Potential of Bacillus thuringiensis subsp. kurstaki (3a 3b) on young larval instars of rice stem borer, Chilo suppressalis

摘要

Bacillus thuringiensis is a biological control agent which is used for a wide range of crop pests in the world. B. thuringiensis subsp. kurstaki (3a 3b) is more effective than other serotypes in controlling lepidopteran pests. Rice stem borer is one of the most destructive pests in the north of Iran. In order to reduce insecticide application, B. thuringiensis was used in 1998-99 in the western Mazandaran rice fields. In this study, experimental design was a split plot in randomized complete blocks with 3 replications. For this purpose, five concentrations of Bt were used (0, 1500, 2000, 2500 and 3000 ppm) and assessments time were made 12, 24, 48, 72 and 96 h after spraying. Then in each experimental unit, 20 larvae (L_1 and L_2 instars) were randomly selected and effects of treatments on the mortality of stem borer evaluated. The analysis of variance showed that there was a significant differences between the different concentrations and the times. Least significant differences (LSD) showed thatthe concentration of 2000 ppm was the best and the time 48 h after spraying was the most effective time for bacterial influence, respectively.