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Pesticide Toxicology Laboratory

ISU Entomology / Pesticide Toxicology Laboratory / Degradation of the Cry1Ab protein within transgenic Bacillus thuringiensis corn tissue in the field

Degradation of the Cry1Ab protein within transgenic Bacillus thuringiensis corn tissue in the field

Authors: Zwahlen, C.; Hilbeck, A.; Gugerli, P.; Nentwig, W.
Journal, Volume, Year: Molecular Ecology, volume 12:765-775, 2003
Summary

Two field studies were conducted in Switzerland examining the degradation of Cry1Ab protein in transgenic Bt corn leaves during a fall, winter, and following spring. The corn used was Syngenta N4640Bt or its near isoline. In the first study, litter bags containing corn material were buried in a corn field after harvest. Monthly, a pair of bags from one location (there were 60 total locations) was removed and brought back to the lab for analysis. In the second field trial, tubular soil cages (made of cloth) were filled with soil from the field and then placed in holes in the field. Corn plant material was placed on top of the soil in the cage and one earthworm (Lumbricus terrestris) was added. The authors state that most of the corn material remained on the surface and this residue was used in the analysis. All of the corn material was analyzed by buffer extraction and ELISA. In the first study, no degradation was observed in the first month, with Cry1Ab concentrations decreasing to ~20% of initial during the second month. During winter, there was not further degradation. In warmer weather degradation began again, but only slowly. Detection (but not quantification) still occurred into June. In the second study, Cry1Ab concentrations decreased until the end of the trial when 0.3% was detected.

Comments

There was very high variability reported for the amounts of protein present at the beginnings of both studies, so conclusions must be qualified. Another study showing persistence for a relatively long time. Takes into account climatic factors that have not been previously explored. First field study removes the interaction with soil. Binding to soil after plant breakdown is occurring will be an important part of the process of Bt protein fate. In the first study insecticidal activity was only observed as sublethal effects (growth) after April, until March. There was some problem correlating insecticidal activity and ELISA detection in the two studies.