Dispersion of gravid Aedes triseriatus (Diptera: Culicidae) from woodlands into open terrain.

Abstract

Activity of gravid Aedes triseriatus (Diptera: Culicidae) was monitored throughout the summer of 1981 in southwestern Wisconsin, USA, using ovitraps in open terrain such as fields between woodlots. Ovitraps were placed at various distances from the woods in various field types, including corn, alfalfa, pasture, mixed plantings, fallow old fields, and an open yard. Weekly ovitrap checks showed that Ae. triseriatus readily dispersed into all types of open areas; however, field type influenced the amount of oviposition activity observed. Dispersion of gravid females was lowest into alfalfa and corn fields, with only 4.3 and 7.6% of ovitrap observations positive for eggs, respectively. Dispersion was greater into wet meadow, old field, and open yard, as 17.9, 33.9, and 40% of ovitrap observations were positive for eggs, respectively. Distance between woodlots did not appear to influence dispersion rates, as a total of 14.5% of observations from all open-terrain ovitraps more than 100 m from woods were positive for eggs. In 1 pastureland site, ovitraps placed 273 m from the nearest woods were positive for eggs in 27.5% of trap observations. Ovitraps placed in fencerows or on isolated trees in open areas were more attractive to ovipositing mosquitoes than traps placed on wooden stakes in all open terrain habitats. Adult male and female Ae. triseriatus were observed in open terrain on a number of occasions. The effect of open-terrain dispersion by Ae. triseriatus on the epidemiology of La Crosse encephalitis virus is discussed.