Virulence of Anagrapha falcifera nuclear polyhedrosis virus to economically significant Lepidoptera

Anagrapha falcifera Nuclear Polyhedrosis Virus (AfNPV) has exceptional commercial potential due to its broad host range among Baculoviridae. We compared the virulence of AfNPV toward 2nd instar corn earworm, Helicoverpa zea (Boddie), tobacco budworm, Heliothis virescens (F.), beet armyworm, Spodoptera exigua (Hubner), fall armyworm, Spodoptera frugiperda (J. E. Smith), and diamondback moth, Plutella xylostella (L.), with homologous and heterologous baculovirus standards. We also investigated effects of a contaminating cytoplasmic polyhedrosis virus (CPV), a fluorescent brightener, and genetic selection on the virulence of MNPV. Based on relative susceptibility to AfNPV, the insect species were ranked (most to least susceptible) as follows: H. virscens > H. zea > S. exigua > S. frugiperda > P. xylostella. Contamination of MNPV with naturally occurring CPV did not have a significant effect on AfNPV virulence. The virulence of AfNPV and AcNPV (Autographa californica nuclear polyhedrosis virus) toward S. exigua and P. xylostella was not significantly different. AfNPV is also as virulent as SeNPV (Spodoptera exigua nuclear polyhedrosis virus) toward S. exigua. AfNPV was significantly less virulent than H. zea nuclear polyhedrosis virus (HzNPV) toward H. zea, but its virulence toward H. virescens was not significantly different from HzNPV. Survival time assays on neonate H. virescens showed that HzNPV killed significantly faster than AfNPV. The addition of a fluorescent brightener, Blankophor (1%, wt:vol) to the virus inocula significantly enhanced AfNPV virulence toward all 4 species tested, but major gains in potency were realized only against S. exigua and P. xylostella. Genetic selection of AfNPV by 10 serial passages through P. xylostella did not significantly improve virus virulence against P. xylostella. We predict that AfNPV may provide acceptable control of H. zea, H. virescens, and S. exigua in the field and may also provide control of P. xylostella with the addition of Blankophor.