Seasonal cycle. Annual mean climatic conditions and mosquito abundances for Cook County (Illinois). A: Climate diagram compiled from temperature (line) and precipitation (bars) measurements used in this study. Location Chicago O’Hare international airport, period 1991–2010, Köppen-Geiger climate classification Dfa. B: Mean number of female Cx. pipiens/restuans per trap night, averaged over the study period of 20 years and 6 trapping sites.