Molting Inhibitory and Lethal Effects of Azadirachtin on the Desert Locust, Schistocerca gregaria (Forskal)

摘要

Dose-response studies of azadirachtin, dissolved in 90% aqueous ethanol and injected into freshly molted crowded fifth (last) instar nymphs of Schistocerca gregaria revealed three kinds of responses: (I) Delay of the next molt and death in the delayed molt, or after apolysis, without being able to escape from the old exuviae; (II) Production of over-aged nymphs surviving up to 83 days without molt or apolysis; (III) Death within 20 days after treatment, without molt, presumably due to a direct toxic effect of the azadirachtin. Solvent injected controls molted to adults within 8-10 days. With increasing doses, response I decreased and response III increased. A dose of 30.4 g g-1 (g azadirachtin per g fresh weight) resulted in response III in all nymphs. A dose of 15.2 g g-1 induced the highest proportion of over-aged nymphs, but even with this dose only 13.1% over-aged nymphs were obtained. With doses lower or higher than 15.2 g g-1, the proportion of over-aged nymphs was even lower. Over- aged male nymphs exhibited sexual behavior, courting and mounting over-aged female nymphs and adult females, without being able to copulate.