Haemolymph ecdysteroid levels in diapause-and nondiapause-bound fourth and fifth instars and in pupae of the European corn borer, Ostrinia nubilalis H übner

Diapause: delaying the developmental clock in response to a changing environment

Seasonal changes can induce organisms to modify their developmental growth. Many holometabolous insects, especially Lepidoptera, trigger diapause, an "actively induced" dormancy, for overwintering. Diapause is an alternative developmental pathway that reversibly blocks developmental growth during specific transitions and enhances the hibernating potential of the organism. Changes in environmental cues, such as light and temperature, trigger modifications in the levels, or in the timing, of developmental hormones. These in turn switch the developmental trajectory (diapause or direct development), strongly altering larval/pupal growth and inducing the appearance of diapause-bound seasonal morphs (polyphenism). We also discuss an example of vertebrate diapause using the killifish embryo as an example where diapause is an environmentally determined developmental switch analogous to that observed in lepidopteran dormancy. Based on the examples discussed here, we propose that the complex physiological responses leading to diapause might evolve quickly by relatively limited genetic changes in the regulation of hormonal signals that program normal developmental transitions.

The pharate adult clasper as a tool for measuring chitin synthesis and for identifying new chitin synthesis inhibitors

A rapid, reliable, repeatable bioassay for measuring chitin synthesis is described. It utilizes the clasper from male pharate adult European corn borers and measures the incorporation of [14C]N-acetylglucosamine. Chitin synthesis is maximum in claspers taken from animals 5 and 6 days postpupation. The system is very sensitive to inhibition by the phenylbenzoyl ureas and polyoxins and should be useful for identifying potential inhibitory agents.