Extraction of local isolates of Bacillus thuringiensis from the soils of Fars province and evaluation of their toxicity on larva of Plodia interpunctella (Hubner)

Bacillu thuringiensis (Bt) produces crystalline proteins that are toxic to various insect species. In this study, Bt strains were isolated from the soils of some areas of Fars province and their toxicity on larva of Plodia interpunctella (Hubner) was investigated. For this purpose, 110 strains were isolated from the soils of Shiraz, Marvdasht, Fasa and Sarvestan. Initial identification of the isolates was carried out on the basis of Gram staining and morphological characteristics of protein crystals using phase-contrast microscopy. The protein crystals of the isolates were spherical and rhombic. Molecular analysis by PCR showed that 40 isolates of the collection were contained Cry1 gene.The isolatestoxicity was studied on third instar larvae of P. interpunctella. According to the results of this study, 2×108 sporeml-1 concentration after 72 hours was considered as the most effective treatment and the three isolates sh20, g44 and FA-16 had the highest mortality (53.33%, 80% and 73.33%, respectively) onlarva of Indian meal moth. Isolates g46-29, g45-5, TA22, 35b, and E8 were ineffective on the third instar larvae of Indian meal moth. In general, the bioassay results showed that the strains isolated from the soils of the study area had considerable toxic effect on Indian meal moth larvae. We hope that introducing these native isolates of Bt will be an important step to produce domestic biological pesticides.