Evaluation of the Influence of Droplet Size and Density of Bacillus thuringiensis Against Gypsy Moth Larvae (Lepidoptera: Lymantriidae)

A study was conducted to determine the effect of spray droplet size and density on the efficacy of a commercial preparation of Bacillus thuringiensis against the gypsy moth (Lymantria dispar L.). A concentration of 5,795 International Units (IU)/µl was used. In the laboratory, various size droplets and densities were tested against larvae using 12-cm2 red oak leaflets. Results show that producing relatively high densities of small (50-150 µm) droplets of B. thuringiensis will increase the efficacy compared with larger droplets (> 150 µm) present at low densities at the same dose. Median lethal dose estimates are made for droplets in three size classes (50-150, 150-250, and 250-350 µm). LD95’s for the generalized size classes of 100, 200, and 300 µm were 10.8, 2.2, and 0.9 drops/cm2, respectively. Implications of these results are discussed.