Environmental Control of Ovarian Diapause in Culex pipiens1,2

Colonies of autogenous and anautogenous Culex pipiens L. established from a single location in Boston, Mass., were used to define environmental conditions for ovarian diapause. Unrestricted ovarian development requires 15 hours or more of light per day at 18°C, while less than 12 hours of light stimulates the entire population to enter diapause. Higher temperatures reduce the prevalence of diapause. The photosensitive period begins on the day of the larvalpupal molt. Only inbred anautogenous mosquitoes enter ovarian diapause,. and, of these, ability to enter diapause is universal in the Boston population. When diapausing adult C. pipens are exposed to 16 hours of light per day, ovaries resume development. Primary follicles generally degenerate leaving a relic and secondary follicles develop beyond diapause, to the stage present in gonoactive non-blood-fed mosquitoes.