Effect of light–dark cycles on adult emergence in the aphid parasite Aphidius smithi

Abstract

Adult emergence in Aphidius smithi is asynchronous in continuous light. A regime of alternating light and dark phases during pupal development and emergence generates a population rhythm. Under long-day conditions (LD 16:8), eclosion is restricted to the photophase, or largely so. When the scotophase is extended (LD 12:12 and 8:16), a variable proportion of adults emerges in the absence of light. Estimates of the time-to-adult that are based on the mean of the discontinuous frequency distribution of emergence time in LD are biased and may not be biologically meaningful. It is suggested that an apparently longer mean developmental time of females than of males in A. smithi may be a statistical artifact that can be produced by the sampling schedule and the "gating" effect of the photoperiod.