Influence of photoperiod on low temperature acclimation for cold‐hardiness in Drosophila auraria

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Abstract
Imagines of Drosophila auraria Peng, a reproductive diapause species, developed cold‐hardiness at low temperatures to a greater extent when exposed to a diapause‐inducing photoperiod (LD10:14 h) than when exposed to a diapause‐preventing photoperiod (LD 16:8h). Imagines kept at 18°C, which was the temperature at which they were reared to eclosion, did not survive a test exposure to ‐5°C for 8 days regardless of age or photoperiod. When transferred to 10 or 5°C, either from eclosion or from 8 days after eclosion, the survival rate, on testing, rose with time since transfer and rose faster and higher with a photoperiod of LD 10:14h than with LD16:8h. Flies transferred to 15°C only showed improved ability to survive the test if they were kept in LD 10:14h. When cultured at 18°C to the age of 8 days after eclosion, diapause was terminated in about 30% of females even at LD 10:14h. In these post‐diapause females the ability to develop cold‐hardiness at lower temperatures was somewhat less than in the diapausing females, but apparently greater than in the non‐diapause females. These results suggest that the physiological mechanism which promotes cold‐hardiness under a diapause‐inducing photoperiod is not directly linked to the process causing reproductive diapause.In Sapporo, flies from a natural population became tolerant to cold in October when they entered diapause and daily mean temperature fell below 15°C and the light/dark cycle fell below LD 12:12h.