Evaluation of the efficacy of household insecticides against Aedes aegypti in Sri Lanka

Abstract

Abstract Background: Mosquito coils and liquid vaporizers are commonly consumed as household insecticides against mosquitoes in Sri Lanka, but their efficacy have not been evaluated. The current study is the first step in evaluating three brands of mosquito coils and liquid vaporizers that are commercially available in the Sri Lankan market against the major dengue vector Aedes aegypti and to find the impact of mosquito knock-down resistance (kdr) on the efficacy of household insecticides. Methods: WHO recommended “Peet-Grady” protocol was followed to evaluate both field and reference strains and the genomic mutation responsible for knock-down resistance (kdr) was examined. Results: Mean knock-down percentage of field strain after 60 minutes of exposure for d-trans-allethrin (w/w 0.12%), dimefluthrin (w/w 0.01%) and metofluthrin (w/w 0.005%) mosquito coils and prallethrin (w/v 1.24%), prallethrin (w/v 1.26%) and transfluthrin (w/v 0.9%) liquid vaporizers ranged from 0 - 10%. A higher percentage of knock-down observation to field strain was recorded from dimefluthrin (w/w 0.01%) (5.5%) mosquito coil and transfluthrin (w/v 0.9%) (5.0%) liquid vaporizer. All three brands of mosquito coils and liquid vaporizers were able to kill less than 5% of field strain and more than 80% of reference strain. KT50 and KT95 values were calculated only for dimefluthrin (w/v 0.01%) mosquito coil and transfluthrin (w/v 0.9%) liquid vaporizer while the remaining tested products showed less than 5% knock-down. The mutant allele (Cys) frequency was 0.72 in mosquitoes that resist household insecticide exposure and 0.67 in susceptible and the mutant allele (Gly) frequency was 0.1 in survived mosquitoes and 0.29 in dead mosquitoes. Conclusions: The present study provides experimental evidence on the development of pyrethroid resistance role in reducing the efficacy of commercial household insecticides as tested all product lost their efficacy against Sri Lankan Ae. aegypti mosquitoes.