Field cage insecticide resistance tests against Culex quinquefasciatus Say (Diptera: Culicidae) in Harris County, Texas, U.S.A.

The ground adulticiding program in densely populated Harris County has been employed on the basis of virus-positive mosquitoes almost exclusively using the 'rotation of chemicals best practices' stratagem. To evaluate its effectiveness, 15 comparative field cage testing events were conducted from 2011-2015 using seven wild population samples from repeatedly collected locations of Culex quinquefasciatus Say and a laboratory susceptible Sebring strain colony reared to adults. A 3 × 3 plot design was employed for exposure to ultra-low volume applications of malathion and synergized permethrin. No significant differences were found in mortality rate among testing dates, year, row placement, or relative humidity. Mortality was significantly different between adulticides (p<0.001) with mean mortality rates for malathion 96.42% (±7.95%) and permethrin 92.38% (±14.04). There was a significant temperature difference for permethrin (p<0.001) but none for malathion (p=0.644). Mosquito population mortality was statistically different by study operational area (p<0.011) and chemical (p<0.001). Susceptible colony adults used as positive controls downwind strongly aided determination of efficacy and resistance to each adulticide, providing evidence of individual application coverage, though comparative analysis was done with overall mortalities by normal methodology.