DDT and pyrethroid resistance status and laboratory evaluation of bio-efficacy of long lasting insecticide treated nets against Culex quinquefasciatus and Culex decens in Ghana.

Nuisance from Culex mosquitoes in Ghana has a serious negative impact on the standard of living in many urban communities. In addition, a perceived lack of efficacy of long lasting insecticide treated nets (LLINs) against nuisance mosquitoes contributes to their discontinued use. This again compromises malaria control, even if Anopheles species themselves would still be susceptible to the insecticides used. Control strategies involve pyrethroid insecticides but information on Culex mosquito susceptibility to these insecticides is limited. A nationwide survey was conducted to address this problem. In adults, susceptibility to permethrin, deltamethrin and DDT as well as enzyme activity and kdr mutation were determined. Cone and tunnel bioassay were also carried out to determine the efficacy of LLINs against the mosquitoes. Culex quinquefasciatus and Culex decens were identified in the study area. Higher deltamethrin and DDT resistance and relatively low permethrin resistance were observed in both species. High enzyme activities and kdr mutations were observed in C. quinquefasciatus but not in C. decens. However, reduced efficacy of LLINs was observed in both mosquito species. This adds up to the evidence of the spread of pyrethroid resistance in mosquitoes and its negative impact on control strategies.