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PROTECTION OF ORGANIC CUCUMBER PRODUCTION
AGAINST STRIPED CUCUMBER BEETLES USING TRAP CROPS

MS.

presented by

Vianney O M. Willot

has been accepted towards fulfillment
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PROTECTION OF ORGANIC CUCUMBER PRODUCTION AGAINST STRIPED
CUCUMBER BEETLES USING TRAP CROPS

By

Vianney O M. Willot

A THESIS

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

MASTER OF SCIENCE
Entomology

2010

ABSTRACT

PROTECTION OF ORGANIC CUCUMBER PRODUCTION AGAINST STRIPED
CUCUMBER BEETLES USING TRAP CROPS

By

Vianney O M. Willot

Striped cucumber beetles, Accalymma vittatum F. (Coleoptera: Chrysomelidae),
are major pests of cucumber production in the North Eastern United States. The use of
perimeter trap crops is an important striped cucumber beetle management tactic that has
been used successfully in conventional cucumber production when insecticides are
applied to the trap crop but has been less successfully applied in organic pest
management. I assessed the potential of four winter squash varieties: blue hubbard
(Cucurbita maxima Duchesne), burgess buttercup (Cucurbita maxima Duchesne),
waltham butternut (Cucurbita. moschata Duchesne), table queen acorn (Cucurbita
moschata Bailey) to be used as trap crops under green house and field conditions. Results
showed burgess buttercup and blue hubbard are the most attractive varieties. Burgess
buttercup has an advantage under low beetle population because of its good
marketability. I also assessed the potential of the trap crop combination, blue hubbard
(Cucurbita maxima Duchesne) with waltham butternut (Cucurbita moschata Poir),
compared to each cultivar alone. Furthermore, I assessed the potential of Pyganic® (an
OMRI approved insecticide) and insect vacuums to control cucumber beetles on trap
crops. Results showed that blue hubbard combined with waltham butternut were as
efficient as blue hubbard alone in attracting beetles. The experiments also demonstrated

the importance of flowers in the attractiveness of the trap crops.

ACKNOWLEDGEMENTS

I would like to thank Dr. Michael Brewer for initiating my research project and
for his continuing help and support. I thank Dr. Matt Grieshop for the help and advice
given in writing this thesis. Merci to Dr. Mathieu Ngouajio, my outside discipline
committee member, for his advice and support. Thanks to Bill Chase and all the worker
of the horticulture farm for their help as well as the undergraduate students that assisted
me, particularly Jonathan Landis and Aristarque Djoko. Thanks to Dr. Ed Grafius for his
comments and help in preparing this thesis during his writing seminar. Thanks to Takuji
Noma for his help, support, assistance, advice and patience across two years of research.
Thanks a lot to Alicia Turcsanyi for the many hours that she spent reading this thesis,
correcting my grammar and supporting me. Thanks to all the entomology graduate
students that listened to me complaining about everything. Thanks to all the people in the
Integrated Pest Management lab and the Organic Pest Management lab, in particular:
Beth Bishop, Joy Landis, David Epstein, Paul Jenkins, Lynnae Jess, Tracy Aichele,
Andrea Buchholz, Krista Buehrer, Emily Pochubay and Ben Phillips. Thanks to the staff
in the Entomology business office for their help: Heather Lenartson-Kluge, Ballory
J arriell, Carolyn Lewis, Linda Gallagher, J an Eschbach, Brooke Gallagher, and Chrissi
Smith. Thanks to the numerous professors of the entomology department that assisted me
with coursework and Dr. Ian Dworkin for his help with data analysis. Thanks to my
family for their support and for always being there for me despite the presence of the
Atlantic between us. I dedicate this work to both my grandfathers, although they are not

here to see it.

iii

TABLE OF CONTENTS

 

 

 

LIST OF FIGURES -- - - - _ - VI
CHAPTER 1 _ -- - - - - -- - -- ....... 1
LITERATURE REVIEW -- -- -- -- -- -- - - 1
VEGETABLE PRODUCTION IN THE UNITED STATES AND MICHIGAN .................................. 1
THE CUCUMBER BEETLE COMPLEX .................................................................................. 2
PEST MANAGEMENT ......................................................................................................... 4
PERIMETER TRAP CROPS .................................................................................................. 7
OBJECTIVES .................................................................................................................... 11
CHAPTER 2 - _- ...... - _ l3

 

ATTRACTIVENESS AND TRAP CROP POTENTIAL OF FOUR VARIETIES OF
WINTER SQUASH TO STRIPED CUCUMBER BEETLES (COLEOPTERA:

 

CHRYSOMELIDAE) - _- ..... - -- -- -- - 13
ABSTRACT: ..................................................................................................................... 13
INTRODUCTION ............................................................................................................... I 4
MATERIALS AND METHODS ............................................................................................ I7
Greenhouse Experiment: ........................................................................................... 1 7
Field experiment: ....................................................................................................... 19
RESULTS ......................................................................................................................... 21
Greenhouse experiment: ............................................................................................ 21
Field experiment: ....................................................................................................... 21
DISCUSSION .................................................................................................................... 27

CHAPTER 3- -- ..... - _ - -- - - - -- _- 35

 

POTENTIAL OF WINTER SQUASH VARIETAL MIXTURES TO IMPROVE
STRIPED CUCUMBER BEETLE TRAP CROP PERFORMANCE IN ORGANIC

 

 

CUCUMBER PRODUCTION ......... -- - - - - - - - -- 35
ABSTRACT: ..................................................................................................................... 35
INTRODUCTION ............................................................................................................... 36
MATERIALS AND METHODS ........................................................................................... 40

2007 Field experiment: .............................................................................................. 40
2009 Field Experiment: ............................................................................................. 41
RESULTS ......................................................................................................................... 43
2007 Field experiment: .............................................................................................. 43
2009 experiment: ....................................................................................................... 44
DISCUSSION .................................................................................................................... 45

CHAPTER 4- -- - - .......... - - -- 57

PERIMETER TRAP CROPS FOR STRIPED CUCUMBER BEETLES:

CONCLUSIONS AND FUTURE RESEARCH - -- - . -- 57

 

iv

SYNTHESIS ..................................................................................................................... 57

 

FUTURE RESEARCH ......................................................................................................... 60
APPENDIX 1.1 -__ 62
REFERENCES CITED - H - - 64

 

LIST OF FIGURES

Figure 2.1: Mean percentage of striped cucumber beetles (iSEM) found on trap crops
versus cucumbers. Bars with different letters are significantly different (Tukey’s
honest significant difference test alpha = 0.05). -- - -- - -- -- - 31

 

Figure 2.2: Average number of striped cucumber beetles (iSEM) observed on trap
crops, across all observation dates for the 26 day transplants a) on trap crop variety
and cucumber pairs b) on trap crop flowers or leaves, fruits and stems. Numbers
above bars represent the ratio of beetles on flowers to leaves and stems. Bars with
different letters are significantly different (Tukey’ s honest significant difference
alpha=0. 05). - -- - - -- - _ - -- - - -- - 32

 

Figure 2.3: Average number of striped cucumber beetles (:tSEM) observed on trap crops,
across all observation dates for the 16 day transplants a) on trap crop variety and
cucumber pairs b) on trap crop flowers or leaves, fruits and stems. Numbers above
bars represent the ratio of beetles on flowers to leaves and stems. Bars with different
letters are significantly different (Tukey’ s honest significant difference alpha=0. 05).

_ __ -_ - _ - 33

 

Figure 2.4: Average number of striped cucumber beetles observed on burgess buttercup
flowers or leaves, stems, and fruits (iSEM) using (a) 26 day Old or (b) 16 day Old
transplants. - - - -- - - - - -- - - -- 34

 

Figure 3.1: Average number of striped cucumber beetles (iSEM) observed on trap crops
across all observation dates for the 2009 experiment. a) On flowers. b) On flowers
and leaves, stems and fi'uits. Numbers above bars represent the ratio of beetles on
flowers to leaves and stems. Bars with different letters are significantly different
(Tukey’s honest significant difference alpha=0.05). - 51

 

Figure 3. 2: Average percentage plant mortality (:I:SEM) on July 17th and August 25‘“.
Bars with different letters are gnificantlysi different (Tukey’ s honest significant
difference alpha=0. 05).... .......... - .............. 52

 

Figure 3.3: Average number of striped cucumber beetles by treatment at each sample
date for the 2007 experiment. The black and dotted arrows indicate dates of vacuum
and Pyganic® applications, respectively. .......... - 53

 

Figure 3.4: Average sum (is EM) of striped cucumber beetles on flowers or leaves stems
and fi'uits for each sample date between June 15 and July 17 for the 2009
experiment. a) blue hubbard alone, b) blue hubbard + waltham butternut, c) waltham
butternut alone, (1) cucumber alone. - - -- - .............. -- - 54

 

vi

Figure 3.5: Ratio of striped cucumber beetles found on blue hubbard to total beetles
found in the blue hubbard + waltham butternut, blue hubbard + waltham butternut +
vacuum, and blue hubbard + waltham butternut + Pyganic® treatments in the 2007
experiment. Bars provide the ratio over seven sampling periods. Bars with different
letters are significantly different (T test alpha = 0.05). 55

 

Figure 3.6 Ratio of striped cucumber beetles found on blue hubbard to total striped
cucumber beetles observed in the blue hubbard + waltham butternut plots in the 2009
experiment. Bars provide the ratio over eight sampling periods. Bars with different
letters are significantly different (T Test alpha = 0.05). - -- 56

 

vii

CHAPTER 1

Literature review

Vegetable production in the United States and Michigan

The United States (USA) is the third largest vegetable producer worldwide afier
China and India (USDA 2008b). In 2008, the top five vegetable crops in the USA were
potato, tomato, lettuce, onion and carrots with 18.7, 11.5, 5.1, 3.6, and 1.6 million tons,
respectively (Jackson et al. 2005b, USDA 2008b). Cucumbers are also an important
vegetable crop with 2008 USA fresh and pickled cucumber production estimated at 0.9
million tons. Michigan vegetable production in 2007 was around 763,820 tons with a
value of $211 million and a crop surface of 110,100 acres (USDA 2008b). Pickling
cucumbers represented the largest single 2007 vegetable production crop in Michigan,
with 30,000 acres producing 156,350 tons of cucumbers, with a value of$35.961 million.
Fresh cucumber production was the fourth largest vegetable production in Michigan in
2007, with 11,700 acres producing 38,919 tons Of cucumbers, representing a value of
$15358 (USDA 2008b). Michigan’s fresh cucumber production is the fourth largest in
USA with 9.8% of national production. In 2008, 2,500 USA farms produced organic
vegetables on a surface of 130,436. acres, representing a value of $685 million (USDA
2008a). Michigan organic vegetable production represented a surface of 1,730 acres for a

value of $4.5 million (USDA 2008a).

Pest management is an important aspect of vegetable production. Vegetable fields
are a resource for insects, diseases and also a good environment for weeds. In 1990, pest
insects caused a loss of 4 to 21% of the farm-gate for USA vegetable production (Howard
at al. 1994). The farm-gate cost was estimated to be between 8 and 23% for diseases and
8 and 13% for weeds, respectively (Howard et al. 1994). In 1987, crop losses for USA
cucumber production, from insects and disease was estimated at 15% and 21%,
respectively (Howard et al. 1994). Several diseases attack cucurbits crops such as:
Angular leaf spot (Pseudomonas syringae pv. Lachrymans Smith & Bryan), bacterial wilt
(Erwinia tracheiphila Smith), Anthracnose (Colletotrichum orbiculare Berk. & Mont),
powdery mildew (Erysiphe cichoracearum DC), and cucumber mosaic virus (Howard et
al. 1994, Swiader and Ware 2002). There are also several insect species that attack
cucurbits plants such as: squash bug (Anasa tristis De Geer), squash vine borer (Melittia
satyriniformis Hiibner), European earwing (F orficula auricularia L.), Melon aphid
(Aphis gossypii Glover), Seedcorn maggot (Delia platura Meigen), Tarnished plant bug
(Lygus lineolaris Palisot de Beauvois), and the cucumber beetle complex (Howard et al.

1994, Burgio et al. 1997, Swiader and Ware 2002, Jackson et al. 2005a).

The Cucumber Beetle Complex

The cucumber beetle complex (Coleoptera: Chrysomelidae) makes up the
principal insect pests of cucurbits in the USA and consists of: the striped cucumber beetle
(A calymma vittatum F.), the spotted cucumber beetle (Diabrotica undecimpuctata

howardi Barber), and the banded cucumber beetle (Diabrotica balteat Leconte). In

2

Michigan and Southern central Canada, the striped cucumber beetle is considered the
most important of these Species. Crop losses from striped cucumber beetles were
estimated at 15% in Ontario Canada if no control methods were implemented (Howard et
a1. 1994). Adult striped cucumber beetles damage cucurbits by feeding on the flowers,
fruits, leaves, and stems while larvae feed on the roots. At the seedling stage, feeding by
adults can kill the plants. Older plants are more capable of tolerating defoliation. Brewer
et al. (1987) showed that zucchini attacked at the second and third-leaf stages compensate
for damage occurring before fruit production. When adult cucumber beetles feed on the
fruits they cause scars that limit the cucumber’s marketability. Furthermore, striped
cucumber beetles can transmit bacterial wilt (Erwinia tracheiphila Smith) when feeding
on the foliage (Brust and Rane 1995, Mitchell and Hanks 2009) and damaging the
flowers (Sasu et al. 2010). This disease kills the plants and currently no curatives are
available. Therefore, cucumber beetles must be maintained at very low levels in regions
where this pathogen occurs. In Michigan, bacterial wilt occurrence is sporadic, allowing
for higher tolerance of cucumber beetles and providing increased opportunities to manage
them with certified organic tactics.

In the North Central region of the USA, the striped cucumber beetle is usually
monovoltine. Adult beetles generally emerge from their overwintering Sites at the end of
May or beginning of June, and start to colonize the cucurbits fields when temperatures
exceed 12°C (Radin and Drummond 1994a). This often coincides with early growth of
cultivated cucurbits and can have a severe impact on the production, leading to reduced
stand or delayed plant maturation (Brewer et al. 1987, Ayyappath et al. 2002). The

female beetles lay their eggs at the base of the plants. The larva then feed exclusively on

3

the cucurbits roots, causing damage that reduces the development of the roots. Ellers-
Kirk et al (2000) showed that reducing the population of cucumber beetle larvae
increased the root length and density of cucumbers in organic and conventional systems.
The summer generation emerges at the end of July or beginning of August. They are
usually less damaging to crops, particularly cucumbers, because crops are often ready for

harvest prior to peak beetle emergence.

Pest Management

High consumer expectations/aesthetic criteria for vegetables make their
production challenging compared to field crops. This leads to a lower tolerance of pest
damage and makes the implementation of Integrated Pest Management (1PM) challenging
(Foster and Flood 2005). Conventional farmers rely principally on pesticides to achieve
economic levels of pest control. Physical control methods such as trapping, vacuuming,
flaming, and use of mulch are also useful methods, particularly for organic farmers
(Vincent et al. 2003). Cucumber farmers can also use conservation or augmentative
biological control (Fiedler et al. 2008). Cultural methods such as crop rotation, host plant
resistance, or cover crops are also important pest management tactics (Way and van
Emden 2000, Ngouajio and Mennan 2005). Integrated Pest Management emphasizes the
use biological, physical, and cultural methods to limit the use pesticides, especially those
that are harmful to both the environment and natural enemies. Conventional farmers have
a variety of chemical options to protect cucurbit crops against striped cucumber beetles.
Farmers are advised to use systemic soil insecticides before planting and foliar

insecticides after planting if striped cucumber beetles are present (Howard et al. 1994,

4

Swiader and Ware 2002). Active substances available in cucumber production are
Carbaryl, Pennethrin, or Bifenthrin (Foster and Brust 1995, Brust et al. 1996, Zehnder et
al. 1997, Maclntyre-Allen et al. 2001, J asinski et al. 2009, Bird et al. 2010). Farmers also
have access to efficient physical methods against striped cucumber beetles. The physical
method commonly use in cucurbit productions against cucumber beetles are traps, mulch,
and row covers (Barrett et al. 1971a, Hoffmann et al. 1996b, Ibarra et al. 2001, Jackson et
al. 2005b, Lam 2007, Cline et al. 2008). Traps are usually used to monitor cucumber
beetle populations in fields (Hoffmann et al. 1996b, Jackson et al. 2005b, Lam 2007,

Cline et al. 2008).

In organic production, pesticide use is limited due to a paucity of organic OMRI
certified products available The list of the product available for organic farmers is
available on the Organic Materials Review Insititute (OMRI )web site (OMRI Institut
2010). Available OMRI approved insecticides include: natural pyrethrums, neem oil,
Citrus oil, kaolin film, garlic oil, hot pepper oil, and Bacillus thuringiensis. Organic
pesticides are also typically much less efficient than conventional pesticides in
controlling striped cucumber beetle (Karagounis et al. 2006, Cross et al. 2007, Kamminga
et al. 2009) and there is abundant literature showing the variable efficacy of organic
insecticides on pests (Abdel-Moniem et al. 2004, Barry et al. 2005, Glenn and Puterka
2005, Karagounis et al. 2006, Cross et al. 2007, Trdan et al. 2007, Cloyd et al. 2009,
Gomez Jimenez and Poveda 2009, Kamminga et al. 2009). Organic pesticides also have
shorter residual than conventional and thus require more frequent treatments compared to
their conventional counterparts (Karagounis et al. 2006, Miresmailli and Isman 2006,

Cross et al. 2007, Kamminga et al. 2009). The limited chemical tools available to
5

organic farmers makes the solid understanding of pest and plant biology and ecology
essential to economically viable organic pest management. Furthermore, a very low
recommended threshold makes striped cucumber beetle management a primary concern
for organic farmers (Brust and Foster 1999). Thus, organic farmers are forced to rely

more on biological, physical, and cultural pest management tactics.

Biological control tactics ranging from conservation to augmentation can be used
to manage striped cucumber beetles. A variety of research has been conducted on the
natural enemies of cucumber beetles and manipulation of the environment (Gould 1944,
Bach 1980, Dix et al. 1997, Platt et al. 1999, Ellers-Kirk et al. 2000, Snyder and Wise
2001, Cline et al. 2008). Gould (1944) observed that the parasite tachnid fly (Jiaetophleps
setosa, Coq) is the most efficient natural enemy Of striped cucumber beetles. Platt et al.
(1999) showed that using a border of buckwheat increases the presence of tachnid flies,
leatherwings and parasitic wasps while decreasing the presence of striped cucumber
beetles. Snyder and Wise (2001) Showed that lycosid spiders reduce the striped cucumber
beetle density at the beginning of the season and that carabids affect the squash bug
population by predation. They also Showed that the presence of these two predators
together reduced the effect of each one to control cucurbit pests suggesting the presence
of infra-guild predation. Ellers-Kirk et al. (2000) showed that when applied to the soil,
entomopathogenic nematodes had a significant impact on striped cucumber beetle
emergence, however nematodes are expensive and their efficacy varies greatly depending
on soil conditions (Kaya and Gaugler 1993). Dix et al. (1997) showed that the presence

of Shelter did not affect the presence of striped cucumber beetles.

Physical pest management tactics, such as plastic mulch and row covers (Vincent
et al. 2003) have also been employed against striped cucumber beetle with fair success,
especially in organic systems (Matthewsgehringer and Houghgoldstein 1988, Cline et al.
2008, Nair and N gouajio 2010). Row covers are expensive but this tactic may also
provide additional benefits beyond insect pest management such as increased humidity,
increased air temperature that lessen plant growth, and increased soil temperature that
lead to faster development. Ibarra et al. (2001) showed that the use of row covers and
plastic mulch increased Muskmelon yield. Vacuuming can also be used to remove adult
beetles (Kuepper and Thomas 2002). It has been used efficiently against Lygus bug in
organic strawben'ies and Colorado potato beetles (Leptinotarsa decemlineata) in organic

potato (Kuepper and Thomas 2002).

Cultural striped cucumber beetle management tactics are also available. Crop
rotation is commonly used by organic farmers because adults overwinter in and around
cucurbit fields (Russo and Kindiger 2007). Implementing perimeter trap cropping is also
an efficient cultural method to manage cucumber beetles when combined with
insecticides (Maclntyre-Allen et al. 2001, Boucher and Durgy 2004, Adler and Hazzard
2009, Cavanagh et al. 2009). However the perimeter trap cropping system has seen less
success in organic agriculture compared to conventional agriculture (Boucher and Durgy

2004, Hazzard and Cavanagh 2005, Adler and Hazzard 2009, Cavanagh et al. 2009).

Perimeter Trap Crops

Shelton and Badenes-Perez (2006) define trap crops as: “plant stands that are, per

se or via manipulation, deployed to attract, divert, intercept, and/or retain targeted insects
7

or the pathogens they vector in order to reduce damage to the main crop.” They further
differentiate two types of trap crops as: the dead-end trap crop and the conventional trap
crop. A dead-end trap crop refers to plants that are highly attractive to the pest but are not
a sustainable host for the development of offspring. An example is the use of Yellow
Rocketcress (Barbarea vulgaris var. arcuata Opiz ex J.& K. Presl) to protect cabbage
production against diarnondback moth, Plutella xylostella (Shelton and Nault 2004).

A conventional trap crop is a crop that is planted close to a high value crop to
attract pest and limit damage. Conventional trap crops are the more commonly used.
There are many examples of trap crop use in conventional production. For example, corn
and wheat are used as trap crops to divert cabbage seedpod weevil (Conoderus spp
Barber) in sweet-potatoes (Seal et al. 1992), squash is used in peanut production to
protect against Spotted cucmnber beetles (Barbercheck and Warrick 1997), alfalfa is used
in cotton production to protect against Lygus bugs (Lygus hesperus Knight) (Godfrey and
Leigh 1994), eggplant and squash are used in bean production to protect against sweet
potato whitefly (Bemisia argentrfolii Bellows & Perring) (Smith et al. 2000, Smith and
McSorley 2000), and winter squash are used in cucurbit production to protect against
striped cucumber beetles, and spotted cucumber beetle (Radin and Drummond 1994b,
Hoffinann et al. 1996a, Pair 1997, Boucher and Durgy 2004, Hazzard and Cavanagh
2005, Cavanagh 2008, Adler and Hazzard 2009, Cavanagh et al. 2009).

In cucurbit production, trap crops are usually implemented as perimeter trap crop.
A perimeter trap crop consists of series of rows of trap crops that surround a field of the
economic crop (Boucher and Durgy 2004, Hazzard and Cavanagh 2005, Cavanagh et al.

2009). The goal of this tactic is to contain the pest on the border of the field (Radin and

8

Drummond 1994b). Containment of the pest in the perimeter trap crop allows more
precise application of insecticides. The reported advantages of perimeter trap crops are
reduced damage to the main crop through the diversion of cucumber beetles, as well as
reduced insecticide use (Boucher and Durgy 2004, Adler and Hazzard 2009, Cavanagh et
al. 2009). Cavanagh et a1 (2009) showed that the use of perimeter trap crops can lead to a
94% reduction in insecticide use. However, trap crops alone typically do not provide
sufficient damage control when cucumber beetles occur in large numbers (Maclntyre—

Allen et al. 2001, Brewer et al. 2006).

In the case of striped cucumber beetles, winter squash cultivars are the most
commonly used perimeter trap crops. Some varieties of winter squash that are
particularly attractive to cucumber beetles include buttercup Cucurbita pepo Alef and
blue hubbard Cucurbita maxima Wall (Caldwell and Stockton 1998, Maclntyre-Allen et
al. 2001 , Bellows and Diver 2002, Boucher and Durgy 2004, Cavenagh 2008, Adler and
Hazzard 2009). The relative attractiveness of different cultivars has been attributed to the
presence of cucurbitacin, which has been identified as a phagostimulant and an arrestant
(Metcalf et al. 1980, Ferguson et al. 1983, Brust and Foster 1995, Schroder et al. 2001,
Martin et al. 2002, Smyth et al. 2002, Jackson et al. 2005b), as well as volatile attractants
from blossoms (Andersen and Metcalf 1986, Lewis et al. 1990, Metcalf et al. 1995, Mena
Granero et al. 2004, Ferrari et al. 2006, Andrews et al. 2007, Theis et al. 2009, Sasu et al.

2010).

Interestingly, cucurbitacin has been proven to be very toxic and is a deterrent

compound for most insects (Howe et al. 1976, Metcalf et al. 1980, Nishida and Fukami

1990, Walsh et al. 2008). However, striped cucumber beetles evolved closely with
cucurbits and consuming cucurbitacin does not present any real physiological cost
(Tallamy and Gorski 1997, Tallarny et al. 1997). Eben et a1 (1997) showed that
diabroticine beetles in choice tests are more attracted to plants with cucurbitacin than
plants without. All plants of the cucurbit family produce cucurbitacin and volatile
attractants but the attractiveness among plant Species is highly variable. This may be
because plants can contain a great diversity of cucurbitacin molecules (Chen et al. 2009).
Eben et al 1997 showed that diabroticine beetles have a preference for some types of
cucurbitacin molecules (Eben et al. 1997). The Striped cucumber beetles ability to detect
cucurbit plants from a long range is primarily due to volatile attractant and not

cucurbitacin because of its poor volatility (Branson and Guss 1983).

Volatile compound concentration can also vary within a single plant and may also
affect the attractiveness of cucurbit varieties. Sasu et al (2010) showed variation of
attractiveness within C. pepo plants, with male flowers attracting more cucumber beetles
than female flowers. Insect feeding can also affect the attractiveness of plants. Theis et al.
(2009) demonstrated that beetle feeding increases the floral fragrance in male flowers yet
delays the appearance of flowers. The attractiveness of a plant is reinforced by the
presence of male aggregation pheromone (Smyth and Hoffrnann 2003, Morris et al.
2005). Smyth and Hoffmann (2003) showed that several males as lures are more efficient

to attract conspecifics than one male alone.

Research has been conducted on the potential of winter squash varieties to attract

striped cucumber beetles (Bellows and Diver 2002, Cavanagh 2008, Adler and Hazzard

10

2009). Much of this research has focused on the varieties available for conventional
farmers and has usually concluded that blue hubbard has high trap crop potential.
(Caldwell and Stockton 1998, Maclntyre-Allen et al. 2001, Bellows and Diver 2002,
Boucher and Durgy 2004, Cavenagh 2008, Adler and Hazzard 2009). The identification
of alternative varieties that can be used as trap crops limits risk of shortage for seeds,

particularly for organic farmers.

The main limitation of perimeter trap crops for organic farmers is the lack of
affordable and efficacious insecticides. Furthermore, the short residuals, typical of
organically acceptable insecticides, lead to the need of multiple insecticide applications.
Alternatives to currently available OMRI approved pesticides are needed. Methods to
improve the efficiency of trap crops without use of insecticide could be useful for
farmers. One potential way to increase the efficiency of trap crops is to mix different
varieties of winter squash. To date, this possibility has not been explored. A better
understanding of which parts of the plants attract the most striped cucumber beetles could

also help to improve the trap crop management.

Objectives

1- Determine the attractiveness and trap crop potential of four varieties of
winter squash, for management of striped cucumber beetles

2- Determine the potential of winter squash varietal mixtures to improve
striped cucumber beetle trap crop performance in organic cucumber

production

11

3- Determine the relative importance of different trap crop parts (i.e. flowers,

leaves, fruit) to the attractiveness of trap crop varieties

12

CHAPTER 2

Attractiveness and trap crop potential of four varieties of
winter squash to striped cucumber beetles (Coleoptera:
Chrysomelidae)

Abstract:

Striped cucumber beetles, Accalymma vittatum F. (Coleoptera: Chrysomelidae), are
major pests in organic cucumber production. Trap crops are an important tool in
management of striped cucumber beetles but have limits in organic pest management. In
this study we assessed the trap crop potential of four winter squash varieties: blue
hubbard (Cucurbita maxima Duchesne), burgess buttercup (Cucurbita maxima
Duchesne), waltham butternut (Cucurbita moschata Duchesne), table queen acorn
(Cucurbita moschata Bailey) under greenhouse and field conditions. Results show that
burgess buttercup and blue hubbard are the most attractive varieties. No significant
difference was observed between these two varieties. Burgess buttercup has an advantage
under low beetle population with its good marketability. The study showed the
importance of flowers in the attractiveness of the trap crops and thus the management of

striped cucumber beetles.

13

Introduction

The cucumber beetle complex (Coleoptera: Chrysomelidae) makes up the
principal insect pests of cucurbits in the USA and consists of: the striped cucumber beetle
(A calymma vittatum F.), the Spotted cucumber beetle (Diabrotica undecimpuctata
howardi Barber), and the banded cucumber beetle (Diabrotica balteat Leconte). In
Michigan, the striped cucumber beetle is considered the most important of these three
Species. Adult striped cucumber beetles damage cucurbits by feeding on flowers, fruit,
leaves, and stems while larvae are root feeders. At the seedling stage, feeding by adults
can kill the plants. However, older plants are more able to tolerate some defoliation
(Burkness and Hutchison 1998). Brewer et al. (1987) showed that zucchini attacked at the
second and third-leaf stage compensate for gowth delay before fi'uit production. Adult
cucumber beetle feeding on fi'uit causes scars that limit cucumber marketability.
Furthermore, striped cucumber beetle also transmits bacterial wilt (Erwinia tracheiphila
Smith) (Mitchell and Hanks 2009). This disease kills the plants and currently no curatives
are available. Thus, in regions where this pathogen occurs, cucumber beetles must be
maintained at very low levels. Brust and Foster (1999) advise a threshold of one
beetle/per plant if bacterial wilt is present. In Michigan, bacterial wilt occurrence is
sporadic, allowing higher tolerance for cucumber beetles and providing increased

opportunities to manage cucumber beetles with certified organic tactics.

In the North Central region Of the USA, the pest is univoltine. The first generation
of the striped cucumber beetle is initiated by overwintering adults with adult beetles

Spreading from overwintering Sites to cultivated fields at the beginning of June. This

14

Ofien coincides with early growth Of cultivated cucurbits and can have a severe impact on
the production, leading to reduced stand or delayed plant maturation (Brewer et al. 1987,
Ayyappath et al. 2002). Eggs are laid at the base of the cucurbit plants and larvae hatch
and feed on the roots. Larval feeding is usually less damaging than feeding by
overwintering adults because the plants are well established when the larvae begin
feeding (Bellows and Diver 2002) The second generation of beetles emerges at the end of

July beginning of August.

Trap crops function by attracting pests to a restricted area where the pest is either
diverted from the protected plant, is more easily controlled, or both (Shelton and
Badenes-Perez 2006). In the case of cucumber beetles, trap crops are usually varieties of
winter squash. Some varieties of winter squash that are particularly attractive to
cucumber beetles include Cucurbita pepo Alef and Cucurbita maxima Wall. The
difference in attractiveness among varieties has previously been reported to be due to the
concentration of cucurbitacin in the plants (Bellows and Diver 2002). Winter squash trap
crops are usually planted on the edges of a cucumber field as perimeter trap cropping
(Hokkanen 1991, Maclntyre—Allen et al. 2001, Hazzard and Cavanagh 2005, Cavanagh et
al. 2009). The reported advantages of trap crops are reduced damage to the main crop
through the diversion of cucumber beetles as well as reduced insecticide use (Boucher
and Durgy 2004, Adler and Hazzard 2009, Cavanagh et al. 2009). However, trap crops
alone typically do not provide sufficient damage control when cucumber beetles occur in

large numbers (Maclntyre-Allen et al. 2001, Brewer et al. 2006).

15

In conventional cucumber production perimeter trap cropping is typically tied
with use of an insecticide (Hazzard 2005, Adler and Hazzard 2009, Cavanagh et al.
2009). This method typically reduces the amount of insecticide necessary to achieve
economic control. For example, Cavanagh and Hazzard (2009) showed that perimeter
trap cropping reduced the use of insecticide by 94% compare with conventional methods.

A surface of 15% of trap crop is recommended (Radin and Drummond 1994a).

Striped cucumber beetle management options available for certified organic
production vary greatly in efficacy and cost and can be classified into low-input or high-
input strategies. Examples of low-input strategies include use of different densities and
varieties of trap crops (Hazzard and Cavanagh 2005), which may be integrated with: light
traps (Barrett et al. 1971b) , vacuum removal of adult beetles (Smith 2000), and
biological control (Reed et al. 1986, Barbercheck and Wanick 1997, Ellers-Kirk et al.
2000). High-input strategies include row covers on cucumber (Matthewsgehringer and
Houghgoldstein 1988), organic insecticides, and trap crop plus organic insecticides,
(Hazzard and Cavanagh 2005). These strategies may be more efficient than low-input
strategies but are typically also more expensive. Perimeter trap crops are thus an
attractive pest management option for organic farmers. However, the acquisition of
organically produced attractive trap crop seeds can be challenging especially considering
most of the available information on trap crops has been developed using conventional

varieties.

Furthermore, the integration of organically acceptable insecticides with perimeter

trap cropping is challenging because there are few effective organically approved

16

insecticides and they typically require fi'equent treatment due to short residual activity.
Thus, the potential for the effective use of perimeter trap crops in organic cucumbers
depends on the use of highly attractive cultivars. The attractiveness of a cultivar is due to
cucurbitacin which is a phagostimulant and an arrestant (Metcalf et al. 1980) and the
volatile attractant from blossoms (Andersen and Metcalf 1986, Lewis et al. 1990, Metcalf
et al. 1995). The attractiveness of a plant is reinforced by the presence of male
aggregation pheromone (Smyth and Hoffrnann 2003, Morris et al. 2005). Smyth and
Hoffmann (2003) Showed that several males as lures are more efficient to attract

conspecifics that a male alone.

The primary objective of this study was to assess the potential of different winter
squash varieties easily found as organic seeds. The second objective was to evaluate
which parts of these potential trap crops (1'. e. flower, fi'uit, leaves and stem) contribute the

most to their relative attractiveness for striped cucumber beetles.

Materials and methods

Greenhouse Experiment: We measured the relative attractiveness of cucumbers to
striped cucumber beetles versus four different varieties of squash at three time periods
with three different simulated damage scenarios under greenhouse conditions. Cobra (C.
sativus L.) (Seedway: Elizabethtown, PA) was selected as our cucumber cultivar while
the four trap crop varieties used in the experiment were: Blue Hubbard (Cucurbita
maxima Duchesne) (F edco seeds Waterville, ME), Burgess Buttercup (Cucurbita maxima
Duchesne), Waltham Butternut (Cucurbita. moshata Duchesne ex Lam) and table queen

acorn (Cucurbita. pepo Bailey) (High Mowing Seeds Wolcott, VT). Plants were grown
l7

and the experiment conducted in greenhouses located at the Michigan State University
(MSU), Center for Integrated Plant Studies (CIPS) (East Lansing, Michigan). Plants
were grown in organic certified substrate, in 15.5 cm diameter 17.5 cm tall pots. Plants
did not receive additional fertilizer but were watered three times a week. Plants were 12 (1

old when each experimental run took place.

The experimental design was a factorial randomized block design with two
experimental factors: a five-way cucumber vs. trap crop factor and a three way damage
factor. Four replications for each cultivar with three damage treatment were evaluated for
each of the three experimental runs, yielding a total of eight replicates, with time and date
used as a blocking factor. The five levels of the trap crop variety factor were established
with experimental units consisting of a single cucumber (the protected crop) plant planted
with one of each of the four trap crop plants or a second cucumber plant (control). For the
damage factor either the trap crop plant was damaged, the trap crop plant and the
cucumber plant were damaged, or both plants were left undamaged. Simulated damage
was accomplished by scratching two leaves using a dissection probe without fully
piercing the leaves. Plants were damaged 30 minutes prior to the initiation of each
experimental run. A transparent plastic cage (14 cm diameter and 37 cm tall) was set over
the two plants in each pot. Ten field collected striped cucumber beetles were placed in
each cage. New beetles were collected for each run. The different experiments run were
started at 1pm and terminated 24 hours later. Our response variable was the number of
striped cucumber beetles on each plant or not on either plant within each cage at l, 5, and

24 h after their release.

18

We calculated the percentage of beetles on the trap crop varieties by dividing the
number of beetles on each the trap variety by the number of beetles release in each cage
(10 beetles). We analyzed the percentage of beetles on trap crop using a three by three by
three by eight (type of damage, time sample, date, repetition) factorial and post hoc
Tukey’s honest significant difference multiple comparison procedure was performed (R

Development Core Team 2008).

Field experiment: The relative attractiveness of cucumber versus itself and four different
varieties of squash with four different levels of artificial damage to striped cucumber
beetles was assessed under field conditions. The squash varieties and cucumber cultivar
employed were the same as those used in the greenhouse experiment. Plants were grown
in the greenhouse and transplanted into a field located at the MSU, Horticulture Farm
(Holt, Michigan). Pairs of squash seedling and cucumber seedlings were transplanted
into the field with a spacing of 20 cm between plants within a pair and 2 m of bare soil
between pairs. The control treatment paired two cucumber plants. Plots were manually

weeded on a weekly basis. Plants were watered regularly but received no fertilization.

Two independent experiments were performed with transplants of different ages.
The first experiment was done with 26 (1 old transplants and the second with 16 (1 Old
seedlings. Both experiments represented a full factorial randomized complete block
consisting of two factors: a five-way cucumber versus trap crop factor and a four-way
damage factor. There were Six blocks of each cultivar combination and damage level.
The five levels of the trap crop variety factor were established with experimental units

consisting of a single cucumber (the protected crop) plant planted with one of each of the

19

four trap crop plants (blue hubbard, burgess buttercup, waltham butternut, table queen
acorn) or a second cucumber plant (control). For the artificial damage factor either the
trap crop plant was damaged, the cucumber plant was damaged, the trap crop plant and
the cucumber plant were damaged, or neither the cucumber nor the trap crops were

damaged. Simulated damage was accomplished as in the greenhouse experiment.

Plants used in the experiment with 26 (1 Old transplants were planted on 17 June
2008 while plants used in the experiment with 16 d old transplants were planted on18
June 2008. Artificial damage was applied on19 June 2008 in both experiments. Our
response variable was the number of beetles present on flowers, fruit, leaves and stems
twice weekly on cucumber (The protected crop) and trap crop plants. We also assessed
percentage defoliation and mortality. Defoliation was estimated on a scale fiom 0% to
100% defoliation. Data were taken twice weekly between June 20 and August 11.
Number of beetles present on plant, defoliation and mortality were recorded at each

sample date between 7 am and 11am.

Mortality data was transformed using the arcsine transformation to normalize the
data. The number of beetles across the field season was summed and normalized using a
base 10 Logarithm transformation and analyzed using a six by five by four (block,
cultivar, artificial damage) factorial and post hoc Tukey’s honest significant difference
multiple comparison procedure (R Development Core Team 2008, Team 2009).The ratio
number striped cucumber beetles on flowers to the number Of striped cucumber beetles
on leaves, stems were also analyzed for each cultivar. Data were normalized using a base

10 Logarithm transformation and analyzed using a six by five (block, cultivar) ANOVA.

20

Results

Greenhouse experiment: We observed a significant difference in the percentage of
beetles on trap crops among the five trap crop varieties (F = 50.01; df = 4, 307; P <
0.001) (Fig 1.1). The mean percentages of beetles observed on trap crop were 57%, 52%,
34%, 29%, and 23% on blue hubbard, burgess buttercup, waltham butternut, cucumber
and table queen acom, respectively. Significantly more beetles were observed on burgess
buttercup than waltham butternut, table queen acorn and cucumber. Significantly more
beetles were observed on blue hubbard than waltham butternut, table queen acorn and
cucumber. Significantly more beetles were observed on cucumber and waltham butternut
than table queen acorn. We observed a significant difference between the three sampling
times (F = 4.78; df = 2, 307; P = 0.008). The mean percentages of beetles observed on
trap crop were 40%, 43% and 36% at 1 hour, 5 hours and 24 hours afier release,
respectively. We did not observed a Si gnificant difference between repetition (F = 0.79;
df = 7, 307; P = 0.59), dates (F = 2.47; df = 2, 307; P = 0.086) and artificial leaf damage
treatments (F = 2.83; df = 2, 307; P = 0.061). Nor did we observe a significant interaction
effect between times sampling time and trap crop varieties (F = 1.27; df = 8, 307; P =
0.26), between artificial leaf damage treatments and trap crop varieties (F = 1.43; df = 8,
307; P = 0.18) and between times sampling and artificial leaf damage treatments (F =

1.21; df=4, 307; P = 0.31).

Field experiment: For the 26d transplant experiment we Observed a significant
difference in the total number of beetles on trap crop among the five trap crop varieties (F

21

= 62.16; df= 4, 107; P < 0.001) (Fig 1.2). The mean sum of beetles observed were 443,
278, 72, 62, and 37 on burgess buttercup, blue hubbard, table queen acorn, waltham
butternut and cucumber, respectively. Significantly more beetles were observed on
burgess buttercup than waltham butternut, table queen acorn and cucumber. Significantly
more beetles were observed on blue hubbard than waltham butternut, table queen acorn
and cucumber. Significantly more beetles were observed on table queen acorn than
cucumber. We did not found any artificial damage effect on attractiveness of trap crop (F
= 1.84; df= 3, 107; P = 0.14).

Furthermore we observed a significant difference in the total number of beetles on
the flowers among trap crop varieties (F = 95.24; df = 4, 107; P < 0.001) (Fig. 1.2) with
mean sums of 395, 236, 55, 40 and 6 beetles observed on burgess buttercup, blue
hubbard, table queen acorn, waltham butternut and cucumber, respectively. Significantly
more beetles were observed on burgess buttercup than waltham butternut, table queen
acorn and cucumber. Significantly more beetles were Observed on blue hubbard than
waltham butternut, table queen acorn and cucumber. Significantly more beetles were
observed on table queen acorn than cucumber and significantly more beetles were
observed on waltham butternut than cucumber. We also found a difference in the total
number of beetles counted on leaves and stems among trap crop varieties (F = 9.70; df =
4, 107; P < 0.001) (Fig. 1.2) with mean sums of 48, 43, 18, 21 and 29 beetles observed on
burgess buttercup, blue hubbard, table queen acorn, waltham butternut and cucumber,
respectively. Significantly more beetles were observed on burgess buttercup than table
queen acorn and waltham butternut. Significantly more beetles were Observed on blue

hubbard than table queen acorn and waltham butternut. We did not analyze the data on

22

the number of beetles found on trap crop fi'uits due to the low number of beetles found
(only 9 beetles were Observed across all the season).

We did not observe a Si gnificant difference in the total number of beetles on
cucumber among the five trap crop varieties (F = 1.82; df = 4, 107; P= 0.13) (Fig 1.2) nor
any artificial damage effect on attractiveness of trap crop (F = 0.28; df = 3, 107; P =
0.84). Furthermore we did not observe difference in the total number Of beetles Observed
on cucumber flowers among the five trap crop varieties (F = 2.21; df = 4, 107; P = 0.073)
nor in the total number of beetles observed on cucumber leaves and stems among the five
trap crop varieties (F = 1.12; df = 4, 107; P = 0.35). We found 46 beetles on cucumber
fruits and no difference in the total number of beetles observed on cucumber fi'uits among
the five trap crop varieties (F = 1.69; df = 4, 107; P = 0.16).

In the burgess buttercup vs. cucumber treatment we observed significantly more
beetles on burgess buttercup (t= 9.53, df= 23.85, P<0.001) (Fig. 2.2). In the blue hubbard
vs. cucumber treatment we Observed significantly more beetles on blue hubbard (t= 8.25,
df= 24.8, P<0.001) (Fig. 2.2). In the table queen acorn vs. cucumber treatment we
observed significantly more beetles on table queen acorn (t=2.04, df= 45.99, P: 0.047)
(Fig. 2.2). In the waltham butternut vs. cucumber treatment we did not Observe any
significant difference (t= 1.92, df= 45.99, P= 0.061) (Fig. 2.2). In the cucumber vs.
cucumber control we did not observed any Significant difference (t= -0.15, df= 44.90, P=
0.88) (Fig. 2.2).

We observed a Significant difference in the mortality of plants among the five trap
crop varieties at the end of the experiment (F = 3.25; df = 4, 24; P =0.029). The

percentage mortality was 17%, 29%, 13%, 0% and 42% on burgess buttercup, blue

23

hubbard, table queen acorn, waltham butternut and cucumber, respectively. Significantly
more cucumber died than Waltham butternut. No Significant difference was observed in
the percentage of dead cucumber plants associated with the trap crops among the five trap
crop varieties (F = 2.66; df = 4, 24; P =0.057).

We Observed a significant difference in the ratio of beetles on flowers to beetles
on leaves, stems and fruits among the five trap crop varieties (F = 28.09; df = 4, 20; P <
0.001) (Fig. 2.1). The ratios of beetles on flowers to beetles on leaves, stems and fruits
observed were 8.6, 5.8, 3.4, 2.3 and 0.18 on burgess buttercup, blue hubbard, table queen
acorn, waltham butternut and cucumber, respectively. The ratio calculated for the
cucumber treatment was significantly lower than for burgess buttercup, blue hubbard and
table queen acorn. The ratio calculated for the table queen acorn and waltham butternut
treatments was significantly lower than for burgess buttercup, blue hubbard and table
queen acorn (Fig. 2.2).

For the 16d transplant experiment we found a difference in the total number of
beetles observed on trap crop among the five trap crop varieties (F = 47.89; df = 4, 107; P
< 0.001) (Fig 2.3). The mean sum of beetles observed were 224, 212, 79, 40, and 47 on
burgess buttercup, blue hubbard, table queen acorn, waltham butternut and cucumber,
respectively. Significantly more beetles were observed on burgess buttercup than
waltham butternut, table queen acorn and cucumber. Significantly more beetles were
observed on blue hubbard than waltham butternut, table queen acorn and cucumber.
Significantly more beetles were observed on table queen acorn than cucumber and
waltham butternut. We did not found any artificial damage effect on attractiveness of trap
crop (F = 0.79; df= 3, 107; P = 0. 50).

24

Furthermore, we observed a significant difference in the total number of beetles
counted on the flowers among trap crop varieties (F = 70.14; df = 4, 107; P < 0.001) (Fig.
2.3) with mean sums of 192, 174, 66, 30 and 2 beetles Observed on burgess buttercup,
blue hubbard, table queen acorn, waltham butternut and cucumber, respectively.
Significantly more beetles were observed on burgess buttercup than waltham butternut,
table queen acorn and cucumber. Significantly more beetles were Observed on blue
hubbard than waltham butternut, table queen acorn and cucumber. Significantly more
beetles were observed on table queen acorn than cucumber and waltham butternut and
significantly more beetles were observed on waltham butternut than cucumber. We also
found a difference in the total number of beetles counted on leaves and stems among trap
crop varieties (F = 19.10; df= 4, 107; P < 0.001) (Fig. 2.2) with mean sums of 32, 38, 14,
10 and 43 beetles observed on burgess buttercup, blue hubbard, table queen acorn,
waltham butternut and cucumber, respectively. Significantly more beetles were observed
on burgess buttercup than table queen acorn and waltham butternut. Significantly more
beetles were Observed on blue hubbard than table queen acorn and waltham butternut.
Significantly more beetles were observed on cucumber than table queen acorn and
waltham butternut. We did not analyze the data on the number of beetles found on trap
crop fi'uits due to the low number of beetles found (only 13 beetles were observed across
all the season).

We did not find a difference in the total number of beetles observed on cucumber
among the five trap crop varieties (F = 2.40; df = 4, 107; P= 0.055) (Fig 1.2) nor any
artificial damage effect on the attractiveness of trap crops (F = 0.16; df = 3, 107; P =

0.92). Furthermore we did not Observe differences in the total number of beetles on

25

cucumber flowers among the five trap crop varieties (F = 1.23; df = 4, 107; P = 0.30). We
did observe a difference in the total number of beetles on cucumber leaves and stems
among the five trap crop varieties (F = 2.84; df = 4, 107; P = 0.028). Significantly more
beetles were observed on burgess buttercup with 38 beetles than waltham butternut with
20 beetles. We did not analyze the data on the number of beetles found on cucumber
fi'uits as only 22 beetles were Observed across all treatments.

In the burgess buttercup vs. cucumber treatment we Observed significantly more
beetles on burgess buttercup (t= 8.80, df= 28.89, P<0.001) (Fig. 2.2).In the blue hubbard
vs. cucumber treatment we observed significantly more beetles on blue hubbard (t=
13.73, df= 27.43, P<0.001) (Fig. 2.2). In table queen acorn vs. cucumber treatment we
observed Significantly more beetles on table queen acorn (t=6.56, df= 43.24, P<0.001)
(Fig. 2.2). In the waltham butternut vs. cucumber treatment we observed significantly
more beetles on waltham butternut (t= 3.31, df= 42.09, P=0.002) (Fig. 2.2). In the
cucumber vs. cucumber control we observed significantly more beetles on trap crop
cucumber (t= 2.25, df= 34.31, P=0.031) (Fig. 2.2).

We observed a significant difference in the percentage mortality of plants among
the five trap crop varieties at the end of the experiment (F = 8.85; df = 4, 24; P<0.001).
The percentage mortality was 17%, 13%, 8%, 0% and 63% on burgess buttercup, blue
hubbard, table queen acorn, waltham butternut and cucumber, respectively. Significantly
more cucumber died than waltham butternut and table queen acorn. However, no
significant difference was observed in the percentage of dead cucumber associated with

the trap crops among the five trap crop varieties (F = 2.66; df = 4, 24; P =0.057).

26

We observed a significant difference in the ratio of beetles on flowers to beetles
on leaves, stems and fruits the five trap crop varieties (F = 8.72; df = 4, 20; P < 0.001)
(Fig. 2.1 ). The ratios of beetles on flowers to beetles on leaves, stems and fruits observed
were 6.4, 5.7, 5.2, 3.5 and 0.03 on burgess buttercup, blue hubbard, table queen acorn,
waltham butternut and cucumber, respectively. The ratio calculated for the cucumber
treatment was significantly lower than for burgess buttercup, blue hubbard and table

queen acorn (Fig. 2.3).

Discussion

Burgess buttercup is as efficient as blue hubbard in attracting striped cucumber
beetles and may have the advantage of being marketable. The greenhouse experiment
showed that blue hubbard and burgess buttercup are both considerably more attractive to
striped cucumber beetles than cucumbers (Fig. 2.1). In contrast, waltham butternut and
table queen acorn did not Show any potential to be used as trap crops in cucumber
production (Fig. 2.1). The two field experiments did not Show a difference in
attractiveness between burgess buttercup and blue hubbard. Thus, both varieties Showed
potential to be used as trap crops (Fig.2.2 and 2.3). These results confirmed the higher
attractiveness of the blue hubbard and burgess buttercup squash (Caldwell and Stockton
1998, Bellows and Diver 2002, Boucher and Durgy 2004, Cavenagh 2008). These results
also suggest that blue hubbard and burgess buttercup may have the potential to be used as
trap crops in waltham butternut and table queen acorn production. Furthermore, we did

not observe a higher mortality of burgess buttercup compared to blue hubbard in either

27

field experiments. The greenhouse experiment and the field experiments showed that

Simulated damage did not affect the attractiveness of trap crops.

One advantage Of burgess buttercup over blue hubbard is the relative ease in
finding organic seeds. Another advantage is that buttercup provides an alternative
marketable crop, thus reducing the cost of perimeter trap cropping. Burgess buttercup is a
more easily marketable squash compared to blue hubbard, which produces very large
squash that are difficult to sell (Whalen et al. 2000, Cavanagh 2008). Furthermore, even
when beetles feed on the trap crops, the squash fruits are not frequently attacked. Only
0.2% and 0.4% striped cucumber beetles were found on fi'uits in the 26d Old transplant

and the 16d Old transplant experiment, respectively.

These results also highlight that the attractiveness of varieties within the same
species can be highly variable. For example, burgess buttercup showed high
attractiveness while table queen acorn showed low attractiveness for striped cucumber
beetles, although both are C. pepo (Fig. 2.1, 2.2 and 2.3). This result is very meaningful
because it clearly indicates that describing the trap crop potential of variety by its species

can be misleading.

Our data also suggest that it is very important to provide a floral resource on trap
crops to manage striped cucumber beetles. The presence of flowers has a large impact on
the attractiveness of the trap crops to the striped cucumber beetle (Andersen and Metcalf
1986, Lewis et al. 1990, Metcalf et al. 1995, Ferrari et al. 2006). The ratio of beetles on
flowers to beetles on leaves and stems Observed in the field experiments varies between

5.7 to 8.5 for blue hubbard and burgess buttercup, 2.3 to 5.2 for waltham butternut and
28

table queen acorn, and 0.03 to 0.2 for cucumbers. The low flower/vegetative plant part
ratio on cucumbers may be explained by the very small size of cucumber flowers
compared to the winter squash flowers. Whereas variation in the concentration of
volatiles between waltham butternut and table queen acorn may explain the lower
attractiveness of thiese two cultivars compared to blue hubbard and burgess buttercup.
Sasu et al (2010) Showed variation of attractiveness inside plant for C. pepo, with male
flowers more attractive to cucumber beetles than female. Figure 2.4 Shows the position of
the striped cucumber beetles on the plants and the effect of flowers in the number of
beetles found. The two experiments are independent but took place during the same time
and in the same field. They Showed the importance of the age of the plant in the
appearance of the flowers. In the experiment with 26d transplants, flowers appeared
around July 1, more than two weeks sooner than in the 16d transplants. Striped cucumber
beetles started to appear in the field around June 26. Furthermore, Theis and a1 (2009)
demonstrated that flowers attract striped cucumber beetles and feeding delays the
appearance of flowers. Older transplants ensure earlier appearance of flowers in the field,
thus increasing the protection potential of trap crops. Cucurbitacin may also play a role in
the difference of attractiveness observed between varieties (Metcalf et al. 1980, Andersen

and Metcalf 1986, Schroder et al. 2001).

This study showed that burgess buttercup has the same potential to be used as a
trap crop as blue hubbard in cucumber, table queen acorn, or waltham butternut
production. Burgess buttercup could be more financially beneficial for farmers than using

blue hubbard (Cavanagh 2008). Lastly, the study showed the importance of the transplant

29

age to ensure an optimal protection of the cucumbers through continuous provisioning of

floral resources on the trap crop.

Acknowledgment: I thank Bill Chase and all the workers at the horticulture farm for
their help, the several undergraduate students that assisted me, particularly Jonathan
Landis and Aristarque Djoko. Thanks to Mathieu Ngouajio for his help and advices to

prepare this work and Ed grafius for his comments.

30

H N W g 0" 01 \l
O O O O O O
I

 

Percentage beetles on trap crop

 

O

Blue hubbard Burgess Waltham Cucumber Table queen
buttercup butternut acorn

Figure 2.1: Mean percentage of striped cucumber beetles (:I:SEM) found on trap crops
versus cucumbers. Bars with different letters are significantly different (Tukey’s honest
significant difference test alpha = 0.05).

31

550
500
450
400

g 300
‘63 250

100

Number of striped cucumber

550

450

§

150

§

Number of striped cucumber beetles
U1
c

O

.3 200 -.
150 -

 

U!
DO

500

f

350
300 "
250 "

 

- Figure 2.2 a
. I Beetles on trap crop

“ I beetles on cucumber
350 ‘

"1

 

Burgess Blue hubbard Table queen Waltham Cucumber
buttercup acorn butternut

 

 

Figure 2.2 b
I beetles on flowers trap crop
“I U beetles on leaves and stems trap crop
6.42 5.70 5.19 3.48 0.03
a
a
b A
k CI+I
. fl..- -___- -—-—. ,

Burgess Blue hubbard Table queen Waltham Cucumber
buttercup acorn butternut

Figure 2.2: Average number of striped cucumber beetles (iSEM) observed on trap
crops, across all observation dates for the 26 day transplants a) on trap crop variety and
cucumber pairs b) on trap crop flowers or leaves, fruits and stems. Numbers above bars
represent the ratio of beetles on flowers to leaves and stems. Bars with different letters
are significantly different (Tukey’s honest Significant difference alpha=0.05).

32

 

 

 

 

 

550 “ Fi ure 2.3 a
E 500 - I beetles on trap crop g
E 450 i
I
g 400 , beetles on cucumber
U
1, “350 :
g ,2, 300 .
*3 £250 ~
“6 200 -+
t; 150 -
D b
g 100 “ C c
z 50 “
0 ..
Burgess Blue Table queen Waltham Cucumber
buttercup hubbard acorn butternut
. 550 i _
g 500 - I beetles on flowers trap crop Figure 2.3 b
g 450 ~
3 400 .1 CI beetles on leaves and stems trap crop
1‘; ”350 r
a 0300 .. 6.42 5.70 5.19 3.48 0.03
a. 7..
'3 “250 a a
H O
.12 a 200 a
3 150 ,
3 100 b
5 so 8 C B c [—I—JA
g 0 - m,-#h { fl
Burgess Blue Table queen Waltham Cucumber
buttercup hubbard acorn butternut

Figure 2.3: Average number of striped cucumber beetles (:I:SEM) observed on trap crops,
across all Observation dates for the 16 day transplants a) on trap crop variety and
cucumber pairs b) on trap crop flowers or leaves, fruits and stems. Numbers above bars
represent the ratio of beetles on flowers to leaves and stems. Bars with different letters
are significantly different (Tukey’s honest significant difference alpha=0.05).

33

+Beetles on flower transplant 1 month old Figure 2.4 a

 

 

 

 

a, 25 ..
0
f; d “-A- Beetles on leaves, stems and fruits transplant 1
.3 2° month old
0
E 15 Appearance of flowers
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- Fi ure 2.4b
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Figure 2.4: Average number of striped cucumber beetles observed on burgess buttercup
flowers or leaves, stems, and fruits (iSEM) using (a) 26 day old or (b) 16 day Old
transplants.

34

CHAPTER 3

Potential of winter squash varietal mixtures to improve striped
cucumber beetle trap crop performance in organic cucumber
production

Abstract:

Striped cucumber beetles, Accalymma vittatum F. (Coleoptera: Chrysomelidae), are
major pests in organic cucumber production. Trap crops are an important tool in
management of striped cucumber beetles but have limited efficacy in organic pest
management. In this study we assessed the trap crop potential of combinations blue
hubbard (Cucurbita maxima Duchesne) with waltham butternut (Cucurbita moschata
Poir), compared to each cultivar alone. We also assessed the potential of Pyganic®
insecticide and vacuum applications to control cucumber beetles on trap crops. Results
showed that blue hubbard combined with waltham butternut is as efficient as blue
hubbard alone. The waltham butternut has an advantage in the case of low beetle
population with its good marketability. No differences were observed between treatments
where insecticide and vacuum were used compared to control. The study also showed the
importance of flowers in the attractiveness of the trap crops and thus the management of

striped cucumber beetles.

35

Introduction

The striped cucumber beetle (Acalymma vittatum F.) is a member Of the cucumber
beetle complex that also includes: the spotted cucumber beetle (Diabrotica
undecimpunctata howardi Barber), banded cucumber beetle (Diabrotica balteata
Leconte), western spotted cucumber beetle (Diabrotz'ca undecimpunctata
undecimpunctata Mannerheim), and western corn root worm (Diabrotica virgifera
virgifera)(Bellows and Diver 2002). This complex makes up the most prevalent and
serious pests of cucurbit crops in the mid-west. In Michigan, where this research was
conducted, striped cucumber beetles are the most common pest found on cucurbitaceous
crops. Michigan’s fresh cucumber production is the fourth largest in US with 9.8% Of
national production. Around 4,900 acres were planted in 2007, with total sale of 15.4

million dollars (Kleweno and Matthews 2008).

The striped cucumber beetle’s host range is primarily plants in the family
Cucurbitacea (McKinlay. Roderick. G 1992) and adult beetles feed on the leaves, stems,
and fruits. Damage resulting from adult feeding can kill the plant, decrease yields, or
reduce fruit value through scarring. Brewer et a1 (1987) showed that although plants at
the third true leaf stage were able to resist and compensate for foliar feeding, younger
plants ofien died. Adult cucumber beetles also transmit Bacterial Wilt (Erwinia
tracheiphila Smith) by feeding on foliage (Brust and Rane 1995, Mitchell and Hanks
2009) or damaging flowers (Sasu et al. 2010). Larva feed exclusively on cucurbits roots,

causing damage that reduces the development of the roots. (Ellers-Kirk et al. 2000)

36

showed that reducing the population of cucumber beetle larvae increased the root length

and density of cucumbers in organic and conventional systems.

In the North Central region of the USA, the striped cucumber beetle is typically
monovoltine. Adult beetles usually emerge from their overwintering sites at the end Of
May or beginning of June, and start to colonize cucumber fields when temperatures
exceed 12°C (Radin and Drummond 1994a). This often coincides with early growth of
cucumbers and can have a severe impact on production through reduced stand and/or
delayed plant maturation (Brewer et al. 1987, Maclntyre-Allen et al. 2001, Ayyappath et
al. 2002). Female beetles lay their eggs at the base of the plants and the next generation
emerges at the end of July or beginning Of August. The summer generation is usually less
damaging to crops, particularly cucumbers, because crops are often ready for harvest

prior to peak beetle emergence.

Brust and Foster (1999) recommend an economic threshold of one beetle per plant
if bacterial wilt is present, making striped cucumber beetle management a primary
‘ concern for farmers. Organic striped cucumber beetle management tactics are limited
compared to conventional methods. Organic farmers have access to very few insecticides,
most of which contain natural pyrethrums and are much less efficacious than their
pyrethroid, carbamate, or organophosphate counterparts used in conventional cucumber
plantings (Barry et al. 2005, Karagounis et al. 2006, Cross et al. 2007, Kamminga et al.
2009). Ellers-Kirk et a1. (2000) showed that entomopathogenic nematodes applied to the
soil had a significant impact on striped cucumber beetle emergence, however nematodes

are expensive and their efficacy varies greatly depending on soil conditions (Kaya and

37

Gaugler 1993). Organic farmers also have access to physical management methods, such
as plastic mulch and row covers. These are important to organic growers and have been
employed with fair success (Matthewsgehringer and Houghgoldstein 1988, Cline et al.
2008, Nair and Ngouajio 2010). (Ibarra et al. 2001) showed that the use of row covers
and plastic mulch increases Muskmelon yield compared to treatment without. Vacuuming
can also be used to remove adult beetles (Smith 2000). Finally, the perimeter trap
cropping system with organic insecticides is also used by organic farmers but with less
success compared to conventional agriculture (Boucher and Durgy 2004, Hazzard and
Cavanagh 2005, Adler and Hazzard 2009, Cavanagh et al. 2009). Cavanagh et al (2009)
Showed that in conventional agriculture, perimeter trap cropping can lead to a 94%

reduction in insecticide use.

Trap crops function by attracting pests to a restricted area where the pest is either
diverted from the protected plant, more easily controlled, or both (Shelton and Badenes-
Perez 2006). In the case of cucumber beetles, the trap crop is usually a winter squash
(Cucurbita maxima Duchesne) variety. Some varieties Of winter squash that are
particularly attractive to cucumber beetles include burgess buttercup and blue hubbard
(Willot 2010). The difference in attractiveness among varieties has previously been
reported to be due to the concentration of cucurbitacin in the plants (Metcalf et al. 1980,
Ferguson et al. 1983, Brust and Foster 1995, Schroder et al. 2001, Martin et al. 2002,
Smyth et al. 2002, Jackson et al. 2005b), but flowers have also been shown to play an
important role in the attraction of the cucumber beetles to the cucurbits (Andersen and

Metcalf 1986, Lewis et al. 1990, Ferrari et al. 2006) (Willot et al. 2010).

38

Winter squash trap crops are often planted around the edges of the cucumber field
in a tactic referred to as perimeter trap cropping (Hokkanen 1991 , Hazzard and Cavanagh
2005, Cavanagh et al. 2009). The reported advantages of perimeter trap crops are reduced
damage to the main crop through the diversion Of cucumber beetles, as well as reduced
insecticide use (Boucher and Durgy 2004, Adler and Hazzard 2009, Cavanagh et al.
2009). However, trap crops alone typically do not provide sufficient damage control

when cucumber beetles occur in large numbers (Brewer et al. 2006).

The lack of affordable and efficacious insecticides has severely limited the use of
perimeter trap crops in organic cucumber production. One possible way to increase the
efficiency of trap crops is to mix different varieties of winter squash. To date, this
possibility has not been explored. Our hypothesis is that mixing varieties of winter squash
with different flowering periods and different attractiveness can increase the efficiency of
trap crops compared to a highly attractive variety of winter squash alone. Thus the main
objectives were to determine whether different trap crop combinations might reduce the
incidence of striped cucumber beetles on commercial cucumbers. In addition, we
assessed the impact of flowers on the efficiency of trap crops as well as the potential of
vacuum and organic insecticide applications to assist trap crops in managing striped

cucumber beetles.

39

Materials and Methods

2007 Field experiment: We evaluated the effects of mixing different trap crop varieties
with or without Pyganic® or insect vacuum applications on the striped cucumber beetle
management provided by trap crops for cucumbers. We used blue hubbard ( C ucurbita
maxima Wall) (Fedco seeds Waterville, ME) and waltham butternut (Cucurbita moshata
Poir) (High Mowing Seeds Wolcott, VT) as our two trap crops. The experimental design
was a full factorial randomized complete block consisting of one factor with four
treatments. Treatments one through three alternated three blue hubbard with three
waltham butternut repeated four times to form a row of 24 plants. Pyganic® (McLaughlin
Gonnley King Company, MN) insecticide or an insect vacuum were applied in
treatments two and three, respectively. Treatment four was 24 blue hubbard plants
without insecticide or vacuum treatments. Each treatment was repeated four times,

yielding a total of four blocks.

The experiment was performed at the Michigan State University (MSU)
Horticulture Farm (Holt, Michigan). Trap crop transplants were grown at the MSU
Center for Integrated Plant Studies (CIPS) greenhouse. Plants were grown in certified
organic substrate, in 10.5cm by 10.5cm by 12.5 cm tall pots with no additional fertilizers
or other inputs. Each experimental unit was composed of one central row of 24 trap crop
plants, spaced 30 cm apart with three rows of cucumbers on either side of the central row.
One m of bare SOil was maintained between rows and each replicate was separated by 6
m of bare soil. Trap crops were transplanted in the field at the three leaves stage on May

30, 2007 while cultivar Cobra cucumbers (C. sativus L.) (Seedway: Elizabethtown, PA)

40

were planted by direct seedling on June 7, 2007. Insecticide or vacuum treatments were
applied when a threshold of two beetles per plant was reached. Weeding was done
mechanically and manually to keep the field as clean as possible. Pyganic® was applied
by back pack sprayer (16.8 ml per Liter) and is a certified organic product. Vacuuming
was performed using a hand leaf blower (STIHL BG55, VA) converted to a vacuum

(STIHL vacuum kit).

We counted the number Of beetles present on the trap crops, the number Of beetles
on the two rows of cucumber closest of the treatments and assessed the mortality of the
trap crops twice weekly. The number of beetles on the trap crops and on the rows
surrounding the treatments across the field season were summed and analyzed using four
by four (treatment, block) ANOVA. We analyzed plant mortality using a four by four
(treatment, block) ANOVA. For treatment one, two and three (blue hubbard + waltham
butternut, blue hubbard + waltham butternut + insecticide, blue hubbard + waltham
butternut + vacuum) we calculated the ratio: number of striped cucumber beetles on blue
hubbard to the number of striped cucumber beetles on blue hubbard + waltham butternut
for two time periods of seven consecutive samples. Sample dates prior to July 2 were
excluded because less than 10 beetles were collected per plot. Ratios were normalized
using a base 10 Logarithm transformation. A T test was used to compare differences
between the two time periods. All data were analyzed using the R statistical language (R

Development Core Team 2008).

2009 Field Experiment: In the 2009 experiment we Shifted our focus to assess the

efficacy of mixing two trap crop varieties compared to a single variety or cucumber
41

alone. The winter squash varieties and the cucumber cultivar used were the same as in the
2007 experiment, and the agronomic details of the experiment identical to the 2007
experiment. The experimental design was a full factorial randomized complete block
consisting Of four blocks of one treatment factor with four levels. Treatment one
alternated three blue hubbard with three waltham butternut squash repeated four times to
form a row of 24 plants. Treatment two was composed of 24 blue hubbards, treatment
three of 24 waltham butternuts and treatment four of 24 cucumbers. Each treatment was
repeated four times, yielding a total of four blocks.

The cucumbers were planted on June 5th but a heavy rain flooded the fields, thus,
we reseeded the field on June 24th, 2009. The trap crops were transplanted on June 11‘“,
2009. We counted the number of beetles present on flowers and leaves, stems and fruits
of trap crops, the number of beetles on the two rows of cucumber closest of the
treatments twice weekly and assessed the mortality of the trap crops. At the end of the
season, we harvested the cucumbers within each plot and classified them as saleable or
not saleable by visually assessing the number of scars and by measuring cucumber
weight.

The number of beetles on the flowers, leaves, stems and fruits of trap crops trap
crops and on the rows surrounding the treatments across the field season was summed
and normalized using a base 10 Logarithm transformation and analyzed using a four by
four (block, treatment) ANOVA and post hoc Tukey’s honest significant difference
multiple comparison procedure. Percentage trap crop mortality data was transformed
using the arcsine transformation to normalize the data and analyzed using a four by four

(treatment, block) ANOVA. The number and weight of saleable cucumbers and non-

42

saleable cucumbers were normalized using a base 10 Logarithm transformation and
analyzed using a four by four (block, treatment) ANOVA.

We calculated the ratio of the number of striped cucumber beetles on blue
hubbard to the ntunber of striped cucumber beetles on blue hubbard + waltham butternut
for two time periods consisting of eight consecutive sampling dates in the waltham
butternut + blue hubbard treatment. Sample dates prior to July 2 were excluded because
fewer than 10 beetles per treatment were collected. A T test was used to compare
differences between the two time periods. All data were analyzed using the R statistical

language (R Development Core Team 2008, Team 2009).

Results

2007 Field experiment: We did not observe a difference in the number of striped
cucumber beetles found on the trap crops among the four treatments (F = 1.34; df = 3, 9;
P = 0.32) with 394, 456, 502, 492 beetles observed on blue hubbard, blue hubbard +
waltham butternut, blue hubbard + waltham butternut + vacuum and blue hubbard +
waltham butternut + insecticide, respectively (Fig. 3.1). Similarly, we did not observe
differences in the number of beetles counted in the cucumber rows surrounding the
treatments (F = 0.503; df = 3, 9; P =0.689), nor in plant mortality among treatments (F =
0.909; df = 3, 9; P = 0.47). The ratio of striped cucumber beetles on blue hubbard to blue
hubbard + waltham butternut among the two time periods assessed in 2007 was
Significant (F = 24.31; df = 17, 1; P < 0.001) with 0.84 (10.006) and 0.66 (10.036)

observed for the first and second time period, respectively (Fig. 3.5). No difference was

43

observed in the ratio of striped cucumber beetles on blue hubbard to blue hubbard +

waltham butternut among treatments (P = 0.027; df = 17, 2; P = 0.204).

2009 experiment: In 2009 we found a significant difference in the total number of
beetles observed on trap crops among the four treatments (F = 28.49; df = 3, 9; P < 0.001)
(Fig. 3.2) with 1051, 743, 503, 246 beetles Observed on blue hubbard, blue hubbard +
waltham butternut, waltham butternut and cucumber, respectively. Significantly more
beetles were observed on the blue hubbard, waltham butternut, and combined trap crop
treatments compared to the cucumber alone treatment and more beetles were observed On
the blue hubbard compared to the Waltham butternut treatment (Fig. 3.1).

We also found a Significant difference in the total number of beetles observed
among the four treatments on the leaves, stems and fi'uits (F = 4.257; df = 3, 9; P = 0.039)
(Fig. 3.1) with 162, 120, 91, 207 beetles observed on blue hubbard, blue hubbard +
waltham butternut, waltham butternut and cucumber, respectively. Significantly more
beetles were counted on the leaves, stems and fruits of the cucumber alone treatment vs.
waltham butternut alone treatment.

Furthermore we observed a significant difference in the total number of beetles
found on flowers among treatments (F = 31.45; df = 3, 8; P < 0.001) (Fig. 3.1) with 890,
622, 412, and 33 beetles Observed on blue hubbard, blue hubbard plus waltham butternut,
Waltham butternut and cucumber, respectively. Significantly more beetles were Observed
on flowers in the blue hubbard alone treatment vs. the cucumber alone treatment and the
waltham butternut alone treatment, and significantly more beetles were observed on the
blue hubbard plus waltham butternut treatment vs. to the cucumber alone treatment

(Fig.3. 1). As in the 2007 experiment, we did not observe difference in the number of
44

beetles counted in the cucumber rows surrounding the treatments (F = 0.93; df = 3, 9; P =
0.465).

We did observe a difference in the mortality of trap crops between treatments at
the end of the experiment (F = 25.96; df = 3, 9; P < 0.001), we also analyzed the
mortality on July 17, 2009 corresponding to the maturity of cucumbers and did not
observe difference among treatments (F = 2.47; df = 3, 9; P = 0.13) (Fig. 3.3).

We harvested the squash at the end of the experiment and obtained 201 kg, 114 kg
and 102 kg of squash for the treatments Waltham butternut, blue hubbard, blue hubbard +
waltham butternut, respectively. For the treatment blue hubbard + waltham butternut we
harvested 51 kg for each variety.

No differences were found among the number of saleable cucumbers (F = 0.58; df
= 3, 9; P = 0.64) and non-saleable cucumbers per treatment (P = 2.03; df = 3, 9; P =
0.179). Additionally, we did not observe a difference in the total weight of saleable
cucumbers among the treatments (F = 0.1180; df = 3, 9; P = 0.947), nor in the non-
saleable cucumbers (F = 2.597; df= 3, 9; P = 0.125).

The ratio of striped cucumber beetles on waltham butternut to the number striped
cucumber beetles found on blue hubbard for the treatment waltham butternut + blue
hubbard varied among the two time periods assessed in 2009 was significant (t= 6.32, df=

3, P: 0.008 ) (Fig. 3.6).

Discussion

Although neither experiment showed a difference in the number of striped

cucumber beetles found in the ‘blue hubbard alone’ compared to the ‘blue hubbard mixed

45

with waltham butternut’ treatments mixing the two trap crops may provide a benefit
compared with the use of either variety alone by providing an alternative saleable crop,
reducing the cost associated with establishing a perimenter trap crop and/or by extending
the useful life of the perimeter trap crop (Fig. 3.1). In the 2009 experiment, the ‘waltham
butternut alone’ treatment attracted significantly less beetles than ‘blue hubbard plus
waltham butternut’ or ‘blue hubbard alone’ treatments (Fig. 3.1). This confirmed the
higher attractiveness of the blue hubbard compared to the waltham butternut squash

(Willot et al.2010, Bellows and Diver 2002, Caldwell and Stockton 1998).

An advantage of mixing blue hubbard with waltham butternut is that butternut
provides an alternative crop, thus reducing the cost of perimeter trap cropping. Butternut
is a more easily marketable squash compared to blue hubbard, which produces very large
squash that are difficult to sell (Zandstra et al. 1986, Whalen et a1. 2000) Furthermore,
even when beetles feed on the trap crops, the squash fruits are not frequently attacked
(Willot 2010) (Fig. 3.1). In 2009, we obtained 51 kg of marketable waltham butternut
squash, without any input, from ‘blue hubbard + waltham butternut’ from a total of 48

butternut plants.

Another potential advantage of mixing the two trap crop varieties is that the
addition of a lesser attractive trap crop may extend the useful life of the trap crop rows
due to differences in the temporal pattern of mortality and/or flowering period between
the two varieties. In both experiments the blue hubbard variety was the most attractive
but we Observed a movement of the beetles from the blue hubbard to the waltham

butternut later in the season (Fig. 3.5 and 3.6). In the 2009 experiment, there was a

46

substantial variation observed between June 15 and beginning of July due to the absence
of flowers and a low number of beetles observed during this time (Fig. 3.6). One
explanation for why we did not observe the same phenomenon in the beginning of the
2007 experiment is that the beetles arrived when both trap crops were already blooming.
In 2009, we observed a movement of beetles from the blue hubbard to the waltham
butternut between the two time periods (Fig 3.6). In 2007, we observed the same
phenomenon between the two time periods (Fig. 3.5). Two hypotheses to explain the
movements of the beetles are: either there is a difference of mortality between the blue
hubbard and waltham butternut (Fig. 3.2), or the flowering period of these two varieties

are temporally divergent (Fig. 3.6).

The fact that none of the plants in the ‘waltham butternut alone’ treatment died
during the 2009 experiment and only one out of 48 waltham butternut plants died in the
waltham butternut + blue hubbard treatment while 20% of blue hubbard plants died and
26% of plants died in the blue hubbard alone treatment supports the first hypotheses (Fig.
3.2). The observed numerical difference in mortality might be explained by the blue
hubbard’s higher attractiveness and susceptibility to bacterial wilt (Y 30 et al. 1996). We
noticed higher mortality of plants in the ‘cucumber alone’ treatment, with an average rate
of 67% (Fig. 3.2). However, this result is a bit deceptive as the cucumber cultivar ‘cobra’
reaches maturity after 60d and by the end of the experiment the cucumbers were 97d Old.
In contrast, blue hubbard squash reach maturity at 95d and the waltham butternut at 105d.
When cucumber mortality was measured on July 17’ 2009, their point of maturity, the
average mortality was only of 6% and no significant differences were observable among

treatments (Fig. 3.2).
47

Another explanation for the movement of the beetles to the waltham butternut
from the blue hubbard is the slightly longer cycle of butternut. Waltham butternut start
flowering later and therefore attract beetles later (Fig. 3.6). The tangle of the plants could
also play a role. Squash plants totally cover the ground and form an edge at the end of the
season. So bigger the plants grow and harder it must be for the beetles to distinct between

the two varieties, particularly because the two varieties are sustainable hosts.

Our data suggest that it is very important to ensure a floral resource to manage
striped cucumber beetles. The presence of flowers has been shown to have a large impact ’
on the attractiveness Of the trap crops to the striped cucumber beetle (Willot 2010, Ferrari
et a1 2006, Lewis et a1 1990, Andersen and Metcalf 1986). Greater than 75% of the
beetles Observed in the ‘blue hubbard alone’, ‘waltham butternut alone’, and ‘blue
hubbard plus waltham butternut’ treatments were found on the flowers. In contrast, in the
‘cucumber alone’ treatment, only 15% of the beetles were found on the flowers (Fig. 3.1).
This may be explained by the very small size of cucumber flowers compared to the
winter squash flowers. Figure 3.4 shows the movement of the beetles from the leaves and

stems to the flowers when flowers started to appear in the field.

No detectable pest management benefit was observed when we combined
Pyganic® or vacuum applications with the trap crops. This failure might be explained by
a low population of striped cucumber beetles. To illustrate, in 2007, we began to observe
beetles in the field around the June 25"‘, while in 2009 we had already recorded a
substantial number of beetles by June 15'“. There are three other possible explanations for

these findings: limited effect of vacuum application, effect of the Pyganic® on the entire

48

experimental plot and not only in the treated areas, or a failure of the insecticide to kill
striped cucumber beetles. Vacuum applications were likely not effective at removing
sufficient numbers of beetles relative the entire plot. Furthermore, beetles were primarily
Observed in the flowers where the vacuum was unable to capture them. Pyganic®
applications may have reduced the number of beetles in every treatment, not only those
where the insecticide was applied. Figure 3.3 shows that after each insecticide application
there is a decrease of the beetle population in all treatments. This is likely due to the high
mobility of the cucumber beetles and their tendency to change plants regularly (Dudley
and Searles 1923, Radin and Drummond 1994a, b), pyrethrum repellency could also

affect the movements of beetles (Kamminga et al. 2009).

In conclusion our study demonstrates that trap crop mixtures of blue hubbard and
waltham butternut have the potential to provide increased protection of cucumber. This
effect is likely due to either the lower mortality of waltham butternut as well as its later
flowering period. Furthermore, a trap crop mixture including waltham butternut might
financially benefit farmers by providing an alternative salable crop. An interesting future
study would be to combine waltham butternut with another very attractive variety, such
as burgess buttercup, that also has good marketability, to see if a similar complementary

effect is observed.

Acknowledgment: Thanks to Bill Chase and all the worker of the horticulture farm for

their help, the several undergraduate students that assisted me, particularly Jonathan

49

Landis and Aristarque Djoko. Thanks to Mathieu Ngouajio for his help and advices to

prepare this work and Ed grafius for his comments.

50

Figure 3.1 a
a

 

     

m 1200 “j
:3 g I Beetles on trap crop
g 1000
a;
"E: 800 “j b
= i
U
3 600 4
8
-§‘ 400 -- c
til
0..
0
Ir»
.9
E 2...“... 2-.....
5
Cucumber alone Waltham Blue hubbard + Blue hubbard
butternut alone Waltham alone
butternut
1200 Cl Beetles on leaves, stems, and fruits Figure 3.1 b
1000 Z I Beetles in flowers
3 0.27 4.51 5.58
800

 

Number of striped cucumber

   

 

 

 

 

Cucumber alone Waltham butternut Blue hubbard + Blue hubbard alone
alone Waltham butternut

Figure 3.1: Average number Of striped cucumber beetles (:tSEM) observed on trap crops
across all Observation dates for the 2009 experiment. a) On flowers. b) On flowers and
leaves, stems and fruits. Numbers above bars represent the ratio of beetles on flowers to
leaves and stems. Bars with different letters are significantly different (Tukey’s honest
significant difference alpha=0.05).

51

80‘ a

23 “‘ Mortality July 17th
50 r I Mortality August 25th
40 “

 

Percentage mortality

30 -

20 i

10 . NS "5 i .

o -+ -- —- __-I. e

Waltham Blue hubbard + Blue hubbard Cucumber
butternut alone Waltham alone alone

butternut

 

Figure 3.2: Average percentage plant mortality (iSEM) on July 17th and August 25’“.
Bars with different letters are Significantly different (Tukey’s honest significant
difference alpha=0.05).

52

300 ‘1 -o—B|ue hubbard + Waltham
butternut

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butternut + insecticide

   

 

 

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Figure 3.3: Average number of striped cucumber beetles by treatment at each sample
date for the 2007 experiment. The black and dotted arrows indicate dates of vacuum and
Pyganic® applications, respectively.

53

Number of

Number of

Number of beetles

beetles

Number of beetles

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Figure 3.4: Average sum (:I:SEM) of striped cucumber beetles on flowers or leaves stems
and fruits for each sample date between June 15 and July 17 for the 2009 experiment. a)
blue hubbard alone, b) blue hubbard + waltham butternut, c) waltham butternut alone, (I)
cucumber alone.

54

 
   

 

 

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Figure 3.5: Ratio of striped cucumber beetles found on blue hubbard to total beetles
found in the blue hubbard + waltham butternut, blue hubbard + waltham butternut +
vacuum, and blue hubbard + waltham butternut + Pyganic® treatments in the 2007
experiment. Bars provide the ratio over seven sampling periods. Bars with different
letters are Significantly different (T test alpha = 0.05).

55

 
   

 

 

 

 

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Figure 3.5: Ratio of striped cucumber beetles found on blue hubbard to total beetles
found in the blue hubbard + waltham butternut, blue hubbard + waltham butternut +
vacuum, and blue hubbard + waltham butternut + Pyganic® treatments in the 2007
experiment. Bars provide the ratio over seven sampling periods. Bars with different
letters are significantly different (T test alpha = 0.05).

55

 

 

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Figure 3.6 Ratio of stn'ped cucumber beetles found on blue hubbard to total striped
cucumber beetles observed in the blue hubbard + waltham butternut plots in the 2009
experiment. Bars provide the ratio over eight sampling periods. Bars with different letters
are significantly different (T Test alpha = 0.05).

56

CHAPTER 4

Perimeter Trap Crops for Striped Cucumber Beetles:
Conclusions and Future Research

Synthesis

The application of Integrated Pest Management (IPM) is essential to successful
and profitable cucumber production in the Northeastern US (Cavanagh 2008, Cavanagh
et al. 2009). This is especially true for organic farmers who have limited pest
management options, two of which are row covers and perimeter trap cropping. Row
covers ensure protection of plants until blooming thus limiting the need for insecticides.
However, at the start of the flowering stage, row covers must be removed to allow for
pollination, requiring careful monitoring of pests thereafter. Trap cropping is another
important management method for farmers, leading to a substantial reduction of
insecticides use (Cavanagh et al. 2009). The usual variety of trap crop employed is blue
hubbard which can be difficult for farmers to find, particularly if they require certified
organic seed. Thus, farmers need alternative squash varieties that are as efficient as blue

hubbard yet readily available in certified organic seed.

My results showed that burgess buttercup is as efficient as blue hubbard in
attracting striped cucumber beetles in cucumber production (Fig. 2.1, 2.2 and 2.3) and

therefore is a viable alternative. Burgess buttercup is also more marketable than blue

57

hubbard (Whalen et al. 2000, Cavanagh 2008). This is a potential advantage for farmers
because trap crop squash fruits are not commonly attacked by striped cucumber beetles.
The observation of the position of the beetles on plant showed that flowers are the most
attractive part of the trap crop with approximately 80%, 19.6%, and 0.4% of the total
beetles observed on flowers, leaves and stems, and fi'uit, respectively. Furthermore,
because fruits are the least attractive part of the plants, they might be harvest regularly

without decreasing the efficacy of trap crops.

Trap crops alone typically do not provide sufficient damage control when
cucumber beetles occur in large numbers (Brewer et al. 2006). In conventional
agriculture, trap crops are usually assisted by insecticide to reduce the pest pressure
(Radin and Drummond 1994b, Boucher and Durgy 2004, Adler and Hazzard 2009,
Cavanagh et a1. 2009). However, in organic agriculture, insecticide options are limited,
expensive, and less efficient. Thus, alternative methods that increase the efficiency of
trap crops are needed. My results showed that mixing blue hubbard with waltham
butternut as trap crops may provide a benefit compared with the use of either variety
alone. Neither experiment in chapter 3 showed a difference in the number of striped
cucumber beetles found in the ‘blue hubbard alone’ compared to the ‘blue hubbard mixed
with waltham butternut’ treatments (Fig.3. 1 ). Like burgess buttercup, waltham butternut
provides an alternative crop, thus reducing the cost of perimeter trap cropping (Zandstra
et al. 1986, Whalen et al. 2000). Waltham butternut has a slightly longer cycle than blue

hubbard, and therefore, begins flowering later (Fig.3.6). This leads to a longer flowering

58

period when blue hubbard and waltham butternut are mixed together compared to each

cultivar alone.

The results show the importance of the presence of flower in the attractiveness of
trap crops (Fig 2.2; 2.3; 2.4; 3.1and 3.6). The majority of the beetles were found on the
flowers of the winter squash. The highest ratio beetles on flower to beetles on leaves and
stems were found on the most attractive varieties, such as blue hubbard and burgess
buttercup (Fig 2.2; 2.3 and 3.1). Figure 1.4 shows that the number of beetles on burgess
buttercup increased when the flowers appeared. When flowers were not present, the
number of beetles found on the attractive trap crops was only slightly higher than found
on the cucumbers. This suggests that management of the trap crop flowering period is
crucial to ensure adequate protection of cucumbers. Cucumbers have a short cycle,
arriving at maturity after only 60 d. In comparison, squash have a life cycle of 90-1 10 (1.
Thus, it is important to use trap crop transplants that are old enough to guarantee a

protection of the cucumber in their most sensitive stages.

In the experiment presented in chapter three testing the potential benefit to use
vacuum and Pyganic® insecticide we did not observe a significant difference between
treatments. This might be due to the experimental design or the limited residual activity
of the insecticide. The vacuum utilized did not prove effective at removing beetles within

flowers.

59

Future research

Flowering period management appears to be critical in ensuring the efficiency of
perimeter trap cropping systems. Additional research needs to be conducted on the affect
of using different ages of transplants of the same variety compared to a mixture of
varieties. It would also be interesting to assess the impact of harvesting the squash fruits
from the trap crops on the number of flowers and the attractiveness of trap crops. Another
potential area of study would be using a combination of row covers and trap crops in

organic farming to assess the benefits provided by the two tactics relative to their costs.

My experiment on the potential of using Pyganic® with trap crops was largely
inconclusive. Data are needed on the efficiency of organic insecticides for striped
cucumber beetles. This will help to optimize the use of trap crops with organically
approved insecticides. Furthermore, some organic pesticides are known to have a
deterrent effect. Using these could be beneficial if applied as part of a Push and Pull
strategy (Dunnusoglu et al. 2003, Riba et al. 2003, Green et a1. 2004, Cook et al. 2007,
Gomez Jimenez and Poveda 2009). On the other hand, repellant insecticides might be
incompatible with perimeter trap crops if they lead to the movement of the pest into the

cash crop.

Finally, much work remains to be done on striped cucumber beetle foraging and
host selection behavior. Striped cucumber beetles appear to be very attracted to flowers
but they are also easily attracted by yellow sticky traps. A better understanding of the

relative importance of visual olfactory cues could lead to improved of pest management

60

and offer new solution for pest control. This could help to develop more efficient traps to

control striped cucumber beetles and improved trap crops management.

61

Appendix 1.1

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.: 2010-02
Title of thesis or dissertation (or other research projects):
PROTECTION OF ORGANIC CUCUMBER PRODUCTION AGAINST STRIPED
CUCUMBER BEETLES USING TRAP CROPS
Museum(s) where deposited and abbreviations for table on following sheets:
Entomology Museum, Michigan State University (MSU)
Other Museums:
Investigators Name(s)
Vianney Willot
Date June 10 2010

*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.

62

Appendix 1 .1

Voucher Specimen Data

Page_____ot_____Pages

L

amaze: 3:. .. €22 9.. 5 £88

 

 

 

 

 

 

 

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A5888 a $85. HESS 83

 

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32 32.00

322 E5“. 93.39.51
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63

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