Toxicity of Four Dibenzoylhydrazine Correlates with Evagination-Induction in the Cotton Leafworm

Treatment of last-instars of the cotton leafworm, Spodoptera littoralis, with four dibenzoylhydrazines, RH-5849, tebufenozide (RH-5992), halofenozide (RH-0345), and methoxyfenozide (RH-2485), revealed premature molting leading to death. Methoxyfenozide was the most toxic, followed by tebufenozide, halofenozide, and RH-5849. The potency of the four ecdysone agonists to induce evagination in cultured imaginal discs excised from last-instars was measured and compared with the natural insect molting hormone, 20-hydroxyecdysone (20E). In parallel, competition percentages for binding were analyzed with whole imaginal wing discs cultured with 3H-labeled ponasterone A and different concentrations of ecdysone agonist. We found that the four compounds tested caused the effect as agonists of 20E in vitro. The order of toxicity of the four ecdysone agonists corresponded with that for evagination-induction and binding competition with whole imaginal discs.