- 1Adult face flies, Musca autumnalis De Geer, respond to short photoperiods by entering diapause. Diapause responses to different photoperiods at a mean temperature of 17°C varied among seven laboratory face fly strains. Old strains lost much of their diapause responses.
- 2To analyse the nature of diapause inheritance, hybrids and their back-crosses were made between two strains that showed the greatest difference in diapause introduction at 10:14 h(L:D), and 17°C.
- 3Responses of hybrids to the short photoperiod were intermediate to those of their parents. Joint scaling tests showed that diapause did not fit an additive model and the lack of fit was attributed to incomplete dominance. No cytoplasmic effect was detected, but diapause was partially sex linked.
- 4Diapause heritabilities were 47% and 30% in the broad and narrow senses, respectively.
- 5Estimates of the minimum number of diapause genes suggested a small number.
- 6Developmental rates of egg to adult, ovarian follicle growth, and pterin accumulation were inversely correlated with diapause propensities, suggesting pleiotropy or linkage.