Study of virulence and molecular characteristics of some Bacillus thuringiensis isolates on cotton bollworm and diamondback moth

Bacillus thuringiensis bacteria because of many advantages such as specific effect on pest insects larvae, no adverse effects on the environment and non-target organisms and also easy combination with other methods of pest control, has an important role in pest management programs. The first step as a basis for doing research on this bacteria is to study virulence of different isolates and strains of the pathogen in the control of the target pest. In this research, the virulence of three native isolates and a commercial product (Dipel®) was evaluated on the larvae of cotton bollworm, Helicoverpa armigera and diamondback moth, Plutella xylostella at 27oC, a relative humidity of 65% and 16L:8D photoperiod. Based on the calculated results, 50% lethal concentration (LC50) of three native isolates of KD2, 20, 6R and commercial product of Dipel on the 2nd larval instars of H. armigera were obtained as 1.21×107, 8.8×107, 1.39×107 and 6.91×107 spore ml-1, respectively and KD2 isolate was the best strain among others. Results of 50% lethal concentration (LC50) bioassay of three native isolates and commercial sample of Dipel on the 2nd larval instars of P. xylostella were calculated as 6.1×104, 3.4×103, 2. 9×105 and 8.8×104 spore ml-1, respectively and isolate of 20 was the best strain among others. The molecular analysis of the isolates revealed that isolates cry genes are not identical.