Effects of ecdysone injection on diapause termination in Pieris brassicae pupae . Evidence for a stimulatory action on endogenous ecdysone production

system, leading to a neosynthesis of ecdysone. A dose of 500 ng/pupa was sufficient to obtain synchronous adult development. Ecdysone injected either in whole or in decapitated pupae induced a neosynthesis of ecdysone, starting on day 5 after treatment, and the onset of imaginal development. Thus, we suggest that ecdysone can act independently of the brain, and that its stimulatory action on ecdysone neosynthesis is probably indirect, according to the long delay (5 days) necessary for this reactivation. In addition, isolated abdomens from diapausing pupae injected with the same dose of ecdysone also developed, but did not synthesize any ecdysteroid. This suggests that the injected hormone has also a direct morphogenetic effect on target tissues. The significance of this ecdysone neosynthesis is discussed.