNRC and DF are
depicted in Figure 2.4. Commencement of research at CHRES (May 26) falls within the
ﬁrst peak of the TNRC + DF trend (May 24 - May 30). Preceding this date, TNRC and
DF had 2 occasions of plum curculio capture (April 28 and May 8) in baited and non-
baited traps. The ﬁrst substantial catch in both baited and nonbaited pyramid traps at
TNRC and DF occurred at bloom. Peak catch in the baited traps was recorded at petal
fall. In contrast, peak catch in the nonbaited trap occurred 16 days later. After fruit set, a
increasing trend in plum curculio catch in nonbaited traps was observed.

Differences in mean plum curculio captures in baited or nonbaited traps varied by
location. For all locations combined, the average number of plum curculio captured in

baited traps was signiﬁcantly greater than nonbaited traps (P 2 0.0169). An average of

4.14 i 1.75 more plum curculio were caught per trap in baited than in nonbaited traps

49

over time (Figure 2.5). Mean difference were also signiﬁcant for TNRC only and TNRC
+ DF data. Baited traps at CHRES and DF; however, did not catch signiﬁcantly more
plum curculio than their nonbaited pairs.

All trap locations, except for CHRES, resulted in positive mean differences in baited
- nonbaited traps. Numbers of curculios captured was then partitioned into time intervals.
All mean differences at all time intervals for TNRC + DF and TNRC alone were
signiﬁcantly greater than 0 (Table 2.2). None of the DF mean differences were
signiﬁcantly greater than 0. However, means within each time interval were not
signiﬁcantly different from each other.
DISCUSSION

This is the ﬁrst report of synthetic grandisoic acid enhancing capture of plum

curculio in pyramid traps in Michigan orchards. We have found that the lure was indeed
effective, increasing the total number of plum curculio captured in pyramid traps. Of
greater importance however is the outstanding performance of pyramid traps baited with
pheromone compared to nonbaited traps at and just before ﬁ'uit set when plum curculio
begin to damage fruit. The information gathered during this time period will be essential
for determining plum curculio movement into the orchard and for making decisions about
curculio control. The results shown here are promising for use of the synthetic grandisoic
acid as an attractant lure used in conjunction with traps for plum curculio monitoring.

Few plum curculios were caught at CHRES compared to the other locations. This
may be due to differences in experimental design. Chemical control of plum curculio at
the CHRES location may especially contribute to the inconsistent results. In a recent
evaluation of trap types conducted by Prokopy et al. (in press), pyramid traps were used

in commercial plots where insecticide sprays were used to control plum curculio and

50

were covered with a plastic bag to prevent residue build-up. When evaluated in
commercial plots in Massachusetts, baited pyramid traps do not capture more curculios
than nonbaited pyramid traps (Prokopy et al. in press). After insecticide sprays, curculios
do not crawl up tree trunks before ovipositing (Prokopy et al. 1999); however, curculio
behavior associated with pyramid traps in sprayed orchards, regardless of being covered
during application, is not known. Curculio behavior in sprayed plots probably does not
deviate from that in unsprayed plots given its ability to return to levels of economic
importance within 3 years after pesticide use has been discontinued (Glass and Lienk
1971, Hagley et al. 1977, Hall 1974).

A couple of beetles were caught soon after traps were deployed during late April at
TNRC and DF well before bloom when the trend in trap catch began to increase for both
baited and nonbaited pyramid traps. A delay occurs between emergence of curculio from
overwintering sites and appearance in host trees (Garman and Zappe 1929, Lathrop 1949,
Smith and F lessel 1968). Although beetles come from hibernation beginning in April
(Garman and Zappe 1929), curculio begin to appear in the orchard sometime between the
pink and calyx period and do not become abundant until later (Garman and Zappe 1929).
Paradis (1956) found that arrival of curculios peaks between 6 d before petal fall and 10 d
after petal fall. First appearance in the orchard is closely related to temperature and host
plant development (Chapman 193 8, Cox 1951, Garman and Zappe 1929, Quaintance and
Jenne 1912, Smith and Flessel 1968, Snapp 1930, Whitcomb 1929). Beetles ﬁrst appear
in the orchard following several days of either a mean temperature of 15° C or above
(Quaintance and Jenne 1929) or a maximum of 24° C or above (Whitcomb 1929).

When plum curculio enter the orchard, they tend to remain on the orchard ground

51

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54

until optimal environmental conditions stimulate tree climbing and foraging (Chouinard
et al. 1993, Chouinard et al. 1994). Before much movement is detected in the tree, adults
may congregate in equal ratios of males and females within the ground cover at the base
of the tree in the orchard perimeter rows when the they arrive in the orchard in early
spring (Chounard 1991, Racette et al. 1991). Plum curculios gradually invade trees
between pink and petal fall, (Chouinard et al. 1994) after spending several days on the
ground (Racette et al. 1991). Curculios are found on the ground at pink protected by tufts
of grass and 30% resting at the base of tree trunks at bloom prior to their invasion into
trees. Between full bloom and fruit set, 54% were found on the ground with constant
movement between trees and the ground. Pyramid traps capture beetles crawling up the
trap which mimics a tree trunk (Prokopy and Wright 1997a). About two-thirds of the
curculios capture by pyramid traps arrive on the traps by crawling onto them rather than
by ﬂying onto them (Prokopy and Wright 1997a). Adults in ﬂight are much less likely to
orient towards and be captured by pyramid traps than are crawling adults (Prokopy and
Wright 1998). Pyramid traps that inaccurately estimate the population throughout the
orchard ﬂoor early in the season could accurately estimate plum curculio population with
use of an attractant that would enhancing climbing early in the season.

The trend in trap catches at TNRC and DF supports theories associating host-ﬁnding
behavior of plum curculio and phenological stage of host trees (Chouinard et al. 1993,
Chouinard et al. 1994, McGiffen and Meyer 1986, Racette et al. 1991). Obviously, both
organisms respond to environmental conditions such as soil and air temperature and
photoperiod. Curculios are most active between tight cluster and June drop and display

greatest activity at fruit set (Laﬂeur and Hill 1987, Racette et al. 1991). Highest

55

population densities have been recorded 1-2 weeks after petal fall (Chapman 193 8, Cox
1951, Garman and Zappe 1929, Quaintance and Jenne 1912, Smith and F lessel 1968,
Snapp 1930, Whitcomb 1929) but highest rates of movement occurs at full bloom
(Chouinard et al. 1993). A decrease in trap catches at TNRC and DF occurred for both
baited and non-baited traps after full bloom. This may be due to poor weather conditions
that may have discouraged plum curculio from foraging within the tree canopy.
Chouinard et al. (1993, 1994) reported that plum curculio increases its rate of movement
from bloom until fruit set. Baited pyramid traps more accurately record beetle activity
compared to nonbaited pyramid traps during bloom and fruit set. The number of curculio
in baited traps at TNRC and DF was highest during bloom and from petal fall through
fruit set.

Peak trap catch in nonbaited traps occurred 16 days after fruit set at which time the
number of curculio caught in baited traps was equal to that in nonbaited traps. In
nonbaited traps, captures increased fruit set to June 20. Oviposition begins at fruit set
(Armstrong 1958, Paradis 1956) when fruit is about 6 mm in diameter (Garmen and
Zappe 1929). Egg laying continues for three weeks until early July (Paradis 1956b) then
decline abruptly. There is a lag time between plum curculio entry into the tree canopy
and injurywhich may be due to a physiological need to feed and mate before commencing
oviposition (McGiffen and Meyer 1986). This trend in entering trees for oviposition
closely follows the trend in captures in nonbaited traps at TNRC and DF.

An overall increase in activity during petal fall would result in equivalent increases
in the number of curculios found in baited and nonbaited traps. However,

overwhelmingly more curculios were found in baited traps than nonbaited traps during

56

petal fall. Leskey et al. (1997) found that hexane and water extracts of twigs, leaves, and
fruit at petal fall are the most attractive extracts compared with those from any other tree
developmental stage. Curculios may be more attracted to the tree canopy than non-baited
pyramid traps during petal fall. By the same token, curculios are more attracted to
pheromone more during petal fall than at any other time interval studied. If natural
activity is odor-mediated, then pheromone and host-plant odor may be more attractive
than either one alone.

Little research has been conducted on this subject due to the limited production of
synthetic pheromone. Pyramid traps baited with males, females, immature McIntosh,
mature Fuji, or ammonium carbonate do not catch more curculios than nonbaited traps.
This observation may occur because conspeciﬁcs emit stress sounds that repel and
attractants need to be at higher concentrations in order to compete with ﬁ'uit odor sources
on adjacent trees. Alternatively, attraction may rapidly loose attractiveness due to
composition change (Prokopy and Leskey 1997). In the lab, males are attracted to
females plus plums in signiﬁcantly greater numbers than to plum alone versus males plus
plums, males alone, or an empty bag. Females are attracted to males plus plums in
signiﬁcantly greater numbers than to males alone or the empty bag with an intermediate
attraction to plums alone (Leskey et al. 1998).

Many tools have been developed to monitor plum curculio activity within and
around the orchard, although the inadequacy and inefficiency of these techniques have
persisted despite creative design adoption efforts. Ideally, a tool for effective plum
curculio monitoring in an [FM program should accurately predict and/or represent plum

curculio activity, estimate population size, involve low maintenance, and be cost-

57

effective. The goal of this experiment was to determine if baited pyramid traps caught
signiﬁcantly more plum curculio than non-baited pyramid traps. However, this study did
not produce direct results on the efficiency or adequacy of baited traps for use in
commercial orchards. Although baited traps caught signiﬁcantly more plum curculio
than non-baited traps, baited traps caught an average of only 4.14 i 1.75 more plum
curculio per trap than non-baited over the entire sampling period. It is yet to be
determined weather this quantiﬁcation of lure performance warrants its use with pyramid
traps for monitoring plum curculio in a commercial setting. Economic feasibility and the
ability of captures to be translated into potential for damage needs to be understood.
Until then, pheromone chemistry and sufficiency in conjunction with chemical control

must be further investigated to thoroughly designate its role in an IPM scouting program.

58

CHAPTER 3

PYRAMID AND CIRCLE TRAPS BAITED WITH PHEROMONE AND
PLUM ESSENCE FOR MONITORING PLUM CURCULIO, CONOTRA CHEL US
NENPHAR (HERBST)

Introduction

Integrated pest management (IPM) strategies are multifaceted approaches to pest
management involving the selection of and decision making for optimal control of pests
and are comprised of tactical components including control methods, monitoring, and
economic injury levels (Kogan 1998). Insect monitoring is the principle and most
complete component of apple IPM; however, plum curculio is the only primary pest
where monitoring and economic injury levels do not exist (Whalon and Croft 1984).
Therefore, the primary goal for developing plum curculio IPM strategies is to establish a
decision making tactic that accurately determines plum curculio movement into the
orchard from overwintering sites before signiﬁcant damage occurs and quantiﬁes the
population size within the orchard. Tools that are currently available for this tactic are
inadequate. Historically, limb jarring (Le Blanc et al. 1984, Racette et al. 1990, Snapp
1930, Wylie 1951) and visual observation of fruit for damage (Hoyt et a1. 1983, LeRoux
1961, Le Blanc et a1. 1984, Prokopy 1985, Prokopy et al. 1980, Prokopy et al. 1983,) do
not represent the plum curculio population in the orchard, do not predict damage levels of

fruit during the season or at harvest, and are not economically feasible for tree ﬁ'uit IPM.

59

To date, the most practical method for monitoring plum curculio activity has been
placement of pyramid traps under tree canopies in border-rows adjacent to overwintering
sites (Mitzell et a1. 1996, Prokopy et al. 1996, Schmitt and Berkett 1995).

Many insect species exhibit male-produced pheromones of which Curculionids are
the most proliﬁc (see review by Landolt 1997). Male-produced pheromones have been
identiﬁed for at least 21 Curculionids of which most are economically important
including cotton boll weevil, Anthonomus grandis Boheman (Cross 1973); pepper weevil,
Anthonomus eugenii Cano (Patrock et al. 1992); and pecan weevil, Curculio caryae
(Horn) (Hedin et al. 1997). Synthetic pheromones for cotton boll weevil (White et al.
1977), pepper weevil (Eller et al. 1994), and pecan weevil (Hedin et al. 1997) have each
been incorporated into various trap designs in an analogous manner to female sex
pheromone traps. The circle trap is an example of a weevil trap that was recently
developed for monitoring pecan weevil in Oklahoma (Mulder et al. 1997). This trap is
wrapped around the tree trunk thereby funneling weevils walking up the tree trunk into a
collection cylinder.

A male-produced aggregation pheromone, grandisoic acid, has been identiﬁed for
plum curculio (Eller and Bartelt 1996) and synthetic pheromone lures available. In
Chapter 2 it was shown that pyramid traps baited with synthetic pheromone lures capture
signiﬁcantly more plum curculio than nonbaited traps. Pheromone lures are currently
expensive and need enhanced performance by optimizing release methods (release rate
and kinetics, lure type, etc.) or the addition of other attractants. Landolt (1997) reported
that half of the Curculionid species exhibiting a male produced aggregation pheromone

also demonstrate a host-plant volatile enhancement. Therefore, weevil traps baited with

60

both pheromone and host plant volatiles have been incorporated into IPM programs. For
example, retention traps baited with pheromone and host plant volatiles were
recommended for the control of palm weevil, Rhynchophorus palmarum (L.), in coconut
(Jaffe et al. 1993). Plum curculio responds to host plant volatile cues, speciﬁcally fruit
volatiles (Butkewich and Prokopy 1997, Calkins et al. 1976, Leskey et al. 1999b), but the
combination of pheromone and host plant volatiles has yet to be tested.

The goal of the research presented here was to design a better monitoring tactic for
IPM strategies for plum curculio control that attracts plum curculio early in the season,
was in accordance with tree fruit IPM, was economically feasible, and was reliable. Five
sets of hypotheses were tested to attain these goals. (1) The ﬁrst set of hypotheses
compared the performance of pyramid traps compared to a new trap design, a modiﬁed
circle trap (H0: total capture in each trap type was not signiﬁcantly diﬂerence than 0; H0:
total capture in pyramid traps > total capture in circle traps). The circle trap design and
deployment were modiﬁed to more optimally capture beetles based on known plum
curculio behavior. (2) We analyzed pheromone and host plant volatile lures alone and in
combination for enhancing beetle capture (H0: total capture in traps baited with each
attractant lure was not significantly diﬂerence than 0; H0: no significant diﬂlerences in
total trap capture when traps baited with plum essence + pheromone, plum essence
alone, or none). The host plant volatile lure was comprised of a plum essence that is
used to enhance ﬂavor and aroma of food and juice products. Pyramid and circle traps
baited with plum essence + pheromone, plum essence alone, pheromone alone were
compared to nonbaited traps. (3) The interaction of trap type and attractant lures (H0: no

signiﬁcant interaction between trap type and attractant lure) and enhancement of beetle

61

capture by certain trap type and attractant lure combinations (H0: no signiﬁcant
differences between trap type and lure combinations) were examined. (4) A test for
synergistic effect when both lures were present in a trap was performed (H0: combination
of pheromone and plum essence was purely additive). (5) Finally, we looked at trap type
and attractant lure performance over time (H0: each trap type and attractant lure alone
and in combination at each sample date was not significantly diﬂ'erent than 0; H0: time
was not a significant factor when comparing trap types, attractant lures, or any of their

combinations).
Materials & Methods

Field Site

Research was conducted at Trevor Nichols Research Center in F ennville, MI. Four
apple plots were chosen based on history of high plum curculio pressure. The following
plots were utilized: burgundy (Red Delicious, 0.4 hectares), orange (Macspur 0.6
hectares), gray (Gala, 2.4 hectares), and indigo (Red Delicious, 3.3 hectares). Plots were

not treated with insecticides during the experiment.

Trap Type

Pyramid and circle traps (Great Lakes IPM, Vestaburg, MI) were compared for
efﬁciency of plum curculio capture. Pyramid traps (Tedders and Wood 1994) consist of
two pieces of interlocking, pyramid-shaped black tempered press board and are topped
with a cotton boll weevil funnel trap and stand approximately 1 m tall (see Figure 1.1).
Circle traps were modeled after a design for trapping pecan weevil, Curculio caryae, in
peaches (Mulder et al. 1997). The design was a funnel trap with an oversized funnel for a

base that can be wrapped around and fastened to a tree branch (Figure 3.1). This funnel

62

leads into a cotton boll weevil trap whose frame has been cut down to yield the screen
apex and the collecting vessel. Circle traps were fastened to major scaffold branches of

borderrow trees 1 to 1.5 In high while pyramid traps were staked under the canopy

 

Figure 3.1. Schematic drawing of modiﬁed circle trap on main scaffold branch

between the tree and the overwintering site. Traps were placed in or next to every other
tree in border rows adjacent to potential overwintering sites (i.e. woodlots, brush piles,
fence rows, etc.). Traps were placed approximately 14, 12.6, 12, and 6.6 m apart in

burgundy, orange, gray, and indigo, respectively.

Attractant Lures

The four attractant treatments were plum essence alone, pheromone alone, plum
essence + pheromone, and no attractant. Plum essence (Milne Fruit Products, Prosser,
WA) was loaded into a 1 ml polyethylene sample vial (Fisher Scientiﬁc, Pittsburgh, PA)

with a pinhole in the cap to allow volatiles to escape. Plum essence lures were

63

replenished with essence when the volume was observed to be approximately 1/3 of the
original volume. Pheromone lures (ChemTica Intemacional, S.A., Heredia, Costa Rica)
were loaded into a membrane lure with approximately 25 mg of >95% pure grandisoic
acid. The membrane lure consists of an interior slow release matrix in which the
pheromone was impregnated and the exterior was composed of a slow release membrane
of approximately 1 cm in diameter (C. Oehlschlager, personal communication).
Pheromone lures were replaced once during the study (32 days aﬁer deployment). Both
plum essence and pheromone lures were placed upright in the collection vessel of the

traps.

Trap deployment and data collection.

The 8 treatments (2 trap types x 4 attractants) were randomly assigned to every
other tree in a predetermined border row. Traps were set up on May 4 just before pink
and checked weekly 8 times during the study. Traps were last checked 53 d aﬁer

deployment.

Statistical Analysis
Total trap catch analysis

A randomized complete block design with a two way treatment structure blocked by
location was used to evaluate two levels of the trap type factor and four levels of the
attractant factor resulting in a total of 8 trap type x attractant treatments. Since data were
counts that were not continuous and have a Poisson distribution, a chi-square test of
independence was used (Sokal and Rohlf 1995) to test if trap type and attractants are
independent of plum curculio caught in traps and if there was an interaction between trap

type and attractant. Data were analyzed for main effects of each factor and factor

64

interactions using a generalized linear model I‘I2 test of likelihood (PROC GENMOD) in
SAS (SAS Institute 1997). If the trap type had a signiﬁcant main effect than the null
hypothesis (H0: total capture in pyramid traps > total capture in circle traps) was
rejected. If there was a signiﬁcant attractant lure main effect than the null hypothesis
(H0: no significant differences in total trap capture when traps baited with plum essence
+ pheromone, plum essence alone, or none) was rejected. If there was a signiﬁcant trap
type by attractant lure interaction than the null hypotheses (H0: no signiﬁcant interaction
between trap type and attractant lure) would be rejected.

Mean separation using least-squares comparisons of marginal and simple effects
were conducted using Wald H2 test (Sokal and Rohlf 1995) (PDIFF Option in LSMEANS
statement). Signiﬁcant marginal effects explain the within factor differences averaged
over the other factor. Simple effects explain the differences within each factor
combination. Signiﬁcant simple effects would result in rejection of the null hypothesis
(H0: no signiﬁcant differences between trap type and lure combinations). The Wald
xz test was also used to determine if means were signiﬁcantly different from 0. If there
was a signiﬁcant marginal mean for each trap type than the null hypothesis (H0: total
capture in each trap type was not significantly diﬂerence than 0) was rejected. If there
was a signiﬁcant marginal mean for each attractant lure than the null hypothesis (Ho:
total capture in traps baited with each attractant lure was not significantly diﬂerence
than 0) was rejected. If there was a signiﬁcant simple mean for each attractant lure than
the null hypothesis (Ho: no significant diﬂerences between trap type and lure

combinations) was rejected.

65

Synergy analysis

The generalized linear model procedure was also used to test for additive or
synergistic relationship between plum essence and pheromone lures. In this analysis,
main effects were generated for a two-way treatment structure with two levels of
pheromone (present or absent) and two levels of plum essence (present or absent) when
data were (1) summed across time and trap type, (2) summed across time for pyramid
trap data only, and (3) summed across time for circle trap data. A signiﬁcant main effect
for the plum essence by pheromone interaction indicates a synergistic effect, therefore the
null hypothesis (Ho: combination of pheromone and plum essence was purely additive)
would be rejected.
Repeated measures analysis

To evaluate trap and attractant performance over time, the square-root transformation
was used for normalization of count data (Sokal and Rohlf 1995). Data were analyzed
for main effects of each factor and interactions of each factor combination with univariate
repeated measures analysis using the mixed linear model procedure (PROC MIXED) in
SAS (SAS Institute 1997). A signiﬁcant time effect would result in the rejection of the
null hypothesis (Ho: time was not a significant factor when comparing trap types,
attractant lures, or any of their combinations). Least-squares mean comparisons of
marginal main effects and simple effects were conducted using Student’s t -test (Sokal
and Rohlf 1995) (DIFF option in LSMEAN S statement). A signiﬁcant marginal or main
effect would result in rejection of the null hypothesis (H0: each trap type and attractant

lure alone and in combination at each sample date was not significantly diﬂkrent than 0).

66

Results

Total Trap Catch

Mean number of plum curculio captured in both circle and pyramid traps, averaged
across attractant lures, was signiﬁcantly different than 0 (Wald )8 test, on = 0.05).
However there was not a signiﬁcant trap type main effect (Table 3.1). In other words,
mean number of plum curculio captured in circle traps, averaged across attractant lures,
was not different than those captured in pyramid traps (Figure 3.2). However, there was
a signiﬁcant main effect of attractant lure (Table 3.1) meaning that there were signiﬁcant

Table 3.1. Total trap catch x2 test of likelihood main effects for trap
type and attractant lure, and their interaction (on = 0.05).

 

Source Df I12 P-value
Trap type 1 0.001 0.9888
Attractant lure 3 29.152 < 0.0001
Trap type*volatile interaction 3 2.249 0.5469

 

differences between the four levels of attractant lures. Figure 3.2 shows that when
averaged across trap type, the mean number of plum curculio captured in traps baited
with plum essence + pheromone was signiﬁcantly different than all other attractant lures.
Traps baited with plum essence alone and pheromone alone were not signiﬁcantly
different from each other but each were signiﬁcantly different than the nonbaited traps.
There was not a signiﬁcant interaction between trap type and attractant lure (Table 3.1);

therefore, these two factors independently determine the mean number of total plum

67

 

 

 

 

 

 

a. Trap type
2
h I.”
0 V’ 1.5
._ H
g g
:l
a g 1
C 0
8 E
E 2 0.5
O.
o @—
Circle trap Pyramid trap
b. Attractant lure
2.5
a
2 1 ’
~_ m
o w
u. -H
3 «3 1.51
E a
E ‘5
C 0
8 E 1 .
s 3 ‘
a.
0.5 <
0 .70 7 7 7 7

 

Plum essence +
Pheromone

Plum essence alone

Figure 3.2. Mean number of plum curculio for (a) trap type and (b) attractant lure.
Means, within attractant factor, with the same letter are not signiﬁcantly different

(Wald x 2 test, a = 0.05).

68

 

Pheromone alone

 

 

 

curculio captured. That is, there is not a synergistic effect between trap type attractant
lure, therefore effects are additive.

Mean comparisons Of simple effects for trap type by attractant lures are reported
in Figure 3.3. Mean number of plum curculio captured for each trap type by attractant
lure combination was different than 0 (Wald )8 test, a = 0.05). For circle traps, plum
essence + pheromone were different from pheromone alone and none (P 2 0.05) but not
plum essence alone. Plum essence alone and pheromone alone were not signiﬁcantly
different than each other and, of these two lures, only plum essence was signiﬁcantly
different than no lure at all. For pyramid traps, plum essence was signiﬁcantly different
than no lure only. Plum essence alone and pheromone alone were not signiﬁcantly
different than each other and, of these two lures, only pheromone was signiﬁcantly
different than no lure. Circle and pyramid traps with the same lure treatment were not

signiﬁcantly different from each other (Wald )6 test, on = 0.05).

Synergy analysis

Results of the test for additive or synergistic effects of plum essence and
pheromone when summed over trap type and for each trap type are reported in Table 3.2.
For all three groups, there was not a signiﬁcant interaction between plum essence and
pheromone; therefore, the addition of plum essence to pheromone, regardless of trap
type, was purely additive and not synergistic. For data summed over trap type and
pyramid trap data, there was a signiﬁcant main effect (P S 0.01) for both plum essence
and pheromone. In other words, each attractant lure contributed to beetles captured when
data were averaged across trap type and for trap type data. However, in circle traps, there

was a signiﬁcant main effect for plum essence but not pheromone. Therefore there was

69

a. Circle trap

 

 

   

 

 

 

   

2.5
8 a
g 2 - ab
3 7
2
:l
0 1.5 —
E
E c
Q
‘6 1 <
h
0
.D
E
2 0.5—
C
N
a
E

o 0
Plum essence + Plum essence Pheromone none
pheromone
b. Pyramid trap

2.5
3,4 a
*3 2
:3, ab 3
h
3
0 1.5
E
a b
‘-
o 1
h
0
A
S
: 0.5 <
C
N
O
E

o .

Plum essence + Plum essence Pheromone none
pheromone

Attractant Lure

Figure 3.3. Mean number of plum curculio for (a) circle traps and (b) pyramid traps
simple effects of total trap catch analysis for trap type x attract lure interaction for.
Means for attractant lures, within each trap type, with the same letter are not
signiﬁcantly different (Wald x 2 test, or = 0.05).

 

no signiﬁcant difference (P = 0.1973) between the total number of plum curculio
captured in pheromone baited or nonbaited circle traps when averaged across plum
essence presence; however, traps baited with plum essence were signiﬁcantly different

from nonbaited traps when averaged across pheromone presence.

Table 3.2. Synergy l'I2 test of likelihood analysis of main effects for
plum essence, pheromone, and their interaction for all traps
combined, pyramid traps only, and circle traps only (or = 0.05).

 

Source DF ['12 P-value
Summed over trap type
PE 1 19.8636 0.0001
PH 1 9.0964 0.0026
PE+PH 1 0.3011 0.5832
Pyramid traps
PE 1 6.51 0.0107
PH 1 8.75 0.0031
PE+PH 1 0.22 0.6376
Circle traps
PE 1 14.12 0.0002
PH 1 1.66 0.1973
PE+PH l 0.04 0.8389

 

Repeated Measures Analysis

Main effects for the repeated measures analysis are reported in Table 3.3. There
were no signiﬁcant differences between neither trap types when averaged across
attractant lure and the 8 levels of time (P = 0.8386) nor attractant lures when averaged
across trap type and the 8 levels of time (P = 0.2003). Beetle capture on a particular day,
when averaged across trap type and attractant lure, had a signiﬁcant main effect. In other

words, plum curculio capture varies over time. Figure 3.4 is a graph of the mean number

71

of plum curculio captured over time. Mean number of plum curculio averaged over trap

type and attractant lure for days 1 and 40 aﬁer trap deployment were not signiﬁcantly

different from 0 (Student’s t test, on = 0.05). The mean number of plum curculio captured

on day 5, 12, and 46 were signiﬁcantly different from all other days. On day 5 after tap

deployment, apple trees were at approximately 50% bloom and were at fruit set by day

12.

Table 3.3. Repeated measures univariate AN OVA analysis of main
effects for trap type, attractant lure, time, and two and three component

interactions (or = 0.05).

 

Source df F value P-value
Trap type 1 0.04 0.8386
Attractant lure 3 1.69 0.2003
Time 7 8.77 < 0.0001
Trap type * time 7 2.18 0.0382
Attractant lure * time 21 0.89 0.5978
Trap type * attractant lure "' time 24 0.97 0.5144

 

The trap type by time interaction was signiﬁcant (P = 0.03), however there was not a

signiﬁcant interaction between attractant lure and time (P = 0.5978). In other words, trap

type and time, when averaged across attractant lures, do not independently determine the

number of plum curculio captured; thereby making trap type differences more

pronounced during speciﬁc sample dates. Figure 3.5 presents the mean number of plum

curculio captured in each trap averaged over attractant lure over time. Beetle capture in

both circle and pyramid traps were signiﬁcantly different than 0 on days 5, 15, and 56 d

after trap deployment (Student’s t test, or = 0.05). Trends in catch were different for the

two trap types which was expected since the main effect established that trap type and

72

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73

a. Trend in plum curculio caught over time

3.5 #— —-- ._ 777 __7 7
I- l

i —0— Circle I 1

 

j *1“. Pyramid‘ ’

___ 7 ._____J

 

Mean number of plum curcullo

 

 

 

0 10 2O 30 4O 50

 

b. Mean comparisons within date

 

3'51 — 00—; 00 77777 -0 77...- 7 77 7

1 j oCircle l
1

Mean number of plum curculio t SE

 

Days after trap deployment

Figure 3.5. Mean number of plum curculio captured over time for circle and pyramid
traps summed over attractant lure. (a) Trends of means over time for each trap type.

Asterisk (*) denotes a signiﬁcant main effect for nap type (univariate AN OVA F test,
a = 0.05). (b) Mean comparisons of trap type for dates with signiﬁcant rmin effects.

Means within each date with the same letter are not signiﬁcantly different (t test, a =
0.05).

74

time do not independently determine the number of plum curculio captured. Day 12 was
the only day when the circle trap outperformed the pyramid trap. Figure 3.6 presents the
mean number of plum curculio captured with each attractant lure averaged over trap type
over time. All the mean number of beetles captured on days 19, 33, and 40 d after trap
deployment were not different than 0 (Student’s t test, a = 0.05). Here, time and
attractant lure independently determine the number of plum curculio captured.
Therefore, the trend in trap catch with lures was similar although their magnitudes
differed. Nonetheless, there were marginal within date effects for 5, 12, and 19 d after
trap deployment. On each day, plum essence + pheromone was signiﬁcantly different
than no lure (P S 0.04). Yet this effect was not observed for neither plum essence alone
nor pheromone alone. Also, neither plum essence alone nor pheromone alone were
different than no lure (P 2 0.05).

Table 3.3 reports that the trap type by attractant lure by time main effect was not
signiﬁcant; therefore, when combined, each factor independently determines the number
of plum curculio captured. In other words, no one trap type and attractant lure
combination outperforms another combination due to a time effect; nonetheless, this does
not exclude the potential for signiﬁcant differences between trap type and attractant lure
within a sample date. Trends of each trap type and attractant lure combination and within
date mean comparisons are graphically depicted for over time for circle traps alone
(Figure 3.7), pyramid traps alone (Figure 3.8), and both traps (Figure 3.9). For circle
traps alone (Figure 3.7), the mean number of plum curculio captured was not
signiﬁcantly different from 0 on day 33 and 53 after trap deployment for any attractant

lure and circle trap combination (Student’s t test, or = 0.05). Days 5 and 19 after trap

75

3. Trend In plum curculio caught overtime

 

 

 

 

 

 

 

 

3.5 1—— “ - —— —1
1 .F PE + PH “1 1
3 1 1 -—t— PE alone 1 1
g 1 —— PH alone 1
3
2 2.5 14% none 1 1
3 1
E l
3
a 2 1 1
E - =1: * at: 1
a 1 1
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§ 1 ' . I
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1 ..................... - ./_. , 1
i 0*- """ - 7» - , .0 7 j ........... ~ x" .. e
0 '7_ 7 .777, 7 77 ._.7 77’“. _:_7;'ﬁ_-_7*:7I‘..7 7 7 77~71
1t 5 1o 15 20 25 30 35 4o 45 50 515
01 _ _____~__0-5
b. Mean comparisons within date
3.5 1 77,1
' 1 . PE + PH 7 1
m 3 1 1 . PE alone 1 1
to . . 1
H 1 1 . PH alone 1 1
0 1 .
= 2.5 1 - none '
g 1 17 77 1 1
3 1 1
s 2 1
a 1 1
“O- 1 5 1 f a 1
I. - 1 .
g 1 1 a 1
g 1 l ab 1
c 1 1 f
C ,
:8 lab 1 1
0'5 1 lab 1 ab ia E 1 1
1 -.- 5” Eb t a 1‘. . i 1
o -~~J‘F———— 7 777 ~—~1————:g— —-.—————. 77177 L— -_. 77773.71
1) 5 10 15 20 25 30 35 4o 45 50 515
-0 5 1 ._ ._-—-.__ 777-7 7 _. .7 .77 7. 7771

 

Days after trap deployment

Figure 3.6. Mean number of plum curculio captured over time for attractant lures
summed over trap type. (a) Trends of means over time for each trap type. Asterisk (*)
denotes a signiﬁcant main effect for attractant lure (univariate AN OVA F test, on =
0.05). (b) Mean comparisons of attractant lure for dates with signiﬁcant main effects.

Means within each date with the same letter are not signiﬁcantly different (t test, on =
0.05).

76

deployment were the only with within date differences. On these days, circle traps baited
with plum essence + pheromone were signiﬁcantly different from nonbaited circle traps.
NO other differences were found within each day. For pyramid traps alone (Figure 3.8),
the mean number of plum curculio captured was not signiﬁcantly different from 0 on day
19 and 33 for any attractant lure and pyramid trap combination (Student’s t test,

a = 0.05). Days 12 and 53 were the only with within date differences. On day 12,
pyramid traps baited with plum essence alone were signiﬁcantly different than nonbaited
pyramid traps. No other differences were found on this day. On day 53, pyramid traps
baited with pheromone alone were signiﬁcantly different than nonbaited pyramid traps
and no other differences were found.

For all trap and attractant combinations (Figure 3.9), the mean number of plum
curculio captured for each attractant lure and trap type combination 33 and 40 d after trap
deployment was not signiﬁcantly different from 0 (Student’s t test, or = 0.05). Days 5,
12, 19, and 53 contained signiﬁcant within date main effects in which there were
signiﬁcant differences between attractant lure and trap type combinations. Within trap
type differences between attractant lure and trap type combinations were reported above.
Attractant lure and trap type combinations with differences between trap type are not
reported above. On day 12, all circle trap and attractant lure combination captured more
beetles than nonbaited pyramid traps. Also on this day, circle traps baited with plum
essence + pheromone captured signiﬁcantly more beetles than pyramid traps baited with
plum essence + pheromone and pheromone alone. On day 53, pyramid traps baited with
plum essence + pheromone captured more beetles than circle traps baited with plum

essence + pheromone.

77

a. Trend in plum curculio caught over time

 

 

 

 

 

 

 

 

 

 

 

 

3.5 -
* 1:— Circle PE + P171
3 o 3|:
1 7.7 Circle PE alone
% 1 ~ 0— Circle PH alone.
‘5’ 2'5 ' 1 31-:----Circle none _1
u , , ——-—-——
e 1 1
2 2 1 . 1
2'
g 1 , e
3 1.5 1 .’
5 11 '
O 1 "A
E 1 e A 11
.1 " _7___1_ , F . 7 0 7 4‘21" ‘ , L1
1 5 1o 15 20 25 30 35 4o 45 so 515
1
-o.5 L —
b. Mean comparisons within date
3.5 ~—-- — . 777 777 7777 -— 0
1 . 0. 1
1 0 Circle PE + PH 1
3‘, 31 1 1 .CirclePEelone 1
+1 1 n Circle PH alone 1 1
-.‘_-? 2.5 1. 1 . 1
g 1 1—. Circle none “—1 1
a 1
g 2 1 1
a 1 1 1
E 1 5 1‘ 13 1 1
8 1 , 1
g 1 1 1"" 7 ‘ 1
C i r 1 1
s 1 * ta 1 1
E 1 .
0.5 1.
r ab 1
1 1 - g l 1
011— . . +52 . 7,7 +1
1 5 1o 15 2o 25 30 35 4o 45 so 515
o 5 1777777 77 77 7 7 1

 

Dasys after trap deployment

Figure 3.7. Mean number of plum curculio captured in circle traps over time for trap
type x attractant lures combination (a) Trends of meam over time for each trap type x
attractant lure combination. Asterisk C“) denotes a signiﬁcant main effect for trap type

x attractant lure (univariate AN OVA F test, on = 0.05 ). (b) Mean comparisons of trap
type x attractant lure for dates with signiﬁcant main effects. Meats within each date

with the same letter are not signiﬁcantly different (t test, on = 0.05 ).

78

a. Trend in plum curculio caught over time

 

 

 

 

 

3.5 1 1
3 1' -.— Pyramid PE + PH 1
1 1 —-~-— Pyramid PE alone 1
0
§ 15 1 1 ~- 1+~Pyramid PH alone 1
3 : L;Z;QET“MT__ 1
e 1 1
2 —.
a.
.. , * * 1
O - 1
3 A
a 1.5 1
E I
3
C
5 1
O
a 1
0.5 ~ ' g ...a,“ .- ._ -_e ‘
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1111 l/ _ __ﬁt—Q- _- __ __g V ...-.375- 1“..Ic..'..-:'. I
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o 5 1o 15 20 25 30 35 4o 45 50 55
-o.5 ——- ~-~—————— — —~

 

 

b. Mean comparisons within date

 

 

 

 

 

 

 

 

 

 

35 ——-—Ar~+-* ~~ w~ h.“‘ —~1
F . Pyramid PE + PH 1 1
:3 3 4 1 I Pyramid PE alone 1
+1 1 ' o Pyramid PH alone
.54: 2.5 « 1 1
a 1 v. Pyramid none 1
0 * .
I-
3
0 2 .l
E 1
.3. 1 1
Q
“5 1.5 1 1 - 1a 1
I... T a I 1
i l 1
a 1 1
c 1 1
c .-
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. - # 1 i ml
17 1 ah i T i L I ab1
err———~——-"«— r~—-ie—~——-~—1~—1- r -—~-—-ﬁ—~:+1
T 5 10 15 20 25 30 35 40 45 50 5'5
1
o 5 — ---— -— —— —~ —- -—— ~—~ —1
Days after trap deployment

Figure 3.8. Mean number of plum curculio captured in pyramid traps over time for trap
type x attractant lures combination (a) Trends of means over time for each trap type x
attractant lure combimtion Asterisk (*) denotes a signiﬁcant main effect for trap type

x attractant lure (univariate AN OVA F test, or = 0.05 ). (b) Mean comparisons of trap
type x attractant line for dates with signiﬁcant main effects. Means within each date

with the same letter are not signiﬁcamly different (t test, a = 0.05 ).

79

a. Trend ln plum curculio caught over time

3.5 1 ——<—-
* ,

 

 

 

 

 

 

 

 

 

 

 

 

1
* * .—-—-- _ 1 alt 1
3 1 . 1 Am- clrole PE + PH . 1
o i 1 0— Pyramld PE + PH
'5 .— Circle PE alone 1
g 2.5 1 1 . 1
a ----- Pyramld PE alone
5 1 - 1 ---o~--Circle PHelone 1
3. 2 a 1 1 1 -- »- —~ Pyramid PH alone 1
”II . .
2 ~——- Circle none 1 1
1 e
g 1.51   , Pyramldnone ‘ ‘ 1
3 ‘ e 1
c 3’ ‘\
5 1 l x ‘ l
0 I: ‘.
s I; A ‘\ 1
0.5 4 ’ . )1 — “4‘13; . 1
0 ‘ r::- 1 '1‘":1:71;;Bnuf::r‘z‘~;.--,-’__ I “‘—£”’ 7 r 1‘; J
20 25 30 35 4o 45 50 5%
-o.5 l
b. Mean comparisons within date
3 5 7w ——— ~— —-— __e,__, *— #_ —— —-~7—-~1 ﬁﬁw ___, in.
1 1
31 13 1 oCirclePE+PH 1 1
:3 , 1 - Pyramid PE + PH 1 1
‘0‘ 251 1 ACirclePEalone 1 1
§ I 1 -r Pyramid PE alone 1 1
E 2 1 0 Circle PH alone 1 i
E 1 . t Pyramid PH alone 1 1
5 l .
'6. ' r | Circle none 1 g l
'6 1-5 1 3' ~ 1 UP ramid none ' A. la 1
. | 1 ab 1 ' V 1 .. " 1
‘2 ' n. t 1
g 1 1 tag 1
- a A r .
s l I i la l 1
o '0' a I v
0.5 . e 1 T . ' '
l _ 1 i ’- 1 EB
oteeveesamwa_hae *muwmm
1 5 10 ‘ 15 20 25 30 L 35 4‘0 45 50 ‘ 515
.05 L ___—___ .____~o __ %__l
Days after trap deployment

Figure 3.9. Mean number of plum curculio captured over time for trap type x attractant
lures combination. (a) Trends of means over time for each trap type x attractant lure
combimtion. Asterisk (*) denotes a signiﬁcant main eﬂéct lbr trap type x attractant

lure (univariate ANOVA F test, a = 0.05). (b) Mean comparisom of trap type x
attractant lure tbr dates with signiﬁcant main effects. Means within each date with the

same letter are not signiﬁcamly different (t test, a = 0.05 ).

80

Discussion

This is the ﬁrst study to report a host plant volatile enhancement for plum curculio
traps baited with grandisoic acid. This study was also the ﬁrst ﬁeld experiment with
pheromone and host plant volatiles for trapping plum curculio. Most notably, this study
provides insight into the role of pheromone and host plant volatiles over time and their
association with trap design.

Circle traps baited with pheromone alone were not different from nonbaited circle
traps whereas plum essence + pheromone and plum essence alone both increased trap
catch signiﬁcantly. J affe et al. (1993) reported that American palm weevil pheromone,
rynchophorol, has an anemotactic action at a distance from the point source and host
plant volatiles elicit responses in close range situations. This suggests that if host plant
volatiles and pheromone attract beetles at short and long ranges, respectively, circle traps
perform better in short range situation. Pyramid traps, on the other hand, may be better at
attracting beetles undergoing long range movement since pyramid traps baited with plum
essence was the only combination that signiﬁcantly increased trap catch over nonbaited
pyramid traps. This suggests that inner canopy structure and inner canopy beetle
behavior associated with circle trap capture differs from that associated with pyramid
traps.

Prokopy and Wright (1997a) reported that a majority of beetles arrive at pyramid
traps by crawling onto them, therefore curculio were more than a meter away when they
begin to orient to the pyramid traps. Both 1997 (Chapter 2) and 1998 research resulted in
differences between mean number of plum curculio captured in pheromone baited

pyramid traps and nonbaited pyramid traps (Figure 2.5 and Figure 3.3). Pheromone

81

presence therefore may enhance plum curculio orientation and movement toward
pyramid traps before they begin to crawl onto the trap. Circle traps baited with
pheromone alone may draw curculio into the tree but were not more attractive than
nonbaited circle traps. Circle traps baited with plum essence attract just as many curculio
as plum essence + pheromone, however the combination of attractants was quantitatively
higher.

Although plum essence and pheromone were not synergistic, there was deﬁnitely a
host plant volatile additive enhancement of pheromone for both pyramid and circle traps.
Plum essence + pheromone baited traps caught the highest number of curculio and were
statistically different from nonbaited traps (Figure 3.3). Landolt (1997) reports that of 20
Curculionid species with male-produced aggregation pheromone, not including plum
curculio, 10 have been shown to have a pheromone/ plant volatile enhancement (Table
3.4). Statistically signiﬁcant synergism between pheromone and host plant volatiles was
not was not observed for any of these species listed with plant/ pheromone enhancement
(Booth et al. 1983, Dickens 1986, Fontaine and Foltz 1982, Giblin-Davis et al. 1994,
Hallet et al. 1193, Rochat et al. 1991, Weissling et al. 1993). Rochat et al . (2000)
reported synergist effect in the attraction of American palm weevil, Rhynchophorus
(Armstrong 1958, Garman and Zappe 1929, Paradis 1956) of which 15 to 20 d were
apportioned to pupation (Stedman 1904, Garrnan and Zappe 1929). Therefore, the
second capture peak appears to be capture of the partial summer generation aﬁer
emergence. On day 46 after trap deployment both trap type and attractant combinations
were signiﬁcantly different from O (Wald )8 test, a = 0.05). The observation of this trend

will be a vital piece of information necessary to optimize insecticide spray for

82

 

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83

control of plum curculio. This will be a key improvement in a pest management ability
to detect plum curculio migration into Michigan orchards.

Fruit set occurred around day 12 after trap deployment, after which plum curculio
immediately begin to oviposit and feed on fruit (Armstrong 195 8, Paradis 1956). Also at
this time, hexane washes of all plant structures are more attractive to plum curculio than
any other structures at any other time. This was the only day when circle traps
outperform pyramid traps and there were no differences between lure type in circle traps.
On this same day, there was no difference between attractant lures in circle traps (Figure
3.7). Therefore; I hypothesize that at petal fall and fruit set, circle traps were capturing
curculio based on random scaffold branch movement not in response to a particular
attractant lure due to the overwhelming olfactory cue of the host and the physiological
state of plum curculio.

The three days of the ﬁrst peak in plum curculio capture - day 5, 12, 19 after trap
deployment (Figure 3.8) will be crucial for evaluating the reliability of a monitoring
strategy as an insecticide timing tool. On each day, circle traps baited with plum essence
+ pheromone caught the highest average number of curculio for all trap type by attractant
combination. On day 12, which corresponds to fruit set and the commencement of plum
curculio injury to the fruit, the average number of plum curculio was 2.99 and was 2.22
times greater than the next closest mean of 1.34 for plum essence baited pyramid traps.
This greater trap catch efﬁciency during the crucial decision window may greatly
inﬂuence the pest manager’s conﬁdence in timing plum curculio sprays in commercial
plots. Therefore, efﬁcient plum curculio capture at and just before petal fall could be the

fundamental criterion for predicting damage. More research needs to be focussed on this

84

period of time to correlate trap catch with damage. This correlation information could
then be used to establish an economic injury level or action threshold for plum curculio
control in Michigan orchards.

With these experiments, importance of trap type and attractant combinations for
developing a monitoring tool has been demonstrated. I feel that this was a signiﬁcant
step toward developing a monitoring strategy suitable for decision making in IPM
programs targeting plum curculio. More research is needed to determine how plum

curculio capture in circle traps relates to general activity in the orchard and the onset and

magnitude of fruit injury.

85

APPENDIX I

86

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.: 2901-06

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

Trap designs and attractants for monitoring plum curculio. Conotrachelus nenuphar Herbst.

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

Entomology Museum. Michigan State University (MSU)

Other Museums:

Investigators Name(s) (typed)
Andrea B. Coombs

 

 

 

Date: to May 2001

'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.

87

Appendix 1.1

Voucher Specimen Data

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88

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89

 

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