Abstract: Effects of a new type of nosteroidal ecdysone agonist W200013 on the fourth instar larvae of the cotton bollworm (Helicoverpa armigera) were studied by transmission electron microscopy. These observations revealed that W200013 initiated a precocious and lethal larval moult. At 6 h post treatment (pt), the deposition of additional layers of endocuticle, a dramatic increase in rough endoplasmic reticulum and a decrease in glycogen particles were noted in the epidermis. At 12 h pt, the ecdysial space had formed and epidermal cytoplasts appeared “frozen”. At 24 h pt, a double cuticle separated by the ecdysial space had formed and the epidermis was highly vacuolated. At 36 h pt, new epicuticle coated an incomplete new procuticle containing only a small number of lamellae, and the epidermis showed increasing signs of degeneration. As a result, the treated larvae died without normal ecdysis. At the same time, comparison with RH-5992 revealed that the two insect growth regulators produced similar toxic symptoms, bioassay results and ultrastructural changes of the integument.

Key words: cotton bollworm, W200013, RH-5992, moulting, ultrastructure