OCCURRENCE OF NONSTATIONARY LARVAL MOLTS DURING DIAPAUSE IN THE CORN-STALK BORER, SESAMIA NONAGRIOIDES (LEPIDOPTERA, NOCTUIDAE)

Last-instar larvae of the corn stalk borer, Sesamia nonagrioides (Lep. : Noctuidae), enter a facultative diapause under short photoperiods. I n this noctuid, diapause development is characterized by the ability o f larvae to perform several larval moults (up to seven) before pupatio n, Surprisingly, these supernumerary moults were not stationary and la rval growth did occur as shown by growth in head-capsule width and wei ght of diapausing larvae, These heavy diapause larvae produced heavier pupae than non-diapausing strains. The number of supernumerary moults varied for insects, although they were reared under the same conditio ns, Pupal weight of diapause larvae was independent of the number of s upernumerary moults performed. Using a radiochemical assay, we show th at corpora allata from Sesamia nonagrioides larvae produced juvenile h ormone (JH) -III, JH-II and their respective diols and acids. Although corpora allata of day-4 diapause-destined larvae exhibited the same b iosynthetic pattern, no labelled products could be detected in the inc ubation medium containing corpora allata from non-diapausing larvae of the same age, Biosynthetic activity of the corpora allata was detecte d throughout diapause. (C) 1997 Published by Elsevier Science Ltd.