Effects of RH 5849, the first nonsteroidal ecdysteroid agonist, on larvae of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae)

The effects of RH 5849 on the larval molt and larval‐pupal metamorphosis in Spodoptera littoralis (Boisd.) were examined. Application of RH 5849 to newly ecdysed 3rd and 6th (last) instar larvae induced a larval molt within the first day after application. Symptoms included cessation of feeding and larval weight, extrusion of gut, loss of hemolymph, and a developmentally abnormal and subsequent lethal larval ecdysis. Treated larvae died shortly afterwards. Treated 6th instar larvae, which did not appear to be affected before pupation, showed an abnormal and lethal pupation process. Differences in the protein pattern of the cuticle between treated vs. untreated 6th instar larvae, demonstrated by using PAGE, indicated that in the newly induced larval cuticle some proteins were missing or expressed with less intensity. The lack of several bands in the pattern of cuticular and hemolymph proteins of treated vs. untreated 6th instar larvae, probably from proteins specific for the pupal instar, is suggested as a cause of unsuccessful pupation in the treatment.