Hibernaculum choice in Culex pipiens.

A population of hibernating Culex pipietis was studied during the winters of 1969–1970 and 1970–1971 in an abandoned mine in Illinois. Initial choice of hibernaculum is governed to the extent of 22.7% by light. Distance from the entrance appears unimportant. Texture and dampness of the wall also appear unimportant. Mosquitoes leave hibernacula exposed to frost and then tend to concentrate in the side passages. Movement may be in response to air currents. Although some mosquitoes remain in the same hibernaculum for months, there is extensive movement by most of the population even during midwinter. Most deaths appear to take place at the beginning of hibernation or near the end. Time of the first frost may be important in initiating hibernation. The possible role of hibernating C. pipiens as a vector is discussed.