Persistence of the spores of B. thuringiensis subsp. kurstaki from Foray bioinsecticide in gleysol soil and on leaves

- B. thuringiensis spores from Foray can survive in the forest environment.
- Reduction in the spore number was noted six months after the pesticide application.
- No B. thuringiensis was noted on leaf surface one year after Foray spraying.
- No B. thuringiensis was noted in soil after one and a half years of Foray application.
- Relatively short persistence time of spores does not pose environmental risk.

The aim of this study was to determine how long the spores of Bacillus thuringiensis subsp. kurstaki HD-1 from Foray bioinsecticide persist in soil and on leaf surface after application of the bioinsecticide in an oak forest. Foray 04UL was sprayed over a 195-hectare oak forest on the Krotoszyn Plateau in Poland. B. thuringiensis was isolated from soil samples and tree leaves taken from randomly chosen sites. B. thuringiensis subsp. kurstaki HD-1 in the samples was identified upon clonal analysis of the cultured isolates by using the RAPD method. One month after Foray spraying, the number of B. thuringiensis increased in soil and decreased on leaf surface comparing to the number estimated two days after the application. The reduction in the number of B. thuringiensis was noted six months after the pesticide application and the number was decreasing during the following months. No B. thuringiensis was noted on leaf surface one year after Foray spraying and in soil after one and a half years. The study showed that B. thuringiensis spores from biopesticide can survive in the forest environment; however, relatively short persistence time does not pose environmental risk.