Studies on bioassay methods for a granulovirus formulation, BCGV-01, infectious to both the oriental tea tortrix, Homona magnanima and the smaller tea tortrix, Adoxophyes honmai

Abstract

An insect virus formulation, BCGV-01, which contains both the oriental tea tortrix, Homona magnanima ganulovirus (HomaGV) and the summer fruit tortrix, Adoxophyes orana fasciata, granulovirus (AdorGV) was investigated pathogenically against neonates of H. magnanima and A. honmai by four kinds of bioassay methods (egg mass dipping, peroral droplet feeding, diet mixing, and leaf dipping). A. honmai was more susceptible to BCGV-01 than H. magnanima although the degree of susceptibility varied in the four bioassay methods. The concentrations giving about 50% infection were different among the four bioassay methods. The lowest effective concentration was in a leaf dipping method, increasing with diet mixing, peroral droplet feeding and egg mass dipping method. About 1,000 fold differences occurred between the minimum value by the leaf dipping method and the maximum one by the egg mass dipping method. However the variance of mean infection was largest in the leaf dipping method and the least in a droplet feeding one. These results suggest an appropriate bioassay method for granulovirus formulation should be chosen from the standpoints of sensitivity, reliability, and simplicity depending on the bioassay objective.