Evaluation of the efficacy of two nucleopolyhedroviruses to suppresswhitemarked tussock moth populations

Abstract: The nucleopolyhedroviruses of Orgyia leucostigma (OrleSNPV) and Orgyiapseudotsugata (OpMNPV) were compared to assess their potential as microbial biologicalcontrol agents against the whitemarked tussock moth (WMTM). The influence of virus species,dose and larval instar at inoculation on larval mortality was determined in laboratory bioassays.Mortality rates of larvae infected with OrleSNPV and OpMNPV were comparable, althoughOpMNPV had slightly higher efficacy at lower doses when fed to early-instar larvae. LT50experiments demonstrated that OrleSNPV carried a slight but significant advantage on the time tomortality. Manipulative field bioassays were also performed to determine the influence of preandpost-ingestion diet on the mortality caused by both viruses. Both pre- and post-virusingestionnutrition impacted the mortality rates of larvae infected by each virus equally, whichmay be associated with varying nutritional qualities, especially protein content, of the diet andfoliage used.