Study of the role of ecdysteroid for insect diapause

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Many researches suggested that larval and pupal diapauses are maintained by ecdysteroid deficiency, however, the endocrinological cue to trigger diapause is still not very clear. We therefore examined the role of ecdysteroid for the induction of the larval diapause of Haritalodes basipunctalis. When non-diapausing larvae of H. basipunctalis were injected with an ecdysteroid inactivating enzyme ecdysteroid-22-oxidase(E22O) identified from Nomuraea rileyi, they survived for a few months without eating anything. The E22O-injected larvae also acquired high cold-hardiness, a characteristic often observed in insects in diapause. Furthermore, they resumed development after being exposed to chilling conditions, which is the environmental stimulus to break diapause in many insect species. These developmental and survival characteristics were indistinguishable from those of the normal diapausing larvae, suggesting strongly that the E220 injection induced the larval diapause in H. basipunctalis. To the best of our knowledge, this is the first report indicating that a reduction in the ecdysteroid titer is a sufficient endocrinological stimulus to induce diapauses in insects.