Field Evaluation of an Improved Formulation of Gypchek (a Nuclear Polyhedrosis Virus Product) Against the Gypsy Moth (Lepidoptera: Lymantriidae)

Prior to 1994, Gypchek^® (USDA Forest Service, Washington, DC), the gypsy moth nuclear multicapsid polyhedrosis virus (LdMNPV), was used in operational programs against gypsy moth Lymantria dispar (L.) dispersed in a standard molasses-lignosulfonate tank mix and applied twice at the rate of 5 × 10¹¹ polyhedral inclusion bodies (PIB) per ha per application in a volume of 19 liters per ha. In 1995, we evaluated a commercially-produced carrier and operational options that would make Gypchek application more efficient and less costly without reducing efficacy. Specifically, the standard tank mix formulation and application procedure was compared against a premixed commercial carrier, Carrier 038 (Novo Nordisk, Franklinton, NC) applied by three different application options. Option 1 consisted of double applications of Gypchek at the rate of 5 × 10¹¹ PIB per ha per application in volumes of 9.5 liters per ha. Option 2 was identical to Option 1 except that application volume was reduced to 4.8 liters per ha. Option 3 consisted of a single application of Gypchek dispersed in 9.5 liters per ha at the rate of 1 × 10¹² PIB per ha. There was also a fifth treatment consisting of unsprayed control plots. All treatments were evaluated in replicated 4-ha forest plots 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 α = 0.05 from such mortality resulting from the single application of Gypchek in Carrier 038. However, both of the double-application treatment options (but not the single application option) of Gypchek dispersed in Carrier 038 had significantly higher levels (α = 0.05) of LdMNPV than the double-application treatment of Gypchek dispersed in the standard tank mix. Defoliation was significantly different among the four Gypchek treatments, but all were significantly lower than the controls. These results indicated that all three options using Carrier 038 provided a level of efficacy equal to or better than the standard tank mix formulation applied twice at 19 liters/ha. Economic assessment indicated that the single application option was more efficient and/or less expensive than the other options.