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Leguminous and Graminaceous Cover Crops for the Control of Insect Pests in Organic Squash

Permanent Link: http://ufdc.ufl.edu/UFE0022711/00001

Material Information

Title: Leguminous and Graminaceous Cover Crops for the Control of Insect Pests in Organic Squash
Physical Description: 1 online resource (131 p.)
Language: english
Creator: Scott, Corraine
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: aphids, covercrops, grasses, leguminous, organic, pearlmillet, sorghumsudangrass, squash, sunnhemp, velvetbean, whiteflies
Entomology and Nematology -- Dissertations, Academic -- UF
Genre: Entomology and Nematology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Leguminous and graminaceous cover crops were evaluated for the control of aphids and whiteflies Bemisia argentifolli (Bellows and Perring) in organic summer squash. Two monoculture legumes, sunn hemp SH (Crotalaria juncea L.) and velvet bean VB (Mucuna pruriens (L.) DC. var. pruriens), two monoculture grasses, sorghum sudangrass SSG (S. bicolor x S. sudanense) (Piper) Stapf and pearl millet PM (Pennisetum glaucum (L.) R. Br.), and two legume-grass mixtures, sunn hemp/pearl millet SH/PM and sorghum sudangrass/velvet bean SSG/VB were evaluated during 2006 and 2007. Results from unbaited yellow sticky traps showed that the monoculture grasses, specifically SSG, has the best potential for suppressing aphids and whitefly populations in organic summer squash. The diculture, legume-grass mixture consisting of SSG/VB also demonstrated potential to reduce pest numbers by enhancing the natural enemy populations: specifically parasitoids and predators. Sorghum sudangrass is especially known for harboring coccinellids. High numbers of the whitefly predator, Delphastus pusillus were recorded in SSG plots, which provided effective control of whiteflies. During both years of study, there was good evidence to conclude that residual populations of natural enemies from incorporated cover crops can suppress pest populations in the subsequent squash cash crop. However, alternate resources surrounding the field will need to be present to support natural enemy populations until the squash crop is established. Overall, insect pest populations had a density dependent effect on squash yields following cover crop incorporation into the soil. Both legumes, VB and SH attracted more aphids and whiteflies compared with the weedy fallow and therefore would not be recommended for use prior to organic squash. The PM and SSG were able to increase squash yields, while suppressing key pest populations (aphids and whiteflies) in squash. Future research should involve analyzing both grass cover crops for chemical compounds that may be responsible for suppressing pests, with the goal that these compounds could be used for pest control in organic systems.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Corraine Scott.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Liburd, Oscar E.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022711:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022711/00001

Material Information

Title: Leguminous and Graminaceous Cover Crops for the Control of Insect Pests in Organic Squash
Physical Description: 1 online resource (131 p.)
Language: english
Creator: Scott, Corraine
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: aphids, covercrops, grasses, leguminous, organic, pearlmillet, sorghumsudangrass, squash, sunnhemp, velvetbean, whiteflies
Entomology and Nematology -- Dissertations, Academic -- UF
Genre: Entomology and Nematology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Leguminous and graminaceous cover crops were evaluated for the control of aphids and whiteflies Bemisia argentifolli (Bellows and Perring) in organic summer squash. Two monoculture legumes, sunn hemp SH (Crotalaria juncea L.) and velvet bean VB (Mucuna pruriens (L.) DC. var. pruriens), two monoculture grasses, sorghum sudangrass SSG (S. bicolor x S. sudanense) (Piper) Stapf and pearl millet PM (Pennisetum glaucum (L.) R. Br.), and two legume-grass mixtures, sunn hemp/pearl millet SH/PM and sorghum sudangrass/velvet bean SSG/VB were evaluated during 2006 and 2007. Results from unbaited yellow sticky traps showed that the monoculture grasses, specifically SSG, has the best potential for suppressing aphids and whitefly populations in organic summer squash. The diculture, legume-grass mixture consisting of SSG/VB also demonstrated potential to reduce pest numbers by enhancing the natural enemy populations: specifically parasitoids and predators. Sorghum sudangrass is especially known for harboring coccinellids. High numbers of the whitefly predator, Delphastus pusillus were recorded in SSG plots, which provided effective control of whiteflies. During both years of study, there was good evidence to conclude that residual populations of natural enemies from incorporated cover crops can suppress pest populations in the subsequent squash cash crop. However, alternate resources surrounding the field will need to be present to support natural enemy populations until the squash crop is established. Overall, insect pest populations had a density dependent effect on squash yields following cover crop incorporation into the soil. Both legumes, VB and SH attracted more aphids and whiteflies compared with the weedy fallow and therefore would not be recommended for use prior to organic squash. The PM and SSG were able to increase squash yields, while suppressing key pest populations (aphids and whiteflies) in squash. Future research should involve analyzing both grass cover crops for chemical compounds that may be responsible for suppressing pests, with the goal that these compounds could be used for pest control in organic systems.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Corraine Scott.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Liburd, Oscar E.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022711:00001


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1 LEGUMINOUS AND GRAMINACEOUS COVE R CROPS FOR THE CONTROL OF INSECT PESTS IN ORGANIC SQUASH By CORRAINE ATHOL SCOTT A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2008

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2 2008 Corraine Athol Scott

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3 To my parents, Stanhope and Sonia, for encouraging my academic interests and my sense of scholarship, making this milestone possible

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4 ACKNOWLEDGMENTS I wish to thank m y major pr ofessor, Dr. Oscar Liburd, for giving me the opportunity to acquire my masters degree at the University of Florida. His guida nce and support throughout this project were critical for its completion. I al so wish to thank all th e members of the Small Fruits and Vegetables Integrated Pest Manage ment (IPM) lab for their tremendous help in collecting field data. I thank Dr. Carlene Chase a nd Dr. Rob Meagher for critical review of this thesis. I am very thankful to Jim Wiley (DPI Gainesville, FL) and Gregory Evans (USDA-ARS Beltsville, MD) for their help in parasitoid identification; and Dr. Susan Halbert (DPI, Gainesville, FL) for aphid identification. I also wa nt to thank Meghan Brenna n for statistical help and Manish Bhan for pertinent re search data. I am extremely gr ateful to all my family and friends who have encouraged and supported me th roughout this project. I w ould especially like to thank Seth McNeill who, throughout my res earch, provided encouragement and distractions, which made the rough times good and the good times better. Above all, I thank God for his guidance, grace and unending blessings.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........8 LIST OF FIGURES.......................................................................................................................10 ABSTRACT...................................................................................................................................11 CHAP TER 1 INTRODUCTION..................................................................................................................13 Justification.................................................................................................................. ...........15 Goal and Hypotheses..............................................................................................................16 Specific Objectives.................................................................................................................16 2 LITERATURE REVIEW.......................................................................................................17 Aphids.....................................................................................................................................17 Biology and Behavior of Aphids............................................................................................17 Whiteflies..................................................................................................................... ...........19 Biology and Behavior of Whiteflies....................................................................................... 20 Management of Insect Pests Using Natural Enemies............................................................. 21 Coccinellidae (Ladybird beetles) ..................................................................................... 21 Carabidae (Ground beetles)............................................................................................. 22 Syrphidae (Syrphid Flies)................................................................................................22 Parasitoids........................................................................................................................23 Management of Insects Using Cover Crops........................................................................... 25 Leguminous Cover Crops................................................................................................27 Graminaceous Cover Crops............................................................................................. 28 3 POPULATION DYNAMICS OF APHIDS, WHITEFLIES AND THEIR ASSOCIAT ED NATURAL ENEMIES IN MONOCULTURE AND DICULTURE COVER CROP SYSTEMS....................................................................................................30 Materials and Methods...........................................................................................................33 Assessment of Aphids, Whiteflies and Natural Enemies with Unbaited Yellow Sticky Traps .................................................................................................................34 Assessment of Ground Predators with Pitfall Traps........................................................ 35 Assessment of Lepidopteran Pests.................................................................................. 35 Statistical Analysis.......................................................................................................... 36 Results.....................................................................................................................................36

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6 Population of Aphids and Whiteflies with in Cover Crop Treatm ents (Yellow Sticky Traps)...........................................................................................................................38 Assessment of Ground Arthropods from Pitfall Traps....................................................41 Assessment of Lepidopteran Pests.................................................................................. 42 Discussion...............................................................................................................................43 4 INSECT POPULATION DYNAMICS IN ORGANIC SQUASH FOL LOWING INCORPORATION OF COVER CROPS............................................................................. 60 Materials and Methods...........................................................................................................61 Assessment of Key Pests and Natural Enem ies wi th Unbaited Yellow Sticky Traps..... 63 Blue Pan Trap Captures...................................................................................................63 Visual and Leaf Disc Counts........................................................................................... 63 Assessment of Lepidopteran Pests.................................................................................. 64 Sentinel Squash Plants and Peripheral Sampling............................................................ 64 Squash Silver Leaf Disorder Rating................................................................................65 Statistical Analysis.......................................................................................................... 65 Results.....................................................................................................................................66 Visual Counts of Insect Pests on Squash......................................................................... 66 Leaf Disc Count...............................................................................................................68 Blue Pan Trap Results.....................................................................................................69 Periphery Yellow Sticky Trap Results............................................................................70 Unbaited Yellow Sticky Trap Results............................................................................. 70 Squash Silvering..............................................................................................................71 Adult Lepidoptera Results...............................................................................................71 Discussion...............................................................................................................................71 5 INFLUENCE OF PEST POPULATIONS FROM COVER CROPS ON TOTAL AND MARKETABLE YIELD OF SUM MER SQUASH............................................................... 91 Methods..................................................................................................................................92 Field Experiments............................................................................................................92 Aphids and Whitefly Sampling.......................................................................................93 Yield Sampling................................................................................................................ 94 Statistical Analysis.......................................................................................................... 94 Results.....................................................................................................................................94 Insect Population.............................................................................................................94 Total Squash Yield.......................................................................................................... 95 Marketable Squash Yield................................................................................................ 96 Discussion...............................................................................................................................96 6 TECHNIQUES FOR MONITORING APHI DS (HEMIPTERA: APHIDIDAE) AND WHITEFLIES (HEMIPTERA: ALEY RODIDAE) IN SUMMER SQUASH ..................... 103 Materials and Methods.........................................................................................................105

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7 Aphids............................................................................................................................105 Whiteflies..................................................................................................................... .107 Statistical Analysis........................................................................................................ 107 Results...................................................................................................................................107 Aphids............................................................................................................................107 Whiteflies..................................................................................................................... .108 Time Required Per Monitoring Technique.................................................................... 108 Discussion.............................................................................................................................109 LIST OF REFERENCES.............................................................................................................118 BIOGRAPHICAL SKETCH.......................................................................................................131

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8 LIST OF TABLES Table page 3-1 Aphid population dynamics in monoculture and diculture treatments in 2006................. 483-2 Aphid population dynamics in monoculture and diculture treatments in 2007................. 493-3 Whitefly population dynamics in monocu lture and diculture treatments in 2006............. 503-4 Whitefly population dynamics in monocu lture and diculture treatments in 2007............. 513-5 Parasitoid population dynamics in monoculture and di culture treatments in 2006........... 523-6 Parasitoid population dynamics in monoculture and di culture treatments in 2007........... 533-7 Delphastus pusillus population dynamics in monoculture and diculture treatments in 2006....................................................................................................................................543-8 Delphastus pusillus population dynamics in monoculture and diculture treatments in 2007....................................................................................................................................553-9 Mean number of ground arthropods captu red from pitfall traps in 2006 and 2007...........573-10 Mean number of adult lepidoptera captured from floral volatile baited bucket traps in 2006 and 2007....................................................................................................................584-1 Aphid and whitefly means from in situ squash leaf counts from various cover crop treatments in 2006............................................................................................................. .774-2 Aphid and whitefly means from in situ squash leaf counts from various cover crop treatments in 2007............................................................................................................. .784-3 Mean number of natural enemies from in situ squash counts from cover crop treatments in 2006............................................................................................................. .794-4 Mean number of natural enemies from in situ squash leaf counts from cover crop treatments in 2007............................................................................................................. .804-5 Mean number of whitefly eggs recorded from squash leaf disc counts during 2006 and 2007.............................................................................................................................814-6 Mean number of whitefly immatures recorded from squash leaf disc counts during 2006 and 2007....................................................................................................................824-7 Syrphid fly populations from each treatme nt in 2006 and 2007 from blue pan traps.......854-9 Population dynamics of key pests from peripheral habitats surrounding an organic field in 2007.......................................................................................................................87

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9 4-10 Mean number of adult lepidoptera captured from pheremone baited bucket traps in squash during 2006 and 2007............................................................................................905-1 Mean total squash yield from each c over crop treatment for the 2006 and 2007 field seasons.............................................................................................................................1015-2 Mean marketable squash yield from each treatment for the 2006 and 2007 field seasons.............................................................................................................................1026-1 Comparison techniques for monitoring aphids in summer squash throughout the entire season in Citra, FL.................................................................................................1146-2 Comparison techniques for monitoring whiteflies in summer squash throughout the entire season in Citra, FL.................................................................................................116

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10 LIST OF FIGURES Figure page 3-2 Percentage of total natu ral enem y population from pitf all traps averaged across all cover crops.........................................................................................................................564-1 Major parasitoid families in an organic squash field......................................................... 834-2 Syrphid fly populations in an orga nic squash field in A) 2006 and B) 2007.....................844-3 Populations of whitefly immatures with s quash silver leaf di sorder rating in 2007..........884-4 Relationship of immature whiteflies w ith squash silverleaf disorder rating...................... 895-1 Relationship between aphids with tota l squash yield in A) 2006 and B) 2007.................995-2 Relationship between whiteflies with total squash yield in A) 2006 and B) 2007.......... 1006-1 First day trap captures in situ counts, yellow sticky traps (YST) and blue pan traps (BPT) for aphids in summer squash................................................................................. 1136-2 First day trap captures in situ counts and yellow sticky traps (YST) for whiteflies in summer squash.................................................................................................................1156-3 Time taken (minutes) to assess aphids and whiteflies for blue pan traps (BPT), yellow sticky traps (YST) and in situ counts for aphids and whiteflies in summer squash...............................................................................................................................117

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11 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science LEGUMINOUS AND GRAMINACEOUS COVER CROPS FOR CONTROL OF INSECT PESTS IN ORGANIC SQUASH By Corraine Athol Scott August 2008 Chair: Oscar E. Liburd Major: Entomology and Nematology Leguminous and graminaceous cover crops were evaluated for the control of aphids and whiteflies [ Bemisia argentifolli (Bellows and Perring)] in organic summer squash. Two monoculture legumes, sunn hemp [SH] ( Crotalaria juncea L.) and velvet bean [VB] ( Mucuna pruriens (L.) DC. var. pruriens), two monoculture grasses, sorghum sudangrass [SSG] ( S. bicolor x S. sudanense ) (Piper) Stapf and pearl millet [PM] ( Pennisetum glaucum (L.) R. Br.), and two legume-grass mixtures, sunn hemp/pearl millet [S H/PM] and sorghum sudangrass/velvet bean [SSG/VB] were evaluated during 2006 and 2007. Results from unbaited yellow sticky traps showed that the monoculture grasses, specifically SSG, has the best potential for suppressing aphids and whitefly populations in organic summer squash. The diculture, legum e-grass mixture consis ting of SSG/VB also demonstrated potential to reduce pest numbe rs by enhancing the natural enemy populations specifically parasitoids and predators. Sorghum sudangrass is especially known for harboring coccinellids. High numbers of the whitefly predator, Delphastus pusillus were recorded in SSG plots, which provided effective control of whiteflies. During both years of study, there was good eviden ce to conclude that residual populations of natural enemies from incorporated cove r crops can suppress pest populations in the

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12 subsequent squash cash crop. However, alternate resources surrounding the fi eld will need to be present to support natural en emy populations until the sq uash crop is established. Overall, insect pest populations had a density dependent effect on squash yields following cover crop incorporation into the soil. Both le gumes, VB and SH attracted more aphids and whiteflies compared with the weedy fallow and therefore would not be recommended for use prior to organic squash. The PM and SSG were ab le to increase squash yields, while suppressing key pest populations (aphids and whiteflies) in squash. Future research should involve analyzing both grass cover crops for chemical compounds th at may be responsible for suppressing pests, with the goal that these compounds could be us ed for pest control in organic systems.

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13 CHAPTER 1 INTRODUCTION Organic farm ing is a method of crop and livestock production that emphasizes biological and ecological processes to improve soil healt h, manage soil fertility and optimize pest management while excluding the use of conventiona l commercial fertilizers, synthetic pesticides and synthetic antibiotics and growth hor mones (Treadwell 2007, Gold 2008, Martin 2006, Bachmann 2002). Within the past decade, organi c farming has gained significant momentum within the United States resul ting in $13.8 billion USD in orga nic food sales in 2005 (Crawford 2007, Oberholtzer et al. 2005) and is estimated to continue to increase annually by 9-16% (Oberhotlzer et al. 2005). In 2005, 98,525 vegetabl e acres were certified organic in the U.S, which was more than twice the acreage certifie d in 1997 (Economic Research Service 2008). It is clear that fresh, organic vegetables are in demand. In particular, squash was ranked 4th among the top organic vegetables that were purchased in the U.S. (Oberholtzer et al. 2005). Summer squash ( Cucurbita pepo L.) is a major vegetable crop grown commercially in Florida for fresh market sales (R oberts and Pernezny 2001). It is also one of the few crops that is shipped out of Florida every month of the y ear to grocery stores nationwide (AgMRC 2007, Mossler and Nesheim 2001, Roberts and Pernezn y 2001). During the 2007 squash field-season, Florida growers harvested approximately 11,000 acres of squash, with a value of ~ $53 million USD (NASS, 2008). In recent years the growth of organic squash production in Florida has increased (Juan Carlos Rodriguez personal communication). With the continued growth of the organic squash market, insect pest management becomes exceedingly important. Squash plants ar e significantly damaged by squash bugs, Anasa nistis (DeGeer), seedcorn maggot, Delia platura (Meigen), wireworms ( Limonius spp. and others), leafminers Liriomyza spp., western spotted ( Diabrotica undecimpuncta ta undecimpunctata L., )

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14 and stripped cucumber beetle, Acalymma trivittatum (Mannerheim), various armyworm Spodoptera spp., cabbage looper Trichoplusia ni (Hbner) and various forms of powdery mildew. However, more serious diseases are caused by viruses vectored by aphids [ Aphis gossypii Glover, Myzus persicae (Sulzer)] and whiteflies, Bemisia argentifolii (Bellows and Perring), which are key insect pests of squash (Molinar et al. 2007, Kucharek and Purcifull 2001). Squash crops are very sus ceptible to aphids and white flies (Frank and Liburd 2005, Kucharek and Purcifull 2001). Aphids transmit over 50 viruses in cucurbit s resulting in loss of yield and extreme symptoms such as deformed seed s, flower necrosis, leaf chlorotic spotting and fruit bumps (Hooks et al. 1998, Kucharek and Purcif ull 2001). Five of thes e viruses are present in Florida including the papaya ringspot virus, the watermelon mo saic virus, the zucchini yellow mosaic virus, the cucumber mosaic virus, a nd an unnamed potyvirus (Kucharek and Purcifull 2001). A sixth virus called the squash mosaic virus is not as frequent in Florida but is transmitted by the cucumber beetle Acalymma vittatum (Fabricius), not by aphi ds (Kucharek and Purcifull 2001). Feeding by whiteflies, Bemisia argentifolli (Bellows and Perring) significantly damages squash plants via introduced t oxins that cause chlorosis, distortion of new growth, and physiological disorders such as the squash silv erleaf (SSL) disorder (Liburd and Frank 2007). The SSL is one of the most important physiologi cal disorders in cucurbits caused by immature whitefly feeding. This disorder produces silvering of the leaf veins, which eventually progresses to cover the surface of the leaf. The yield of the silvered squash plant is consequently lower because of a reduction in photosynthesis. In severe cases of silvering the fruit, stem and flowers of the squash become bleached (McAuslane et al. 1996). In addition to transmitting viruses,

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15 aphids and whiteflies suck sap juices from plants and excrete honeydew, which promotes the growth of sooty mold ( Capnodium spp.) that eventually reduces the vigor and marketability of the vegetable (Palumbo et al. 2000). Justification Generally, aphids and whiteflies are conventiona lly controlled by several broadspectrum insecticides from classes including organophosphates, carbamates, formamidines and cyclodienes (Dewar 2007, Palumbo et al. 2001, We bb 2007). However, this method of control has become increasingly problematic over the years primarily because of the resistance of aphids and whiteflies to these chemicals. Some of these synthetic insecticides ca n enhance the spread of non-persistent, aphid-vectored viru ses especially in cucurbits (Sta pleton et al. 2002). In addition to pest resistance, insecticides have an overa ll negative effect on the environment by destroying non-target organisms including natural enemies a nd pollinators (Pimental et al. 1992). Florida experiences mild winters and heavy precipitation, which can encourage the persistence of pests year round. All these issues raise serious econom ic and environmental health concerns from growers, scientists and the genera l public. Therefore a more sustai nable approach for insect pest control in organic systems is needed. The use of cover crops is required in organic production. It is possibl e that their use for protecting and improving soils a nd suppressing weeds may affect the population of pest and beneficial insects in a cropping system. Interest in the use of leguminous and graminaceous cover crops for pest management have been c ontinually re-evaluated over the past few years (Bugg et al. 1991, Creamer and Baldwin 2000, Tillman et al. 2004). Cover crops act as a source of food, and an excellent microhabitat for divers e communities of generalis t predators to attack insect pests of vegetable crops, in addition to protecting and improvi ng soils (Bugg et al. 1991, Lu et al. 2000, Sullivan 2003, Costello and Altie ri 1995). In addition, the evaluation of various

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16 summer cover crops for use in vegetable product ion systems in North Carolina resulted in increased biomass within short periods of time, and increased soil fertility (in the case of legumes) (Creamer and Baldwin 2000). Cool-season cover crops have been shown to increase the establishment of the predacious big-eyed bug, Geocoris punctipes (Say), via nectar and other arthropods thereby reducing egg masses of heliothine species on cantaloupe plants (Bugg et al. 1991). Cover crop combinations of leguminous and graminaceous species that establis h quickly and increase soil nitrogen can have benefits by reducing weed pest populations in subsequent cash crops (Creamer and Baldwin 2000). Goal and Hypotheses The overall goal of m y research was to evaluate the effects of summer cover crops on insect pests and beneficials in an organic system before and after the planting of a squash ( Cucurbita pepo L.) cash crop. I hypothesized that 1) the establishment of cover crops, especially legume-grass mixtures would enhance natural enemy populations in the organic field 2) residual populations of natural enemies following cover crop incorporation will suppress pest populations in the subsequent s quash crop, and 3) cover crops w ould lead to increased squash yield as a result of reduced pest pressures. Specific Objectives To study the population dynam ics of aphids, whit eflies and beneficials (selected parasitoids and predators) in monoculture and diculture (mixed cover crop stands). To determine whether residual populations of be neficials from incorporated cover crops can still suppress pest populations in squash. To determine how pest populations from cover crop treatments affect squash yield. To compare several monitoring techniques for aphids and whiteflies for improvement of management techniques on organic farms.

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17 CHAPTER 2 LITERATURE REVIEW Aphids There are over 4700 species of aphids in the world, but only about 100 from the fa mily Aphididae are considered to be major pests of agricultural and horticultural crops (Powell et al. 2006, Dixon 1977, Blackman and Eastop 2007). Approximate ly 2 billion aphids per acre can live on above ground plant parts and an additional 260 million can live belowground. Their small size, high reproductive rates, dimo rphic migratory form, and ability to transmit numerous viruses enhance their effectiveness as pests (Awmack and Leather 2007, Petterson et al. 2007, Dixon 1977). Aphids vector and transmit between up to 275 viruses in many plant species (Frank and Liburd 2005, Kucharek and Purcifull 2001, Zha ng and Hassan 2003, Nebreda et al. 2004, Powell et al. 2006). Some of these viruses include th e papaya ringspot virus type W, the watermelon mosaic virus 2, the zucchini yellow mosaic virus, the cucumber mosaic virus and an unnamed potyvirus (Kucharek and Purcifull 2001). These aphid-transmitted viruses have been major impediments to the consistent production of squa sh in Florida, and they produce symptoms that include plant stunting, leaf strappi ng, leaf chlorotic spotting, redu ced weight, distorted stamens, interveinal and flower necors is, green mottling, deformed seeds and ringspots (Kucharek and Purcifull 2001). Biology and Behavior of Aphids According to Dixon (1977) m any aphids have complex life cycles. Aphids have a heteroecious or monoecious life cycle based on how they utilize their host plants (Williams and Dixon 2007). Heteroecious or host al ternating aphids live on a primary host plant in the winter and a different secondary host plant in the summ er and eggs are laid on the primary host after

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18 mating. However, monoecious aphids are associated with only one or very closely related host plants to complete their lif e cycle (Williams and Dixon 2007). Aphids have main two types of reproduction that is used to complete their life cycle: hololytic and anhololytic. Hololy tic (sexual) reproduction in aphi ds involves the production of eggs followed by parthenogenesis (the production of offspring without males) whereas in anhololytic (asexual) reproduction, female aphids reproduce parthenogenetica lly all throughout the year (Williams and Dixon 2007). Parthenogenesi s doubles the intrinsic rate of population increase, thereby presenting a definite reproduct ive advantage by reducing the time for the aphid to become sexually mature (Dixon 1997). Short day length is known to induce a change from asexual to sexual reproduction in aphids (Dixon 1977). This res ponse is measured by a biological clock within aphids, which corr elates with a photoperiodic recep tor within the mid dorsal region of the aphids brain a nd causes this change. Aphid dispersal is accomplishe d by two distinct morphs: a winged (alate) form and a wingless (apterous) form. Walking is the active m ode of dispersal for apterous aphids, whereas for alate aphids, walking and flying are the main m odes of dispersal. An aphid is able to move from one point to the other ei ther voluntarily or involuntarily Voluntary aphid movement is prompted by extrinsic factors such as food, mate, oviposition, escape responses from sensed attack of a natural enemy or the chemical comp osition of a deteriorating host plant (Irwin et al. 2007). Involuntary aphid movement is usually as a result of the force of gravity, air currents, farm machinery or animals. Aphids will selectively choose their host plants via successive sensory and behavioral patterns. They respond phototactic ally to different plant-reflec ted wavelengths and volatiles, which trigger pre-alighting behavi or. Aphids will walk back a nd forth across the leaf surface

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19 assessing surface cues before stylet insertion. Probing of the epidermis is followed by repeated stylet penetrations into the mesophyll, parenchyma and phloem sieve tubes to allow for sap extraction and ingestion (Powell et al. 2006). Following ingestion of sap juices, aphids excrete a sticky substance called honeydew as a waste product. Honeydew promotes the growth of black mold on the plant but also attracts honeydew-l oving ants, which tend to the aphids and defend them from their natural enemie s (Palumbo et al. 2000, Hooks et al. 1998). Some aphids can also inject toxic salivary secretions into plants, whic h cause deformed and disc olored leaves, galls on leaves, stems and roots and overall stunted plant grow th (Drees 1993). Whiteflies Whiteflies are econom ically destructive pest s on a global scale causing great damage to horticultural crops, ornamentals, greenhous e plants, and vegetables such as Brassica spp. (McAuslane 2005, Simmons 2002, Nebreda et al. 2005, Simmons et al. 2002, Goolsby et al. 1998). In 1998, whiteflies were responsible for almost $1 billon USD worth of crop loss, job displacement and control measures (Goolsby et al. 1998). Bemisia argentifolli, the silverleaf whitefly, extracts large quantities of phloem sap a nd reduces yields by up to 50% in vegetables and cotton (Chu et al. 2001, Byrne and Bellows 1991). Female whiteflies lay eggs on the lower leaf surface and cause heavy infestations (Nebreda et al. 2005). Honeydew excretions from adults and nymphs promote the growth of s ooty mold, and cause additional discoloration on parts of the plant that are used for food (Byrne and Bellows 1991, Nebreda et al. 2005). In cucurbit crops such as squash, B. tabaci Biotype B causes severe physiological disorders such as the squash s ilverleaf disorder (McAuslane et al. 1996). Im mature crawlers feed voraciously on squash causing the characteristic silvering of the adaxial leaf surface and blanching of the fruit in as little as 2 weeks (Frank and Liburd 2005).

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20 Biology and Behavior of Whiteflies Whiteflies are parthenogenetic and arrhenot okous (unm ated females produce males, and mated females produce males and females), and th e adults are sexually dimorphic (males are smaller than females) (McAuslane 2005, Byrn e and Bellows 1991). Mating occurs once the wings of the whiteflies have expanded and ha rdened (McAuslane 2005). In fall and spring, mating occurs 3 days after eclosion and copulation can last up to 8 hrs in the summer months. Whiteflies are multivoltine with up to 6 generations per year and will continue to reproduce as long as temperatures permit (Bryne and Bellows 1991). Oviposition by female whiteflies depends heav ily on host plant quality and temperature. The female selects suitable host plants via colo r cues for alighting pur poses, but the odor of crushed plants will also serve as an attractant (Byrne and Bellows 1991). Once the female whitefly lands on a plant, she goes to the lower surface, probes the leaf and ingests a small amount of sap with her piercing mouthpart in order to test the suitability of the plant. Once the plant is deemed suitable, the female begins to feed and eventually will deposit eggs on the underside of the leaves depending on the temperature and quality of the host (McAuslane 2005, Byrne and Bellows 1991). Female whiteflies can produce between 48 to 394 eggs with an average of 252 eggs at a temperature of 28.5 C in the summer months (Byrne and Bellows 1991). Once crawlers hatch, they rapidly walk over the leaf surface, movi ng within and between healthy feeding areas, eventual ly settling down and remaining se ssile until they become adults (Smith 1999, McAuslane 2005, Byrne and Bellows 1991) The sessile nature of the crawlers makes them very susceptible to parasitoids, predators and pathogens (Smith 1999). Once the adults emerge from a T-shaped slit in the last nymphal instar, they fly up the same plant or move to another plant (McAusla ne 2005). Whitefly migrations tend to be short

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21 ranged, and in most cases dispersal within distan ces of more than a few hundred meters are aided by humans. Two dispersal morphs exist in populations of B. argentifolli : a migratory morph and a trivial-flying morph, with th e latter being the most comm on (Byrne and Bellows 1991). Migratory morphs can travel up to 7 km whereas trivial-flying morphs can only disperse up to 150 m (McAuslane 2005, Byrne and Bellows 1991). On ce food quality deterior ates, migration to another food source is enabled by wind currents, where whiteflies tend to be transported like aerial plankton. They will land on suitable hosts by chance. Short range migration allows for well-established colonies on closely spaced vegetation (Byrne and Bellows 1991). Management of Insect Pests Using Natural Enemies Coccinellidae (Ladybird beetles) Predacious ladybird beetles are im portant in suppressing pest populati ons and have been more widely used in biological control programs compared with other taxa of predacious insects (Obrycki and Kring 1998). They are especially important predators of aphids, whiteflies, mealybugs, scales and mites (Ped igo 2002, Frank and Mizell 2004). The whitefly predator, Delphastus spp. is predacious on th e greenhouse and silverleaf whiteflies throughout their adult lives (Heinz et al. 1999). Bo th males and females are known to consume high numbers of whiteflies, the female s have a high fecundity and a total generation time of 19 to 20 days. They work well with para sitoids to reduce whitefl y numbers because of their selective nature for the type of whiteflie s that they consume. Th ese coccinellids prefer healthy whiteflies, and can distinguish between th ose that have already been parasitized (Heinz et al. 1999). Coccinella septempunctata L. is an example of an aphidophagous coccinellid and is one of the most predacious beetles on different aphid species worldwide (Shannag and Obeidat 2006). Other aphidophagous coccinellids like C. septempunctata have responded to the presence of

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22 aphids on plants by depositing e ggs near the prey and significa ntly reducing their populations where there is a buildup of aphi d refuge (Obrycki and Kring 1998). Voracity, abundance, timing and length of coccinellid generation in relation to aphid population are fa ctors which influence the efficacy of ladybird beetles as natu ral enemies (Shannag and Obeidat 2006). Carabidae (Ground beetles) In sustainable organic system s, carabids ar e well known as natural enemies for insect pests. They are polyphagous, have a long life cycle and are efficient at suppressing pest outbreaks. However, carabids are very sensitive to anthropogenic influences. Agrochemicals can significantly influence their composition, abundance and spat ial distribution (Lvei and Sunderland 1996, Kromp 1999). As generalist predator s, there is still some debate about the effectiveness of carabids as biocontrol agents in terms of host specif icity (Symondson et al. 2002). There are some ground-dwelling beetles that are able to feed exte nsively on aphids as they move throughout the plant via wind or rain dislodgement (Brewer and Elliott 2004). Many beetles exhibit iteroparity (the abil ity to breed and reproduce multiple times throughout their life cycle). Eggs can be laid singly or in batche s with up to several hundred per female in one season (Lvei and Sunderland 1996) Eggs hatch as elong ated larvae that taper towards the end. Mature beetle larvae will pupate in the soil. The life cycle usually takes 12 months to be completed, and adult ground beetles can live for as long as 3 years. Both larvae and adult beetles are known to be voracious pred ators on insect pests (Lyon and Purrington 2007). Syrphidae (Syrphid Flies) Syrphid flies are voracious on several species of aphids and becom e abundant during heavy aphid densities (Brewer 1995, Antonelli 2003). They have high reproductive rates and high mobility which allows them to take advant age of aphid colonies (Ambrosino et al. 2006). The adult flies are harmless and feed on honeydew, nectar (used as an energy source), and pollen

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23 (used as a source of protein for egg production) (Smith and Chaney 2007). However, the larval stage is the stage that is predacious on aphids with one larva consuming as many as 500 aphids during its 3 week developmental period (Antonelli 2003). Once the adult females lay eggs in early summer within aphid colonies, larvae will emerge 3 to 4 days later. Syrphid flies are multivoltine and can produce 3 to 7 generations pe r year, going from egg to adult in 16 to 28 days depending on weather and location (Antonelli 2003). Parasitoids The use of parasitoids as natural enem ies for insect pest management has been practiced for as long as 1600 years in China (Wei et al. 2005). Parasitoids occupy similar feeding guilds with predators such as coccinellids or carabids. Interestingly, these predators can affect parasitoid reproductive opportunities by feeding on parasi tized insects (Taylor et al. 1998). In order to understand the efficacy with which pa rasitoids can suppress pest populations, it is necessary to understand the dynamic multitrophi c (plant-herbivore-parasitoid/predator) interactions that occur (Kalul e and Wright 2005). Bottom up f actors such as plant nutrient quality affect the insect pest, and eventually th e self-sustainability and efficacy of the natural enemy (Kalule and Wright 2005). It is also a common occurrence for gene ralist predators to disrupt the biocontrol of a pest species by a parasitoid (Kalule and Wright 2005, Symondson et al. 2002). Braconids and ichnuemonids are the two most common groups of parasitoids that attack aphids. Aphids such as Brevicoryne brassicae (L.) and Myzus persicae (Sulzer) are both attacked and parasitized by the braconid Diaeretiella rapae (McIntoch) (Costello and Altieri 1995). This parasitoid specializes on crucif erous aphids but is also known for attacking other polyphagous aphids (Zhang and Hassan 2003, Costello a nd Altieri 1995). In living mulches, D. rapae

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24 consistently kept aphid populations at a minimu m compared with clean cultivation (Costello and Altieri 1995). Alternatively, the a phelinid parasitoid, Encarsia formosa Gahan, is well known for its control of whiteflies on greenhous e crops and vegetables (Hoddl e et al. 2007). Eggs mature within 8 to10 days and the adults reduce whitefly populations by either consuming the hemolymph of their immature hosts or by ovi positing (Hoddle et al. 2007 ). Also, braconid parasitoids such as Aphidius spp. can also have a significa nt negative impact on aphid populations. With a complete life cycle of 10 da ys, females can attack as many as 300 aphids (Moschetti 2003). Lepidopteran pests usually have e gglarval parasitoids such as Ascogaster spp. and Chelonus spp. that use polydnaviruses and venom to induce premature metamorphosis of the host, thereby allowing the paras itoid to emerge from the pre-pupal stage of the host (Beckage and Gelman 2004). Presently, the most well known e gg parasitoids of lepidopteran pests come from 33 species in three families which in clude: Trichogrammatidae, Scelionidae and Encyrtidae. They attack a wide ra nge of lepidopteran pests including Helicoverpa spp., T. ni (Hbner), P. xylostella L., Manduca sexta L., P. rapae L ., Ostrinia nubilalis Hbner, and Mamestra brassicae L. (Sithanantham et al. 2001). Insect pests attacked by parasi toids are usually parasitized an d tend to die slowly. The life cycle of a parasitoid is complex. A single immature parasitoid or several hundred immatures may develop within or on one host and ultimately kill the host via different hormonal pathways before emerging as an adult (Hoffmann and Frodsham 1993, Pedigo 2002). Parasitoid wasps have many methods of manipulating their host in order to create a medium that will support and promote the developm ent of their offspring (Beckage and Gelman

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25 2004). Parasitoids can be regulators or conforme rs. Regulators use hormonal or neurohormonal strategies to disrupt developmental pathways in their host, whereas conformers have similar endocrine signaling pathways with the host th at simultaneously coordinates developmental activites such as molting (Beckage and Gelman 2004). The final instar of the host will eventually show disruption of feeding ac tivites, molting and metamorpho sis that was induced by the parasitoid (Beckage and Gelman 2004). Management of Insects Using Cover Crops The idea of developing a m ore environmen tally friendly approach towards pest management in fruits and vege tables offers several benefits to the grower and is more sustainable. Two hypotheses have been proposed to e xplain how cover crops reduce herbivore damage (pest outbreaks) in complex, mixed crop communities. The natural enemies hypothesis proposes th at more diverse food sources (nectar, pollen, prey host species) allow for the establishment of higher densities of predators, parasitoids and parasites, which regulate pest populations in diverse habitats. Alte rnatively, the resource concentration hypothesis predicts that specialist herbivores will choose to remain in pure stands (monocultures) as opposed to more diverse plan t habitats (Root 1973). As a result, there is decreased pest pressure in complex plant communities. Cover crops, which are an integral part of sustainable organic agriculture provide an excellent poten tial alternative for managing economically important insect pests (Lu et al. 2000, Treadwell 2007, Creamer and Baldwin 2000). Cover crops can be annual, biennial or pere nnial herbaceous plants grown singly or in mixed species stands throughout th e year (Sullivan 2003). In temper ate climates cover crops are usually winter annuals that are pl anted in late summer to give soil cover in the winter (Lu et al. 2000, Sullivan 2003). Barley, ryegrass and rye, for example, are excellent winter grass cover

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26 crops because of their hardiness (Lu et al. 2000). Legume cover crops such as hairy vetch, clovers, medics and field peas are also used. They all have high nitrogen content in addition to being hardy (Lu et al. 2000, Sullivan 2003). Summer cover crops are warm-s eason species that are used to improve soil conditions and prepare the land for a subsequent crop. Legum inous summer cover crops include cowpeas, VB, guar, crotalaria, soybeans, sesbania, and a nnual sweetclover, whereas graminaceous summer cover crops include sorghum-sudangrass, mille t and forage sorghum (Creamer and Baldwin 2000, Sullivan 2003). Cover crops have a variety of roles includi ng suppressing weeds, insects and nematode populations, holding soil particle s together, providing nitrogen for subsequent crops, reducing erosion runoff and pollution of surface water, removing excess salt, preventing leaching of nitrates and influencing insect life cycles (Creamer 1999, Creamer and Baldwin 2000, Hanna et al. 1995, Lu et al. 2000). Cover cr ops also influence insect popul ation dynamics. In orchards, well managed cover crops divert generalist pests, confuse specialist pest s, reduce pest success by altering host plant nutrition, changing the microclimate and by increasing natural enemy abundance (Bugg and Waddington 1994). Much interest has also been shown in combining leguminous and graminaceous cover crops in vegetable agroecosystems possibly beca use of the enhanced protection that can be gained from attracting a greater diversity of bene ficial insects due to in creased plant diversity (Creamer 1999). Mixing of leguminous and gram inaceous cover crops can also combine the benefits only pure strands could provide (Creamer 1999). Growers will not utilize cover crops if they are not economica lly feasible. Inputs costs such as fertilizer applications, use of plastics a nd reduced pesticides should amount to practical

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27 savings when compared with conventional syst ems (Lu et al. 2000). The cover crops that I focused on in my research included two legume speices: SH ( Crotalaria juncea ) and VB ( Mucuna pruriens ), and grass species: PM ( Pennisetum glaucum ) and sorghum-sudangrass (Piper) Stapf. Leguminous Cover Crops Sunn hemp [SH] ( Cr otalaria juncea L.): This plant is an herbaceous tropical legume that is tolerant to drought a nd grows well in high and low pH soils (Ragsdale 2006, Balkcom and Reeves 2005). It is fast growing (60 to 80 days) and can grow to approximately 3 m in height; thereby, acting as a good weed suppressant (Ragsdale 2006, Rich et al. 2003). It remains succulent for about 8 weeks after being plan ted and becomes more fibrous as it matures (Creamer 1999). Sunn hemp produces high biomass yields (2.4 to 3.4 tons of dry mass per ha) and nitrogen (381 to 504 kg per ha) for subsequent crops before the first frost period (Creamer 1999, Balkcom and Reeves 2005). High nitrogen fixation coupled with resistance against southern root-knot and sting ne matodes makes it an excellent green manure and cover crop (Rich et al. 2003, Wang and McSorley 2004). However, SH seeds may require inoculation with the appropriate Rhizobium bacteria for nitrogen fixation. And, although seed prices are fairly high ($3.30 to $8.80 per kilogram / $1.50 to $4.00 pe r pound), high seeding rates produce more succulent stems (Ragsdale 2006, Creamer 1999). With these limitations, SH is still considered a very good cover crop for use in North-Central Florid a because very few insect or diseases affect its establishment or production (Ragsdale 2006, Rich et al. 2003). Velvet bean [VB] ( Mucuna pruriens L.): This plant is native to Asia and is an annual tropical legume that has spread throughout the US as a graz ing and green manure cover crop (Rich et al. 2003). It grows vigor ously in droughty, sandy and infe rtile soils and requires a long frost-free growing season (100 to 250 days to reach maturity) (Rich et al. 2003, Creamer 1999).

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28 The stem reaches up to approximately 2.8 m in vine cultivars, the pods are hairy and the leaves are trifoliate with large, ovate leaflets (Creamer 1999). This cover crop adds a considerable amount of nitrogen to the soil and is known to be resistant and antagonistic towards nematodes (Rich et al. 2003). It also produ ces high biomass yield (2 to 2.8 tons per ha); thereby, supplying the subsequent cash crop with 570 to 790 kilogram s of fixed nitrogen (R agsdale 2006). Although the VB caterpillar, Anticarsia gemmatalis (Hbner), is a major pest of this cover crop, it tends to be generally free of diseases and ot her insect pests (Rich et al. 2003). Graminaceous Cover Crops Pearl m illet [PM] ( Pennisetum glaucum (L.) R. Br .): This grass is the most important millet for food and feed on the world market accounting for > 55% of global millet production (ICRISAT). This cover crop is a fast growing, high-yielding, high-quality grass that can be widely grown throughout Florida (Chambliss and Ad jei 2006). This warm-season annual is able to grow up to 3.6 m in height, and grows best on well drained soils, but is tolerant of drought and acidic soil conditions (Chambliss and Adjei 200 6). Planting usually takes place between April and July and the crop matures in 60 to 70 days (Creamer 1999). Pearl millet also has a fast growing, extensive network of root s that takes advantage of moistu re and nutrients. The plant is able to accumulate nitrates during a drought if nitrogen was previously applied before the drought (Chamblis and Adjei 2006). Although PM grows slowly as a seedling, it competes well with late-emerging weeds and has an average pr oductivity of 128 kg per ha (Myers 2002). This grass does not demand a large supply of nutrients to grow well. As a graminaceous cover crop, it is unable to fix nitrogen in the soil, but its nitr ogen needs can be obtained from animal manure, a leguminous cover crop, or nitrogen fertilizer (Myers 2002). The onl y significant disease problem associated with this cover crop is downy mildew caused by Sclerospora graminicola (Sacc.) J. Schrot. Chinch bugs and the European corn borer are common insect pests that pose occasional

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29 problems for this plant but the only important pe st is the European corn borer (ICRISAT, Myers 2002). Sorghum sudangrass [SSG] ( Sorghum bicolor x S. sudanense (Piper) Stapf ): This grass is well known and has been frequently used in Florida for decades (Ragsdale 2006). It is a cross between grain sorghum and sudangrass, and is a warm seas on cover crop that produces 2 to 2.8 tons of biomass per ha (Ragsdale 2006, Cream er 1999). It is an excellent suppressor of weeds, insects and nematode populations, help s to control erosion, grows rapidly, and has allelopathic properties (Creamer 1999). A high C N ratio is present in large fibrous stems that act to reduce decomposition and prevent leaching (Ragsdale 2006). It does well when planted in mixtures but often attracts armyworms and corn silk flies which can harm vegetable crops (Ragsdale 2006).

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30 CHAPTER 3 POPULATION DYNAMICS OF APHIDS, WHITEFLIES AND THEIR ASSOCIATED NATURAL ENEMIES IN MONOCULTURE A ND DIC ULTURE COVER CROP SYSTEMS The production of summer squash ( Cucurbita pepo L.) in Florida had a value of $53 million USD in 2007 (USDA NASS 2008). Over the last decade, the number of small and medium-sized farms involved in organic squa sh production has signifi cantly increased (Juan Carlos Rodriguez personal communication) due to consumer demands for organic vegetables over conventionally grown produce (Bonina an d Cantliffe 2005). Regardless of production methods (conventional or organic) squash produc tion is currently threatened by major economic pests such as aphids and white flies. If not effectively contro lled, these pests are capable of causing millions of dollars in damage and lo st yield (Palumbo et al 2001, Simmons et al. 2000, McAuslane 2002). Aphids have extremely high growth and deve lopmental rates between temperatures of 78 and 80 C (Awmack and Leather 2007, Dixon 1977, Webb 2006). Typically, aphids start reproducing 7 to 10 days after egg hatch, and many aphids have telescoping generations, which enables an adult female to have offspring insi de her that are simultaneously producing their own daughters by parthenogenesis (Powell et al 2005, Metcalf and Metcalf 1993, Awmack and Leather 2007). This rapid reproducti ve behavior can result in severe crop damage if no effective management is employed. Furthermore, some aphids ar e able to survive in the soil for 48 days at 3 C and eggs are known to survive temperat ures lower than 40 C (Dixon 1985). Such longevity and persistence, increases their importan ce as economic pests. Whiteflies are generally multivoltine having 2 to 6 generations per year. They can continue to reproduce as along as temperatures are favor able (Bryne and Bellows 1991). Their life-cycles can be as short as 2 weeks under warm temperat ures and the adult female can produce 252 eggs at 28.5 C (Byrne and Bellows 1991, Webb 2006). Bo th aphids and whiteflies suck sap juices

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31 from plants and excrete honeydew, which promotes sooty mold growth and transmits viral diseases, all of which reduce the vigor and marketability of the vegetable. Generally, aphids and whiteflies are conventio nally controlled by several broad-spectrum insecticides from classes including organophosphates, carbamates, formamidines and cyclodienes (Webb 2007, Palumbo et al. 2001, Dewar 2007). Although neonicotinoids are a newer class of insecticides that are effective against aphids a nd whiteflies, many aphid species have become resistant to other insecticides (Dixon 1985). Some of these synthetic insecticides can enhance the spread of non-persistent viruses especially in cucurbit s (Stapleton et al. 2002). Similarly, for whiteflies, all stages of the life cy cle are resistant to numer ous insecticidal sprays (Peet 1995, Palumbo et al. 2001). These insectic ides also threaten non-target organisms including natural enemies, and have a negative effect on the environment by entering waterways via runoff or drift, or depositing on vegetation th at may be later contacted or eaten by wildlife (Pimentel et al. 1992). Organic farms use cultural and bi ological control techniques to manage key insect pests. Cover crops are an integral com ponent of organic farming and su stainable vegetable culture, and can be used in several ways for insect manageme nt practices. For instance cover crops act as a sink and source when intercropped with a cash crop by attracting and further enhancing the number of natural enemies for eventual releas e into the cash crop following senescence of the cover crop (Bugg 1991, 1992). Also, in terms of cultu ral control cover crops are used to reduce the colonization, dispersal and reproduction of pest s on vegetable crops. Th is is accomplished in several ways: 1) acting as a sink fo r various pests, 2) by visually or olfactorally confusing pests 3) by having nutritional effects on host plants, or 4) by reducing the success of the pest via microclimatic changes (Bugg 1992). Parajulee et al (1997) demonstrated that the intercropping

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32 of cotton with several cover crops enhanced the conservati on of cotton aphid predators. Recently, Tillman et al. (2004) also showed that crimson clover (a cover crop used extensively) was responsible for the transfer of big-eyed bug predators onto cotton, but also reported an increase in several ladybird species. Earlier, Bugg et al. (1991) recorded an increase in big-eyed bug predators and successfully tr ansferred these predators from subterranean clover to cantaloupe, which housed sentinel eg g masses of the fall armyworm. Effective organic management strategies for aphid and whitefly pests in cucurbits warrant attention in light of increasing organic production and a general public drive to reduce the use of chemical pesticides. The implementation of c over crops will depend on the growers primary needs, the structure and conditi on of the landscape, and the su bsequent cash crop (Sarrantonio 1998). A leguminous cover crop will add nitrogen to the soil that can be available for the subsequent cash crop. Alternatively, grass cove r crops scavenge for nutrients and take up nitrogen from the soil, but some species produce large amounts of residue that can exceed the amount of organic matter that leguminous cove r crops can provide (Bowman et al. 1998). Legume-grass mixtures may be more effective th an using a legume or a grass independently. The benefits of legumes and grass mixtures include at tracting a greater range of beneficial insects. However, one disadvantage of usi ng mixtures is that they are co mplicated to manage and must be mixed suitably to respond to soil, weathe r and pest conditions (Bowman et al. 1998). Additionally care should be taken when selecting the best cover crop because they can harbor both beneficial and harmful arthropods (Bugg 1991) It is therefore im portant to evaluate different cover crops to determin e which one could provide the greatest benefit in terms of pest suppression.

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33 The primary goal of this research was to study the population dynamics of aphids, whiteflies and beneficials in monoculture and mixe d cover crop stands in an organic system to assess their likely impact on a subsequent cas h crop. My hypothesis was that mixed cover crop cultures would increase the number of beneficial arthropods and potentially suppress aphids and whitefly pests. Materials and Methods The experim ent was conducted at the Universi ty of Florida Plant Science Research and Education Unit in Citra, FL in 2006 and repe ated in 2007. The experimental design was a completely randomized block with four replicates of seven treatments. Seven treatments were evaluated, which included two legumes, sunn hemp [SH] ( Crotalaria juncea L.) and velvet bean [VB] ( Mucuna pruriens (L.) cv. GA Bush); two grasses, sorghum sudan grass [SSG] ( S. bicolor x S. sudanense cv. Brown-Midrib) and pearl millet [PM] ( Pennisetum glaucum L. cv. Tifleaf3); two legume-grass mixtures, sunn hemp/pearl m illet [SH/PM] and sorghum sudangrass/velvet bean [SSG/VB], and a weedy fallow plot (control). Each treatment plot measured 12 m x 12 m. Each plot was separated by mowed alleys that were 12 m wide, wh ich was intended to reduce the movement of pest and benefici al arthropods between plots. Th e size of the field measured 7.2 acres, but the total cul tivated area was 2.05 acres. Both legumes, SH and VB, were broadcast at a rate of 40 lbs/ acre ( 45 kg / ha) and 100 lbs/ acre (112 kg / ha) respectively, while PM an d SSG were each planted in rows approximately 18 cm apart at the rate of 25lbs / acre (28 kg / ha) and 40 lbs / acre (45 kg / ha) respectively. The SH/PM mixture was planted usi ng a Sukup 2100 planter at of th e recommended seed rate of SH, 20 lbs / acre (22 kg / ha) plus 2/3 the recommended seed rate of PM, 17 lbs / acre (19 kg /ha).

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34 Prior to the beginning of the experiment in 2006, the experimental area was treated with spent mushroom compost (Quincy Farms, 190 Mannic Counn Road) at 10 tons / acre to enhance soil nutrient content. Southern cowpea cover crop, Vigna unguiculata L. cv. White Acre, (Alachua Seed and Lumber, Alachua, FL) was in corporated in the soil using a John Deere 6615 tractor (Marion Tractor, Inc., Ocala, FL) at 50 lbs / acre (56 kg / ha) at a depth of 5 cm prior to establishing the cover crop treatments to improve soil and nutrient fertility. In 2007, 3 weeks prior to cover crop planting, el emental sulfur (Tiger 90) was applied to the entire field at 8lb/plot with a check dr op spreader (Newton Crouch Inc., Griffin GA) to reduce the alkalinity of the soil. One application of sulfomag (8.2l bs / plot) was applied to all treatment plots 24 hrs before cover cr op planting using a Catch drop spreader. Assessment of Aphids, Whiteflies and Natural Enemies w ith Unbaited Yellow Sticky Traps In 2006 and 2007 aphids, whiteflies and natu ral enemies (selected parasitoids and predators) were monitored using one unbaited yellow sticky trap placed in the center of each plot (Great Lakes IPM, Vestaburg, MI). Yellow sticky traps were left in the field for 48 hours then brought back to the lab where they were wrapped in clear plastic a nd stored in a refrigerator until they were ready to be processed. Ground predat ors and lepidoptera were assessed separately. Aphids and whiteflies on yellow sticky traps were assessed by using a sub-sampling technique as outlined by Finn (2003) due to the high aphid and whitefly densities. This subsampling technique eliminates counting errors an d reduces the time spent per trap. Each yellow sticky trap was overlaid with a gr idded transparent paper divided in to 63, 1inch squares. Fortyeight of these squares were co lored in, while 15 were left tr ansparent (Figure 3-1). The area under these 15 transparent 1inch squares were examined unde r a X 40 dissecting microscope and the number of aphids and whiteflies were reco rded. Parasitoid numbers were low, therefore,

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35 the parasitoids in all 63 squares on the sticky tr aps were counted and recorded for each unbaited yellow trap. Assessment of Ground Predators with Pitfall Traps Carabid (ground) beetles were m onitored using locally m ade pitf all traps. These traps were left in the field for approximately 6 days. A 25% antifreeze solution (Zerex G-05, Ashland Inc. Lexington, KY) was poured into the pitfall trap until the solution was just below the wiremeshed holes. The antifreeze solution was responsibl e for killing the insects and preventing rapid decomposition before the traps were serviced each week. Each week the contents from the intact cup was emptied into a plastic co ntainer and taken back to the laboratory for analysis. In 2007 when the experiment was repeated a 5% deterg ent solution (Colgate Palmolive Co. New York, NY) was used instead of the 25% antifreeze solution as a more environmentally friendly approach. Assessment of Lepidopteran Pests In 2006 and 2007, cover crops were sam pled weekly for lepidopteran larvae, and levels of parasitism. Two sampling techniqu es were used to sample for lepidopterans. They included: Drop-cloth method (for lepidopteran larvae) Bucket trap method (for lepidopteran adults) The first sampling technique was the drop-cloth method, which involved placing a 45 cm x 45 cm white cotton fabric on the ground and vigor ously shaking 7 randomly selected plants from the center of each treatment plot 5 times. All larvae which fell on the drop cloth were counted, collected and brought back to the la boratory for identification. Dead larvae were placed into 70% ethanol for storage and identification. Recovere d live larvae were placed into rearing cups containing synthetic diet (Shaver and Raulston 1971) so that deve lopment of hosts or parasites could be completed (Browning et al. 1985). All sp ecimens were placed into an environmental

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36 chamber (Percival, Boon, IA) (28 C, photoperiod of 14:10 [L:D] h) and allowed to complete development. The second sampling technique that was used for capturing adult lepidoptera involved the use of tri-colored (yellow, white and green) bucket traps. Bucket traps were baited with the floral volatiles phenylacetaldehyde and linalool. Vapor-strip s were placed at the bottom of the traps to kill the lepidopterans entering the traps. One buc ket trap was placed in the middle of each block (totaling 4). Adult lepidoptera were collected weekly by emptying the buckets and bringing them back to the laboratory for identification. Statistical Analysis The data for aphids, whiteflies, pa rasitoids and the whitefly predator, D. pusillus (yellow sticky trap counts) were squareroot transformed and analyzed us ing repeated measures analysis (PROC MIXED, SAS Institute 2003) to examine the interaction effect between treatment and time (sampling week). Values for least square means were assessed and those means were compared to determine the effect s of the cover crop treatments. Data from ground arthropods in pitfall traps as well as lepidopteran larvae and adult counts were analyzed using analysis of variance (ANOVA) followed by mean separation using least significant differe nce (LSD) test (SAS Institute 2003) .The data were square root transformed where necessary to meet the assumptions for the ANOVA. Results were considered significant if P 0.05. Results During 2006, som e cover crops were affected by diseases. In particular, PM was infected with the Pyricularia leaf spot di sease, SSG had Southern blight di sease and SH was infected with Leaf margin necrosis. The monoculture SSG had small patchy sections onl y at the edges of the field compared with other treatments and about 40% of the VB plots contained weeds. In 2007,

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37 the horizontal and vertical alle yways (between cover crop treatme nts) were covered with weeds during the first few days of cover crop establishment. Following the removal of the weeds from the alleyways, approximately 60% of the VB tr eatment plot still contained weeds. Additionally, plants in the VB plots showed yellowing leaves and were fairly dry. Generally, the overall growth of the cover crop treatments during 2007 was good. There were several groups of natural enemies that were collected from the sticky traps, which included various parasitic diptera, aphidophagous syrphid f lies (Diptera: Sy rphidae) such Toxomerus marginatus (Say) and T. geminates (Say) various coccinellid species that included the whitefly predator, Delphastus pusillus (LeConte), the convergent ladybird beetle, Hippodamia convergens Gurin-Mneville, the seve n spot ladybird beetle, Coccinella septempunctata L. and the multicolored Asian ladybird beetle, Harmonia axyridis Pallas.There was no significant difference in natural enemy numbers between treatments with the exception the coccinellids, which will be discussed in more detail further on. There were also several groups of pest spec ies collected via sticky trap sampling. These included aphids, whiteflies, leafhoppers and pl ant hoppers. The aphid species caught depended on the type of cover crop treatment in the fiel d. The legumes, SH and VB mainly harbored the black legume aphid, Aphis craccivora Koch, the green citrus aphid, Aphis spiraecola Patch, the melon aphid, Aphis gossypii Glover and the green peach aphid Myzus persicae (Sulzer), whereas the grasses, PM and SSG, har bored the corn leaf aphid, Rhopalosiphum maidis (Fitch), the yellow sugar cane aphid, Sipha flava (Forbes), and Hysteroneura setariae (Thomas). Both sets of mixtures, SH/PM and SSG/VB, harbored aphids th at were common to gra sses and legumes. The weedy fallow (control) plots also had aphid species from both grasses and legumes.

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38 Bemisia argentifolii (Bellows and Perring), the silverleaf whitefly was the main species found in the treatment plots. The only natural enemies of whiteflie s that were observed included Delphastus pusillus LeConte, which was present in both 2006 and 2007. Population of Aphids and Whiteflies within C over Crop Treatments (Yellow Sticky Traps) Aphids 2006. During 2006, the SH had a 90% decline in adult aphid populations over the 3 week sampling period when cover crops we re in the field. There was no significant difference in the number of aphids in the SH compared with PM or the corresponding SH/PM mixture (Table 3-1). However, all three cover crop treatments did have significantly fewer aphids than the weedy fallow control on the 3rd (final) week of sampling ( F = 2.93; df = 3, 6; P = 0.0357). Overall, there was no interaction between treatment and time. Alternatively, aphid populations in SSG and the SSG /VB mixture we re consistently low (< 1 aphid per plot) throughout the sampling period. Only at the end of the sampling period did SSG have significantly fewer aphids than the weedy fallow control and the VB ( F = 2.93; df = 3, 6; P = 0.0357). Overall there was no interaction be tween treatment and time (Table 3-1). 2007. During 2007, SH had significantly more aphids than SH/PM mixture and the weedy fallow control ( F = 4.02; df = 3, 6; P = 0.01) during the first week of sampling (Table 3-2). Similarly, VB had significantly more aphids the weedy fallow control (F = 4.02; df = 3, 6; P = 0.01). However, at the end of the season, ther e were no significant differences in aphid populations among the treatments (Table 3-2). Fluc tuations in the number of aphids per week was due to the significant time effect ( F =7.11; df = 2, 6; P =0.0262). There was also a significant interaction be tween cover crop and time (sampling period) ( F = 3.64; df = 12, 54; P = 0.0005). There were only treatment differences in the 1st of the 3 week sampling.

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39 Whiteflies 2006. During the first week of sampling, the SH treatment had significantly higher populations of whiteflies (~ 290 per plot) compared with SH/ PM mixture (~ 48 whiteflies per plot) or single stand PM (~ 12 whiteflies per plot) ( F = 2.69; df = 3, 6; P = 0.048) but was not significantly different from the weedy fallow control (Table 3-3). Although whitefly populations in SH declined ~55% by the end of the sampling period, whitefly populations was still significantly higher than PM or the SH/PM mixture ( F = 5.44; df = 3, 6; P = 0.0023). Both PM and the SH/PM mixture had significantly fewer whiteflies throughout the sampling period compared to the weedy fallow control. The VB treatment had a significantly higher number of whiteflies than SSG in the 1st ( F = 2.69; df = 3, 6; P = 0.0480), 2nd ( F = 7.14; df = 3, 6; P < 0.0001) and 3rd week ( F = 5.44; df = 3, 6; P = 0.0023), but was not significantly different from the weedy fallo w control in both of those weeks (Table 3-3). At the end of the sampling period, although there was a 60% decrease in the number of whiteflies in VB, this plot still had 4 times as many whiteflies when compared to SSG or the SSG/VB mixture. There was no significa nt difference between SSG and its corresponding mixture. However, both plots had significantly fewer whiteflies than the control. There was also a significant time effect for the treatments ( F = 10.94; df = 2, 6; P = 0.01). There was a significant decline in whitefly numbers in the PM treatment between the 1st and 3rd week of sampling. Also, between the 2nd and 3rd week of sampling there was a decline in the number of whiteflies in the VB and the SSG/VB mixture. There was no significant interaction between treatment and time for the 2006 field-season. 2007. During the 2007 field-season, SSG and the SH/PM mi xture consistently maintained a low population of whiteflies throughout the season (Table 3-4). Significantly fewer whiteflies in the 1st week ( F = 4.62; df = 3, 6; P = 0.0052) and 3rd week ( F = 4.65; df = 3, 6; P =

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40 0.0051), were observed in both monoculture gr asses (PM and SSG) and the legume-grass mixtures (SH/PM and SSG/VB) compared with th e weedy fallow control (Table 3-4). There was a significant interaction between trea tment and time (sampling period) ( F = 2.80; df = 12, 54; P = 0.0048) Treatment differences were observed in the 1st and 3rd week of sampling. Parasitoids 2006. The majority of the natural enemies identified within the cover crop treatments were parasitoids. These included: Aphelinidae: Aphelinus sp., Braconidae: Aphidius sp., Chelonus sp., and Lysiphlebus testaceipes (Cresson), Icheumonidae, Bethylidae, Sclelionidae: Telenomus sp., Eucoilidae, Mymaridae, Chalcidi dae, Eulophidae: Tetrastichinae, Trichogrammatidae, and Encyrtidae: Metaphycus sp. Many of the br aconids were aphid parasitoids. The family Aphelinidae may have included whitefly parasitoids, but no whitefly parastioids were specifically identified. During 2006, in the first week, SH and PM monocultures had significantly fewer parasitoids compared with the weedy fallow control ( F = 2.68; df = 3, 6; P = 0.0491) [Table 35], but the SH/PM mixture had high numbers of pa rasitoids that were no t significantly different compared with the weedy fallow ( F = 2.68; df = 3, 6; P = 0.0491). Overall, there was an 82% increase in the number of parasitoids in PM over the 3 week sampling period. Alternatively, there was a 67% decrease in parasitoid numbers in the weedy fallow control over the same sampling time (Table 3-5). Similarly, the SSG/VB mixture had significantly higher numbers of parasitoids than VB ( F = 2.68; df = 3, 6; P = 0.0491) [Table 3-5] but was not signi ficantly different from SSG or the weedy fallow control. Overall, there was a signi ficant interaction between treatment and time ( F = 2.20; df = 12, 54; P = 0.0245). Treatment differences were found in the 1st of the 3 sampling periods.

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41 2007. In 2007, SH had significantly higher numbers of parasitoids in the 2nd week compared with all other treatments ( F = 3.21; df = 3, 6; P = 0.0480) [Table 3-6]. There was no significant time effect or interact ion between treatment and time. Coccinellids ( Delphastus pusillus ) 2006. During the first week of sampling, SSG and the SSG /VB mixture had significantly more D. pusillus all other treatments except PM ( F = 2.96, df = 3, 6; P = 0.0346) [Table 3-7]. By the end of the sampling period, SSG and the SSG/VB mixture, had significantl y more coccinellids (F = 8.97; df = 3, 6; P < 0.0001) [Table 3-7] than most other treatments; however, PM was not significantly different th an the SSG/VB treatment. There was a significant interaction e ffect between treatments and time ( F = 2.20; df = 12, 54; P = 0.0246). 2007. In the 1st and 2nd weed of sampling there were no significant differences among the treatments. However in the 3rd week of sampling SSG had significantly higher number of D. pusillus compared with all other treatments ( F = 2.79; df = 3, 6; P = 0.0425) [Table 3-8]. The number of whitefly predators in 2007 was 10 times lower than in 2006. There was also a significant ( F = 1.98; df = 12, 54; P = 0.0443) interaction between treatment and sampling period. Treatment differences were observed in 3rd week of sampling. Assessment of Ground Arthropods from Pitfall Traps Data from 2006 and 2007 field-seasons showed that Formicidae comprised the majority (~ 90%) of the arthropods that were co llected from the pitfall traps (Figure 3-2a). Overall, there was a larger diversity of predators collected in 2006 (~ 8 families) compared with ~ 5 families in 2007 (Figure 3-2). Scarabs were collected in 2006, but were not found in 2007 (Figure 3-2b). During 2006 when the pitfall trap data were pooled across sampling dates and examined according to each treatment, VB treatment had the highest numbers of predatory arthropods compared with all other treatments except PM ( F = 6.74; df = 3, 6; P = 0.0007) [Table 3-9]. In

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42 2007, the weedy fallow control had the highest numb er of predators compared with the other treatments except the two legume-grass mixtures, SH/PM and SSG/VB ( F = 9.32; df = 3, 6; P < 0.0001) [Table 3-9]. Assessment of Lepidopteran Pests During 2006 and 2007, the adult lepidopteran popul ations, which were m onitored by block using floral volatile baited bucket traps produced six comm on species that include: VB caterpillar, Anticarisa gemmatalis (Hbner), Mocis spp., the bella moth, Utetheisa ornatrix L., the fall armyworm, S. frugiperda (J. E. Smith), the beet armyworm, S. exigua (Hbner), and the southern armyworm, S. eridania (Stoll). The population of VB mo th adults was significantly higher than that of all other moth speci es collected via bucket traps in 2006 ( F = 6.78; df = 5, 3; P = 0.0017) and 2007 ( F = 2.87; df = 5, 3; P = 0.0519) (Table 3-10). Ot her species that were found periodically included: the corn earworm Helicoverpa zea (Boddie), the soybean looper, Pseudoplusia includens (Walker), the melonworm Diaphania hyalinata L., the sharp-stigma looper, Ctenoplusia oxygramma (Geyer), the golden looper Argyrogramma verruca (F.), and other miscellaneous noctuid species. There was on ly one incidence of an armyworm larva being parasitized by a tachniid fly. The majority of the lepidopteran larvae coll ected from drop cloth samples by treatment were VB caterpillars. In 2006, a tota l of 47 lepidopteran larvae we re collected from drop cloths over the 3 week period. Of these, 31 survived and were successfully rear ed to adults in the laboratory, all of which were VB caterpillars. There were signifi cantly more VB caterpillars in the SH and VB monoculture compar ed with the other treatments ( F = 8.04; df = 3, 6; P = 0.0003) (Table 3-11). In 2007 a total of 21 lepidopteran larvae were collected from the drop cloth method. Of these, 20 were VB moths and one was a fall ar myworm. There were significantly more VB

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43 larvae collected from SH compared with the other treatments ( F = 5.52; df = 3, 6; P = 0.0021) (Table 3-11). Discussion During the 2006 and 2007 field-seasons, SSG ha d significantly fewer aphids and whiteflies com pared with the control and other cover crop tr eatments. This grass monoculture has the best potential to prevent the buildup of key pests (aphids and whitef lies) in an organic field and consequently could diminish the number of pe st problems that could become established on subsequent cash crops. My results were contrary to Bugg and Ellis (1990) who reported that sorghum grass, Sorghum bicolor L., harbored high numbers of aphids and coccinellids. The hybridization of sorghum and sudangr ass could perhaps have resulted in increased resistance to aphids as well as other pests. Valenzuela a nd Smith (2002) found cultiv ars of SSG hybrids, which have resistance to diseas es, insects and nematodes. Also, SSG hybrids have been reported to possess allelopathic propertie s that can suppress the growth of weeds (Valenzuela and Smith 2002), thereby potentially reducing the number of av ailable hosts for aphids and other pests. Low parasitoid populations in 2006 corresponded to higher aphid numbers (~ 2.6 aphids) per plot, whereas higher parasitoid populations in 2007 corresponded to fewer aphids numbers (~ 0.8 aphids) per plot. Aphidius spp. and L. testaceipes are the two main aphidiine parasitoids that were captured. These parasitoids have high fecunditi es (~ 300 to 1800 eggs per female) [Vlkl et al. 2007] and take 14 to 21 days depending on temp erature to complete th eir life cycle (Ferguson 2005). Both parasitoid species have a wide range of aphid hosts from several species (Rodrigues and Bueno 2001). Many of these host aphids we re captured with the yellow sticky traps. Therefore, these parasitoids may have had some effect in regulating aphid populations. With regards to predators, during 2006, adu lt syrphid flies were captured with yellow sticky traps, but these numbers were extremely low, and there were no differences among any of

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44 the treatments. During the 2007 field-season, blue pan traps were placed in the cover crop plots to enhance the capture of syrphid flies that were observed in the previous year, but none were captured. Therefore, aphidophagous syrphid flies were believed to play a minor role in regulating aphid populations. There were no specific whitefly parasitoids that were recorded from the field, therefore, I assumed that the differences in whitefly num bers among treatments were probably due to coccinellids. In 2006 and 2007, SSG had between 2 to 47 times and 2 to 16 times more whitefly predators respectively, compar ed with other treatments. Delphastus pusillus was the principal predator found in the SSG treatment. It is a vor acious predator of whiteflies. Hoelmer et al. (1993) reported that D. pusillus fed on all whitefly stages and consumed almost 1000 whitefly eggs before it pupating. Other cover crop treatments were also able to suppress aphid and whitefly populations. For instance, SH and PM also had lower aphid populati ons than with the control. However, PM may have a slight advantage over SH in terms of its applicability because this grass treatment had higher numbers of parasitoids and ground arthropods (compared with SH). In 2007, the addition of sulfur to the soil may have reduced the numbe r of soil arthropods in the PM, as well as other treatments. Crcamo et al. (1998) has shown that sulfur contamination can negatively affect soil macroinvertebrates such as carabid beetles, staph ilinids and spiders, most of which were found in the pitfall traps in 2007. Pearl m illet may also be a good choice for suppressing whitefly numbers possibly due to the high number of predators and parasitoids that this cover crop harbored. Both VB and the weedy fallow control had significantl y higher whitefly numbers than any other cover crop treatments. Although VB is ab le to fortify the so il with nitrogen for subsequent cash crop,

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45 the high numbers of whiteflies found in these tr eatments strongly suggests that it is not a good cover crop to establish before planting cucurbits, which is susceptible to whiteflies. In 2006, both dicultures, SH/PM and SSG/VB had significantly fewer aphids than the weedy fallow control, however in 2007, they were significantly different to the control, which had high aphid populations. However, the SSG/VB di culture was able to maintain significantly fewer whiteflies than the SH/PM mixture in both years. Throughout both field seasons, there was no significant difference between the SSG /VB diculture and the SSG monoculture. However, the diculture always had significantly fewer whitefl ies than the VB monoculture. Mixed cultures had more predaceous ground arth ropods including carabid beetles, scarabid beetles, dermapterans and ants (based on pitfall trap counts). The greater number of beneficials recovered from the diculture plots supports th e natural enemies hypothesis by Root (1973) who proposed that higher plant diversity leads to an increase in the number of natural enemies and potentially more regulation in pest population. In 2007, the wee dy fallow had the highest number of ground arthropods because it was the most divers e in terms of the number of different species of weeds present. Several of the carabid species found in the pitfalls were Scarites spp. Carabid beetles are known to feed on agricultural pests such as aphi ds (Kromp 1999, Mundy et al. 2000). They feed on aphids early in the season when their densities are still low and consume aphids that have fallen off the plants unto the ground (Kromp 1999) Laub and Luna (1992) concluded that cover crop mulches provided a suitable habita t for carabid predators including Pterostichus spp. and Scarites spp. Velvet bean (VB) moths and larvae were th e most abundant Lepidoptera recovered from bucket traps, and reared from larval samples in both 2006 and 2007. This inse ct is a serious pest

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46 of legumes and grasses (Gregory et al. 1998). The floral lures used in this study can attract for a relatively long distance (bigger than the 12 x 12 m plots). Also, these lures were chosen because previous research (Meagher and Landolt 2008) showed that VB cat erpillars were attracted to these lures. Although the SH and VB treatments harbored many VB caterpillars, they also harbored many parasitoids including Eulophidae and Braconidae or egg pa rasitoids including Trichogrammatidae, which are known for suppressing lepidopteran pests and providing some control. Demapterans and various species of ants are also predators of the VB caterpillar (Barbara 2000). Ants were the largest group of ground arthropods recovered from the pitfall traps in both 2006 and 2007. The diversity of the pitf all trap captures furt her supports the fact that there was great potential for the adequate su ppression of the pestifer ous lepidopteran in the plots. Overall, the results from this study have show n that the monoculture grasses, specifically SSG, have the best potential for hosting lower populations of aphids and whiteflies in an organic system. Some of these monoculture grasses hold potential to be used as cover crops when subsequent cash crops that are susc eptible to aphids and whiteflies. The SSG/VB diculture is also worthy of mention because it had the best potential for enhanc ing the natural enemy population. These results can help to devel op sustainable pest management pr actices for organic growers, but also shows exceptional promise for the develo pment of future orga nic pest management programs.

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47 Figure 3-1. Gridded transparency used to count aphids and whiteflies on unbaited yellow sticky traps.

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48 Table 3-1. Aphid population dynamics in monoc ulture and diculture treatments in 2006 Mean SEM aphid numbers in 2006 Treatment Week 1a Week 2b Week 3c SH 3.50 2.87 0.00 0.00 0.25 0.25c PM 0.00 0.00 0.25 0.25 0.00 0.00c SH + PM 0.25 0.25 0.25 0.25 0.00 0.00c SSG 0.00 0.00 0.25 0.25 0.00 0.00c VB 4.00 3.67 1.50 1.19 1.75 0.75ab SSG + VB 0.25 0.25 0.00 0.00 0.50 0.28bc Weedy fallow (Control) 3.00 1.91 0.75 0.75 2.00 1.08a Aphid data were square root transformed before analysis, but the means shown represent untransformed values. Means followed by the same letters are not significantly different ( P = 0.05 according to least square means test following re peated measures analysis, LS). a F = 0.81; df = 3, 6; P = 0.5725 b F = 1.09; df = 3, 6; P = 0.4048 c F = 2.93; df = 3, 6; P = 0.0357

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49 Table 3-2 Aphid population dynamics in monoculture and diculture treatments in 2007 Mean SEM aphid numbers in 2007 Treatment Week 1a Week 2b Week 3c SH 5.75 1.25a 0.00 0.00 0.00 0.00 PM 3.00 1.58abc 0.25 0.25 0.00 0.00 SH + PM 0.75 0.47cd 0.00 0.00 1.75 1.75 SSG 0.50 0.50cd 1.00 0.40 0.75 0.75 VB 4.25 1.87ab 0.25 0.25 1.75 0.85 SSG + VB 1.25 1.25bcd 0.25 0.25 1.25 0.47 Weedy fallow (Control) 0.00 0.00d 0.00 0.00 4.00 1.77 Aphid data were square root transformed before analysis, but the means shown represent untransformed values. Means followed by the same letters are not significantly different ( P = 0.05 according to least square means test following re peated measures analysis, LS). a F = 4.02; df = 3, 6; P = 0.0100 b F = 2.33; df = 3, 6; P = 0.0764 c F = 1.59; df = 3, 6; P = 0.2072

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50 Table 3-3. Whitefly population dynamics in monoculture and dicult ure treatments in 2006 Mean SEM whitefly numbers in 2006 Treatment Week 1a Week 2b Week 3c SH 289.50 28.23a 76.50 10.25a 115.75 36.79a PM 11.75 6.34c 1.25 0.94c 1.25 1.25d SH + PM 47.75 32.17c 4.75 2.17bc 2.25 1.60cd SSG 81.25 72.91c 3.00 2.04bc 3.50 2.59cd VB 242.25 78.98ab 57.25 13.60a 56.25 11.07b SSG + VB 95.25 30.26bc 19.25 14.07b 20.50 6.43c Weedy fallow (Control) 169.25 128.02abc 67.00 10.34a 68.00 36.14ab Whitefly data were square root transformed before analysis, but the means shown represent untransformed values. Means followed by the sa me letters are not significantly different ( P = 0.05 according to least square means test fo llowing repeated measures analysis, LS). a F = 2.69; df = 3, 6; P = 0.0480 b F = 17.99; df = 3, 6; P < 0.001 c F = 5.44; df = 3, 6; P = 0.0023

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51 Table 3-4. Whitefly population dynamics in mo noculture and dicult ure treatments in 2007 Mean SEM whitefly numbers in 2007 Treatment Week 1a Week 2b Week 3c SH 57.00 18.81ab 4.25 1.43 47.75 13.74a PM 2.50 1.89c 2.00 0.57 1.25 1.25d SH + PM 5.50 2.61c 2.25 0.75 5.25 2.78dc SSG 2.00 1.41c 1.50 0.64 3.25 1.37dc VB 11.50 2.95bc 1.00 1.00 15.50 6.91bc SSG + VB 8.50 3.22bc 0.50 0.28 3.00 1.47dc Weedy fallow (Control) 158.00 106.67a 8.25 7.26 26.50 11.98ab Whitefly data were square root transformed before analysis, but the means shown represent untransformed values. Means followed by the sa me letters are not significantly different ( P = 0.05 according to least square means test fo llowing repeated measures analysis, LS). a F = 4.62; df = 3, 6; P = 0.0052 b F = 0.91; df = 3, 6; P = 0.5117 c F = 4.65; df = 3, 6; P = 0.0051

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52 Table 3-5. Parasitoid populati on dynamics in monoculture a nd diculture treatments in 2006 Mean SEM parasitoids in 2006 Treatment Week 1a Week 2b Week 3c SH 1.50 1.19bc 0.75 0.47b 1.25 0.25 PM 1.00 0.71bc 2.00 1.22ab 5.50 2.66 SH + PM 5.00 1.58ab 4.50 1.19a 2.75 1.03 SSG 3.00 0.91abc 0.75 0.47b 1.25 0.75 VB 0.25 0.25c 2.00 0.71ab 3.00 0.57 SSG + VB 5.00 1.47ab 1.75 0.85ab 2.50 1.55 Weedy fallow (Control) 10.75 5.34a 1.25 0.62b 3.50 0.86 Parasitoid data were square root transformed before analysis, but the means shown represent untransformed values. Means followed by the sa me letters are not significantly different ( P = 0.05 according to least square means test fo llowing repeated measures analysis, LS). a F = 2.68; df = 3, 6; P = 0.0491 b F = 2.19; df = 3, 6; P = 0.0922 c F = 1.35; df = 3, 6; P = 0.2861

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53 Table 3-6. Parasitoid populati on dynamics in monoculture a nd diculture treatments in 2007 Mean SEM parasitoids in 2007 Treatment Week 1a Week 2b Week 3c SH 13.25 4.36 10.75 3.35a 25.75 12.75 PM 4.75 1.03 2.75 0.47b 6.00 2.34 SH + PM 6.25 2.17 2.75 0.85b 11.75 3.66 SSG 6.75 1.49 2.50 1.19b 8.25 1.54 VB 11.00 5.14 5.00 1.58b 13.25 6.94 SSG + VB 7.50 2.02 4.25 0.63b 13.75 6.00 Weedy fallow (Control) 3.50 0.64 3.00 1.47b 7.25 2.32 Parasitoid data were square root transformed before analysis, but the means shown represent untransformed values. Means followed by the sa me letters are not significantly different ( P = 0.05 according to least square means test fo llowing repeated measures analysis, LS). a F = 1.79; df = 3, 6; P = 0.1580 b F = 4.25; df = 3, 6; P = 0.0077 c F = 1.87; df = 3, 6; P = 0.1465

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54 Table 3-7. Delphastus pusillus population dynamics in monoculture and diculture treatments in 2006 Mean SEM whitefly predator numbers in 2006 Treatment Week 1a Week 2b Week 3c SH 0.75 0.25b 0.25 0.25c 0.00 0.00c PM 2.75 1.75ab 2.25 0.63c 2.75 1.18bc SH + PM 1.25 0.63b 1.00 0.40c 0.25 0.25c SSG 6.25 2.42a 21.75 4.95a 19.00 4.91a VB 0.25 0.25b 0.50 0.28c 0.50 0.28c SSG + VB 6.00 2.27a 12.75 5.00b 9.25 0.25b Weedy fallow (Control) 0.50 0.29b 0.75 0.47c 1.25 0.75c Means for Delphastus pusillus data are untransformed values. Means followed by the same letters are not significantly different ( P = 0.05 according to least square me ans test following repeated measures analysis, LS). a F = 2.96; df = 3, 6; P = 0.0346 b F = 11.01; df = 3, 6; P < 0.0001 c F = 8.97; df = 3, 6; P = 0.0001

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55 Table 3-8. Delphastus pusillus population dynamics in monoculture and diculture treatments in 2007 Mean SEM whitefly predator numbers in 2007 Treatment Week 1a Week 2b Week 3c SH 0.00 0.00 0.25 0.25 0.00 0.00b PM 0.50 0.28 0.25 0.25 0.25 0.25b SH + PM 0.00 0.00 0.00 0.00 1.25 1.25b SSG 1.25 0.47 0.00 0.00 2.75 0.47a VB 0.25 0.25 0.00 0.00 0.00 0.00b SSG + VB 1.00 0.71 0.00 0.00 0.75 0.47b Weedy fallow (Control) 0.50 0.29 0.25 0.25 0.50 0.28b Delphastus pusillus data were square root transformed befo re analysis, but the means shown represent untransformed values. Means followed by the sa me letters are not significantly different ( P = 0.05 according to least square means test fo llowing repeated measures analysis, LS). a F = 1.53; df = 3, 6; P = 0.2248 b F = 0.69; df = 3, 6; P = 0.6589 c F = 2.79; df = 3, 6; P = 0.0425

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56 Figure 3-2. Percentage of total natural enemy population from p itfall traps averaged across all cover crops. Carabidae 2.2% Formicidae 91.8% Scarabidae 0.36% Dermaptera 0.85% Elateridae 2.4% Cicindellidae 0.33% Coccinellidae 0.97% Other 0.85% 91.8% 2.2% 0.36% 0.85% 2.4% 0.33% 0.97% 0.85% Carabidae 5% Demaptera 3.85% Elateridae 0.11% Formicidae 90% Other 1% 90% 5% 3.85% 0.11% 1% A. B.

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57 Table 3-9. Mean number of ground arthropods captured from pitfall traps in 2006 and 2007 Treatment 2006a 2007b SH 2.00 0.71d 4.00 0.71cd PM 13.00 1.77ab 1.75 0.75d SH + PM 4.75 2.25cd 23.00 3.18ab SSG 3.75 1.54cd 7.25 1.31c VB 21.00 4.30a 16.50 2.32b SSG + VB 8.25 3.47bc 21.5 5.95ab Weedy fallow (control) 7.00 1.47bcd 28.00 6.16a Ground arthropod data were square root transformed before analysis, but the means shown represent untransformed values. Also, means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 6.74; df = 3, 6; P = 0.0007 b F = 9.32; df = 3, 6; P = 0.0001

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58 Table 3-10. Mean number of adu lt lepidoptera captured from flor al volatile baited bucket traps in 2006 and 2007 Moth species 2006a 2007b Anticarsia gemmatalis (VB moth) 36.00 13.54a 5.00 1.77a Mocis sp. 8.00 3.34b 1.25 .94b Spodoptera frugiperda (Fall armyworm) 0.25 0.25b 0.00 0.00b Spodoptera eridania (Southern armyworm) 1.00 0.71b 0.50 0.50b Spodoptera exigua (Beet armyworm) 1.25 0.94b 1.50 1.50b Utetheisa ornatrix (Bella moth) 0.25 0.25b 0.50 0.50b Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 6.78; df = 5, 3; P = 0.0017 b F = 2.87; df = 5, 3; P = 0.0519

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59 Table 3-11. Mean number of lepidopteran larv ae recorded from drop cloths in 2006 and 2007 Treatment 2006a 2007b SH 4.25 1.10a 8.00 2.97a PM 0.25 0.25b 1.00 1.00b SH + PM 0.00 0.00b 2.00 0.41b SSG 1.00 0.40b 0.00 0.00b VB 5.75 1.65a 2.00 1.00b SSG + VB 0.00 0.00b 0.75 0.47b Weedy fallow (control) 0.50 0.28b 0.25 0.25b Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 8.04; df = 3, 6; P = 0.0003 b F = 5.52; df = 3, 6; P = 0.0021

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60 CHAPTER 4 INSECT POPULATION DYNAMICS IN ORGANIC SQUASH FOLLOWING INCORP ORATION OF COVER CROPS The United States is the fifth largest supp lier of squash and pumpkins in the world (Economic Research Service 2004). The number of squash-producing farms has increased over the past 30 years and in 2006, the U.S. produced 430,100 metric tons (MT) of squash valued at $229 million USD (Smith 2008). Florida currently ranks as the leading producer of summer squash ( Cucurbita pepo L.) with a value of $53 mill ion USD (USDA NASS 2008). Many cucurbits including summer squash are severely affected by a wide range of key agricultural pests including aphids and whiteflies. Many aphid species affect squash plants; so me of the most pestiferous being the green peach aphid ( Myzus persicae Sulzer), the cotton aphid (Aphis gossypii Glover) and the cowpea aphid ( Aphis craccivora Koch) (Mossler and Nesheim 2001) Aphids cause plant damage by directly feeding on phloem (Pettersson et al. 2007). The injected saliva causes twisting and curling of leaves which ultimately causes gradua l wilting, discoloration and death (Mossler and Nesheim 2001). Aphids also tran smit 275 viruses to squash plants (Nault 1997) usually in a nonpersistent manner. This allows for rapid spread of the virus in a give n area (Frank and Liburd 2005). The silverleaf whitefly, Bemisia argentifolli (Bellows and Perring) also feeds on squash plants causing the squash silverleaf (SSL) disorder. This disorder causes dramatic reductions in marketable crop yield (Hooks et al. 1998). In order to avoid total crop loss, farmers have used various broad-spectrum chemical insecticides to control aphids and whiteflies. The widespread use of these insecticides has led to increased resistance within key pest populati ons. Additionally, some pesticides may have increased the spread of virus diseases in cu curbits, possibly because of increased aphid

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61 movement (Webb 2007). These issues warrant the investigation of sustainable pest control strategies that are e nvironmentally friendly. Several methods of cultural control i nvolve manipulation of the environment by increasing plant diversity (Wratten et al. 2007 ). Many studies have focused on intercropping several cover crop species (monocultures and dicu ltures of legumes and grasses) with a cash crop, and have successfully shown that intercroppi ng can result in a build-up of natural enemies, which in turn are relayed to the cash crop to provide pest control (Parajulee et al. 1997, Tillman et al 2004). However, in some cases the interc ropped system did not reduce pest densities (Bugg et al. 1991). In these studies, the key idea was the conservation of natural enemy populations for pest suppression. However, to-d ate there has been no studies which document the effects of incorporating cover crops into th e soil to provide on pest suppre ssion in a subsequent cash crop. My goal was to determine if the incorporati on of cover crops into th e soil could lead to pest suppression due to increase in the number of natural enem ies or potentially better plant nutrition. In this case it is presumed that the natural enemies will migrat e to nearby refugia of secondary hosts until the cash crop is plante d. After the cash crop is established, it is hypothesized that the natu ral enemies will leave th e refugia in preference for pests on the cash crop. Materials and Methods Field experiments were conducted on organi cally certified land at the University of Floridas Plant Science Research and Education Un it in Citra, FL. Prior to the beginning of the experiment, the area was treated with spent mushroom compost (Quincy Farms, 190 Mannic Counn Road) at 10 tons / acre to enhance soil nutrient content and amend soil pH. Southern cowpea cover crop, Vigna unguiculata L. cv. White Acre, (Alachua Seed and Lumber, Alachua, FL) was planted in each plot at 50 lbs / acr e (56 kg / ha) prior to establishing cover crop

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62 treatments to improve soil and nutrient fertili ty, and also to increas e nematode populations. Experimental design was a completely randomized block with four replicates of seven treatments. The seven cover crop treatments incl uded a weedy fallow plot which served as the control, two legumes, sunn hemp [SH] ( C. juncea) and velvet bean [VB] ( M. pruriens var. pruriens ), two grasses, sorghum sudangrass [SSG] ( S. bicolor x S. sudanense ) and pearl millet [PM] ( P. glaucum ), and two sets of legume-grass mixt ures: 1) sunn hemp and pearl millet combination [SH/PM], and 2) a sorghum sudandgr ass and velvet bean combination [SSG/VB]. The legume-grass mixtures were selected becaus e they are suppressive to rootknot nematodes and produce large amounts of bi omass for weed suppression. Each treatment plot measured 12 m x 12 m. E ach plot was separated by mowed alleys that were 12 m wide, which was intended to reduce the movement of pest and beneficial arthropods between plots. Both legumes, VB and SH, were broadcast, whereas both grasses, PM and SSG were planted with a Sukup tr actor (CHAPTER 3). In 2006, afte r 8 weeks, the cover crop treatments were flail-mowed and incorporated into 25.4 cm into the soil by disking (New Holland Flail Mower, Purdy Tracto r and Equipment Inc., Hillsdal e, MI). Yellow squash (Cougar F1 cultivar, Harris seeds) was direct seeded into each treatment plot on October 19, 2006; 3 weeks after cover crop incorporation. However, due to the poor germination of the squash plants, areas with no emergence had to be re-seed ed. Re-seeding was done on October 30, 2006. This delayed arthropod sampling in squash for 7 w eeks after cover crop in corporation. In 2007, squash plants were direct seeded on October 10, 2007; 7 days after cover crops were incorporated. Insect sampling in sq uash began 4 weeks after planting.

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63 Key pests and beneficials in squash were sa mpled using unbaited yellow sticky traps, blue pan traps, in situ counts, leaf disc counts and pitfall traps. Adult lepidopteran populations were sampled using bucket traps. Assessment of Key Pests and Natural Enem ies w ith Unbaited Yellow Sticky Traps In 2006 and 2007 natural enemies in each squash plot were monitored using one unbaited yellow sticky trap (Great Lakes IPM, Vestaburg, MI) and one blue pan trap (Packer Ware Bowls, Gainesville, FL). The inner two rows of the squash plots were sampled as to eliminate edge effects. Traps were left in the field for 48 hours then brought back to the lab where they were wrapped in clear plastic wrap and stored in a refrigerator until th ey were ready to be processed. The number of parasitoids on each sticky trap were counted and recorded. Blue Pan Trap Captures Blue water p an traps were supported by tomato wire cages (45 cm x 15 cm x 20 cm), filled with water and detergent [5% detergent soluti on] (Colgate Palmolive Co. New York, NY) to break the surface tension (Webb et al. 1994). One blue pan trap was placed diagonally across from an unbaited yellow sticky trap on the opposite end on the plot to mo nitor syrphid flies. Traps were left in the field for one week. At the end of the week, the contents from each trap were emptied and into a small plastic container, labeled accordingly and taken back to the lab to be analyzed. The aphids and natural enemies from the blue traps were counted under a 40 X dissecting microscope and the contents placed in 15 x 45 mm vials (Fisherbrand, Fisher Scientific, Pittsburgh, PA) with 70% ethanol for storage. Visual and Leaf Disc Counts Each week visual ( in s itu ) counts were conducted in the fi eld to record the number of aphids (alate and apterous), whiteflies, as well as other insects. All insects were visually assessed

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64 by randomly examining the leaves of eight squash plants from each of the two inner rows for ~1 minute. Circular leaf discs were also used to estimate the number of whitefly nymphs and eggs on squash plants (Frank and Liburd 2005). Every tw o weeks, eight plants were randomly chosen from the two inner rows and one leaf was random ly picked from each of the 8 plants and taken back to the lab. Two circular (2.5 cm diameter) sections were cut from each leaf using a cork borer. Leaf discs were then examined under a 40 X dissecting microscope for whitefly eggs and immatures (Frank and Liburd 2005). Assessment of Lepidopteran Pests In 2006 and 2007 field plots were also sam ple d weekly for adult lepidopterans using tricolored bucket traps. Bucket traps were baite d with floral volatiles, phenylacetaldehyde and linalool and vapor-strips were plac ed at the bottom of the traps to kill the lepidopterans entering the traps. One bucket trap was placed in the middl e of each block (each bl ock had 4 replicates). Adults were collected weekly by emptying the buckets and brought back to the laboratory for identification. Sentinel Squash Plants and Peripheral Sampling During the 2007 field-season two potted sentinel squash plants were placed on the edge of each plot 2 hours following cover crop incorporat ion into the soil to m onitor the dispersal of aphids, whiteflies and natural enemies. Sentinel plants were placed in the plots on 3 October 2007 and taken out of the field on 15 October 2007. For each sentinel squash plant, aphids, whiteflies and natural enemies were assessed via in situ counts once per week for two weeks. On the third week, the sentinel plants were removed to allow for direct seeding of squash into the treatment plots.

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65 Sentinel squash plants were raised and potte d in the Small Fruit and Vegetable greenhouse at the University of Florida a nd transported to the field on the day of cover crop incorporation. Sentinel squash plants were approximately 30 cm in height when placed in the field. Plants were placed diagonally across from each other (approxi mately 15 m apart) within in each treatment plot. In addition to sentinel squash plants, 20 unbaited yellow sticky traps were placed on the periphery of the field to assess residual natural enemy populations from incorporated cover crop treatments. Yellow sticky traps were placed along the periphery of the field on the 3rd, 6th and 9th October 2007. Traps remained in their periphera l location for 48hrs. They were then covered with plastic wrap and brought back to the la b for processing. Traps we re approximately 50 m apart. The vegetation bordering the field was divi ded into three types: 1) fruit trees (orange) 2) woods and 3) grass/weeds. Squash Silver Leaf Disorder Rating In 2007, we noticed squash silver leaf (SSL) diso rder in the field and recorded the severity of the disorder based on the following scale 0 = no silvering (0% silv ering), 3 = moderate silvering (50% silvering), 5 = co mplete silvering (100% silvering). Four plants from the middle of the inner two rows were sampled and rated based on the above scale. Sampling was done 2 weeks after planting and at the end of th e field-season (8 weeks after planting). Statistical Analysis Data from aphids, whiteflies and natural enemies from all the sampling techniques along with the SSL disorder rating were square root transformed and analyzed using analysis of variance (ANOVA) PROC GLM (SAS Institute 2003) because there was no interaction between treatment and time. Treatment means were separated using the least significant difference (LSD) separation procedures. Results were considered significant if P 0.05. Regression analysis

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66 (PROC REG, SAS Institute 2003) was also carrie d out to assess the relationship between the number of whitefly immatures a nd the presence of SSL disorder. Parasitoid data from peripheral traps were analyzed using repeated measures analysis (PROC MIXED, SAS Institute 2003) to examine interaction effect between the different habitats and time (sampling weeks). Key pest (aphid a nd whitefly) data from peripheral yellow sticky traps were analyzed using analysis of va riance (ANOVA) PROC GLM (SAS Institute 2003) because there was no interaction between habitat and time (sampling weeks). Results The aphids that were observed via in situ counts on squash plants included the m elon aphid, Aphis gossypii Glover and the green peach aphid Myzus persicae (Sulzer). Bemisia argentifolii (Bellows and Perring), the silverleaf whitefly was the main species found in the treatment plots. The natural enemies obser ved were the converge nt ladybird beetle, Hippodamia convergens Gurin-Mneville, and the multicolored lady beetle Harmonia axyridis (Pallas). Aphid mummies were observed on squash leaves about 3 weeks into sampling. The parasitoids that emerged from mummies included Aphidius sp. and L. testaceipes (Cresson). Visual Counts of Insect Pests on Squash Aphids. In 2006, squash planted in PM, SSG, VB and SSG/ VB plots had significantly lower aphid populations compar ed with the weedy fallow ( F = 6.21; df = 3, 6; P = 0.0011) [Table 4-1]. Squash in the SHPM and SH plots had high aphid numbers that were not significantly different compared w ith the weedy fallow (Table 4-1). In 2007, squash planted in the SH treatment had the lowest aphid population compared with all other treatments including the weedy fallow ( F = 40.5; df = 3, 6; P < 0.0001). Squash planted in treatments with PM had si gnificantly fewer aphids than SSG ( F = 40.5; df = 3, 6; P < 0.0001), but neither was significantly different from the control. Squash plants in the weedy

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67 fallow control had significantly fewer aphids comp ared with squash planted in treatments that had both legume-grass mixtures (Table 4-2). Whiteflies. In 2006, squash planted in PM and SSG monoculture treatments had significantly fewer whiteflies compared with the weedy fallow control ( F = 7.61; df = 3, 6; P = 0.0004), but whitefly numbers on squash in SSG pl ots were not significa ntly different than whitefly numbers from SH and SSG/VB treatments. Squash planted in treatments where VB was incorporated into the soil had significantly more whiteflies compared with the control. Squash planted in treatments where SH/PM mixture was incorporated into the soil had significantly fewer whiteflies than the weedy fallow control (Table 4-1). In 2007, squash growing in the weedy fallow control and in areas where SH/PM mixture was incorporated into the soil had significantl y fewer whiteflies compared with corresponding monocultures of squash from the SH and the PM treatment plots ( F = 3.10; df = 3, 6; P = 0.0289) (Table 4-2). Squash planted in areas where SSG/V B mixture was incorporated into the soil also had significantly higher whiteflies comp ared with the weedy fallow control ( F = 3.10; df = 3, 6; P = 0.0289). Squash planted in treatments where SSG and VB monoculture s were incorporated into the soil were not significantly different from the weedy fallow control (Table 4-2). Melonworm. Melonworms were recorded only in 2007 on squash plants. Melonworms were significantly lower on squash plants in treatments where PM was incorporated in the soil compared with the weedy fallow control ( F = 3.30; df = 3, 6; P = 0.0228) (Table 4-2). Natural enemies. In 2006, squash planted in plots where VB and SH/PM mixture were incorporated into the soil had significantly more ants than the weedy fallow control, but were not significantly different compared with the monocultures PM an d SSG or the SSG/VB mixture ( F

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68 = 2.36; df = 3, 6; P = 0.0740) [Table 4-3]. There was no si gnificant difference in the number of spiders, parasitoids, or ladybird beetles among any of the treatments (Table 4-3). Similarly, in 2007, ant populations on squa sh plants where SH/ PM mixture was incorporated into the soil was significantly highe r than all other treatments including the weedy fallow control ( F = 6.46; df = 3, 6; P = 0.0009). Squash plants grow ing in areas where the SH treatment was incorporated had the lowest numbe rs of ants compared with other treatments including the control (Table 44). Although there were no differe nces in the number of spiders observed in each treatment, there was a significant difference in the number of parasitoids and aphid mummies among treatments. Squash plan ted in areas where SSG monoculture was incorporated into the soil had significantly more parasitoids than all other treatments including the weedy fallow control ( F = 11.01; df = 3, 6; P < 0.0001). Squash plants in the SH treatment had the lowest numbers of parasitoids, but was not significantly different from PM, VB or the control ( F = 11.01; df = 3, 6; P < 0.001) (Table 4-4). Aphid mumm ies were significantly higher on squash planted in areas where PM, VB and SSG/ VB mixture were incor porated into the soil ( F = 12.02; df = 3, 6; P < 0.0001). Squash plants from the weedy fallow control treatment had the lowest number of aphid mummies, but these were not significantly different from those plants growing in areas where SH/PM mixture or SSG was incorporated into the soil (Table 4-4). Leaf Disc Count Whitefly eggs. In 2006, there was no difference between whitefly eggs on squash plants from any of the treatments (Table 4-5). However, in 2007, squash plants growing wher e VB was incorporated in the soil had significantly higher number of whitefly eggs compared with all other treatments ( F = 10.06; df = 3, 6; P < 0.0001). Also, squash plants growing in areas where SSG and SH treatments were incorporated, as well as both legume-grass mi xtures, SH/PM and SSG/VB, had significantly

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69 lower number of whitefly eggs th an the weedy fallow control ( F = 10.06; df = 3, 6; P < 0.0001) (Table 4-5). Whitefly immatures. In 2006, squash plants from both gr ass treatments, SSG and PM, as well as the SH/PM mixture had significantly fewer whitefly immatures compared with the weedy fallow control ( F = 3.04; df = 3, 6; P = 0.0312) (Table 4-6). In 2007, squash plants from the PM and th e SH/PM mixture had significantly more whitefly immatures compared all other treatments ( F = 14.44; df = 3, 6; P <0.0001). Squash plants from the SSG, VB, SH monocultures and the SSG/VB mi xture did not differ in the number of whitefly immatures (Table 4-6). Blue Pan Trap Results The blue water pan traps captured aphi d spec ies that included Aphelinidae: Aphelinus sp., Braconidae: Aphidius sp., Chelonus sp., and Lysiphlebus testaceipes (Cresson), Icheumonidae, Bethylidae, Sclelionidae: Telenomus sp., Eucoilidae, Mymaridae, Chalcididae, Eulophidae: Tetrastichinae, Trichogrammatidae, and Encyrtidae: Metaphycus sp., Aphidius spp. and Lysiphlebus testaceipes (Cresson). The family Aphelinidae does include whitefly parasitoids, but no whitefly parastioids were specifically iden tified. These water traps also captured the parasitoids and hyperparas itoids that were similar to thos e captured with yellow sticky traps (Figure 4-1). Several species of aphidophagous sy rphid flies (Diptera: Sy rphidae) were found in the blue pan traps including Toxomerus spp., Platycheirus spp. Allograpta spp. and Sphaerophoria spp. (Figure 4-2). Predaceous whitefly predators were not captured during the field-season. During 2006, squash planted in areas where the SSG /VB mixture was incorporated in the soil had significantly higher number of syrphid f lies than all the other treatments including the weedy fallow control (F = 6.48; df = 3, 6; P = 0.0009) (Table 4-7). However, squash planted in

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70 soil with the two monocultures, SSG and VB, had low syrphid fly numbers which was not significantly different from the w eedy fallow control (Table 4-7). However during 2007, squash plants in the VB treatment had a significantly higher number of syrphid flies than all other treatments except PM ( F = 3.50; df = 3, 6; P = 0.0180) (Table 4-7). Periphery Yellow Sticky Trap Results Parasito ids. In the first week, there were significan tly more parasitoids in the grass/ weeds area compared to the fruit tree region ( F = 4.51; df = 2, 4; P = 0.0489) [Table 4-8]. The grass/weeds area had almost twice as many parasitoids than the fruit tree area. At the end of the three week sampling period, there was no significa nt difference between the weeds/grass area and the woods, but the woods had 1.5 times more parasitoids than the fruit tree region ( F = 4.22; df = 2, 4; P = 0.0559) (Table 4-8). The fluctuations in parasitoid numbers during each week were significant ( F = 11.37; 2, 8; P = 0.0046) and there was also a si gnificant interaction between the grass, woods and fruit trees (oranges) ha bitats and the time (sampling periods) ( F = 3.34; df = 2, 24; P = 0.0260). There were significant di fferences among habitats in the 1st and 3rd week. Key Pests (Aphids and Whiteflies). There were significantly more aphids found towards the woods habitat compared with the other habitats ( F = 9.08; df = 2, 4; P = 0.0087) [Table 4-9]. There was no difference between aphids found toward s the orange fruit trees and the grassy area. Whiteflies were also significantly higher in the woods area compared with the fruit tree or grass area (F = 47.20; df = 2, 4; P < 0.0001). There was no significant difference in whitefly numbers between the fruit tree and gr ass habitat (Table 4-9). Unbaited Yellow Sticky Trap Results Parasito ids. In 2006, towards the end of the sampli ng period, SH had significantly more parasitoids than the weedy fallow control ( F = 2.69; df = 3, 6; P = 0.0352). Although there was no significant difference between SH, PM and its corresponding mixture, however, there was an

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71 increasing trend in the number of parasitoids recorded in the SH /PM mixture. There was also a significant time effect ( F = 6.54; df = 4, 12; P = 0.0049). During 2007, there were no signi ficant differences in parasitoid numbers among treatments. Squash Silvering The rating for SSL disorder was highest on s quash plants growing in areas where PM, SH/PM and weedy fallow vegetation was incorporat ed into the soil. The ratings with all o ther treatments did not differ significantly ( F = 21.82; df = 3, 6; P < 0.0001) (Figure 4-3). Overall, the SSL disorder ra tings did increase with the number of whitefly immatures. There was a significant and strong ( P = 0.0081, R2 = 0.78) correlation between whitefly abundance and SSL disorder rating (Figure 4-4). Adult Lepidoptera Results In 2006, there was no significant difference in the num ber of lepidop teran species that were found in the field (Table 4-10). However, in 2007, the VB moth had significan tly higher numbers than any other species ( F = 59.90; df = 3, 3; P < 0.0001). The melon worm and the southern army worm had very low populations. The number of Mocis sp. captured was significantly less than the VB moth, but significantly more than the melon wo rm and the southern armyworm ( F = 59.90; df = 3, 3; P < 0.0001) (Table 4-10). Discussion In this experim ent we evaluated the eff ect of summer crop treatments on pest and beneficial insect populations in subsequent squash plants. Sentinel squash plants placed in each treatment immediately after cover crop incorpor ation yielded no parasitoids, and there was no difference in the number of ants, spiders or syrphid flies among treatments. However, the

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72 presence of parasitoids on yellow sticky traps from peripheral areas closely surrounding the treatment plots strongly suggests th at natural enemies dispersed out of the treatment plots into the surrounding field. When squash plants were established a couple of weeks later, weekly observations of aphid and whitefly populations did not appear to show any pest suppression. However, pooled data from in situ counts of key pests and beneficials showed that the monoculture grass cover crop tr eatments, particularly SSG, we re able to reduce aphid and whitefly numbers when compared with the weed y fallow control. We concluded that this reduction could have been a result of th e residual population of natural enemies. The peripheral vegetation that the parasitoids dispersed into were divided into three distinct areas 1) a fruit tree area to the west of the field, 2) a w ooded area to the north of the field and 3) a grassy/weedy area to the ea st and south of the field. It is not surprising that the majority of the parasitoids were found in the grass/weed y area. This border acted as refuge for the parasitoids, providing alternate prey, nectar/pollen resources from the flowering weeds or oviposition sites. The aphid densities found in the weedy/grass areas may have increased the number of parasitoids (density dependent), whic h later migrated back in to the squash plots, where they helped to reduce pests throughout th e season. Parasitoids an d hyperparasitoids could have been attracted back into the field by attract ive hosts (abundance or aphids and whiteflies) or the honeydew secreted from aphids and whiteflies, which acts as an infochemical for foraging parasitoids and hyperpar asitoids (Buitenhuis et al. 2004). Ho wever, hyperparasitoids are not attracted to honeydew from healthy aphids. Therefor e, squash plants from SH or PM treatment, which had low aphid and parasitoid numbers ma y have had a higher number of hyperparasitoids than squash in other treatment plots.

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73 Grasses such as SSG and PM may have cause d a reduction in pest numbers by 1) altering environmental conditions (change in soil nutrien t composition) 2) suppressing nematode activity and 3) helping to enhance natural enemy populations. Environmental conditions are known to modul ate plant volatile emissions (Par and Tumlinson 1999). Therefore, incorporation of various cover crops into the ground may have resulted in differences in soil nutrient content with each treatment. Slightly stressed squash plants that are not infested by pests may be able to produce more volatile chemicals that effectively attract natural enemies of that pest. For instance, squash plants from grass treatments may not have sufficient nitrogen (grasses are known to be nitrogen scave ngers and have high C:N ratios). Therefore, when these plants are infested with a phids and whiteflies, elev ated levels of volatile chemicals may be produced compared with infest ed but non-nitrogen stressed squash plants. These higher volatile emissions ma y serve to attract more natura l enemies or pests into those plots. There have been numerous studies showing how predators and parasitoids are more highly attracted to plants that are in fested and stressed as a result of compromised environmental conditions (Par and Tumlinson 1999). Sorghum sudangrass (SSG) hybrids are also well known to have allelochemical properties that suppress many nematode species (Bowman et al. 1998). For inst ance, the root knot nematode is one of the most important nemat ode species affecting s quash (Schooley 2005). Therefore, squash plants in the SSG treatment may have had less root knot nematodes than squash in other plots which may have allowed fo r greater resistance to other insect pests and diseases. Also, these allelochemical properties displaye d by incorporated SSG hybrids would go to suppress weeds once the squash was planted in th e fall. Weed suppression potentially causes a

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74 reduction in the number of pests because the weed s would not be available to act as secondary hosts for these pests. In my study, SSG had more coccinellids ( Coccinella septempunctata L., Hippodamia convergens Gurin-Mneville, and Harmonia axyridis (Pallas) than all the other treatments. Relay intercropping studies by Parajulee et al. (1 997) and others (Robinson et al. (1972) and Burleigh et al. (1973) showed that cotton cash crop associated w ith sorghum cover crop also had greater numbers of predators th an cotton associated with some other cover crops. Predaceous whitefly coccinellids (Delphastus pusillus ), which were observed in the cover crop treatments (CHAPTER 2) were not captured during the sq uash cash crop. Usuall y, these predaceous coccinellids require very high populat ions of whiteflies to maintain reproduction (Hoelmer et al. 1993). D. pusillus larvae are known to consume ~167 eggs per day and up to 1000 eggs before pupating (Hoelmer et al. 1993). From my studies, on average, there were not more than 120 whitefly eggs and immatures in 2006 and not more than 20 whitefly eggs and immatures in 2007. Therefore, there may not have been a sufficient number of whiteflies to allow the predator to successfully reproduce. Whitefly eggs in squash were overall mu ch higher in 2006 than in 2007. In 2006, it took ~ 5 weeks after cover crop in corporation to establish the squash crop due to initial crop failure, but in 2007, no problems were encountered with planting schedules and squash crop establishment (took place in only 3 weeks). The longer period of time in 2006, combined with decreasing temperatures may have reduced natural enemy p opulations to the point where they would be insufficient to reduce pest numbers. This may e xplain the limited pest suppression in 2006. The SSG had significantly lower whitefly eggs and immatures during 2006 and 2007 when compared

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75 with the weedy fallow. Like other studies have shown, this grass appears to have potential for suppressing whitefly numbers. When squash silver leaf (SSL) disorder was observed in 2007, SS G and SH monocultures had the lowest number of white flies immatures and significantly lower SSL ratings compared with the weedy fallow. Comparatively, the high numbers of whitefly immatures in PM and SSG also corresponded to high incidences of SSL disorder, which supported the theory that the immatures are the cause of the SSL disorder. Squash plants from SSG/VB mixture had significantly more syrphid flies and mummified aphids than the weedy fallow control. The emergence of Aphidius spp. from these mummies, in addition to L. testaceipes that we captured from unbaited yell ow sticky traps suggest that these parasitoids may be responsible fo r suppressing aphid populations in the field. It is possible that the nitrogen supplied by the VB was scavenge d by the SSG, causing the emission of more parasitoid-attracting volatiles due to a nitrogen stressed squash plant. We were also able to see evidence of re lationships between pest and beneficial populations. High numbers of aphids from squa sh plants in VB pl ots during 2007 and high whitefly populations from the SSG/VB treatment corresponded to the lo w parasitoid numbers that were observed in those treatments. Conversely, squash plants had low aphid numbers with SSG and correspondingly to high parasitoid populations. Although, we observed the potential of the SSG/VB mixture to enhance natural enemy populations, squash plants in the SH/PM mixture had significantly more aphids and whiteflies in both field-seasons compared with the weedy fallow. Therefore we would recommend that the SH/PM mixture is not suitable fo r pest suppression on organic farm s. This is not a surprising

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76 find, because not all cover crop mixtures enhanc e natural enemy populations, in fact increasing the vegetational diversity of agroecosystems have variable results (Bugg 1992, Corbett 1998). A large number of syrphid flies were also captured from squash pl ants in the SSG /VB treatment. Although this treatm ent had the lowest aphid population when sampled, the reduction cannot be attributed to the high syrphid popul ation because Bugg et al. (1992) noted that syrphids tended to discriminate against olde r larger aphid colonies in favor of smaller promising colonies. In 2007, the large number of syrphid flies found on squash plants in VB plots may be due to the greater number of weeds in those plots compared with other cover crop plots. Aphidophagous syrphids respond well to nectar and pollen produced by flowering weeds (Hni et al. 1998). We captured only a small number of melon worm moths, the larvae of which are serious pests of cucurbits. Squash plants from the PM had significantly fewer nu mber of melon worms, Diaphania hyalinata L., compared with other plots. This may be related to the allelochemical activity of PM which indirectly affects the plants resistance to herbivory (Khan et al. 2005). Parasitoids such as Trichogrammatidae, Chal cididae and other egg parasitoids such as Scleionidae may also have been responsible for reduced numbers of lepidopteran pests. Overall, there is good evidence to conclude that residual populations of natural enemies from incorporated cover crops and allelochemicals from selected crops are able to suppress pests in a subsequent cash crop. This pest suppressi on will, however, depend on the diversity of the peripheral vegetation surrounding the field because al ternate food sources need to be present to maintain natural enemy populations until the squash crop is established.

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77 Table 4-1. Aphid and whitefly means from in situ squash leaf counts from various cover crop treatments in 2006 Aphid and whitefly data were squa re root transformed before analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 6.21; df = 3, 6; P = 0.0011 b F = 7.61; df = 3, 6; P = 0.0004 Treatment Mean SEM Aphidsa Whitefliesb SH 157.00 7.71ab 241.50 30.44bc PM 129.75 6.90bc 169.50 21.40d SH + PM 176.25 1.79a 196.00 11.00cd SSG 130.50 14.5bc 182.25 9.63cd VB 119.50 4.97c 344.00 33.49a SSG + VB 122.00 10.87c 223.00 13.22bcd Weedy fallow (Control) 168.00 8.68a 260.00 24.77b

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78 Table 4-2. Aphid and whitefly means from in situ squash leaf counts from various cover crop treatments in 2007 Treatment Mean SEM Aphidsa Whitefliesb Melon wormc SH 161.75 6.82d 65.25 7.18abc 2.50 0.95bc PM 216.00 10.31c 95.57 9.46ab 1.75 1.43c SH + PM 346.25 14.67a 70.25 6.51dc 5.25 2.49bc SSG 250.75 10.81b 80.25 8.46abcd 14.50 4.27a VB 339.00 13.34a 78.00 6.25 bcd 8.50 3.47ab SSG + VB 326.00 18.04a 103.50 14.31a 5.00 2.54bc Weedy fallow (Control) 224.00 3.48bc 63.00 5.11d 6.75 1.93ab Aphid, whitefly and melon worm data were square root transformed before analysis but means shown reflect untransformed data. Means followed by th e same letters are not significantly different P = 0.05 (LSD) a F = 40.5; df = 3, 6; P < 0.0001 b F = 3.10; df = 3, 6; P = 0.0289 c F = 3.30; df = 3, 6; P = 0.0228

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79 Table 4-3. Mean number of natural enemies from in situ squash counts from cover crop treatments in 2006 Mean SEM Treatment Antsa Spidersb Parasitoidsc Lady beetlesd SH 6.25 2.56c 0.00 0.00 0.25 0.25 0.00 0.00 PM 18.00 3.58ab 1.00 0.57 0.25 0.25 0.00 0.00 SH + PM 26.00 9.74a 0.75 0.25 0.25 0.25 0.00 0.00 SSG 15.00 2.67abc 0.00 0.00 0.50 0.28 0.50 0.28 VB 20.75 3.35a 0.75 0.47 0.00 0.00 0.00 0.00 SSG + VB 18.50 4.50ab 0.00 0.00 0.25 0.25 0.25 0.25 Weedy fallow (Control) 7.75 1.81bc 0.00 0.00 0.25 0.25 0.00 0.00 Beneficial arthropod data were square root transformed before analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 2.36; df = 3, 6; P = 0.0336 b F = 2.49; df = 3, 6; P = 0.0620 c F = 0.43; df = 3, 6; P = 0.8503 d F = 2.05; df = 3, 6; P = 0.1108

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80 Table 4-4. Mean number of natural enemies from in situ squash leaf counts from cover crop treatments in 2007 Mean SEM Treatment Antsa Spidersb Parasitoidsc Aphid mummyd SH 5.57 1.65c 1.00 0.57 2.00 1.15c 10.75 1.31b PM 15.50 2.17b 0.75 0.47 4.25 0.75bc 18.75 3.94a SH + PM 37.50 8.10a 0.25 0.25 6.75 1.88b 9.25 2.25bc SSG 17.75 4.80b 0.25 0.25 15.50 0.64a 4.75 2.83bc VB 11.75 1.31b 0.25 0.25 3.77 1.65bc 22.50 2.95a SSG + VB 13.50 2.25b 0.25 0.25 6.50 2.06b 22.25 2.13a Weedy fallow (Control) 12.50 1.93b 0.25 0.25 4.75 1.70bc 3.55 1.55c Beneficial arthropod data were square root transformed before analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 6.46; df = 3, 6; P = 0.0009 b F = 0.89; df = 3, 6; P = 0.5213 c F = 11.01; df = 3, 6; P < 0.0001 d F = 12.02; df = 3, 6; P < 0.0001

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81 Table 4-5. Mean number of whitefly eggs reco rded from squash leaf disc counts during 2006 and 2007 Treatment Mean SEM whitefly eggs 2006a 2007b SH 142.50 3.30 1.25 0.63c PM 153.00 12.04 16.5 3.32b SH + PM 121.50 19.56 2.25 1.31c SSG 170.25 8.16 1.00 0.71c VB 174.25 19.73 25.25 5.57a SSG + VB 94.75 15.78 2.75 1.25c Weedy fallow (Control) 178.00 41.12 16.00 5.88b Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 2.41; df = 3, 6; P = 0.0690 b F = 10.06; df = 3, 6; P < 0.0001

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82 Table 4-6. Mean number of whitefly immatures r ecorded from squash leaf disc counts during 2006 and 2007 Treatment Mean SEM whitefly immatures 2006a 2007b SH 16.00 1.29ab 1.75 1.18b PM 12.00 4.41bc 16.75 1.93a SH + PM 4.75 1.65c 14.25 2.86a SSG 9.50 3.30bc 1.75 1.18b VB 14.00 5.01abc 2.75 1.88b SSG + VB 12.75 3.11abc 3.00 2.12b Weedy fallow (Control) 25.00 4.02a 5.75 1.03 b Whitefly immature data were squa re root transformed before analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 3.04; df = 3, 6; P = 0.0312 b F = 14.44; df = 3, 6; P < 0.0001

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83 4% 73% 2%6% 2%13% 60% 8% 5% Aphelinidae Eulophidae Scelionidae Trichogrammatidae Icheumonidae Aphidius spp. Lysiphlebus spp. Diaeretiella spp. BraconidaeA. 23% 15%12%6% 4% 10% 2% 23% 30% Aphelinidae Eulophidae Trichogrammatidae Encrytidae Scleonidae Ichneumonidae Diaeretiella spp. Lysiphlebus spp. Aphidius spp. 5% BraconidaeB Figure 4-1. Major parasitoid families in an organic squash field.

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84 A. B. Figure 4-2. Syrphid fly populati ons in an organic squash field in A) 2006 and B) 2007.

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85 Table 4-7. Syrphid fly populations from each treatment in 2006 and 2007 from blue pan traps Mean SEM syrphid flies in squash Treatment 2006a 2007b SH 10.00 1.77b 1.25 0.63b PM 9.75 1.54b 3.00 0.91ab SH + PM 9.25 1.65b 1.50 0.28b SSG 4.75 1.54c 2.00 0.81b VB 4.75 1.37c 5.00 0.82a SSG + VB 17.50 3.71a 2.00 0.41b Weedy fallow (control) 2.75 0.85c 1.25 0.63b Syrphid fly data were square root transformed befo re analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 6.48; df = 3, 6; P = 0.0009 b F = 3.50; df = 3, 6; P = 0.0180

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86 Table 4-8. Parasitoid population dynamics from peripheral habitats surrounding an organic field Mean SEM parasito id numbers in 2007 Treatment Week 1a Week 2b Week 3c Grassy/weedy area 52.60 11.46a 38.80 6.7416.00 4.24ab Fruit tree (oranges) 23.20 4.39b 34.20 6.688.00 2.02b Woods 41.00 5.00ab 21.80 1.8225.80 4.98a Parasitoid data were square root transformed before analysis, but the means shown represent untransformed values. Means followed by the sa me letters are not significantly different ( P = 0.05 according to least square means test fo llowing repeated measures analysis, LS). a F = 4.51; df = 2, 4; P = 0.0489 b F = 1.72; df = 2, 4; P = 0.2396 c F = 4.22; df = 3, 6; P = 0.0559

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87 Table 4-9. Population dynamics of key pests fr om peripheral habitats surrounding an organic field in 2007 Habitats Mean SEM key pests Aphidsa Whitefliesb Fruit tree (oranges) 10.80 0.66b 7.00 0.94b Grass 9.40 1.91b 3.00 0.71b Woods 19.20 2.65a 32.40 4.05a Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 9.08; df = 2, 4; P = 0.0087 b F = 47.20; df = 2, 4; P < 0.0001

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88 0 2 4 6 8 10 12 14 16 18 SHPMSHPMSSVBSSVBF TreatmentMean no. of whitefly immatures per plot0 0.5 1 1.5 2 2.5 3 3.5Mean SSL disorder rating Whitefly immatures SSL disorder rating a a A B A B c c bc bc b B B A Figure 4-3. Populations of whitefl y immatures with squash silver leaf disorder rating in 2007

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89 SSL rating = 0.1525immature + 0.9219 R2 = 0.7829 0 0.5 1 1.5 2 2.5 3 3.5 4 024681012141618 No. of whitefly immatures per plantSSL disorder rating Figure 4-4. Relationship of immature whiteflies with squash silverleaf disorder rating

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90 Table 4-10. Mean number of adu lt lepidoptera captured from phere mone baited bucket traps in squash during 2006 and 2007 Mean SEM adult lepidoptera from squash Moth species 2006a 2007b Anticarsia gemmatalis (VB moth) 0.75 0.47 25.00 2.25a Mocis sp. 1.75 1.03 9.75 2.25b Diaphania hyalinata (Melonworm) 0.00 0.00 0.75 0.47c Spodoptera eridania (Southern armyworm) 0.25 0.25 0.50 0.50c Adult lepidopteran data were square root tran sformed before analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 1.39; df = 3, 3; P = 0.3089 b F = 59.90; df = 3, 3; P < 0.0001

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91 CHAPTER 5 INFLUENCE OF PEST POPULATIONS FROM COVER CROPS ON TOTAL AND MARKETABLE YIELD OF SUM MER SQUASH Economically, summer squash ( Cucurbita pepo L.) is one of the most highly profitable vegetables to produce in the world (Kemble et al. 2005). In 2007 Floridas squash production was estimated at 10,900 acres with production of 101 million pounds valued at approximately $52.9 million USD (NASS 2008). Aphids and whitefl ies are highly destructive pests on summer squash because they transmit diseases and inju re the plant by sucking sap from the leaves thereby greatly reducing the yield and profitability of the crop. It is not uncommon for a squash plant to have three or four different aphid-tr ansmitted viruses, which consequently causes poor yields (Molinar et al. 1999). Whiteflies also have caused a re duction in root dry weight of other cucurbits including pumpkins (McAuslane et al. 2004). Cover crops can have positive and negative effects on plant yield. Generally, cover crops improve plant yields by enhancing soil health. Cover crops promote biologically active soil, which helps crops to resist pest pressure s and ultimately increases yield (Phatak 1998, Sarrantonio 1998). Cover crops can also indirectly improve crop yi eld by reducing or eliminating the use of pesticides, which favor s healthy populations of natural enemies of pestiferous insects (Phatak 1998). Tillman et al. ( 2004) have reported that cotton yields were significantly higher when cotton was interplanted with a number of cover crops (crimson clover, rye, a legume mixture and a combination of rye and the legume mixtur e) but that this was not as a result of pest suppression. Conversely, Robertson et al. (1991) reported that ther e was no signifi cant effect on corn, peanut or cotton yield with the addition of a cover crop. In addition to yield, cover crops help to speed up the infiltration of excess surface water, relieve compaction and improve soil structure, enhance nutrient cy cling, and increase soil organic matter that further encourages beneficial soil microbial life (Bowman et al. 1998). For

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92 instance, legume cover crops such as VB and SH have nitrogen-fixing ba cteria in their root nodules, and are able to add nitrogen to the soil This improves the growth of the subsequent cash crop especially if they are used as a green manure (C aamal-Maldonado et al. 2001, Rich et al. 2003). Additionally, when leguminous cover crops are digested by soil microbes, polysaccharide by-products are produced that hold small soil particles toge ther as aggregrates, which provides good soil aeration and less compaction (Sarrantonio 1998). Alternatively, cover crops can negatively imp act crop yields. The addi tion of a cover crop to a field may reduce the amount of water available for the following cash crop. Reduced water levels increase plant stress making it more sus ceptible to insect pests and diseases, which ultimately causes a reduction in yield (Robertso n 1999). Some cover crops are susceptible to nematodes and some may be more attractive to ke y pests than beneficial s. Also, graminaceous cover crops can result in high C:N ratios that can result in less nitrogen being available for crop growth during establishment. Additionally, it is also difficult to manage cover crop residues to prepare a good seed bed. My goal was to determine how pest populations from cover crop treatments can affect total and marketable yield in summer squash. Knowi ng which cover crops to use to improve plant yield is an excellent starting poi nt for successful crop management. Methods Field Experiments Field experim ents were conducted at the Univers ity of Florida, Plant Science Research and Education Unit in Citra, FL. The experimental setup was a randomized complete block design with four replicates of seven treatments. Cover crop treatments included two legumes (sunn hemp [SH] and velvet bean [VB]), two gra sses (pearl millet [PM] and sorghum sudangrass [SSG]), and two legume-grass mixtures (sorghum sudangrass/velvet bean [SSG/VB] and sunn

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93 hemp/pearl millet [SH/PM]). Summer squash (Couga r F1 untreated) was direct seeded with a monosem planter into 8 m x 12 m plots with 4 ro ws. The distance between the 4 rows was 6 feet (1.8 m) whereas the spacing between each squash plant was 18 inches (0.46 m). An organic fertilizer, Nature Safe 10-2-8, (Griffin Indus tries Inc. Diamond Company, FL) was applied through a drop spreader at 33 lbs/pl ot for the squash seedlings on 26th October 2006 and 9th October 2007. Squash was direct seeded on 19 October 2006. Squash fruit was harvested 6 times throughout the 2006 field-season; on the 14th, 19th, 26th of December 2006, and on the 2nd, 8th, and 9th of January 2007. During the 2007 field-season, squash was direct seeded on 10th October, and was harvested 8 times: 21st, 26th, 28th November and 3rd, 6th, 10th, 12th, and 14th of December 2007. Aphids and Whitefly Sampling Each week visual ( in s itu ) counts were conducted in the fi eld for aphids and whiteflies. These key pests were visually assessed by randomly surveying the leaves of eight squash plants from each of the two inner rows. Each squash plant was surveyed for approximately one minute. All other insects encount ered on the leaves were also reco rded. Leaf samples on which aphid mummies were discovered were brought back to the laboratory. Parasito ids were identified upon emergence. Unbaited yellow sticky traps (treated area 406.45 cm2, Great Lakes IPM, Vestaburg, MI), and blue water pan traps (Packer Ware Bowls, Gainesville, FL) with a 5% detergent solution (Colgate Palmolive Co. New York, NY) to break the surface tension (Webb et al. 1994) were used primarily for natural enemy counts. Both traps were placed diagonally across for each other in the middle rows of each treatment plot.

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94 Yield Sampling All four rows within each squash plot were harvested by hand and tota l and marketable yields were assessed in the 2006 and 2007 field-seasons. Squash was harvested 1 to 2 times per week when the fruit reaches 7 cm or more, we ighed with a hand scale, and the data were recorded. Squash is not a cool season crop, and protection of the crop was required in both 2006 and 2007. Meteorological data for Citra, FL were constantly monitored, and for days that were likely to have frost, the squash was harvested 2 or 3 days before signs of frost. Frost blankets were also used to prevent frost damage. Unmarketable fruits were distinguished from marketable fruits ba sed on size, color, and deformities. Unmarketable fruits were less than 5 inches in length, had dark brown discolorations on the surface of the fruit, show ed signs of insect frass contam ination and / or insect dug holes. Fruits that displayed physiological disorders or a dark colored dr y rot especially at the bottom end of the fruit (known as blossom-end rot), were also characterized as un marketable. Fruits that did not show signs as those described above were considered marketable. Once the squash was harvested and weighed, the total and marketable yi eld from each treatment plot was calculated. Statistical Analysis Data from squash numbers and squash yield were analyzed using analysis of variance (ANOVA) with means separated by LSD test ( = 0.05). Means were considered significantly different from each other when P -value 0.05. Results Insect Population Aphids. In 2006, both grasses, PM and SSG ha d significantly lowe r aphid populations com pared with the weedy fallow ( F = 6.21; df = 3, 6; P = 0.0011). The VB and the SSG/VB

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95 mixture also had significantly le ss aphids than the weedy fallow control. The SH and SH/ PM mixture were not significantly different than the control (Figure 5-1a). In 2007, PM had significantly fewer aphids than SSG ( F = 40.5; df = 3, 6; P < 0.0001), but neither was significantly different compared with the control. The weedy fallow control had significantly fewer aphids compared with both mixtures, but had significantly more aphids than SH (Figure 5-1b). Whiteflies. In 2006, the trend for whiteflies was simila r to aphids. Both grasses, PM and SSG, had significantly fewer whiteflies comp ared with the weedy fallow control ( F =7.61; df = 3, 6; P = 0.0004). The VB treatment had significantly more whiteflies compared with the control, but the SH was not significantly different than the control. Of the two legume-grass mixtures only SH/PM had significantly fe wer whiteflies compared with the weedy fallow control. The other mixture was not significantly differe nt than the control (Figure 5-2a). In 2007, the weedy fallow cont rol and SH/ PM mixture and had significantly fewer whiteflies compared with the SH and the PM monocultures ( F = 3.10; df = 3, 6; P = 0.0289) (Figure 5-2b). However, the other mixture, SSG/VB had significantly higher whiteflies compared with the weedy fallow control (F = 3.10; df = 3, 6; P = 0.0289). Both corresponding monocultures, SSG and VB were not significan tly different from the weedy fallow control (Figure 5-2b). Total Squash Yield In 2006, total squash yields were significantly higher with the PM treatm ent compared with all other treatments ( F = 3.53; df = 3, 6; P = 0.0172), except for SH (Table 5-1). All other treatments (including SH) gave low yields that were not significantly di fferent than the weedy fallow control (Table 5-1). There was no correla tion in 2006 between the key pests (aphids and whiteflies) with the total yield).

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96 In 2007, the SH and the SSG had significantly hi gher total squash yields than both legumegrass mixtures, SH/PM and SSG/VB ( F = 3.57; df = 3, 6; P = 0.0166) but were not significantly different from the weedy fallow control (Table 5-1). Also during 2007, there was a strong negative co rrelation between aphids and total yield ( P = 0.0498, R = -0.7550). However, there was no correla tion between whiteflies and total yield. Marketable Squash Yield In 2006, m arketable squash yields were significantly higher in plots of PM compared with all other treatments except for SH ( F = 3.16; df = 3, 6; P = 0.027) (Table 5-2). All other treatments gave low yield that were not significantly different from the weedy fallow control. During the 2006 field-season, ther e was no correlation between eith er aphids or whiteflies and marketable yield. In 2007, squash yields were significantly high er in SSG plots than in the weedy fallow control plots ( F = 4.74; df = 3, 6; P = 0.0046) (Table 5-2), but this yield was not significantly different from plots with SH VB or PM. Also during th e 2007 field-season, there was no correlation between either aphids or whiteflies and marketable yield. The SH/PM plots had the lowest squash yields compared with other treatments except the SSG/VB mixture and the control. Marketable yields averaged between 12 and 29 kg/ 36 m2 per treatment in the 2006 field season compared with 10 to 15 kg / 36 m2 per treatment in the 2007 field season. Discussion Total Squash Yield. High populations of aphids and whiteflies are know n to affect squash yields (Frank and Liburd 2004). In the first year of the st udy, there was a density dependent relationship between in sect pest pressures and squash yield. During the 2006 fieldseason, squash yield was higher in PM plots than the weedy fallow control plot and all other

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97 cover crop treatments except the SH, which was not significantly different than the control. High squash yields from the PM treatment may be due to the significantly lower number of aphids that were observed on squash plants from PM plots when in situ counts were conducted. A lower population of aphids implies that there was a reduction in feedi ng damage and virus transmission to these squash plants. Pearl millet is we ll known for its weed-suppressing allelochemical properties. Once incorporated into the soil, PM may produce allelochemicals that prevent the build up of weeds as hosts for aphids (or wh iteflies), thereby reduci ng pest pressure and influencing yield (Narwal 2006). Alternatively, squash plants in the PM trea tment may have had access to better quality soil due to the incorporation of PM. Healthy soils with adequate nutrients affect the relationship between plant and pests (Hni et al. 1991).Grasses tend to ha ve higher C:N ratios and large amounts of biomass, which improves the soil hea lth when incorporated into the soil (Baldwin and Creamer 2008). The high population of aphids in both the SH/PM mixture and the weedy fallow control could also account for the low squash yields th at were recorded from those treatments. Higher pest pressures imply that the squash plant is e xposed to more feeding damage, diseases and virus transmission, which reduces yield. Although there was a high number of whiteflies on squash in the VB plot, since there was no correlation betwee n whiteflies and total yield, other factors such as poor soil quality or inadequate moisture may have contributed to low squash yield. During the 2007 field-season, SH plots had a si gnificantly higher squash yield than its corresponding SH/PM mixture. Also, SSG had a higher squash yield than its corresponding SSG/VB mixture. For instance, SH plots had significantly lower numbers of aphids and whiteflies than the SH/PM mixture and weedy fallo w control. Significantly lower incidences of

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98 squash silver leaf (SSL) disorder was recorded in the SH plot, which was associated with lower whitefly pressure (CHAPTER 4) and higher yield. Th e SSL disorder (due to whitefly immatures) may have influenced the squash total yield in 2007. Marketable Squash Yield. In 2006 and 2007, both monoculture treatments, SH and PM, had significantly higher marketable squash yi elds than their corresponding mixture. Although there was no correlation between aphids and whiteflies and marketable yield in 2007, there were noticeable density-dependent trends between the key pests and the yield, which should not be ignored. The SH monoculture had significantly mo re aphid mummies than the control plots. The parasitoids that emerged from the mu mmies were identified as various Aphidius spp. These parasitoids suppress aphid populat ions (Powell and Pell 2007), whic h may account for some of the observed lower pest pressure s that could influence yield. The SSG monoculture was also observed to have significantly more parasitoids such as Lysiphlebus testaceipes and various Aphidius spp. than the SSG/VB mixture. Another possi bility is that, varying squash yields may have been due to better soil nutrient and water co ntent based on the incorpor ation of the different cover crop treatments. Overall, there was good evidence to show that higher pest populati ons corresponded with lower squash yields while lower pest populations corresponded with higher squash yields. Future research should involve analyzing PM for chemical compounds that may be responsible for suppressing pests and perhaps be introduced as an organic insecticide for growers. Monocultures that increase the number of beneficial insects should be identified and used in a combination treatment to suppress key pest populations.

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99 Figure 5-1. Relationship between aphids with total squash yield in A) 2006 and B) 2007. A B

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100 Figure 5-2. Relationship between whiteflies with total squash yield in A) 2006 and B) 2007. A B

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101 Table 5-1. Mean total squash yield from each cover crop treatment for the 2006 and 2007 field seasons Mean SEM total yield (kg/36 m2 ) of squash Treatment 2006 2007 SH 26.31 2.02ab 18.60 1.36a PM 35.81 3.87a 17.30 1.86ab SH + PM 22.08 6.38bc 13.48 1.39bc SSG 19.86 2.74bc 18.53 0.90a VB 23.58 2.46bc 15.31 1.27abc SSG + VB 15.17 2.45c 11.73 0.86c Weedy fallow (control) 23.87 5.24bc 14.99 1.83abc Total squash yield data were square root tran sformed before analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 3.53; df = 3, 6; P = 0.0172 b F = 3.57; df = 3, 6; P = 0.0166

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102 Table 5-2. Mean marketable squash yield fr om each treatment for the 2006 and 2007 field seasons Mean SEM marketable yield (kg/36 m2 ) of squash Treatment 2006 2007 SH 21.36 2.18ab 15.36 1.41ab PM 29.09 3.55a 13.75 1.23ab SH + PM 17.71 5.48bc 9.59 1.48d SSG 16.62 2.39bc 16.44 1.06a VB 18.99 1.59bc 12.81 0.93abc SSG + VB 12.21 2.21c 9.87 0.54dc Weedy fallow (control) 19.57 4.41bc 12.69 1.63bdc Marketable squash yield data were square root tr ansformed before analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 3.16; df = 3, 6; P = 0.027 b F = 4.74; df = 3, 6; P = 0.0046

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103 CHAPTER 6 TECHNIQUES FOR MONITORING APHI DS (HEMIPTERA: APHIDIDAE) AND WHITEFLIES (HEMIPTERA: ALEY RODIDAE) IN SUMMER SQUASH Summ er and winter squash are major vegetable crops grown commercially in Florida (Roberts and Pernezny 2001). Florida is the second leading state th at produces squash for fresh market sales and squash is one of the few crops that are shipped out of Florida every month of the year to grocery stores nationwide (A gMRC 2007, Mossler and Ne sheim 2001, Roberts and Pernezny 2001). During the 2007 squash field season, Florida growers harvested 10,900 acres of squash, valued at $53 million USD (NASS 2008). Summer squash ( Cucurbita pepo L.) is highly susceptibl e to several aphid species including, but not limited to, the green peach aphid ( Myzus persicae Sulzer), the melon aphid ( Aphis gossypii Glover) and the cowpea aphid ( Aphis craccivora Koch) (Mossler and Nesheim 2001). These aphids damage and weaken squash by sucking sap from the leaves and excreting honeydew, which promotes the growth of sooty mo ld, eventually resulting in wilting and leaf distortion (Molinar et al 1999). Aphids also transmit over 50 viruses in cucurbits (Molinar et al. 1999, Capinera 2007). The melon aphid in particular is regarded as one of the most destructive pests on squash in the United States (Vsquez et al. 2006) because it transmits potyviruses to cucurbits. Other viruses that are transmitted by aphids include: the papaya ring spot virus type W (PRSV-W), the watermelon mosaic virus 2 (WMV2), the zucchini yellow mosaic virus (ZYMV) and four viroids, which causes yellowing, mosaic, leaf blisters and reduced fruit set (Kucharek and Purcifull 1997, Frank and Liburd 2005, Molinar et al. 1999). Whiteflies are also regarded as a serious pe st of cucurbits. The silverleaf whitefly, Bemisia argentifolii (Bellows and Perring) destroys squash pl ants by sucking plant sap which results in defoliation, stunting, poor plant yi elds and growth of sooty mold from honeydew excretions (Molinar et al. 1999). In Fl orida, the greenhouse whitefly, Trialeurodes vaporariorum

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104 (Westwood) is not an important pest. However the s ilverleaf whitefly is a key pest of squash that causes annual economic losses for growers (M cAuslane 2007, Henneberry and Faust 1999). Feeding of the immature forms of the silverleaf whitefly causes a severe physiological disorder in the squash plant resulting in silvering of the leaf surface and fruit blanching, commonly known as the squash silverleaf (SSL ) disorder (Frank and Liburd 2005). The reproduction of female aphids allow for rapid population increases especially when resources are abundant (Liburd and Nyoike 2008). One aphid fe male can produce 80 offspring per week and can have several overlapping gene rations per year (Woiwood and Hanski 1992). A decline in the quality and quantity of resources elicit a switch from apterous (wingless) to alate (winged) morphs and aphids migrate to search for new host plants. Migration increases the efficiency of disease transmission. In organic agricultural systems, effective and reliable monitoring techniques will aid in the detection and quantification of aphid and whitefly populations in squash plants. Good monitoring techniques will provide information about the pe st, its natural enemies and crop biology, which allows growers to use more timely and appropr iate management techniques to suppress pest populations. Effective monitoring techniques are de pendent on several factors including, labor (time spent to count insects on traps), total trap catches, and first trap catch (Liburd et al. 2000). Several techniques are used to monitor a phid and whitefly populations. For instance, yellow sticky traps are used to monitor aphids, wh iteflies and their associated natural enemies in greenhouse and field conditions (Liburd and Nyoi ke 2008). Blue pan traps with 5% detergent solution have also been used to assess aphi d but not whitefly populat ions (Frank and Liburd 2005, Liburd and Nyoike 2008). In situ counts are another standard technique used to detect the presence of aphids, whiteflies. My objective was to compare several monitoring techniques for

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105 aphids and whiteflies so that growers can use this information to improve their timing of management techniques for key pests on organic farms. Materials and Methods Field experim ents were conducted at the Univers ity of Florida, Plant Science Research and Education Unit in Citra, FL on certified orga nic acreage. The experimental setup was a randomized block design with four replicates of seven cover crop treatments. Each plot measured 12 m x 12 m and was separated by 12 m wide mowed alleys, whic h intended to reduce the movement of pest and beneficial arthropods between plots. After the cover crop treatments were incorporated into the soil, summer squash was dir ect seeded into each treatment plot. Each plot had four rows and each row had 27 squash plants. In 2006, summer squash (Cougar F1 cultivar) was direct seeded by hand with 0.46 m spacing be tween each plant, whereas in 2007 squash was seeded with a monosem pl anter with 0.23 m spacing betw een each plant and thinned. Comparisons of the different monitoring techniqu es were based on total trap catches, early detection and efficiency. Efficiency was measured in terms of labor and time involved in processing traps and was calculated by the product of the average time spent per trap and the cost per hour for counting traps. Aphids During 2006 and 2007, aphids (nym phs and adults ) were monitored once per week for a 4 week period, from 15 November to 11 December and 8 November to 30 December, respectively. The three different sampling methods evaluated were: Unbaited yellow sticky traps Blue water pan traps In situ visual counts

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106 Unbaited yellow sticky traps (treated area 406.45 cm2, Great Lakes IPM, Vestaburg, MI) were used to primarily monitor for alate aphids One yellow sticky trap was tied to a 0.6 m stake and placed in the middle of the inner two rows of squash plants in each treatment plot. Traps were left in the field for 48 h and replaced once each week. Traps that were brought back to the laboratory for analysis was covered with a laye r of plastic wrap and labeled accordingly. Traps were stored in the refrigerator until ready to be processed. Thes e traps were read by counting a sub-sample of 15 from 63 one inch squares on the traps due to high aphid densities (Finn 2003). This sub-sampling technique elimin ates counting errors and reduces the time spent per trap (Finn 2003). Briefly, each yellow sticky trap was overl aid with a gridded transparent paper. The transparency was divided into 63, 1-inch squares. Forty-eight of these sq uares were colored in, while 15 were left transparent. The area under these 15 transparent 1-inch squares was examined under a 40X dissecting microscope, and aphids a nd whiteflies were counted and recorded (Finn 2003). Natural enemies in all 63 squares on the stic ky traps were counted and recorded for each yellow trap. The time taken to count each trap was recorded. Blue water pan traps (Packer Ware Bowls, Gainesville, FL) were the second unbaited trap used in this experiment. These traps were suppor ted by tomato wire cages (45 cm x 15 cm x 20 cm), filled with water and detergent (5% deterg ent solution) (Colgate Palmolive Co. New York, NY) to break the surface tension (Webb et al. 1994). One blue pan trap was placed diagonally across from an unbaited yellow sticky trap on th e opposite end on the plot to monitor aphids and their natural enemies. Blue pan traps were constructed by punching three holes into the top edge of a blue plastic bowl 15 cm in diameter. Traps were left in the field for one week. At the end of the week, the contents from each trap were emptie d and into a small plastic container, labeled accordingly and taken back to the laboratory to be analyzed. The number of aphids and natural

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107 enemies from the blue traps were counted under a 40X dissecting microscope and the contents placed in 15 x 45 mm vials (Fisherbrand, Fisher Scientific, Pittsbu rgh, PA) with 70% ethanol for storage. The time taken to go through each blue pan trap was noted and recorded. Each week visual ( in situ ) counts were conducted in the field for aphids (alate and apterous), whiteflies, as well as other insects. All insects were visually assessed by randomly examining the leaves of eight squash plants fr om each of the two inner rows for ~1 minute. Whiteflies The two different sam pling methods used to evaluate whitefly populations were: Unbaited yellow sticky traps In situ visual counts The techniques used to monitor whitefly popul ations were the same as those used for aphids. Statistical Analysis Aphid data were analyzed using analysis of variance (ANOVA) followed by the least significant difference (L SD) means separation test s (SAS Institute 2003). Whitefly data were analyzed using the Students t-test (SAS Ins titute 2003). Means were considered significantly different from each other when P -values 0.05. Results Aphids Approxim ately 60% of the aphids recorded in the field from in situ counts were alate aphids. Results from the first capture date in 2006 showed that significantly more aphids were observed using the in situ monitoring technique ( F = 77.60; df = 2, 3; P < 0.001) compared with unbaited yellow sticky traps or blue pan traps (Figure 6-1). Unbaite d yellow sticky traps also had significantly more aphids than th e blue pan traps for the first sa mple date (Figure 6-1). For the

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108 2006 season, in situ counts had significantly higher numbe rs of alate aphids than the yellow sticky traps or blue pan traps in summer squash ( F = 1321.29; df = 2, 3; P < 0.001). In situ counts had 3 times more aphids compared with the yellow sticky trap a nd 19 times more aphids than the blue pan trap (Table 6-1). Six times more aphids were captured with yellow sticky traps compared with blue pan traps (Table 6-1). First capture results in 2007 had similar trends to those in 2006. In situ counts recorded significantly higher numbers of aphids than unba ited yellow sticky traps or blue pan traps ( F = 118.13; df = 2, 3; P < 0.001) (Figure 6-1). Also, throughout the 2007 field season, in situ counts had significantly (~3 times) more aphids than the yellow sticky traps and 23 times more aphids than blue pan traps (F = 898.41; df = 2, 3; P < 0.001) (Table 6-1). Whiteflies In 2006, first capture date from both monito ring techniques showed that whiteflies (B. argentifolli ) were significantly higher in ye llow sticky traps compared with in situ counts ( t = 4.66; df = 6; P = 0.0035) (Figure 6-2). However, thr oughout the 2006 field season, there were significantly more whiteflies from in situ counts compared with yellow sticky traps ( t = 20.99; df = 6; P < 0.0001) (Table 6-2). In 2007 the number of whiteflies were significantly higher with in situ counts compared with unbaited yellow sticky traps from first captures ( t = 18.12; df = 6; P < 0.0001) (Figure 6-2). Also, throughout the 2007 field season, similar results to 2006 were observed. Whitefly numbers were significantly higher with in situ counts compared with yellow sticky traps ( t = 20.90; df = 6; P < 0.0001) (Table 6-2). Time Required Per Monitoring Technique During 2006 it took significantly longer to coun t aphids and whiteflies on squash using in situ counts com pared with unbaited yello w sticky traps or blue pan traps ( F = 70.49; df = 2, 9; P

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109 < 0.0001) (Figure 6-3). The time taken to count aphids and whiteflies was approximately 17 minutes per plot while it took approximately 6 to 7 minutes per trap to assess key pests with unbaited yellow sticky traps or blue pan traps. In 2007, the time taken to assess key pests was similar to 2006. In situ counts took twice as long to count aphids and whiteflies ( F = 435.52; df = 2, 9; P < 0.0001) compared with using unbaited yellow sticky traps or blue pan traps (Figure 63). Discussion Aphids. These experim ents indicated that in situ counts can be considered the best method to use when monitoring aphid populations in the field because aphid numbers were significantly higher with this method when compar ed with the two other monitoring techniques. There were significantly higher num bers of aphids that were obs erved on the first capture date using in situ counts during 2006 and 2007 compared with unbaited yellow sticky traps or blue pan traps. This implies that in situ counts are more sensitive than yellow sticky traps or blue pan traps for giving fairly accurate assessments of pe st densities in the field. Choosing a suitable and effective sampling technique is a function of the labor and co st involved in using such a technique. In situ counts can be quite la borious and many hours can be spent in the field inspecting plants. It took twice as long to visually assess aphi d populations in the field using in situ counts compared with yellow sticky traps or bl ue pan traps. Once labor costs are factored in, the efficiency of using in situ counts is reduced compared with yellow sticky traps or blue pan traps. Also, knowing the degree of pest densities on the plants at a very earl y stage will improve the timing to make good pest management decisi ons (Flint and Gouveia 2001) If there are low aphid densities in the field, then in situ counts would not necessarily be the best option for getting a proper estimate.Therefore the use of alternate monitoring techniques could be considered.

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110 Both yellow sticky traps and blue pan traps have been used to m onitor aphid populations (Adlerz 1978, Frank and Liburd 2005, Liburd and Nyoike 2008). Kring (1972) reported that aphids are attracted to both l ong and shortwave light. Yellow light (~ 550 nm) in particular will induce aphids to alight on the yellow surface but shortwave light can be hi ghly attractive as they fly upwards towards the light, even avoiding yellow surfaces in the process. Since the blue color of my water pan traps falls in the shortwave length of light (~ 420 to 480 nm), it would be logical to assume that aphids could potentially be simila rly attracted to blue pan traps as they are to yellow sticky traps. However, my results showed that yellow sticky traps proved to be a more effective monitoring technique because they captur ed significantly more aphids than blue pan traps in both 2006 and 2007. According to Kring (1972) when aphids are in cruising or sniffing flight, they can be repelled by shortwave light (reflected by my blue pan traps) and turn by preference toward longwave light (yellow sticky traps). The time spent to assess aphids on yellow sticky traps was not significantly different from the time taken to assess aphids in blue pan traps. However, it took a significantly shor ter period of time to assess aphids on yellow sticky traps compared with in situ counts. Therefore, in order to save time and labor, it would be more cost effective to consider using yellow sticky traps as alternative to in situ counts or blue pan traps. If sticky traps are chosen, the effectiveness of the yellow sticky trap depends on the stickiness of the adhesive and wh ether the traps are made of cardboa rd or plastic. Plastic appears to be more durable. If the trap gets wet due to he avy rainfall or dirty because of dirt blown on to it by strong winds, then the efficiency of these traps will decline (Flint and Gouveia 2001). Also, the adhesive nature of the sticky card can make accurate aphid identification a challenging task. Whiteflies. For first capture date in 2006, my resu lts showed that unbaited yellow sticky traps had more whiteflies than in situ counts. This is not surprising because whiteflies are

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111 difficult to see when their numbers are low. In ad dition, they are highly at tracted to yellow. In 2007, in situ counts had significantly mo re whiteflies than unbaite d yellow sticky traps. The sensitivity of unbaited yellow sticky traps tend to vary depending on pest densities early in the season. Similar to aphids, in situ counts had higher whitefly numbers than yellow sticky traps throughout the season, which may imply that this is also the best technique for monitoring whitefly populations in the field. It took a si gnificantly longer time to count whiteflies with in situ counts compared with unbaited yellow sticky tr aps. The combination of labor costs and the time involved with in situ counts reduces the efficiency of this method. Additionally, whiteflies are very mobile insects and care has to be ta ken when inspecting leaves so as to prevent whiteflies from flying away once the leaf is disturbed. Unbaited yellow sticky traps are an alternative to in situ counts to monitor and control whitefly populations (Hoelmer 1998, Weinzierl et al. 2005). Like aphids, whiteflies use color cues to find landing sites (Byrne and Bellows 1991) They are also highly attractive to yellow wavelengths (535 to 580 nm) (Chu et al. 2000, By rne and Bellows 1991). Unbaited yellow sticky traps captured fewer whiteflies in 2007 than in 2006, and this could be due to a number of factors. Climatic conditions vary greatly each year in Florida and so weather conditions may have caused the decline in the whitefly numbers in 2007. Reduced numbers could also have been due to increased parasitism in the field. Overall, my studies demonstrated that in situ counts had the highest numbers of aphids and whiteflies, which appears to be a superior method of monitoring aphids and whiteflies. In addition the number of beneficial s could be measured very easil y, which would allow growers to

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112 make the best decision in deciding the type of pest management strategies to adopt in a timely fashion.

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113 Figure 6-1. First day trap captures in situ counts, yellow sticky traps (YST) and blue pan traps (BPT) for aphids in summer squash 0 20 40 60 80 100 120 140 160 180 200 2006 2007Mean no. of aphids per plotDate In situ counts YST BPTa a b b b c

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114 Table 6-1. Comparison techniques for monitoring aphids in summer squash throughout the entire season in Citra, FL. Monitoring techniques used in squash crop Mean SEM aphids from different monitoring techniques 2006a 2007b Blue pan traps 53.75 6.53c 73.00 4.77c In situ visual counts 1003.00 10.59a 1708.50 43.66a Yellow sticky traps 308.75 16.96b 500.50 18.34b Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 1321.29; df = 2, 3; P < 0.0001 b F = 898.41; df = 2, 3; P < 0.0001

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115 Figure 6-2. First day trap captures in situ coun ts and yellow sticky traps (YST) for whiteflies in summer squash 0 50 100 150 200 250 20062007Mean no. of whiteflies per plotDate In situ counts YSTb b a a

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116 Table 6-2. Comparison techniques for monitoring whiteflies in summer squash throughout the entire season in Citra, FL. Monitoring techniques used in squash crop Mean SEM whitefly adults from different monitoring techniques 2006 2007 In situ visual counts 1616.3 71.47a 520.25 23.25a Yellow sticky traps 112.50 4.73b 20.00 5.70b Whitefly egg data were squa re root transformed before analysis but means shown reflect untransformed data. Means followed by the same letters are not significantly different P = 0.05 (LSD) a F = 0.81; df = 3, 6; P = 0.5725 b F = 1.09; df = 3, 6; P = 0.4048

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117 0 2 4 6 8 10 12 14 16 18 20062007 DateMean time taken to assess aphids and whiteflies (min) BPT YST Insitu counts Figure 6-3. Time taken (minutes) to assess aphi ds and whiteflies for blue pan traps (BPT), yellow sticky traps (YST) and in situ counts for aphids and whiteflies in summer squash a a b b b b

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118 LIST OF REFERENCES Adams, D. B. 2000. Commercial production and m anagement of squash and cucumbers. Bulletin 1178. University of Georgia Colle ge of Agricultural and Environmental Sciences Cooperative Extens ion Service, Athens, GA. Adlerz, W. C. 1987. Cucurbit potyvirus transmission by alate aphids (Homoptera:Aphididae) trapped alive. J. Econ. Entomol. 80: 87-92. Gold, M. V. 2007. Organic production/organic food: in formation access tools; March 2008. U. S. Dep. Agric., Alternative Farming Systems Information Center, Washington, D.C. Agricultural Marketing and Resource Center (AgMRC). 2007. Squash. Iowa State University, Ames, Iowa ( http://www.agmrc.org/agmrc/commodity/vegetables/squash/) Ambrosino, M. D., P. C. Jepson, and J. M. Luna. 2007. Hoverfly oviposition response to aphids in broccoli fields Entom ol. Exp. Appl. 122: 99 107. Antignus, Y. 2000. Manipulation of wavelength-dependent behavior of insects: an IPM tool to impede insects and restrict epidemic s of insect-borne viruses. Virus Res. 71: 213-220. Antonelli, A. L. 2003. Hover or Syrphid Flies. Washi ngton State University Cooperative Extension WSU Puyallup RE C PLS-83, Pullman WA. Awmack, C. S., and S. R. Leather. 1998. Growth and Development, pp. 135-152. In H. F. van Emden and R. Harrington [eds.], Aphi ds as Crop Pests. CAB International, Cromwell Press, Trowbridge, UK. Bachmann, J. 2002. Farmers markets marketing and business guides, pp. 1-4 In : Appropriate Technology Transfer for Ru ral Areas (ATTRA) Publication IP146. Balkcom, K. S. and D. W. Reeves. 2005. Sunn hemp utilized as a legume cover crop for corn production. Agron. J. 97: 26-31. Beane, K. A. and R. L. Bugg. 1998. Natural and artificial shelter to enhance arthropod biological control agents, pp. 239-254. In C. H. Pickett and R. L. Bugg [eds.], Enhancing biological control: habitat mana gement to promote natural enemies of agricultural pests. University of California Press, Berkley, CA. Beckage, N. E. and D. B. Gelman. 2004. Wasp parasitoid disruption of host development: implications for new biologically based strategies for insect control. Annu. Rev. Entomol. 49: 299-330.

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119 Bengtsson, J., J. Ahnstrm, and A. Weibull. 2005. The effects of organic agriculture on biodiversity and abundance: a meta-a nalysis. J. Appl. Ecol. 42: 261-269. Blackman, R. L., and V. F. Eastop. 2007. Taxanomic issues, pp. 1-22. In H. F. van Emden and R. Harrington [eds.], Aphids as Crop Pests. CAB International, Cromwell Press, Trowbridge, UK. Bonina, J. and D. J. Cantliffe. 2004. Seed production and seed sources of organic vegetables, HS 981. Institute of Food and Ag ricultural Life Sciences, University of Florida, Gainesville, FL. Bowman, G., C. Shirley, and C. Cramer, 1998. Benefits of cover crops, pp. 8-11 In : A. Clarke [ed.], Managing Cover Cr ops Profitably, Beltsville, MD. Brewer, M. J. 1995. Syrphid flies. Extension Pu blication B-1013.22.University of Wyoming, Laramie, WY. Brewer, M. J., and N. C. Elliott. 2004. Biological control of cereal aphids in North America and mediating effects of host pl ant and habitat manipulations. Annu. Rev. Entomol. 49: 219-242. Browning, H. W., C. W. Melton, and R. R. Saldana. 1985. Release and evaluation of exotic parasites for biologi cal control of the Mexican ri ce borer on sugar cane in the lower Rio Grande Valley, 1983-1985. Texas Ag ricultural and Experimental Station Progress Report. 4344. Bugg, R. L. 1991. Cover crops and control of arth ropod pests of agriculture, pp.167-163. In Cover crops for clean water: Proceedings of an internationa l conference West Tennessee Experiment Station, 9-11 April 1991, Jackson TN. Bugg, R. L. and C. H. Pickett, 1998. Introduction: Enhancin g biological control habitat management to promote natural en emies of agricultural pests, pp. 1-24. In C. H. Pickett and R. L. Bugg [eds.], Enhancing biological control: habitat management to promote natural enemies of agricultural pest s. University of California Press, Berkley, CA. Bugg, R. L. and C. Waddington. 1994. Managing cover crops to manage arthropod pests of orchards. Agr. Ecosyst. Environ. 50:11-28. Bugg, R. L. and R. T. Ellis. 1990. Insects associated with co ver crops in Massachusetts. Biol. Agric. Hortic. 7: 47-68.

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120 Bugg, R. L., F. L. Wckers, K. E. Brunson, J. D. Dutcher, and S. C. Phatak. 1991. Cool-season cover crops rela y intercropped with cantaloupe : influence on a general predator, Geocoris punctipes (Hemiptera: Lygaeidae). J. Econ. Entomol. 84: 408 416. Bugg, R. L., S. Phatak, and J. D. Dutcher. 1990. Insects associated with cool season cover crops in Southern Geor gia: implications for pest control in truck-farm and pecan agroecosystems. Biol. Agric. Hortic. 7: 17-45. Buitenhuis, R., J. N. McNeil, G. Boivin, and J. Brodeur. 2004. The role of honeydew in host searching of aphid hyperpar asitoids. J. Chem. Ecol. 13: 273-285. Burleigh, J. G., J. H. Young, and R. D. Morrison.1973. Strip-croppings effect on beneficial insects and sp iders associated with cotton in Oklahoma. Environ. Entomol. 2: 281-285. Byrne, D.N., and T.S. Bellows. 1991. Whitefly Biology. Annu. Rev. Entomol. 36: 431457. Caamal-Maldonado, J. A., J. J. Jimnez-Osornio, A. Torred-Barrangn, and A. L. Anaya. 2001. The use of allelopathic legume cover and mulch species for weed control in cropping systems. Agron. J. 93: 27-36. Capinera, J. L. 2007. Melon aphid or cotton aphid, Aphis gossypii Glover (Insecta: Hemiptera: Aphididae), EENY-173. Institute of Food and Agricultural Life Sciences, University of Fl orida, Gainesville, FL. Crcamo, H. A., D. Parkinson, and J. W. A. Volney. 1998. Effects of sulphur contamination on macroinvertebrates in Canadi an pine forests. Appl. Soil Ecol. 9: 459-464. Chambliss, C. G., R. M. Muchovej, and J. J. Mulahey. 2003. Cover Crops, SSAGR66. Institute of Food and Agricultural Life Sciences, University of Florida, Gainesville, FL. Chaney, W. 1998. Biological control of aphids in lettuce using in-field insectaries, pp. 73-84. In C. H. Pickett and R. L. Bugg [eds.] Enhancing biological control: habitat management to promote natural enemies of agricultural pest s. University of California Press, Berkley, CA.

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131 BIOGRAPHICAL SKETCH Corraine Athol Scott was born in Manchest er, Jam aica in 1983. She graduated from Glenmuir High School, May Pen, Clarendon, in July 2001. After graduation, she earned a Presidential scholarship to attend Ran dolph Macon Womans College (now Randolph College) in Lynchburg, VA where she earned her BS in biology with minors in chemistry and sociology/anthropology in May 2005. Af ter graduation, Corraine went to Virginia Commonwealth University, where she spent a y ear as an adjunct biology lecturer for introductory biology labs and was the resident director for a freshman residence hall while taking graduate courses. Corraine transf erred to the University of Florida where she pursued her MS degree in entomology in fall 2006. After completing her degree requirements, Corraine will continue her gra duate studies as a PhD entomology student studying various semiochemical strate gies to manage pepper weevil.