Field Efficacy and Deposit Analysis of Bacillus thuringiensis, Foray 48B, Against Gypsy Moth (Lepidoptera: Lymantriidae)

Four aerial treatments of Bacillus thuringiensis (Foray 48B) were evaluated against gypsy moth, Lymantria dispar L., infestations to determine their field efficacy and foliar deposits. From an initial average density of 2,000 egg masses per ha (EM/ha), gypsy moth populations in the untreated (control) blocks increased to 6,570 EM/ha. At a dose of 30 Billion International Units of insecticidal activity per hectare (BIU/ha) applied in 2.3 and in 7.0 liters, the populations decreased significantly to 337 EM/ha (95% control) and to 280 EM/ha (96% control), respectively. At 60 BIU/4.6 and at 90 BIUI 7.0 liters/la, they decreased to 1175 EM/ha (89% control) and to 50 EM/ha (99% control), respectively. EM density differences between treatments after spray were not significant and all were significantly less than the controls. The mean drop density, estimated volume deposit, drop size (Dv05) and relative span (RS) measured on the foliage were 2 drops per cm2, 1.5 nl/cm2, 134 mm Dv0.5, and 0.54 RS for the 2.3 liter/ha application and 8 drops per cm2, 2.2 nl/cm2, 103 mm Dv0.5, and 0.81 RS for the 7.0 liter/ha volume application rates. Nine percent of the leaves collected from blocks sprayed at 2.3 liter/ha had no B. thuringiensis , compared with 2% of the leaves collected from blocks sprayed at 7.0 liter/ha. At 5 or fewer drops per cm2, the differences were 83% and 43%, respectively. The remaining 8% of the leaves collected from the blocks sprayed at 2.3 liter had between 5 and 20 drops per cm2, compared with 49% of the leaves from blocks sprayed at 7.0 liter/ha. The remaining 8% of the leaves collected from blocks sprayed at 7.0 liters/ha were covered with >20 drops per cm2.