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Bt Corn Ceeb Talk


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Outlines research done on quantifying the effects of various species of ladybeetles as well as the carabid beetle.

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Bt Corn Ceeb Talk

  1. 1. Uptake of Cry1Ab-Endotoxins by Generalist Predators in Fields of Bacillus Thringiensis Corn Aaron Samson Department of Entomology University of Kentucky CEEB Symposium 5/12/06
  2. 2. Acknowledgements •Dr. James D. Harwood (post-doctoral scholar) • Dr. John J. Obrycki (chairman) •Casey Bayne (Agricultural Biotechnology undergraduate) Supported in part by grant from the Kentucky Science and Engineering Foundation as per Grant Agreement #KSEF-148-502-04-121 with Kentucky Science and Technology Corporation.
  3. 3. Outline • Bt Overview • Project Methodology • Results • Implications • Future Research
  4. 4. Bacillus thuringiensis • Discovered in 1911 •Approx. 1% of agrochemical market • Contained in bacteria plasmids • Dried spores and toxin crystals • Crystals a protoxin (must be activated for effect) • Activated in increased pH conditions in mig-gut of larvae, then lyses epithelial cells to cause septicemia (safe for humans) • Used genetically since 1996
  5. 5. Bt Classes Protein Crystal Size Gene Shape (kDa) Insect Activity cry I [several subgroups: bipyramidal 130-138 lepidoptera larvae A(a), A(b), A(c), B, C, D, E, F, G] lepidoptera and cry II [subgroups A, B, C] cuboidal 69-71 diptera cry III [subgroups A, B, C] flat/irregular 73-74 coleoptera cry IV [subgroups A, B, C, D] bipyramidal 73-134 diptera cry V-IX various 35-129 various
  6. 6. Purpose • 67 million ha transgenic crops in 2003 • Insecticidal input decreased and crop yield increased without effects on non-target arthropods • Concerns raised over negative effects on arthropod food chain • Tests showed some elevated levels of Bt-endotoxin in non-target herbivores and arthropod predators • Research used antibody-based assays to identify trophic linkages in field
  7. 7. Generalist Predators • Many predators Herbivores exposed to Bt-endotoxin through direct consumption on prey • Slugs and earthworms could provide clues to Detrivores connection with predators (Scarites subterraneus) • Anthesis may mark Arthropod increased Bt-endotoxin Predators in coccinellids
  8. 8. Non-target Predators • Scarites subterraneus, important in agroecosystems for control of Deroceras laeve • Coccinellids including Harmonia axyridis, Coleomegilla maculata, Cycloneda munda, and Coccinella septempunctata
  9. 9. Field Collection • Adult coccinellids hand-collected from Bt- corn field at Spindletop Research Farm • Carabids collected daily from pitfall traps • Carabids and slugs (D. laeve) used for lab feeding collected from ceramic dishes in alfalfa • Carabids and slugs starved 72 hours prior to feeding trials
  10. 10. Feeding Trials D. Laeve feed on leaves for 24 hours Female carabids feed 20 pairs of ad libitum on D. carabids feed laeve for 3 ad libitum on D. hours laeve for 4 weeks
  11. 11. ELISA (Enzyme-Linked Immunosorbent Assay) catalog/assay_kits/nr
  12. 12. Feeding Trial Results All carabids negative - + Bt+ Bt- Bt+1 Bt+2 Bt-1 Bt-2 control control slug slug carabid carabid carabid carabid
  13. 13. Feeding Trial Results All 175 field S. Subterraneus showed values lower than 0.25 ng g-1 Average 57.98 ng g-1 Cry1Ab Bt-endotoxin found in D. laeve slugs fed Bt-corn seedlings, but no effect on egg production rates, mean hatching success, or mean time to hatching with S. subterraneus. Contrast to aphid-spider-carabid linkage
  14. 14. Field-Collected Carabids Many carabids readily consume plant material Contrast to Araneae, Coccinellidae, Heteroptera
  15. 15. Field-Collected Coccinellids Gut screening of 1,126 samples showed significant results: 12.8% C. maculata resulted in positive levels All species showed positive prior H. Axyridis to anthesis and C. maculata screened positive 4-5 weeks post- anthesis
  16. 16. Species Number % positive Coleomegilla maculata 775 12.80% Harmonia axyridis 213 3.80% Coccinella septempunctata 82 2.40% Cycloneda munda 56 3.60% Proportion positive adult coccinellids
  17. 17. Carabid Implications Hypothesis that Bt-endotoxin moves through corn-slug- carabid food chain is rejected  S. subterraneus avoids prey  S. subterraneus employ pre-oral digestion Exposure of Bt-endotoxin to S. subterraneus had no effect on fecundity, fitness Occur earlier in season and before anthesis Scarites quadriceps, Evarthus sodalis in higher densities pre-anthesis Harpalus pennsylvanicus, Amara cupreolata in higher densities post-anthesis
  18. 18. Coccinellid Conclusions Positive results for C. maculata suggests path different than corn- herbivore-coccinellid (non-pollen) Microbial action on pollen transferred to spores and ingested Late results could be H. axyridis Basidiomycota consuming weaker coccinellids or consumption of pollen shed earlier
  19. 19. Future Research • Observation of other species around anthesis • Fitness and fecundity exposure lab trials for other predators • Identification of other possible trophic linkages using field population surveys and quantitative assessments Corn Nabid Coccinellid Corn Orius spp. Coccinellid
  20. 20. Summary • Expansion of Bt-crops prompts need for research • Some arthropods show elevated levels of Bt- endotoxin • Hypothesized that elevated levels of Bt-endotoxin in corn-slug-carabid pathway and around anthesis • No positive samples in field or lab carabids and no effect on fecundity, fitness • Significant positive results in coccinellids, but no connection with anthesis
  21. 21. References Dutton A, Klein H, Romeis J, Bigler F 2002. Uptake of Bt-toxin by herbivores feeding on transgenic maize and consequences for the predator Chrysoperla carnea. Environmental Entomology 27: 441-447. Harwood, J.D., Samson, R.A. & Obrycki, J.J. 2006 No evidence for the uptake of Bt Cry1Ab-endotoxins by the carabid predator Scarites subterraneus (Coleoptera: Carabidae) in laboratory and field experiments. Biocontr. Sci. Technol. 16 Harwood JD, Wallin WG, Obrycki JJ 2005. Uptake of Bt endotoxins by nontarget herbivores and higher order arthropod predators: molecular evidence from a transgenic corn agroecosystem. Molecular Ecology 14: 2815-2823. James C 2003. Global Status of Commercialized transgenic Crops: 2003; ISAAA Briefs no. 30: Preview. ISAAA, Ithaca, NY. Howald R, Zwahlen C, Nentwig W 2003. Evaluation of Bt oilseed rape on the non-target herbivore Athalia rosae. Entomologia Experimentalis et Applicata 106: 87-93. J Li, J Carroll and DJ Ellar, 1991.Nature 353, 815-821 Obrycki JJ, Losey JE, Taylor OR, Jesse LCH 2001. Transgenic insecticidal corn: beyond insecticidal toxicity to ecological complexity. BioScience 51: 353-361. Obrycki JJ, Ruberson JR, Losey JE 2004. Interactions between natural enemies and transgenic insecticidal crops In: Ehler LE, Sforza R, Matielle T, editors. Genetics, Evolution and Biological Control. Wallingford, UK: CAB International. p. 183-206. Raps A, Kehr J, Gugerli P, Moar WJ, Bigler F, Hilbeck A 2001. Immunological analysis of phloem sap of Bacillus huringiensis corn and of the nontarget herbivore Rhopalosiphum padi (Homoptera: Aphididae) for the presence of Cry1Ab. Molecular Ecology 10: 525-533. Shelton AM, Zhao JZ, Roush RT 2002. Economic, ecological, food safety, and social consequences of the deployment of Bt transgenic plants. Annual Review of Entomology 47: 845-881. Way MJ, Van Emden HF 2000. Integrated pest management in practice – pathways toward successful application. Crop Protection 19: 81-103. Wolfenbarger LL, Phifer PR 2000. Biotechnology and ecology – the ecological risks and benefits of genetically engineered plants. Science 290: 2088-2093.