Local Variation in Blood Feeding by Aedes Triseriatus and Aedes Hendersoni (Diptera: Culicidae)1

Resting adult Aedes triseriatus and Ae. hendersoni females were collected in a woodlot enzootic for La Crosse encephalitis (LAC) virus (Cook Co., Illinois) and in an area without LAC virus activity (St. Joseph Co., Indiana). Multiple tests were performed on each specimen to identify the species (cellulose acetate electrophoresis of the thorax), to detect disseminated LAC infection (fluorescent-antibody-stained head squash), to identify the blood meal host of engorged females (precipitin test), and to detect presence of LAC virus in the blood meal (Vero cell plaque assay). No virus was detected in any of the field-collected specimens. However, the techniques performed on specimens in the laboratory were highly effective, indicating their utility in areas with a higher field-infection rate. In the nonenzootic area, Ae. triseriatus fed predominantly on Eastern Chipmunks (61%) and Ae. hendersoni fed predominantly on Red Squirrels and Fox Squirrels (85%). In the enzootic area, both Ae. triseriatus and Ae. hendersoni fed extensively on Gray Squirrels (65 and 95%, respectively). The relative density of the 2 species in resting populations differed between areas. In the nonenzootic area, the ratio of Ae. triseriatus:Ae. hendersoni was 1.89:1, while in the enzootic area, the ratio was 0.43:1. The percentage of the resting Ae. hendersoni population that was blood engorged in the 2 areas ( $\bar x$ = 47.5%) was much higher than that of Ae. triseriatus ( $\bar x$ = 16.5%), suggesting that Ae. hendersoni seeks hosts in the forest canopy and, once blood fed, rests in the forest understory. Results are discussed with reference to the potential influence of local variations in host use on the dynamics of the La Crosse virus cycle.