Résumé
Background :Bacillus thuringiensis produces insecticidal proteins known as Cry and its efficiency and absence of side-effects make it the most widely used biopesticide. There is little information on the role of soils in the fate of Cry proteins from commercial biopesticide formulations, unlike toxins from genetically modified crops that have been intensively studied in recent years. The persistence of Cry in soil was followed under field and laboratory conditions. Results : Sunlight accelerated loss of detectable Cry under laboratory conditions but little effect of shade was observed under field conditions. The half-life of biopesticide proteins in soil under natural conditions was about one week. Strong temperature effects were observed, but they differed for biopesticide and purified protein, indicating different limiting steps. Conclusion : For the biopesticide the observed decline in detectable protein was due to biological factors, possibly including the germination of B. thuringiensis spores and was favoured by higher temperature. In contrast for purified proteins, the decline in detectable protein was slower at low temperature, probably because the conformational changes of the soil-adsorbed protein, that cause fixation and hence reduced extraction efficiency, are temperature dependent.