Bioactivities of cry gene positive Bacillus thuringiensis (Berliner) (Bacillales: Bacillaceae) strains on Ephestia kuehniella Zeller, 1879 and Plodia interpunctella (Hübner, 1813) (Lepidoptera: Pyralidae)

Abstract

Bacillus thuringiensis is the bacterium most commonly used for biopesticide production due to parasporal crystal formation during its growth cycle. As a consequence of repeated use, B. thuringiensis biopesticides may cause the development of resistance in the pests. Therefore, it is necessary to explore new B. thuringiensis strains with a certain degree of bioactivity. In this study (2012-2013), the bioactivity of native B. thuringiensis strains from the Aegean Region of Turkey were tested against second instar larvae of Ephestia kuehniella and Plodia interpunctella. The bioactivity of 21 B. thuringiensis strains with cry1, cry2 or cry9 gene was determined as percent mortality according to Abbott's formula. The highest mortality rates were 42 and 63% in E. kuehniella and P. interpunctella, respectively. These mortality rates were equal to or 1.8 times greater than that of B. thuringiensis subsp. kurstaki. In addition, plasmid profiles of B. thuringiensis strains changed between 5-18 kb. Moreover, SDS-PAGE analysis of the most toxic strains indicated the presence of Cry1 and Cry2 proteins. Two different cry2 gene profiles containing either cry2Aa1 or combination of cry2Aa1 and cry2Ab2 genes were detected by PCR analysis. In addition, partial DNA sequence analysis of cry2A genes indicated phylogenetic differences among the toxic strains and B. thuringiensis subsp. kurstaki. As a result, these B. thuringiensis strains may be used to control both E. kuehniella and P. interpunctella as alternative biopesticides in cases of insect resistance to currently used B. thuringiensis preparations.