Effects of the non-steroidal ecdysone mimic, RH-5849, on diapause and non-diapause larvae of the European corn borer, Ostrinia nubilalis Hbn

Abstract

Topical applications of the non-steroidal ecdysone mimic, RH-5849, as expected, initiated a premature moult in last larval instar of the European corn borer, Ostrinia nubilalis. However, RH-5849 induced a perfect supernumerary larval moult in diapause and non-diapause larvae when the application was performed very early in the instar. The compound induced larval-pupal intermediates and normal pupae if it was applied after 2 days in the last instar of non-diapause larvae and after 5–6 days in diapause larvae. The occurrence of larval-pupal moults and normal pupae demonstrated the onset of pupal commitment of the diapause larvae. Moulting to normal pupae was greatly improved by a double topical application of 1 μg RH-5849 onto diapause larvae. Although the rate of normal pupation was rather low, the ecdysone mimic could break the larval diapause of the European corn borer and produce normal pupae. From these results, the endocrine control of diapause induction is discussed.