Host plant effects on the activity of selected nuclear polyhedrosis viruses against the corn earworm and beet armyworm (Lepidoptera: Noctuidae)

The activity of the nuclear polyhedrosis virus (NPV) of the celery looper, Anagrapha falcifera (Kirby) (AfMNPV), against the beet armyworm, Spodoptera exigua (Hubner), was greatest when the virus was fed to larvae on foliage of tomato, Lycopersicon esculentum Mill., least on cotton, Gossypium hirsutum (L.), and intermediate on collard, Brassica oleracea L. Activity of AfMNPV against the corn earworm, Helicoverpa zea (Boddie), was greatest on corn, Zen mays L., least on cotton, and intermediate on bean, Phaseolus vulgaris L. Survival time (days between the start of the test and death) of larvae that were killed by virus was usually lower on treatments on which rates of mortality were higher, but these differences were usually small (less than or equal to 1 d). Effects of host plants on viral activity were not related closely to their effects on larval feeding rates. Effects of host plants on viral activity were also not specific to AfMNPV; cotton and collard affected AfMNPV and the homologous NPV of the beet armyworm to similar degrees. Similar results were found for AfMNPV and the homologous NPV of the corn earworm on cotton and bean. Levels of control provided by these viruses may thus be higher on tomato or corn than on cotton, and. intel mediate on collard or bean.