Studies were carried out on Anopheles freeborni Aitken in the lower Sacramento Valley of California from 1963 through early 1967 to determine the physiological condition of females which survive winter. Overwintering was accomplished by inseminated females that had undergone a reproductive diapause from September through December. Diapause was primarily characterized by the suspension of reproductive activity and buildup of fat body. The proportion of females taking blood during this critical period was low, but females which did so exhibited gonotrophic dissociation. Field studies indicated a strong possibility that decreasing photoperiod rather than low temperature initiated imaginal diapause. This possibility was supported by laboratory studies in which the proportion of long-day females that took blood meals was significantly greater than was the proportion of short-day females that fed. Additional studies with a laboratory colonized strain indicated that temperature also may play an influential part in controlling the onset of diapause.
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Robert K. Washino (1970) studied this question.