Mosquito abundance is correlated with Cliff Swallow (Petrochelidon pyrrhonota) colony size

We measured the abundance of mosquitoes [primarily Aedes vexans (Meigen) and Culex tarsalis Coquillett] at cliff swallow (Petrochelidon pyrrhonota Vieillot) colonies of different sizes in southwestern Nebraska in 1999. Using CO2 traps placed inside and outside of colonies, we found that total mosquito abundance increased significantly with the number of active cliff swallow nests at a colony site. We found no effect of date or weather conditions on the number of mosquitoes caught at the different sites. By classifying the landscape from aerial photographs within a 2-km-diameter circle centered on each colony site, we found no significant relationships between habitat type near a colony site and cliff swallow colony size or mosquito abundance. Proximity to livestock could not account for our results. Culex tarsalis was proportionately more likely to be caught inside a colony than at traps 30 m away, but the proportion of C. tarsalis inside a colony did not vary with colony size. Our results cannot be explained by date- or weather-related sampling artifacts or by differences in habitat between sites. Most likely, mosquitoes, especially A. vexans, are attracted to the vicinity of large cliff swallow colonies.