Spatiotemporal oviposition and habitat preferences of Ochlerotatus triseriatus and Aedes albopictus in an emerging focus of La Crosse virus.

The number of cases of encephalitis caused by La Crosse virus recently has increased in southwestern Virginia counties. This article presents results of a study conducted from May to September 2000 in Wise County, VA, that examined the area-wide oviposition activity and habitat preferences of Ochlerotatus triseriatus and Aedes albopictus, potential vectors of La Crosse virus in the region. Data from 490 ovitrap collections made throughout the county showed that mean oviposition activity throughout the study was higher for Oc. triseriatus (20.4 eggs/trap-day) than for Ae. albopictus (3.7 eggs/trap-day). The 2 species also had distinct habitat preferences for oviposition, with Oc. triseriatus favoring forested habitats and Ae. albopictus favoring urban/residential habitats. A landcover map of 6 habitat types derived from Landsat satellite imagery of the county showed that 63% of the county was forested and 18% was urban/residential. A Bayesian decision-rule model that incorporated the ovitrap data and landcover map was moderately successful at predicting the occurrence of high oviposition activity and abundance of the 2 species. The predictions reflected seasonal and spatial fluctuations in oviposition activity, with accuracies between 55 and 79% for Oc. triseriatus and 70 and 94% for Ae. albopictus. Kappa (K), a measure of the predictive power of the model, varied from poor (K < 0.4) to good (0.4 < K < 0.75) for both species, and was highest during periods when actual egg abundance was high. This suggests that the predictions were most accurate during periods when the risk for La Crosse virus transmission is greatest. Limitations and suggestions for improving the model are discussed.