• Circadian clock;
  • diapause capability;
  • low-diapause variant;
  • mode of inheritance;
  • photoperiodic response;
  • post-feeding larval period;
  • pupal diapause;
  • pupariation;
  • quantitative photoperiodic time measurement system;
  • Sarcophaga similis

Abstract A variant of the flesh fly Sarcophaga similis, which does not enter pupal diapause even under diapause-inducing conditions, is established by artificial selection. Interline crosses of the wild-type and the variant revealed that the diapause capability is inherited in an incomplete dominant manner. Neither sex linkage nor a maternal factor is involved in the mode of inheritance. Genetic and genetic–environmental interactions are involved in the induction of diapause. In the wild-type, the post-feeding larval period is prolonged in response to short days. However, in the variant, the duration of the larval period under short-day conditions is identical to that under long-day conditions. Long-day responses under short-day conditions at both the larval and pupal stages in the variant indicate that the responses are established by common factors in both stages. The factors causing the long-day responses under short-day conditions at different developmental stages in the variant remain to be identified. However, it is plausible to hypothesize that common factors regulate ecdysteroid release at both the larval and pupal stages, and that malfunction of the system regulating these factors triggers such ecdysteroid release, irrespective of the photoperiod. Hence, the photoperiodic responses disappear in the variant in both stages. The adult stage of the variant has a functional circadian clock, suggesting that the nondiapause phenotype is not necessarily involved in malfunction of the circadian clock.