MULTIPLE-REGRESSION ANALYSIS OF FACTORS INFLUENCING A NUCLEAR POLYHEDROSIS-VIRUS IN POPULATIONS OF FALL ARMYWORM (LEPIDOPTERA, NOCTUIDAE) IN CORN

Samples of fall armyworm, Spodoptera frugiperda (J. E. Smith), were collected from cornfields near St. Gabriel, La., in 1981 and 1982, and near Hammond, La., in 1982 and 1983. Prevalence of a nuclear polyhedrosis virus (NPV) was <15% at the St. Gabriel site, but exceeded 40% at Hammond. Multiple regression analysis indicated that host population factors affected prevalence of NPV at St. Gabriel, and that abiotic factors were more important at Hammond. Medium-sized larvae (third and fourth instars) were more commonly infected than small (first and second instars) or large (fifth and sixth instars) larvae. Disease did not appear sustainable in a population until a threshold density of approximately one larva per corn plant was attained. © 1990 Entomological Society of America.