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; c elery looper, Autographa, californica (Speyer), AcMNPV; corn earworm, Helic overpa zea (Boddie), HzSNPV; and beet armyworm, Spodoptera exigua (Hubner), SeMNPV, were compared in side-by-side bioassays against five insect specie s. Each insect species was tested at a different time, but, for each specie s all viruses were tested at the same time. Against the corn earworm, HzSNP V was the most potent; AcMNPV, the least potent; and AfMNPV, intermediate i n potency. AcMNPV, AfMNPV, and HzSNPV were of similar and high potency agai nst the tobacco budworm, Heliothis virescens (F.). SeMNPV was more potent t han either AcMNPV or AfMNPV against the beet armyworm. AcMNPV and AfMNPV we re of similar low potency against the fall armyworm, Spodoptera frugiperda (J. E. Smith). AcMNPV was more potent than AfMNPV against the diamondback m oth, Plutella xylostella (L.). Among dosages that were included for more th an one virus against the same insect species, no significant differences be tween 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 selec tion of viruses as candidates for genetic engineering to improve their spee d of action.