In several insect species, resistance to pyrethroids and DDT (dichlorodiphenyltrichloroethane) is linked to point mutations in the voltage-gated sodium channel (VGSC) gene. Pyrethroid-based insecticides prolong the opening of sodium channels, causing paralysis known as a "knockdown" effect before mortality occurs. Point mutations in the VGSC gene result in decreased pyrethroid binding and reduced sensitivity to the insecticide-this resistance mechanism is known as knockdown resistance (kdr) as insects do not die but recover from paralysis with time. In Culex mosquito species loss of target site sensitivity to pyrethroids is linked to a number of substitutions, one of which is leucine (L) to phenylalanine (F) at residue 1014 (L1014F) in the VGSC gene. Here we report the identification of kdr-associated pyrethroid resistance and developing resistance in Cx. quinquefasciatus field collections from Collier County, FL. Evaluation of position 1014 of the VGSC in Cx. quinquefasciatus collections from 7 locations in Collier County, FL, revealed a wide range of genotypes from one part of the district to the other. Centers for Disease Control and Prevention bottle bioassay, linear regression analysis, and cage trial evaluations suggest that the L1014F mutation plays a role, at least in part, to the pyrethroid resistance status of Cx. quinquefasciatus collected in Collier County, FL. Furthermore, we identified resistance attributed to both oxidase and esterase activity, indicating that multiple mechanisms are responsible for pyrethroid resistance in Collier County Cx. quinquefasciatus.
Keywords: Culex quinquefasciatus; kdr; metabolic resistance; pyrethroid resistance.