Persistence of the insecticidal toxin from Bacillus thuringiensis subsp. kurstaki in soil
Authors: Tapp, H., Stotzky, G.
Journal, Volume, Year: Soil Biology and Biochemistry, volume 30(4):471-476, 1998
Three soils (Kitchawan: predominantly kaolinite; Mopala: containing montmorillonite and kaolinite; San Alejo: predominantly kaolinite) were amended with toxins of Btk (isolated from Dipel), and the persistence of Btk toxin was evaluated using insect bioassays (tobacco hornworm larvae). Kitchawan soil remained toxic for more than six months; however, reduced toxicity was found after 35 days in Mopala and San Alejo soils. A higher pH, 5.8-7.3 compared with 4.9-5.1, was found in soils with reduced toxicity compared with soils that retained toxicity.
Although insecticidal activity of Btk was observed in this study, the ecological relevance and effects under field conditions can not be easily extrapolated. For example, the Btk toxin used in the study was isolated from Dipel instead of from transgenic plants. Also, to measure insecticidal activity, soil suspensions containing Btk toxin were added to the food of tobacco hornworm larvae. Although this bioassay does measure insecticidal activity, it is not a good indicator of toxic effects to nontarget organisms because it does not represent a �real world� exposure. Finally, persistence was measured qualitatively with insect bioassays instead of quantitatively.