kdr type mutations and enhanced GST based insecticide resistance in dengue vector mosquitoes Aedes aegypti and Aedes albopictus

Pyrethroid resistance has imposed a severe threat to the control programmes of dengue vectors Aedes aegypti and Ae. albopictus in Sri Lanka. Present study investigated the resistance status and underlying mechanisms of these mosquitoes in six provinces of Sri Lanka. Mosquitoes were collected from Badulla (Uva Province), Batticaloa (Eastern), Colombo (Western), Jaffna (Northern), Kandy (Central) and Kurunegala (Northwestern). Adults were exposed to discriminating dosages of permethrin, deltamethrin, λ-cyhalothrin, cyfluthrin and DDT according to WHO guidelines. Survivals from bioassays were tested for kdr type mutations. Elevation of insecticide metabolizing enzymes and insensitivity of acetylcholinesterases, the target site of organophosphates and carbamates, were also tested. A total of 4875 mosquitoes (2687 Ae. aegypti, 2188 Ae. albopictus) were subjected to bioassays. All the populations had high resistance to DDT though it has not been used in the country for more than four decades. In general, Ae. aegypti populations showed more resistance towards pyrethroids. Glutathione S-transferase (GST) activities were enhanced in most of the populations with no enhancement of carboxylesterase and monooxygenase activities. Acetylcholinesterases were not altered in both species. Aedes aegypti showed high resistance to pyrethroids, mainly due to three kdr type mutations; V1016I, S989P and F1534C found in the voltage gated sodium channel which is the target site of pyrethroids and DDT. Both species were highly resistant to DDT mainly through a GST based mechanism. In the absence of elevated esterase-based and insensitive AChE mechanisms, organophosphates and carbamates can be recommended as alternatives for future dengue vector control programmes in Sri Lanka.