Insecticide Susceptibility and Knockdown Resistance Mutations in Aedes aegypti and Culex species in Bangladesh.

Abstract

Insecticide resistance in mosquito populations remains a formidable challenge for the control of vector-borne diseases, especially in developing countries such as Bangladesh. This study investigates known knockdown resistance (kdr) mutations associated with pyrethroid resistance in Aedes aegypti and Culex species mosquitoes collected from Dhaka and Tangail cities. Deltamethrin-based CDC-bottle bioassays showed that Aedes aegypti had resistance rates of 39.5% at 1X and 3X concentrations, decreasing to 27.3% at 5X. In contrast, the Culex pipiens complex showed resistance rates of 74%, 65%, 25%, and 37% at 1X, 3X, 5X, and 10X doses, respectively. Molecular identification via mitochondrial Cytochrome c Oxidase I (COI)- gene confirmed 100% similarity to Aedes aegypti strains, while the Culex specimens clustered with the member of Culex pipiens species complex. Based on the Culex species-specific primer targeting acetylcholinesterase-2 (ace-2) gene, 16 out of 22 were identified as Culex quinquefasciatus. Genetic profiling of the VGSC gene revealed three notable kdr mutant patterns in Aedes aegypti: (1) 989PP + 1016GG, (2) 989PP + 1016GG + 1534CC, and (3) 989PP + 1016GG + 1534FC. Conversely, the Culex quinquefasciatus and the other member of Culex pipiens complex exhibited homozygous L1014F mutation across all samples. Intriguingly, the phenotypic resistance to deltamethrin in the bottle assay in both species suggests the influence of alternative resistance mechanisms. This study presents the first documented evidence in Bangladesh of three kdr mutations in Aedes aegypti and one in Culex quinquefasciatus/pipiens complex, providing a snapshot of the genetic landscape of insecticide resistance and underscoring the need for molecular surveillance.