Control of the Velvetbean Caterpillar by Nuclear Polyhedrosis Virus and Insecticides and Impact of Treatments on the Natural Incidence of the Entomopathogenic Fungus Nomuraea rileyi1

Abstract

Different concentrations of nuclear polyhedrosis virus (NPV) and insecticides (carbaryl and methomyl) were applied to natural infestations of the velvetbean caterpillar (VBC), Anticarsia gemmatalis Hubner, on soybean. Their efficacy in reducing VBC larval populations and their effect on naturally occurring epizootics of the entomogenous fungus Nomuraea rileyi (Farlow) Samson were determined. Persistence of the virus in the field was measured. Virus application rates of 75, 145, and 287.5 larval equivalents (LE)/ha suppressed VBC populations below damaging levels. Most virus-induced mortality occurred at 6, 7, and 8 days after spraying. The virus retained 65 to 70% of its original pathogenicity 7 days after treatment and 25 to 35% at 10 days. All virus doses greatly reduced the magnitude of a N. rileyi epizootic. Carbaryl or methomyl applied once at 0.28 or 0.07 kg AI/ha effectively suppressed VBC populations below economic levels for the remainder of the season. High concentrations of insecticides reduced the impact of N. rileyi by reducing the natural substrate, VBC larvae.