Two characteristics of prehibemating adult Culex pipiens females are a reduction in the blood-feeding drive and the failure of ovarian follicles to mature following a full blood meal. This latter characteristic has great importance to our understanding of the role of overwintering Culex mosquitoes in the winter maintenance of certain arboviruses. New evidence is presented which offers an explanation of how prehibernating female Cx, pipiens mosquitoes may take a viremic blood meal, yet not undergo ovarian development. Females which had been subjected in the laboratory to short daily photophases and cool temperatures (L:D 9:15, 15°C) from the pupal stage to 7 days after emergence were warmed to 25°C for various periods of time, About 45% of those warmed for 72–84 h took full blood meals, and of these, 40% failed to develop mature follicles. We suggest that such warming periods are analogous to situations which may be encountered in nature by prehibernating female Cx. pipiens .
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