Aerial application of the viral enhancer Blankophor BBH with reduced rates of gypsy moth (Lepidoptera: Lymantriidae) nucleopolyhedrovirus

The viral enhancer Blankophor BBH was applied by air to gypsy moth, Lymantria dispar, populations in two formulations of gypsy moth nucleopolyhedrovirus to determine if the enhancer could compensate for reduced rates of virus. Larval mortality due to virus in plots treated with a molasses-based formulation at 2.5 x 10(11) polyhedral inclusion bodies (PIB)/ha (one-fourth the United States Department of Agriculture (USDA) Forest Service recommended rate) was 25% greater than in untreated plots. There was no increase in larval mortality in plots treated with an experimental wettable-powder formulation at 5 x 10(11) PIB/ha (one-half the recommended virus rate) compared to untreated plots but defoliation was 50% lower. The addition of 0.5% (W:V) Blankophor BBH did not increase the efficacy of either formulation. The volume of spray deposited onto leaf surfaces averaged 16.6 and 40.0 nl/cm(2) for the molasses-based formulation and 6.9 and 13.7 nl/cm(2) for the wettable-powder formulation with and without enhancer, respectively. A separate laboratory experiment in which 0.5-mu l droplets containing low (200 PIB/mu l) concentrations of virus with varying concentrations of Blankophor BBH were consumed by End-stage gypsy moth larvae demonstrated that viral enhancement increased with increasing concentration of Blankophor BBH and that a concentration of 0.3% was required to cause >90% larval mortality. This concentration in a 0.5-mu l droplet corresponds to 1.5 mu g of Blankophor BBH, which is proposed as an estimate of the dose required to cause >90% mortality in End-stage gypsy moth larvae. Based on the amount of spray deposited in the field test, only 0.03-0.2 mu g of Blankophor BBH/cm(2) of leaf surface was deposited, which was substantially below the proposed amount required for enhancement. The LC50 was 2.8 times greater when oak rather than lettuce was used as a host substrate without Blankophor BBH and 1.9 times greater with Blankophor BBH. The enhancer reduced LC50 values 213- and 314-fold on lettuce and oak, respectively. (C) 1999 Academic Press.