Aedes aegypti in a Texas coastal county as an index of dengue fever receptivity and control.

Abstract

Since Galveston County, Texas, is one of the high risk areas for the reintroduction of dengue, we have maintained an Aedes aegypti surveillance program since 1977 by using ovitraps to determine the density and distribution of this species in 17 communities. A. aegypti adults were present primarily from May thrugh November, with higher positive ovitrap rates associated with periods of low rainfall. Larvae collected from six different communities, when compared with a standard, insecticide-susceptible strain exhibited only 2 X greater tolerance to malathion and chlorpyrifos. Similar results were obtained with malathion susceptibility tests of adults. Ultra-low volume malathion treatments of caged A. aegypti in a residential city block yielded good kills in the proximal but not the distal half of the block. Ovitraps in a two square-block area, treated with single pellets of chlorpyrifos, were less frequently positive and contained a smaller average number of eggs per trap than untreated traps in the surrounding area.