Photoperiodic control of the maintenance and termination of larval diapause in Wyeomyia smithii (Coq.) (Diptera: Culicidae) with notes on oogenesis in the adult female.

Abstract

Some aspects of overwintering and oogenesis in the pitcher-plant mosquito, Wyeomyia smithii (Coq.), were examined. The species was shown to overwinter in a diapause state as a third-instar larva. The diapausing larvae overwinter within the frozen ice cores of the host plant but they were nevertheless shown to be intolerant of prolonged periods of freezing at temperatures only a few degrees below 0 °C. The winter survival of the species probably depends almost entirely on the insulating benefits of a snow cover. Larval diapause was stable under short-day conditions but was very rapidly broken when the larvae were exposed to long-day photoperiods. The critical photoperiod required to break larval diapause in a population from the Kenora region of Ontario was between [Formula: see text] and 15 h of light per diem. This critical photoperiod did not change during a prolonged period of overwintering. Larvae which experienced 5 or fewer long-day cycles remained in diapause when they were returned to short-day conditions but diapause was irreversibly broken in larvae exposed to 8 or more long-day cycles in succession. Data on growth rates of larvae as a function of temperature and photoperiod were used to predict the seasonal cycle of W. smithii in northwestern Ontario where the species is probably restricted to a maximum of two generations per year. All females of W. smithii were autogenous for the first ovarian cycle and adult diets of carbohydrate did not affect fecundity. Unlike other mosquitoes, the female of W. smithii was found to be precocious, emerging with the ovarian follicles already initiated with development of the follicles up to stage IIIa of Christophers.