Photoperiod-sensitive developmental delay in facet mutants of the drosophilid fly, Chymomyza costata and the genetic interaction with timeless

Previously, we demonstrated that the biological clock gene, timeless (tim), is potentially involved in photoperiodic diapause induction in the larvae of the drosophilid fly Chymomyza costata. Suppression of tim transcription was inevitably associated with the loss of diapause induction even under diapause-promoting short-day conditions. In the present paper, I report a novel gene, facet (fa), which may genetically interact with tim in photoperiodically controlled larval development in this species. I demonstrated the effect of photoperiod on the development of fa morphological mutants. Developmental delay was remarkable in fa larvae under a diapause-preventing photoperiod, 16 h light: 8 h dark/day, in which the wild-type individuals showed normal and synchronous development. The delay was recovered by extension of the light phase of daily light/dark cycles or the introgression of a deficient tim allele.