Maternal and larval effects of photoperiod on the induction of larval diapause in two species of fly, Calliphora vicina and Lucilia sericata.

The induction of larval diapause in the blowflies Calliphora vicina and Lucilia sericata was studied in relation to maternal and/or larval exposure to photoperiod. In C. vicina, maternal experience of short daylength was shown to be more important than larval exposure, although diapause was only observed when the larval rearing temperature was below 15 degrees C. The critical daylength was between 12 and 15 h per day. Recovery from diapause was temperature- but not photoperiod-dependent. Some evidence was obtained, however, to suggest that the rate of recovery was more rapid among larvae from short-day mothers which were bred in pre-diapause conditions of long days. By transferring adult flies from short days into darkness several days before oviposition, it was shown that the important photoperiodic effects were truly maternal. In L. sericata, larval sensitivity to photoperiod was also demonstrated, short days inducing a protracted rate of pupariation. 'Waves' of pupariation in short-day cultures indicated intrinsic differences in diapause intensity. The critical day-length for larval sensitivity was close to 14 h per day. It is suggested that the maternal effects of photoperiod on larval diapause probably involve an unknown maternal factor which is incorporated into the developing oocytes during short-day exposure.