Metabolic energy status of diapausing nervous system inPieris brassicae: Comparison with the relative utilization of metabolic pathways in the whole insect body

Abstract

The temporal evolution of changes in energy metabolism of nervous tissues during postembryonic development in Pieris brassicae has been studied either in nondiapausing or diapausing development. We showed that the nervous system, during the diapause of insects, was characterized by a very large reduction in the quantitative level of metabolism, but the metabolic activity of the nervous system was never completely abolished. We also observed a typical diapausing metabolic pattern in the relative utilization of the catabolic pathways of glucose. The oxidative routes were 95% depressed (from 3‐day‐old to 30‐day‐old pupae), but the pentose cycle retained a relatively high degree (C6/C1≤ 0.25) of activity as compared to the Krebs cycle, clearly showing that synthetic processes were not fully abolished during the diapause period. Thus an apparently static morphological brain condition corresponds to a relatively dynamic state of metabolic activity. This phenomenon remained rather constant during all the time the insects were undergoing diapause and during wintering conditions (short daylight, low temperature for a minimum 3 months) but nevertheless appeared to be necessary to achieve diapause breakdown. After this long wintering period, when insects were replaced into summer conditions, most of them were able to exhibit a large increase of cerebral energy metabolism in both catabolic pathways of glucose. This led to adult emergence and enabled imaginal life. If diapausing insects did not undergo wintering conditions of a sufficiently long period prior to the emergence of the adult, they could not attain threshold levels of nervous system metabolic reactivation and thus would compromise the possibilities of emergence, resulting in the death (>95%) of the most of insects after diapause. J. Exp. Zool. 281:260–269, 1998. © 1998 Wiley‐Liss, Inc.