The influence of two photoperiods (12 and 20 hours of light per day) and different constant (25, 20, 15.5, 12.5 and 4 degrees) and fluctuating temperatures on the hatching of the larvae of Ae. caspius caspius from Bairam-Ali (Turkmenia) has been studied experimentally. The induction of winter egg diapause has been established to be under photoperiodic and temperature control. In eggs laid by short-day treated females the tendency to enter diapause is more expressed (55.9%) as compared with those laid by long-day exposed females (1.6%); in this case the eggs were kept at 12.5 degrees and in shortday regime. The low temperature 4 degrees increases only slightly the number of diapausing eggs (13.9%). The temperature which fluctuate during twenty-four hours being combined with short-day regime is more effective (the action of low temperature coincides with the scotophase). Even in the progeny of long-day exposed females the termorhythms 13--21, 8--20 and 4--20 degrees induce to enter diapause correspondigly 27.4, 22.8 and 59.9 per cent of the eggs.