Effectiveness of different formulations of Bacillus thuringiensis Berliner against Pericallia ricini Fabricius (Lepidoptera: Arctiidae)

The three commercial formulations of Bacillus thuringiensis Berliner, viz., Dipel wettable powder containing 25 x 109 viable spores/g of the final product of B. thuringiensis var. kurstaki (serotype 3 a, b strain HD I), Thuricide HP wettable powder containing 30 x 106 viable spores of B. thuringiensis var. kurstaki (serotype 3a, b strain HD 1) per gm of final product, and Bactospeine containing 1 x 108 viable spores of B. thuringiensis (serotype 1/g of final product) were assessed for their pathogenicity against the black hairy caterpillar, Pericallia ricini Fabricius. Dipel proved to be the most effective, showing the lowest value of LC50 (0.0903). Further investigations on various aspects of this noxious pest were, therefore, conducted with Dipel. All the larval instars were susceptible to the treatment of Dipel. The infected larvae not only showed a remarkable reduction in their length and weight but also a high incidence of mortality. A minimum time of 48 h to initiate the kill and a maximum of 120 h was required toinduce 89.99% mortality at 0.5% concentration. The exposure periods showed a negative correlation with the LT50 The pupae of P. ricini formed from treated larvae were smaller in length and weight. Adult emergence showed a decline and the size, fecundity and longevity of the adults were also reduced significantly.