FEEDING SITES AND DISTRIBUTION OF FALL ARMYWORM (LEPIDOPTERA, NOCTUIDAE) LARVAE ON COTTON

Newly hatched fall armyworm, Spodoptera frugiperda (J. E. Smith), larvae were placed on the under surface of main stem leaves of cotton, Gossypium hirsutum L., emerging at main stem nodes 5, 10, and 15 in greenhouse and field cage studies to determine feeding sites, intraplant distribution, interplant movement, and survival of larvae throughout larval development. Feeding sites and survival of larvae in greenhouse and field cages were similar. First and second instars fed predominantly on leaves. Third instars fed equally on leaves and fruiting structures. Significantly more fourth, fifth, and sixth instars were found feeding on fruiting structures (squares, blooms, or bolls) than on leaves. Release site did not significantly (P < 0.05) affect the survival of larvae. Only 24% of the larvae survived the first 24 h in the greenhouse, whereas 21% survived the first 36 h in the field cage. Most (>74%) first, second, and third instars were found on structures emerging directly from the main stem or nodes 1 to 4 on branches located between main stem nodes 1 and 15. Later instars (fifth and sixth) were observed on middle to terminal portions of the plant, including branch tips. In the interplant movement study, larvae remained predominantly within average distances of 1 to 2.4 plants from the infested plant. No larva moved more than five plants from the site of release. © 1990 Entomological Society of America.