Field evaluation of an improved formulation of Gypchek (a nuclear polyhedrosis virus product) against the gypsy moth (Lepidoptera : Lymantriidae)

Prior to 1994, Gypchek(R) (USDA Forest Service, Washington, DC), the gypsy moth nuclear multicapsid polyhedrosis virus (LdMNPV), was used in operation al programs against. gypsy moth Lymantria dispar (L.) dispersed in a standa rd molasses-lignosulfonate tank mix and applied twice at the rate of 5 x 10 (11) polyhedral inclusion bodies (PIB) per ha per application in a volume o f 19 liters per ha. In 1995, we evaluated a commercially-produced carrier a nd operational options that would make Gypchek application more efficient a nd less costly without reducing efficacy. Specifically, the standard tank m ix formulation and application procedure was compared against a premixed co mmercial carrier, Carrier 038 (Novo Nordisk, Franklinton, NC) applied by th ree different application options. Option 1 consisted of double application s of Gypchek at the rate of 5 x 10(11) PIB per ha per application in volume s of 9.5 liters per ha. Option 2 was identical to Option 1 except that appl ication volume was reduced to 4.8 liters per ha. Option 3 consisted of a si ngle application of Gypchek dispersed in 9.5 liters per ha at the rate of 1 x 10(12) PIB per ha. There was also a fifth treatment consisting of unspra yed control plots. All treatments were evaluated inreplicated 4-ha forest p lots in southwestern Virginia. Levels of LdNPV-induced mortality, of larvae collected live 6 to 11 days after treatment, among treatments receiving a double application were not significantly different at alpha = 0.05 from su ch mortality resulting from the single application of Gypchek in Carrier 03 8. However, both of the double-application treatment options (but not the s ingle application option) of Gypchek dispersed in Carrier 038 had significa ntly higher levels (alpha = 0.05) of LdMNPV than the double-application tre atment of Gypchek dispersed in the standard tank mix. Defoliation was signi ficantly different among the four Gypchek treatments, but all were signific antly lower than the controls. These results indicated that all three optio ns using Carrier 038 provided a level of efficacy equal to or better than t he standard tank mix formulation applied twice at 19 liters/ha. Economic as sessment indicated that the single application option was more efficient an d/or less expensive than the other options.