Effects of temperature and photoperiod of larval stage and temperature of pupal stage on pupal diapause in the onion fly, Delia antiqua (Diptera: Anthomyiidae)

The onion fly, Delia antiqua (Diptera: Anthomyiidae) spends hot summers and cold winters in the pupal stage. Pupal diapause is determined by the temperature and photoperiod of the larval stage and the temperature of the pupal stage.
When the larvae were reared under various photoperiods at 25°C and the pupae were kept at 25°C after pupation, the rate of diapause tended to be slightly lower in photoperiods longer than 13 h in the light period. When the larvae and pupae were kept at 20°C, the rate of diapause was 80% or more in photoperiods with a light period shorter than 13 h. However, the rate of diapause gradually decreased during longer photoperiods, and when the light periods were longer than 16 h, it decreased to approximately 25%.
The larvae were reared under light-dark conditions (12 h light: 12 h darkness) (LD 12: 12), 14: 10, 18: 6, and 24: 0 at 30, 25, and 20°C and the pupae were kept in continuous darkness (DD) at 30, 25, 20, and 15°C. When the larvae were reared at 30 and 25°C and the pupae were kept at 25°C, the rate of diapause was 15% or less regardless of the photoperiod. When the pupae were kept at 30 and 20°C, the rate of diapause was 50−75% and almost 100% at 15°C. When the larvae were reared under LD 14: 10, 16: 8, and 24: 0 at 20°C and the pupae were kept at 25°C, the rate of diapause was 15% or less.
The rate of diapause the pupal temperature of 30°C was 50−75%, at 20°C was 30−65%, and at 15°C was almost 100%. When the larvae were reared under LD 12: 12 at 20°C, the rate of diapause at pupal temperature of 30°C was 50−75%, at 25°C was approximately 55%, and it was almost 100% at 15°C.
When the larvae were reared under LD 12: 12 at 20°C and the pupae were kept for 4 weeks under DD at 20°C after pupation. And the pupae were transferred from 20°C to 7°C and then kept for 10, and 15 weeks at 7°C and then transferred to 25°C. When the pupae were kept for 10 weeks at 7C, adult emergence was concentrated the 11th day (the 109th day after pupation) after transition to 25°C, and on the 10th day (the 143th day). This indicates that diapause was broken by low temperatures (7°C). When pupae were kept under DD at 20°C after pupation, adult emergence started around 50 days after pupation and continued for more than 50 days thereafter. No concentration of emergence was observed even when the temperature was changed to 7°C after the emergence adults. This indicates that diapause was broken at 20°C.
The larvae were reared under continuous light at 15°C and the pupae were kept under DD at 7°C after pupation and transferred to 25°C. When the pupae were kept at 7°C for 1 to 20 weeks, the longer the period of 7°C, the shorter the period from the transition to 25°C adult emergence. Adult emergence was concentrated when the 7°C period was 11 weeks or more, and the tendency was more pronounced as the 7°C period increased.
When the larvae were reared under LD 12: 12 at 30 and 25°C and the pupae were kept under DD at 30, 25, 20, and 15°C, the rates of diapause were compared in 1981 and 2005. When the rates of diapause when the larvae were reared at 20°C, was compared between 1981, 2005, and 2006. When the larvae were reared at 30 and 25°C, the rate of diapause was lower in 1981 than in 2005, regardless of the temperature of the pupae. However, when the larvae were reared at 20°C, the rate of diapause was higher in 1981 than in 2005 and 2006, regardless of pupal temperature. These results indicated that many years of successive rearing influenced pupal diapause decisions. The most interesting finding was that in many years of successive rearing, the selective pressure for diapause changed with the rearing temperature of the larvae. This elucidation will be clarified by through genetic analysis in the future.