Published online by Cambridge University Press: 10 July 2009
A spray trial of a nuclear polyhedrosis virus (NPV) as an insecticide for Euproctis chrysorrhoea (L.) is described. The trial was carried out indoors in the spring on third-instar larvae emerging from overwintering nests onto small potted hawthorn trees (Crataegus sp.); the equipment used was the Turbair Fox Ultra Low Volume Sprayer. Dosages applied ranged from equivalents of 1 × 1011 to 1 × 1013 polyhedral inclusion bodies (PIB) per hectare. Infection was first detected in samples of live larvae after ten days and indicated rates of infection consistently lower than the final mortality attained. Larvae began to die of NPV infections 11 days after spraying, and mortality due to the virus ceased after ca 20 days; most larvae died in the fourth instar. Over the range of virus doses from 1 × 1011 to 5 ×10 12 PIB/ha mortality levels rose with dose, to a maximum of over 90%. Increasing the dosage to 1 × 1013 PIB/ha elicited no further increase in mortality. This preliminary trial suggests that the virus has considerable potential as a control agent, and field trials are, therefore, in progress.