Studies with Bacillus thuringiensis in Relation to the European Corn Borer1

Abstract

High mortality of first-instar corn borer larvae (Pyrausta nubilalis) was obtained after feeding in the laboratory on leaves treated with spores of B. thuringiensis. This mortality showed a direct relationship to spore concentration. The LD50 is at an application rate of approximately 50,000 spores per ml. Older larvae tolerated higher concentrations. Positive relationship was found between the rate of infection and the temp. of incubation for a range between 20[degree]C and 35[degree] C. Failure of B. thuringiensis to control the corn borer in 2 field experiments appeared to be related to the feeding habits of the corn borer larvae in relation to growth of the corn plant.