Overwintering and establishment of Aedes albopictus (Diptera : Culicidae) in an urban La Crosse virus enzootic site in Illinois

In 1997, Aedes albopictus (Skuse) was discovered in Peoria, IL, a known foc us of La Crosse (LAC) virus transmission. This accidental introduction prov ided an opportunity to determine whether Ae, albupictus would reemerge in t he spring or summer and, if successful overwintering occurred. to follow ch anges in the geographic range of Ae, albopictus, and to compare its distrib ution to that of the local treehole mosquito and LAC vector Aedes triseriat us (Say). In 1998 25 oviposition traps were placed in and around the area o f the initial Ending of lie. albopictus, with adult collections by aspirato rs and larval collections from water-holding containers used to identify ar eas of additional activity. Ae. albopictus successfully survived the mild 1 997-1998 El Nino winter, and expanded its range during 1998 By September 19 98, Ae, albopictus oviposited in all 25 traps, including traps near and in wooded sites. Intensity of oviposition activity (number of eggs pet. positi ve trap) ranged from 20-40, lower than the range for Ae. triseriatus, which was us high as 175 eggs per infested trap in mid-August. Prevalence of Ae, albopictus increased through September. where as the prevalence of Ae tris eriatus declined starting in mid-July. Although direct competition between the two mosquito species cannot be inferred based on this surveillance effo rt, a gradual range expansion was observed, and Ae. albopictus eggs were co llected in traps where initially only Ae. triseriatus oviposition activity was detected.