Inheritance of the photoperiodic response controlling larval diapause in the blow fly, Calliphora vicina.

Larvae of the blow fly Calliphora vicina R-D. (Diptera: Calliphoridae) display a diapause in response to the exposure of their parents to short photoperiods. Due to geographic variation in photoperiodic response, flies from a southern, English population show a long-day response to the fixed photoperiod of L:D 15.5:8.5 whilst flies from a northern population from Finland show a short-day response to the same photoperiod. Crosses between these strains have shown previously that diapause incidence is a maternal characteristic; here we demonstrate that the hybrid female offspring of such crosses are not intermediate between the two parental strains but show a photoperiodic response biased towards their maternal line. Thus not only are males unable to influence directly the diapause incidence among their offspring but the indirect effects of inheritance down the male line are weaker than down the female. Diapause duration, in contrast, is influenced by each parent in a similar manner. Diapause lasts longer in larvae with a greater admixture of northern genes regardless of whether they were maternal or paternal.