Occurrence of non-stationary larval moults during diapause in the corn-stalk borer, Sesamia nonagrioides (Lepidoptera: Noctuidae)

Abstract

Last-instar larvae of the corn stalk borer, Sesamia nonagrioides (Lep.: Noctuidae), enter a facultative diapause under short photoperiods. In this noctuid, diapause development is characterized by the ability of larvae to perform several larval moults (up to seven) before pupation. Surprisingly, these supernumerary moults were not stationary and larval growth did occur as shown by growth in head-capsule width and weight 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 conditions. Pupal weight of diapause larvae was independent of the number of supernumerary moults performed. Using a radiochemical assay, we show that corpora allata from Sesamia nonagrioides larvae produced juvenile hormone (JH) -III, JH-II and their respective diols and acids. Although corpora allata of day-4 diapause-destined larvae exhibited the same biosynthetic pattern, no labelled products could be detected in the incubation medium containing corpora allata from non-diapausing larvae of the same age. Biosynthetic activity of the corpora allata was detected throughout diapause.