Winter in Indiana usually brings a reprieve from mosquitoes. However, late this winter (March 2012), temperatures reached 80F (high 20s C). As a result, we had plenty of mosquitoes during the last days of winter. Warm winter temperatures are often followed by below freezing temperatures, that are expected tonight. Will below freezing temperatures kill all the mosquitoes?
Probably not. Mosquitoes have a moderate level of freeze tolerance. A study by Dave Denlinger and colleagues (Journal of Medical Entomology, 43(4):713-722. 2006.) has shown that some mosquitoes can survive more than 24 h of temperatures at -5 C (23 F). Mosquitoes reared at lower temperatures (18C) have better survival than mosquitoes reared at 25 C. A period of cool weather before the freeze may condition the mosquitoes to better tolerate the freeze. We should not expect a mild freeze to wipe out the entire mosquito population.Mosquitoes will seek shelter when temperatures start to cool. This behavior helps mosquitoes harbor in areas with above freezing temperatures, even though ambient air temperature is below freezing. In addition, mosquitoes in the larva and pupa stages are aquatic and water temperatures will remain above freeing during a mild freeze.
Will an early start to the mosquito season mean large hordes of mosquitoes this summer? Not necessarily. Mosquito populations are dependent on the weather. Many mosquitoes will lay eggs that are dormant until rains cause flooding or ponding that soaks the egg. A summer with a lot of rain can build up large populations of mosquitoes. However, a dry summer may have few mosquitoes in spite of an early start.