A Short Term Control of Adoxophyes orana fasciata WALSINGHAM (Lepidoptera : Tortricidae) by a Granulosis Virus in Apple Orchards

Abstract

A suspension of the granulosis virus of the summer fruit tortrix, Adoxophyes orana fasciata, was sprayed in a manner similar to chemical insecticidal application against the egg stage at a dosage of 4, 000 diseased, full-grown larvae per hectare. The effectiveness of virus application was compared with that obtained by the chemical treatment against hatching larvae. The larval mortalities due to the disseminated virus in the virus treated plots were consistently higher than those due to the naturally persisting virus in the chemical treated plots in all generations. No difference was observed between the two treatments with regards to the intensities of other mortality factors. Incorporating observed parameters of the ratios of the population increase, simple population models for the two treatments were constructed. It is shown that (1) the virus spray becomes more effective than the chemical treatment if the larval density exceeds about one larva per branch in the first generation, (2) if it was lower than one larva per branch, few economical problems will arise through virus application, and (3) low densities in the first generation result in a saw-toothed like fluctuation, while high densities result in a dampened fluctuation towards the third generation, irrespective of the treatments.