Abstract
AbstractDuring the last‐larval instar, Ostrinia may display a facultative larval diapause. Diapausing larvae contain very low ecdysteroid titers and exhibit poorly differentiated imaginal wing discs. After diapause, development resumes when larvae are placed in favorable post‐diapause conditions. After a few days in these conditions, a small and transient peak of 20‐hydroxyecdysone was observed in hemolymph before any visible resumption of imaginal wing disc development. [3H]Cholesterol‐labeling experiment confirmed this result. Conversion of [3H]Cholesterol into [3H]ecdysteroids also began before any visible resumption of wing disc development. These data suggest that the resumption of wing disc development is induced by very low concentrations of molting hormone. After this small first peak, ecdysteroid concentrations increase until a second peak, which precedes ecdysis. Increase of titers was correlated with an increase of biosynthetic activity from [3H]cholesterol. Unexpectedly, biosynthetic activity remained very high after the second peak, but the synthesized ecdysone was immediately inactivated into 20‐hydroxyecdysonic acid.
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