Optimizing Biotic Mortality for Management of the Alfalfa Weevil Hypera Postica Gyllenhal (Coleoptera: Curculionidae) Kristopher Lynn Giles Iowa State University
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Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1996 Optimizing biotic mortality for management of the alfalfa weevil Hypera postica Gyllenhal (Coleoptera: Curculionidae) Kristopher Lynn Giles Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Agricultural Science Commons, Agriculture Commons, Agronomy and Crop Sciences Commons, Ecology and Evolutionary Biology Commons, and the Entomology Commons Recommended Citation Giles, Kristopher Lynn, "Optimizing biotic mortality for management of the alfalfa weevil Hypera postica Gyllenhal (Coleoptera: Curculionidae) " (1996). Retrospective Theses and Dissertations. 11371. https://lib.dr.iastate.edu/rtd/11371 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. 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UMI A Bell & Howell lofonnation Company 300 North Zed> Road, Ann Aibor MI 48106-1346 USA 313/761-4700 800/521-0600 Optimizing biotic mortality for management of the alfalfa weevil Hypera postica Gyllenhal (Coleoptera: Curculionidae) by Kristopher Lynn Giles A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department: Entomology Co-Major: Entomology Interdepartmental Co-Major: Ecology and Evolutionary Biology Major Professors: John J. Obrycki and Lois H. Tiffany Iowa State University Ames, Iowa 1996 UMI Number: 9635320 UMI Microform %35320 Copyright 19%, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North 2^eeb Road Ann Arbor, Ml 48103 ii Graduate College Iowa State University This is to certify that the doctoral dissertation of Kristopher Lynn Giles has met the dissertation requirements of Iowa State University Signature was redacted for privacy. r Professor Signature was redacted for privacy. Co-Major Profe^r Signature was redacted for privacy. For the Interdepartmental Major Signature was redacted for privacy. For the Major Department Signature was redacted for privacy. FOT th Graduate College iii TABLE OF CONTENTS GENERAL INTRODUCTION 1 Introduction 1 Objectives 5 Dissertation Organization 5 Literature Review 6 Life Cycle of H. postica in Iowa 6 Effect of H. postica feeding on Alfalfa 7 Yield 7 Quality 8 Photosynthetic Rate 9 Impact of H. postica Natural Enemies in Iowa 9 ^ophthora phytonomi 9 Parasitoids 11 Arthropod Predators 12 Natural Enemies in Hypera postica IPM Programs 13 CHAPTER 1. FIELD RELEASE OF//y/>£:^P0577Ci4GYLLENHAL (COLEOPTERA: CURCULIONIDAE) LARVAE FOR ENHANCEMENT OF ZOOPHTHORA PHYTONOMI ARTHUR (ENTOMOPHTHORALES: ENTOMOPHTHORACEAE) 15 Abstract 15 Introduction 15 Materials and Methods 17 Results and Discussion 19 Acknowledgments 22 References Cited 22 CHAPTER 2. TRANSMISSION AND DEVELOPMENT OF ZOOPHTHORA PHYTONOMI ARTHUR (ENTOMOPHTHORALES: ENTOMOPHTHORACEAE) IN HYPERA POSTICA GYLLENHAL (COLEOPTERA: CURCULIONIDAE) LARVAE EXPOSED TO AN INSECTICIDE 27 Abstract 27 Introduction 27 Materials and Methods 29 Results and Discussion 30 Acknowledgments 32 References Cited 33 CHAPTER 3. INFLUENCE OF REDUCED INSECTICIDE RATES AND STRIP- HARVESTING ON ALFALFA WEEVIL LARVAL POPULATIONS AND PREVALENCE OF ZOOPHTHORA PHYTONOMI ARTHUR (ENTOMOPHTHORALES: ENTOMOPHTHORACEAE) 38 Abstract 38 InU-oduction 39 Materials and Methods 41 Environmental Conditions 41 iv 1994 41 1995 43 Insecticide Applications 1994 & 1995 44 Statistical Analysis 44 Voucher Specimens 45 Results 45 1994 45 1995 46 Discussion 49 Mortality of H. postica from insecticides and harvesting 49 Mortality of H. postica from Z phytonomi 50 Combing Mortality: managment tactics and Z phytonomi 52 ^tegrated Managment of H. postica 53 Acknowledgements 55 References Cited 56 CHAPTER 4. EFFECTS OF REDUCED INSECTICIDE RATES AND STRIP- HARVESTTNG ON ALFALFA WEEVIL LARVAL POPULATIONS AND PARASITISM BY TWO BATHYPLECTES SPECIES 70 Abstract 70 Introduction 71 Materials and Methods 72 Experimental Design 72 Environmental Conditions 72 Treatments 73 Sampling and Rearing 74 Parasitoids 75 Statistical Analysis 75 Voucher Specimens 76 Results 76 Hypera postica larval numbers 76 Parasitism 76 Discussion 78 Impact of Treatments 78 Integrated Control 79 Acknowledgements 81 References Cited 81 CHAPTER 5. REDUCED INSECTICIDE RATES AND STRIP-HARVESTING: EFFECT ON ARTHROPOD PREDATOR ABUNDANCE IN FIRST GROWTH ALFALFA 99 Abstract 99 Introduction 99 Materials and Methods 101 Predators and Altemative Prey 101 Statistical Analysis 102 Voucher Specimens 102 Results 102 Predators, Ames 1994 102 A. pisum, 1994 103 V Predators, Chariton & Ames 1995 103 Discussion 104 Coccinellids, Hemipterans and Aranea 104 Management tactics and Arthrop<^ Predator Abundance 103 Arthropod Predators and H. postica IPM 106 Acknowledgements 108 References Cited 108 GENERAL CONCLUSIONS 118 REFERENCES CITED 122 ACKNOWLEDGEMENTS 132 1 GENERAL INTRODUCTION Alfalfa, Medicago saliva L., is one of the worlds most widely grown forage crops because of its importance in livestock production and crop rotations (Steffey & Armbrust 1991, Pick & Mueller 1989). Additionally, it is an important nectar source for honey bees, habitat for numerous arthropod natural enemies, and an ideal nesting site for birds (Barney & Armbrust 1981, Giles et al. 1994b, Frawley & Best 1991, Buske et al. 1991). The introduced alfalfa weevil Hypera postica Gyllenhal (Coleoptera: Curculionidae) is among the most important alfalfa-feeding insects in the United States and Canada and occasionally causes great economic damage (Steffey & Armbrust 1991). Management of H. postica has relied heavily on imported Hymenopteran paiasitoids to suppress weevil populations (Day 1981). In areas of the northeastern United States where six parasitoid species ate established, 73% of all alfalfa fields do not have sufficient weevil populations to justify the use of insecticides (Day 1981). In the northeastern United States, an estimated 8 million dollars per year is being saved (reduced insecticide use) because of the actions of these natural enemies (Day 1981). In an economic analysis of the alfalfa weevil biological control program, Moffit et aL (1990) concluded that the benefits of this program for the entire United States are $88 million dollars per year (1987 dollar). Despite the success of the biological control program, and the efifectiveness of a naturally occurring entomopathogenic fungus, Zooph^ra phytonomi Arthur (Zygomycetes: Entomophthoraceae), H. postica continues to be a sporadic pest of alfalfa in many locations throughout North America (Harcourt 1985; Harcourt & Guppy 1991; Goh et al. 1989a; Steffey & Armbrust 1991, DeGooyer et al. 1996). Current alfalfa weevil management options include early harvesting, and / or insecticides when populations reach economic thresholds (Wedberg et al. 1980, Higgins et al. 1988, Steffey & Armbrust 1991, Wintersteen et al. 1992). However, harvesting or insecticides used to control H. postica larval populations often reduce 2 natural enemy numbers and their impact (Wilson & Armbrust 1970, Casagrande & Stehr 1973, Walstrom 1974, Hower & Luke 1979, Steffey & Armbrust 1991). Relatively few efforts have been made to integrate H. postica management tactics and natural enemies into holistic management programs that could be used by forage producers. This is caused in part by the lack of detailed information on the interactions between H. postica natural enemies and agronomic practices (Brown & Nordin 1986, Brown 1987, Harper 1987). A model developed by Brown and Nordin (1982) includes Z phytonomi as a component of an implemented management program in Kentocky (Brown 1987). This model produced management recommendations utilizing early-season insecticide decision thresholds and early harvesting. Insecticide applications were used to suppress early weevil outbreaks. However, these applications reduced