Activity of Culex quinquefasciatus in an underground storm drain in San Antonio, Texas.

Published information on Cuhx quinqztifmciutw Say repeatedly affirms that this species responds directly to cool temperatures by extending the length of its life cycle, rather than by interrupting development with a true state of diapause (Eldridge 1966, 1968; Wilton and Smith 1985). Observations of winter activity in populations of Cx. quinquefmciatus in Texas (Hayes and Hsi 1975, Strickman 1983) corroborate the belief that this mosquito can resume activity any time the weather warms sufficiently. With this background, we suspected that a protected site might harbor either concentrations of inactive mosquitoes or a confined population of active adults. We chose a study site in southeastern San Antonio, where populations of Cx. quinqmfmciutus were known to be high. The site is a large square (4 x 4 m) storm drain (designated City Project Number 55) which opens into the San Antonio River. Culverts without catch basins enter the drain under most street intersections. Most of the time, water flowed in a shallow (2 to 6 cm) sheet along the floor of the drain with only a few small pools formed on the cement floor. Adult mosquitoes in the drain were sampled with a battery-operated light trap (Driggers et al. 1980). The trap was hung 2 m above the