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A study was made of the influence of temperature and photoperiod on blood-feeding and related processes in an anautogenous strain of Culex pipiens from West Lafayette, Indiana and a strain of C. quinquefasciatus from Vero Beach, Florida. Pupae and adults were subjected to combinations of four photoperiods (10, 12, 14, and 16 hours) and four temperatures (10°, 15°, 20°, and 25°C). C. pipiens females showed reduced blood-feeding activity in response to a combination of short photoperiod and low temperature when incandescent illumination was used, but under conditions of fluorescent illumination, showed no such response to photoperiod—only a graded blood-feeding response to temperature. The blood-feeding response of C. quinquefasciatus did not vary from one source of illumination to the other. In both cases, there was no response to photoperiod, and a threshold response to temperature.
Gonotrophic dissociation was found to occur sporadically in C. quinquefasciatus under low temperature conditions, irrespective of photoperiod. In C. pipiens, gonotrophic dissociation occurred in response to a combination of low temperature and short photoperiod, but only when post-feeding incubation temperatures were low.
There was no significant difference in the amount of fat developed by blood-fed C. pipiens females showing gonotrophic dissociation and those maintained on a straight sugar diet. The amount of fat developed by blood-fed females showing normal ovarian development, however, was significantly less.
The significance of these findings in regard to the ability of C. pipiens and C. quinquefasciatus to hibernate in nature was discussed, as well as the role of Culex mosquitoes as overwinter carriers of human viruses in the light of the demonstration of gonotrophic dissociation.
Major, MSC, U. S. Army. Present address: Atlantic-Pacific Interoceanic Canal Study Commission, Balboa Heights, Canal Zone.