Relative potency of selected nuclear polyhedrosis viruses against five species of lepidoptera

The potencies of two or three nuclear polyhedrosis viruses (NPVs), selected from among those of alfalfa looper, Anagrapha falcifera (Kirby), AfMNPV; celery looper, Autographa, californica (Speyer), AcMNPV; corn earworm, Helicoverpa zea (Boddie), HzSNPV; and beet armyworm, Spodoptera exigua (Hubner), SeMNPV, were compared in side-by-side bioassays against five insect species. Each insect species was tested at a different time, but, for each species all viruses were tested at the same time. Against the corn earworm, HzSNPV was the most potent; AcMNPV, the least potent; and AfMNPV, intermediate in potency. AcMNPV, AfMNPV, and HzSNPV were of similar and high potency against the tobacco budworm, Heliothis virescens (F.). SeMNPV was more potent than either AcMNPV or AfMNPV against the beet armyworm. AcMNPV and AfMNPV were of similar low potency against the fall armyworm, Spodoptera frugiperda (J. E. Smith). AcMNPV was more potent than AfMNPV against the diamondback moth, Plutella xylostella (L.). Among dosages that were included for more than one virus against the same insect species, no significant differences between viruses in speed of kill were seen. Increasing virus dosage slightly increased speed of kill for HzSNPV against H. tea and for AfMNPV against S. frugiperda, but had no significant effect on speed of kill for other virus/insect combinations. These results should be useful both in the selection of natural virus strains for use against particular pests, and in the selection of viruses as candidates for genetic engineering to improve their speed of action.