Effects of Host Age, Virus Dosage, and Temperature on the Infectivity of a Nucleopolyhedrosis Virus Against Velvetbean Caterpillar, Anticarsia gemmatalis , Larvae 1

Abstract

The inter-instar susceptibility of the velvetbean caterpillar to a nucleopolyhedrosis virus was quantitated. Analysis of response curves revealed a 930-fold range in susceptibility between the most sensitive and the most resistent individuals in these larval populations. The LD ₅₀ values for 2nd, 3rd, 4th, and 5th instars were 103, 432, 682, and 4100 polyhedra/larva, respectively. At 26.7°C the virus replicated efficiently in all larval instars. Virus replication was slower at lower temperatures (15.6°C, 21.1°C) but the cumulative virus mortality at these these temperatures were similar fo that achieved at 26.7°C. Incubation at higher temperatures (32.2°C), however, caused a 30–50% less virus mortality than occurred at lower temperatures.