Abstract
Gypsy moth, Lymantria dispar (L.), populations in three Maryland plots and three West Virginia plots were treated aerially with the gypsy moth multienveloped nuclear polyhedrosis virus product, Gypchek® (U.S. Forest Service, USDA, Washington, DC). The study was a pilot test to demonstrate the efficacy of a single application of Gypchek suspended in the commercially-produced Carrier 038® (Abbott Laboratories, N. Chicago, IL) at 9.5 liters and 1 × 1012 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 significant. Results from treated plots in West Virginia (67.7% posttreatment virus infection) were clearly superior to results from Maryland (49.7% post-treatment virus infection) probably due to more favorable conditions during application in West Virginia. Defoliation averaged 15% in the treated woodlots and 32% in the control woodlots; however, a high degree of variability in the control woodlots, perhaps due to compensatory mortality, probably caused by a late-season epizootic of the fungus Entomophaga maimaiga Humber, Shimazu & Soper, accounted for the treatment effects being statistically non-significant at P = 0.05. Significantly higher levels of virus were found in treated woodlots than in control woodlots in an early-season larval collection made the year following treatment (1997) with virus levels averaging 11.7% in treated plots vs 5.0% in control plots. The second-year effects were particularly striking in the West Virginia plots (12.7% in treated plots vs 3.0% in control plots) suggesting that Gypchek applications may be 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 against the gypsy moth.
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