Efficacy of Gypchek against the gypsy moth (Lepidoptera : Lymantriidae) and residual effects in the year following treatment

Gypsy moth, Lymantria dispar (L.), populations in three Maryland plots and three West Virginia plots were treated aerially with the gypsy moth multien veloped nuclear polyhedrosis virus product, Gypchek((R)) (U.S. Forest Servi ce, USDA, Washington, DC). The study was a pilot test to demonstrate the ef ficacy of a single application of Gypchek suspended in the commercially-pro duced Carrier 038((R)) (Abbott Laboratories, N. Chicago, IL) at 9.5 liters and 1 x 10(12) polyhedral inclusion bodies per ha. This treatment resulted in virus levels that were significantly higher in the treated woodlots (58. 7%) than in paired control woodlots (10.5%),with treatment effects highly s ignificant. Results from treated plots in West Virginia (67.7% post-treatme nt virus infection) were clearly superior to results from Maryland (49.7% p ost-treatment virus infection) probably due to more favorable conditions du ring application in West Virginia. Defoliation averaged 15% in the treated woodlots and 32% in the control woodlots; however, a high degree of Variabi lity in the control woodlots, perhaps due to compensatory mortality, probab ly caused by a late-season epizootic of the fungus Entomophaga maimaiga Hum ber, Shimazu & Soper, accounted for the treatment effects being statistical ly non-significant at P = 0.05. Significantly higher levels of virus were f ound in treated woodlots than in control woodlots in an early-season larval collection made the year following treatment (1997) with virus levels aver aging 11.7% in treated plots vs 5.0% in control plots. The second-year effe cts were particularly striking in the West Virginia plots (12.7% in treated plots vs 3.0% in control plots) suggesting that Gypchek applications may b e particularly desirable in situations where natural virus is low or absent The results of the pilot test now give forest managers the option of using one application (full dose) or two applications (split dose) of Gypchek ag ainst the gypsy moth.