Status of DDT and pyrethroid resistance in Indian Aedes albopictus and absence of knockdown resistance (kdr) mutation.

BACKGROUND & OBJECTIVES: Aedes albopictus is one of the vectors for dengue and chikungunya and emergence of pyrethroid resistance in this species could be of a major concern in controlling the vector. This study reports insecticide susceptibility status of Ae. albopictus to DDT and pyrethroids in some Indian populations and status of presence of knockdown resistance (kdr) mutations. METHODS: Three to four day old adult female Ae. albopictus collected from Delhi, Gurgaon (Haryana), Hardwar (Uttarakhand), Guwahati (Assam) and Kottayam (Kerala) were bio-assayed with DDT (4%), permethrin (0.75%) and deltamethrin (0.05%) impregnated papers using WHO standard susceptibility test kit. Mosquitoes were PCRgenotyped for F1534C kdr-mutation in the voltage-gated sodium channel (VGSC) gene. DDT and pyrethroid resistant individuals were sequenced for partial domain II, III and IV of VGSC targeting residues S989, I1011, V1016, F1534 and D1794 where kdr mutations are reported in Ae. aegypti. RESULTS: Adult bioassays revealed varying degree of resistance against DDT among five populations of Ae. albopictus with corrected mortalities ranging between 61 and 92%. Kerala and Delhi populations showed incipient resistance against permethrin and deltamethrin respectively. All other populations were susceptible for both the synthetic pyrethroids. None of the kdr mutations was detected in any of DDT, deltamethrin and permethrin resistant individuals. INTERPRETATION & CONCLUSION: Ae. albopictus has developed resistance against DDT and there is emergence of incipient resistance against pyrethroids in some populations. So far, there is no evidence of presence of knockdown resistance (kdr) mutation in Ae. albopictus.