Survival of the overwintering house mosquito, Culex pipiens pallens, with special reference to the relation between wing length and survival rate

Abstract

The present investigation was carried out to see relation between longevity of the overwintering house mosquito, Culex pipiens pallens, and their wing length. The long-lived mosquito survived about 60 days after capture when fed with no diet except water and survivorship curve of all the mosquitoes proved to fit well to an equation, R=100-99.63×(0.01517)^<(0.8952)^t>, where R is survival rate (%) on the t'th day after capture. This overwintering population was found to include two different component groups : one was a long-winged group which accounted for about 92% and the other was a short-winged group making up 8% of the population. The rate of mortality increases with age in such a manner that its logarithm is proportional to age in every wing-length category. On the basis of this mortality-age relationship, Gompertz equation, M=kp^<q^t>, was applied to the survival data of each wing-length category, where M is cumulative mortality (%) on the t'th day after capture and k, p, q parameters constant for each category. From this equation the "half-life period" of each wing-length category can be estimated. It follows from this estimation that the longer wings the mosquitoes have, the longer period they survive on the whole with only a few exceptions. Discussions were given of a possibility that the blood-fed mosquitoes belonging to the short-winged group might be capable of taking in Japanese encephalitis virus in late summer, of carrying the virus through the winter and of transmitting to vertebrate hosts in the next spring.