Interactions of Arthropod Predators and Cry1ac-Transgenic Cotton
Total Page：16
File Type：pdf, Size：1020Kb
INTERACTIONS OF ARTHROPOD PREDATORS AND CRY1AC-TRANSGENIC COTTON by JORGE BRAZ TORRES (Under the Direction of John R. Ruberson) ABSTRACT Interactions of predators and Bt-cotton plants (containing a gene from Bacillus thuringiensis that expresses Cry1Ac toxin) were investigated in the field, greenhouse, and laboratory. Abundance of predatory arthropods was monitored from 2002 to 2004 in three pairs of adjacent Bt and non-Bt fields (5 to 15 ha each). Analysis of predator abundance and dynamics showed variation among sampling dates and among seasons for some specific taxa collected through whole plant and drop cloth sampling in favor of either cotton. However, when averaged over three years, differences were nearly all eliminated. Of 65 ground-dwelling arthropods collected in pitfall traps, no differences were found between cotton types for abundance, diversity, and species richness. Field-collected materials (plant-herbivore-predator) were assayed for Cry1Ac toxin using ELISA. Bt-cotton and lepidopteran larvae were positive on all sampling dates, while among seven predator species only Podisus maculiventris and Chrysoperla rufilabris were positive (on one and two sampling dates, respectively) concurrent with high abundance of lepidopteran larvae in the fields. Ingestion of Cry1Ac toxin by four common predatory heteropterans (Geocoris punctipes, Nabis roseipennis, Orius insidiosus, and P. maculiventris) was studied using prey fed Bt-cotton in a greenhouse or dilutions of purified Cry1Ac in the laboratory (Geocoris punctipes). Predatory heteropterans were unable to pick up toxin directly from the plant, despite plant feeding behavior, but may acquire Cry1Ac from prey fed Bt-cotton. The amount of prey consumed by small predatory heteropterans (Orius, Geocoris, and Nabis) seems to limit ingestion of Cry1Ac below detectable levels in their bodies. G. punctipes was able to pick up toxin from Cry1Ac purified dilutions in water at detectable levels but from concentrations higher than levels detected in cotton plants and greater than conveyed by prey fed Bt-cotton. Most of the ingested Cry1Ac, however, was excreted and was not detected in the predators’ bodies or feces more than 48 to 72h after feeding. Prey- and/or plant-mediated effects on the omnivorous predator G. punctipes were studied in the field. Predators were exposed to a combination of prey with and without toxin, and Bt and non-Bt plants from egg hatch until death. The results showed no effect of prey fed-Bt or direct effect of Bt-cotton plants on life history parameters of the predator. INDEX WORDS: Insecta, Bacillus thuringiensis, transgenic cotton, biological control, tritrophic interactions, predatory heteropteran. INTERACTIONS OF ARTHROPOD PREDATORS AND CRY1AC-TRANSGENIC COTTON by JORGE BRAZ TORRES BS in Agronomy, Universidade Federal do Espirito Santo, Brazil, 1993. MSc. Entomology, Universidade Federal de Viçosa, Brazil, 1995. A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY ATHENS, GEORGIA 2005 © 2005 Jorge Braz Torres All Rights Reserved INTERACTIONS OF ARTHROPOD PREDATORS AND CRY1AC-TRANSGENIC COTTON by JORGE BRAZ TORRES Major Professor: John R. Ruberson Committee: Michael J. Adang John N. All S. Kristine Braman Phillip Roberts Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia May 2005 DEDICATION This dissertation is dedicated to my large and lovely family that always gave me support. To my wife Christian for her constant companionship and balance given to our relationship. To all professors along my academic life and especially to my mother and father who with their simplicity showed me the value of education. iv ACKNOWLEDGEMENTS I express my deep gratitude to my major professor Dr. John R. Ruberson, who patiently helped me during every step of this work. Words cannot describe his continuous friendly attitude either during sampling in the cotton fields or helping with presentation practices after hours. To the “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior” (CAPES Foundation, Brazil) for the support given from 2002 to 2005 plus tuitions and fees at the University of Georgia. To the University of Georgia that provided wonderful facilities and the Universidade Federal Rural de Pernambuco that allowed my absence during the doctoral program. To my colleagues at the Universidade Federal Rural de Pernambuco José Vargas, Edmilson Marques, Manoel “Mano” Guedes, Souza Leão and especially Reginaldo “Regin” Barros for taking care on my business during my absence. Not only this work but also my academic life at the University of Georgia would not be possible without the help and assistance of many people since my arrival: Francisco Miguel, David Jenkins, Luciana Cordeiro, Jorge Gonzalez, Deny Frendly, and Mark Dalusky. My academic life was shared with many good friends and a handful of people in the classroom such as Selim Dedej, Christian Torres, Punya Nachappa, Grecthen Pettis, Chris Hartley and “JC”. To the committee members Dr. Michael Adang, Dr. John All, Dr. Kristine Braman and Dr. Phillip Roberts, I have special appreciation for their understanding my limitations and helping v me. I give special thanks to Dr. Phillip Roberts who lent us his projector many times to practice oral presentations. To Jiang (John) Chen and Juan Jurat-Fuentes (UGA, Athens, GA) and Evelyn Folds and Stephen Mullis (UGA, Tifton, GA), who were responsible for my start with laboratory protocols and ELISA assays. To those people who always are reminding us of dates and forms to be completed and are always ready to help: Carol Ireland, Jenny Granberry, Marianne Stephens, Beverly Martin, Haley Carmichael, Detsy Bridges and Nancy Jordan. To the professors at the Department of Entomology for their time spent inside and outside classrooms. Along this four years Melissa Thompson “lab boss”, Russ Ottens, David Griffin and many summer students made the work environment enjoyable: Holly Tawzer, Mel MeClellan, Chad Dunn, Jarret Burns, Abinadi Burns, Eric Douce and Collin Anderson. Finally, I am very grateful to the opportunity given to my wife Christian by Dr. Robert Matthews and Dr. John Ruberson and Department of Entomology of the University of Georgia during her Master program. vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS.............................................................................................................v CHAPTER 1 INTRODUCTION .........................................................................................................1 2 LITERATURE REVIEW ..............................................................................................7 Tritrophic interactions in Bt-cotton fields...............................................................11 Big-eyed bug Geocoris punctipes............................................................................27 Feeding Behavior of Geocoris punctipes ................................................................27 Could Bt-cotton affect Geocoris punctipes?............................................................29 Purpose of this study ...............................................................................................34 3 CANOPY- AND GROUND-DWELLING PREDATOR ARTHROPOD COMMUNITIES IN BT AND NON-BT COTTON FIELDS: PATTERNS AND MECHANISMS ......................................................................................................53 4 ABUNDANCE AND DIVERSITY OF GROUND-DWELLING ARTHROPODS OF PEST MANAGEMENT IMPORTANCE IN BT AND NON-BT COTTON FIELDS ...................................................................................................................93 5 SPATIAL AND TEMPORAL DYNAMICS OF BOLLWORM AND THREE PREDATORS’ EGGS IN BT AND NON-BT COTTON FIELDS ......................129 vii 6 EXPRESSION OF BACILLUS THURINGIENSIS CRY1AC PROTEIN IN COTTON PLANTS, ACQUISITION BY PESTS AND PREDATORS: A TRITROPHIC ANALYSIS FROM LABORATORY TO FIELD EXPERIMENTS ...................165 7 NEITHER BT COTTON-FED PREY NOR BT-COTTON PLANTS AFFECT THE OMNIVOROUS PREDATORY BIG-EYED BUG GEOCORIS PUNCTIPES (SAY) (HET.: GEOCORIDAE) IN THE FIELD .................................................200 8 CONCLUSIONS........................................................................................................232 viii CHAPTER 1 INTRODUCTION Cotton is one of many agriculture commodities that does not need many words to justify its importance not only in the US, but also for many other countries around the world. The economic impact of cotton and the importance of pest management for cotton production is reflected in the recent investments made by biotechnology companies to develop transgenic cotton resistant to insect pests. For instance, the releases of Bollgard, Bollgard II, WidestrikeTM and VipCotTM varieties all sharing the unique goal of managing nearly all lepidopteran larvae, a group of key pests in cotton fields everywhere. The broad acceptance by growers and great potential for Bt- cotton cultivation throughout cotton growing regions fuel many ecological questions from agronomists, ecologists, and especially from entomologists about potential negative impactS of the technology on nontarget organisms. This subject evolved into a major issue for adopting transgenic plants during this past decade, not only as a matter for scientific discussion but also for public debate. Transgenic cotton plants have been produced containing genes that express Cry