Resistance ofSpodoptera frugiperda [Lep.: Noctuidae] to a nuclear polyhedrosis virus in the field and laboratory

Median lethal doses (LD50s) of nuclear polyhedrosis virus (NPV) were determined in neonatal offspring ofSpodoptera frugiperda (J. E. Smith) (Sf) larvae captured in southeastern Louisiana in 1981, 1982, and 1984. These LD50s ranged from 1.8 to 16.3 polyhedral inclusion bodies (PIB)/insect. The LD50s significantly (P<0.05) increased during the season of 1982 but had no pattern in 1981 or 1984. However, the Sf populations increased in heterogeneity of response to the NPV during all 3 years. The LD50 increased from 4.1 to 18.7 PIB/insect in a Sf laboratory colony exposed to the NPV LD80 for 7 generations, whereas in a control colony not exposed to NPV the LD50 was 5.9 PIB/insect after 7 generations.