Toxicity and growth inhibitory effect of Bacillus thuringiensis subspecies tolworthi against lepidopterous insect pests of Kumaon hills

Toxicity and growth inhibitory effect of Bacillus thuringiensis subspecies tolworthi was studied against five important lepidopterous insect pests in Kumaon hills of Uttaranchal. The neonate larvae of cabbage butterfly, Pieris hrassicae and the Bihar hairy caterpillar, Spilarctia ohliqua were found highly susceptible with LC50 of 0.64 and 2.39 µg ml-1, respectively) followed by the tomato fruit borer, Helicoverpa armigera and tobacco caterpillar, Spodoptera litura. However, the diamondback moth, Plutella xylostella was completely insensitive to B. thuringiensis subsp. tolworthi even at the highest test concentration. Except P. brassicae, 3rd instar larvae of other insects did not exhibit adequate larval mortality. But the larval growth of 3rd instar S. litura and H. armigera was severely inhibited (EC50 0.35 and 1.38 µg ml−1, respectively) with poor growth rates in all treatments.