The influence of temperature and photoperiod on ovarian development in Culex tarsalis and Culiseta inornata (Diptera: Culicidae) in southern Manitoba

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Mackay, Andrew James
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Ovarian follicle development in Cx. tarsalis Coquillett, and ovarian follicle development and blood meal utilization in Cs. inornata (Williston), were examined under laboratory and field conditions. In the laboratory, photoperiod (L:D 18:6, 14:10 and 12:12) had a significant influence on the number of Cx. tarsalis entering diapause at two temperatures (19oC and 22oC). Temperature did not have an influence on the proportion of Cx. tarsalis in diapause at 18:6 or 12:12 (L:D). In 1992, Cx. tarsalis emerging under natural conditions did not begin to enter diapause until after the middle of August. At two temperatures (16oC and 19oC), Cs. inornata reared in the laboratory entered diapause at 14:10 and 12:12 (L:D), but many females terminated diapause within 34 days after emergence. ln 1993, Cs. inornata emerging under natural conditions in late August were in diapause, and maintained diapause for at least eighteen days. Females emerging in a state of reproductive diapause do not seek a blood meal, and therefore would not vector a pathogen such as Western Equine Encephalomyelitis virus (WEEV). Should another outbreak of WEEV occur in southern Manitoba, the ability to predict the seasonal timing of diapause induction in Cx. tarsalis would be an important factor in evaluating the transmission potential of a pathogen to new hosts.