Influence of leaves on the biological activity of Bacillus thuringiensis formulation against the common cutworm, Spodoptera litura

Abstract

Lethal and growth inhibitory activities of a Bacillus thuringiensis formulation containing a delta-endotoxin Cry IC as an active ingredient were investigated in bioassays with different instars of the common cutworm larvae, Spodoptera litura by a leaf dip method using four species of plants (cabbage, tomato, strawberry and perilla). Both the lethal and growth inhibitory activities of B. thuringiensis differed among the larval instars, indicating a lower susceptibility in the larger instars. However the levels of lethal and growth inhibitory activities differed from each other, showing that the differences among instars for growth inhibitory activity were less pronounced than for lethal activity. It is interesting that both activities of B. thuringiensis were markedly influenced by the host plant leaves used for the bioassays. When strawberry or perilla leaves were used for the bioassays, the lethal and growth inhibitory activities of B. thuringiensis decreased 1/3-1/30 and 1/10-1/30, respectively, compared to the activities when cabbage or tomato leaves were used.