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Pesticide Toxicology Laboratory

ISU Entomology / Pesticide Toxicology Laboratory / Insect bioassay for determining soil degradation of Bacillus thuringiensis subsp. kurstaki CryIA(b) protein in corn tissue

Insect bioassay for determining soil degradation of Bacillus thuringiensis subsp. kurstaki CryIA(b) protein in corn tissue

Authors: Sims, S.R., Holden, L.R.
Journal, Volume, Year: Environmental Entomology, volume 25(3):659-664, 1996
Summary

Bioassays using larval growth of Heliothis virescens were used to study the environmental fate of Btk Cry1Ab protein. Four treatments were evaluated in this study and included Bt corn tissue with and without soil and non-Bt corn tissue with and without soil. Drummer loam soil was used along with Btk corn plant tissue expressing Cry1Ab toxin that was harvested about 2 weeks after pollen was shed. Treatments were incubated at 24 to 27�C at >80% humidity for 43 days. Each treatment was sampled on 0, 7, 11, 21, 30, and 43 d. After incubation, a series of dilutions was made from each incubated sample, mixed into artificial insect diet, and fed to neonate H. virescens. After 7 days of growth, larvae were weighed, and the bioactivity of Cry1Ab protein was determined using regression analysis of the dose-weight response data. Cry1Ab protein as a component of Bt corn had an estimated half-life of 1.6 d when added to soil compared to 26 d without soil.

Comments

This is one of the few studies that used natural soil and Bt toxin from transgenic crops. It is unclear whether lyophilized or non-lyophilized corn tissue was used in the treatments. This could have a significant effect on the degradation of Btk toxin. Study only used insect bioassay to determine presence of the toxin