Insecticide resistance status, esterase activity, and electromorphs from mosquito populations of Culex quinquefasciatus say (Diptera : Culicidae), inHouston (Harris County), Texas

Culex quinquefasciatus Say is a vector of St. Louis encephalitis (SLE) in T exas. This disease is endemic and prevalent in the Houston area. Disease pr evention through mosquito control is mainly targeted against adults by appl ication of a resmethrin-piperonyl butoxide formulation (Scourge(R)). Immatu re mosquitoes were collected from eight areas in Harris County during 1998. The susceptibility status of these populations to Scourge(R), malathion, a nd resmethrin, the latter alone or with an esterase inhibitor as a synergis t, was determined using a bottle assay with females. The population structu re was investigated by electrophoretic analysis of esterases and their acti vity. Individual females were also analyzed for esterase activity by plate assay and for isoenzyme pattern by native PAGE. Bioassays indicated high le vels of resistance to malathion in all areas. In addition, the effectivenes s of Scourge(R) in mosquitoes from area 51 deteriorated throughout the seas on. A localized, distinctive esterase pattern and activity level was observ ed in mosquitoes from different areas. Overall, the frequency of esterases Est alpha 2 (A2)/Est beta 2 (B2) was higher than that of Est beta 1 (B1). A ltogether, these results indicate the onset of a fragile situation for mosq uito control that should be further analyzed to effectively maintain the SL E prevention program for Harris County.