Megacerus discoidus, A POTENTIAL BIOLOGICAL \ CONTROL AGENT OF HEDGE BINDWEED,IN SOUTHWESTERN VIRGINIA · by Ren\Wang Dissertation submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in ENTOMOLOGY APPROVED: ? , ¤ ¥- L. T. Kok, Chairman ,· r .’ / ’/ Q A ,, ” „’ /7 / /' W · ” "{ —“ P ¢ IA. gig ¢« é?]V‘ „°L R. L. Pienkowski Z/Ö. L. Eaton · ( -l' _ W W ‘— '_‘_;”„,° J r .· = _ /, C - E.’Ö. Turner Jr. K. K. Hatzios \ May, 1985 Blacksburg, Virginia %’ If M£Q䧧IB§ diäggidus, A POTENTIAL BIOLOGICAL CONTROL AGENT OF HEDGE BINDWEED EI IN SOUTHWESTERN VIRGINA N l Ren Wang Committee Chairman: Loke T. Kok Entomology (ABSTRACT) Megacerus discoidus (Say)(Coleoptera: Bruchidae), a native North American seedfeeder, has 4 larval instars and one generation a year. Overwintering occurred in the 4th instar. Larvae fed on 40-50% of the seed content before diapause and the rest of the seed in the following spring. When more than one larvae attacked a seed, only one adult emerged because of cannibalism, which was most common among 2nd and 3rd instars. Adults oviposited mainly under the bracts of host seedpods. The life cycle of the beetle was well synchronized with the host phenology. when diapause of the insect was experimentally terminated under 20°C and 28°C, there was increased mortality and prolonged adult emergence. No adult emergence occurred when infested seeds were maintained in the dark under l0°C for 200 days. However, mortality of the larvae was significantly increased. Humidity and soil coverage of host seeds had no significant impact on the beetle mortality during diapause under field conditions. Of 19 plant species tested, only hedge bindweed and wild sweet potato, Ipomoea pandurata, supported larval development to adults. Oviposition occurred only on seedpods of hedge bindweed and heavenly blue morningglory, Ipomoea tricolor. The latter did not support larvalx development. An infestation rate of 5 M. discoidus eggs per seedpod of hedge bindweed in the field cages was achieved by releasing the adults at a relatively high adult/plant ratio (1.2 pairs/plant) plus inoculation of eggs on all seedpods in the cages. This resulted in a high rate (ca. 70%) of seed infestation, but did not destroy all of the seeds in the field cages. Release of lower number of adults led to lower seed infestation. Seed consumption did not cause any change in reproduction and vegetative growth of hedge bindweed. I consider the use of M. discoidus to be safe but it must be combined with other stress factors to achieve effective control. ACKNOWLEDGEMENTS First, I sincerely thank Dr. Loke T. Kok, my umjor advisor, whose wise advice has helped me solve the puzzles and avoid pit-falls throughout the past three and a half years of my study. His philosophy, encouragement, and sometimes, criticism, has certainly made me a better person, and, a more patient and accurate scientist. Appreciations also go to other members of my advisory committee, Drs. R. L. Pienkowski, J. Ih Eaton, E. C. Turner .Jr. and K. K. Hatzios, for their advice and editorial recommendations on my research and course work. I am especially indebted to the Rockefeller Foundation, under whose generous fellowship, my long—cherished dream has come to reality, to Dr. Joseph R. Bookmyer of the Rockefeller Foundation, and to Drs. Clarence Gray III, Roger A. Teekell, P. Howard Massey Jr., and Bernard E. LaBerge of VPI&SU, each, in his own way, has made all this work possible. Special thanks go to for his technical assistance and advice on supplies and literature searches, to , who have helped to make Blacksburg a much interesting place to stay, and to Thomas F. Wieboldt of the Herbarium, Dept. of Biology, VPI&SU, for identification of weed plants. iv I deeply appreciate the company and help provided by my colleagues, J. These names will always have a special place in my heart. Finally, I wish to express my special thanks to J he and I have been sailing on the same boat for 5 years. Upon sharing our happiness, anguish, and ...homesickness, he, as a true friend, has helped me immeasurably to overcome the odds! v CONTENTS ABSTRACT ........................ II ACKNOWLEDGEMENTS .................... IV Chapter page I. INTRODUCTION ................... 1 II. BINDWEEDS AND THEIR BIOLOGICAL CONTROL ...... 7 The Target Weeds ................ 8 Taxonomy and distribution .......... 8 Economic importance ............. 10 Biology ................... 12 Growth and development .......... 12 Reproduction ............... 15 Response to herbicides and cultural control . 18 Biological control of bindweeds ........ 19 Foliage feeders ............... 21 Root and stem feeders ............ 22 Seed feeders ................ 23 III- LIFE HISTORY OF(COLEOPTERA:BRUCHIDAE), A SEEDFEEDER OF HEDGE BINDWEED, IN SOUTHWESTERN VIRGINIA ..... 26 Introduction .................. 27 Materials and Methods ............. 30 Life cycle ................. 30 Synchronization with host .......... 31 Results and Discussion ............. 32 Life cycle ................. 32 Synchronization with host .......... 39 IV. INFLUENCE OF TEMPERATURE, HUMIDITY AND SOIL COVERAGE ON THE DIAPAUSE OF MEQAQERQS DISCOIDQS (COLEOPTERA:BRUCHIDAE), A SEEDFEEDER OF HEDGE BINDWEED ........ 44 Introduction .................. 45 Materials and Methods ............. 46 Effect of temperature on diapause of M„ discoidus ............... 46 vi Effect of temperature on mortality during diapause and post—diapause development of M. discoidus ............ 47 Effects of humidity and soil coverage of the seeds on overwintering mortality of M. discoidus ............... 48 Results and Discussion ............. 49 Effect of temperature on diapause of M„ ~ discoidus ............... 49 Effect of temperature on mortality during diapause and post-diapause development of M: discoidus ............ 54 Effect of humidity and soil coverage of the seeds on overwintering mortality of M. discoidus ............... 57 V. HOST SPECIFICITY OF MEGACERUS DISCOIDUS (COLEOPTERA:BRUCHIDAE), A NATIVE SEEDFEEDER OF BINDWEEDS................. 58 Introduction .................. 59 Materials and Methods ............. 61 Larval development tests .......... 61 Oviposition tests .............. 63 Results and Discussion ............. 64 Larval development tests .......... 64 Oviposition tests .............. 65 VI. IMPACT OF MEGACERUS DISCOIQUS (COLEOPTERA:BRUCHIDAE) ON GROWTH AND SEED PRODUCTION OF HEDGE BINDWEED ........ 68 Introduction .................. 69 Materials and Methods ............. 70 Impact of M„ discoidus on seed production .. 70 Hedge bindweed growth response to seed infestation .............. 72 Results and Discussion ............. 73 Impact of_M„ discoidus on seed production . 73 Hedge bindweed growth response to seed infestation..............76 VII. SUMMARY AND CONCLUSIONS .............. 79 \ REFERENCES CITED .................... 84 VITA .......................... 93 vii LIST OF TABLES Table page l. Insects and mites that have been evaluated for biological control of bindweeds ......... 24 2. Duration of stages in the field and measurements of Q. discoidus. .................. 33 3. Percent mortalities (2iS.D.) of diapause and post- diapause stages of Q. discoidus.......... 55 4. Percent mortalities (ätS.D.) of Q. discoidus in response to seed coverage and high and low humidity. .................... 56 5. Plant species used in the host specificity tests for Q. discoidus. .................. 62 6. Summary of Q. discoidus larval development tests. 66 7. Seedpod and seed formation of hedge bindweed in response to infestation by Q. discoidus (äiS.D.). 75 8. Responses in vegetative growth of hedge bindweed to infestation by Q. discoidus............ 78 viii LIST OF FIGURES Figure gage 1. Adults of M. discoidus (Say)............. 37 2. Percent of oviposition over M. discoidus female's life span..................... 38 3. Percent bloom of hedge bindweed in the Blacksburg area. ...................... 4O 4. Synchronization of the life cycle of M. discoidus with its host phenology in Southwestern Virginia. 41 5. Percent adult emergence of M. discoidus from overwintering larvae in different treatments. 51 6. Percent emergence of male and female adults of M. discoidus from overwintering larvae maintained at 28°C. ...................... 53 ix Chapter I INTRODUCTION 1 2 A weed is "a plant thatvoriginated under a natural environment and, in response to imposed and natural environments, evolved and continues to do so, as an interfering associate with our crops and activities" (Aldrich 1984). Man has been struggling with weeds since the beginning of agriculture. Traditionally, weed control falls into seven general categories: herbicidal, crop competition, crop rotation, biological, fire, mechanical, and hand labor (Mcwhorter and Shaw 1982). Biological weed control has the advantages of low cost, safety in the environment (such as no residues in the soil), simplicity of operation after establishment of the agent, and compatibility with, other control measures. As a result, biological weed control has captivated increasing attention and research efforts in the last two decades. The majority of the weed biological control programs have involved insects, despite the increasing appreciation of microbial organisms as biological weed control agents. Insects can be used in two ways for biological control of weeds, (1) the classical method, i.e. exotic insects are introduced to control weeds of foreign origin, and (2)