New Cuticle Formation and Molt Inhibition by RH-5849 in the Common Cutworm, Spodoptera litura(Lepidoptera:Noctuidae)

Effects of RH-5849 (1, 2-dibenzoyl-1-tert-butylhydrazine), a synthetic nonsteroidal ecdysone agonist, on the common cutworm, Spodoptera litura, were investigated by means of oral and topical application and injection. The larvae treated with RH-5849 formed new cuticle but eventually died without ecdysis. The last instar larvae treated with RH-5849 exhibited different symptoms, depending on their age. Day-0 larvae died after forming a new larval cuticle, day-1 larvae showed rectal prolapse (projection of their gut from the anus), and day-2 or older larvae died without ecdysis after forming a new pupal cuticle. Day-0 and day-4 (prepupal stage) larvae were about 100 times more sensitive than day-2 larvae in terms of final mortality. Pupal cuticle formation was also observed in isolated abdomens injected with 10 μg of RH-5849 as it was in those injected with 20-hydroxyecdysone. This result suggested that RH-5849 acted directly on the epidermis as ecdysone agonist to induce new cuticle formation.