Field Efficacy of the NRD-12 Strain of Bacillus thuringiensis Against Gypsy Moth (Lepidoptera: Lymantriidae)

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Abstract
Single and double aerial application treatments at 30 billion international units (BIU)/ha of an aqueous formulation (SAN 415 SC 32LV) of the NRD-12 strain of Bacillus Thuringiensis Berliner were evaluated against a moderately dense population of gypsy moth, Lymantria dispar L. Egg mass densities before spray averaged 5,055 egg masses per ha; egg mass density after spray increased to over 19,500 egg masses per ha in the control woodlots but decreased to 2,600 and 4,500 egg masses per ha in the single and double application treatments, respectively. These values were significantly less than the controls but not significantly different from each other. These decreases in egg mass densities represented population reduction estimates of 87% and 77%, which were correlated with the larval population reductions estimated by relative larval densities (83% and 79%) and with the estimated initial larval densities (85% and 72%) of the populations before (1986) and after treatments (1987) with NRD-12. No significant defoliation occurred in the woodlots treated with NRD-12, but control woodlots suffered a significant (33%) defoliation. Larval development in the treated woodlots was delayed significantly compared with the controls. This resulted in an observed but not statistically significant increase in the parasitization rate by Cotesia melanoscelus (Ratzeburg). Fecundity (number of eggs per mass) of the surviving females in the treated woodlots was not adversely affected, nor was the percentage of hatch of their progeny different from that of the previous generation.

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