LETHAL DOSE AND ASSOCIATED EFFECTS OF BACILLUS-THURINGIENSIS IN SPRAYED DROPLETS AGAINST GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE)

Susceptibility of third instar gypsy moth Lymantria dispar L.) to Bacillus thuringiensis in the formulated product Foray 48B (Novo Nordisk Bioindustrials, Inc., Danbury, CT) was evaluated. The bioassay technique involved feeding larvae droplets of the formulation sprayed on leaf discs. The amount of leaf material consumed, time to mortality, and weight increase were measured. The LD95 was 21.1 International Units (IU)/larvae. After seven days, surviving larvae in the B. thuringiensis treatments weighed significantly less than the untreated larvae (p<0.05). The mean treatment time to mortality ranged between 37.7-45.0 h. No significant difference was found in the percentage of leaf material consumed when larvae were exposed to 1.5 IU, or 11.8 IU per leaf disc.