Azadirachtin affects growth and endocrine events in larvae of the tobacco hornworm, Manduca sexta

Injection of azadirachtin in freshly emerged last-instar larvae of Manduca sexta elicited different reactions according to the dose administered. At low doses, pupation occurred in most of the cases, but the resulting pupae were defective for the most part. Individuals treated with higher doses usually did not fully complete development, moulting to supernumerary larvae or dying as larvae (sometimes at the wandering stage) after varying periods of survival. The haemolymph ecdysteroid titre of individuals treated with 2 μg azadirachtin/g bodyweight showed characteristic changes which are presumed to cause the disorders in the last stages that normally lead to pupation. Injection of moulting hormone in azadirachtin-treated individuals at certain times during the penultimate stage elicited no reduction of the azadirachtin-induced effects. It is shown that azadirachtin is able to inhibit development even when individuals performed a complete moult after the treatment.