Submitted to: Journal of Entomological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 1998
Publication Date: N/A
Interpretive Summary: The gypsy moth nuclear polyhedrosis virus (NPV) has been registered as a general use pesticide against the gypsy moth, a serious defoliater of forest and shade trees. Gypchek label recommendations prior to 1996 called for two applications of a standard tank mix three days apart, with a split virus dose. Further work demonstrated that Gypchek added to a premixed carrier was as good as the standard formulation, and was much easier to handle, but recommendations still suggested two applications, three days apart. More recent tests with Gypchek and a new carrier found that one application (with a full, unsplit virus dose) gave results equivalent to the double application, split dose. The single dose option has favorable economic and programmatic implications, but a pilot test was required before the U.S. Department of Agriculture Forest Service would support the one application option for operational use. This pilot test was conducted in Maryland and West Virginia. In 1997, the areas treated in 1996 were evaluated for residual virus levels. This is a report of the biological evaluation of that pilot test. The results of the pilot tests now gives forest managers the option of using one application (full dose) or two applications (split dose) of Gypchek against the gypsy moth. The results should assist our efforts to develop new cost effective aerial application protocols for the virus, which would potentially help all managers of gypsy moth-infested properties (homeowners and local, state, and federal programs) seeking to use this environmentally friendly control material.
Gypsy moth populations in three Maryland plots and three West Virginia plots were treated aerially with the gypsy moth nuclear polyhedrosis virus (LdMNPV) product, Gypchek. This was a pilot test to demonstrate the efficacy of a single application of Gypchek suspended in the commercially-produced Carrier 038 at 9.5 liters and 1 X 1012 polyhedral inclusion bodies (PIBs) per ha. This treatment resulted in LdMNPV 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% post-treatment LdMNPV infection) were clearly superior to results from Maryland, (49.7% post-treatment LdMNPV 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, treatment effects were non-significant . Significantly higher levels of LdMNPV 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 LdMNPV is low or absent.