Susceptibility status of Anopheles culicifacies and Anopheles fluviatilis mosquitoes against DDT and deltamethrin in a tribal malaria zone of India

Anopheles culicifacies and Anopheles fluviatilis are the prominent malaria vector mosquitoes in India and neighbouring countries. The present study focused on the assessment of the susceptibility and development of insecticide resistance in adults of these mosquitoes against DDT (4% a.i.) and deltamethrin (0.05% a.i.) from Jharsuguda district of Odisha state, India. The findings are important in understanding the resurgence in malaria cases in the area. The WHO adulticide bioassays with diagnostic doses of DDT (4% a.i.) and deltamethrin (0.05% a.i.) were conducted to estimate the mortality with % knockdown to assess the resistance status. Correlations between mortality and % knockdown were established. Historical insecticide uses and malaria prevalence were also observed. Anopheles culicifacies showed 25.0 +/- 1.67% mortality with DDT with significantly higher median knockdown time (KT50 = 113.88 min) than those for deltamethrin (95.0 +/- 1.67% mortality, KT50 = 31.64 min). Anopheles fluviatilis was highly susceptibility for both DDT (98.3%) and deltamethrin (100%) which resulted in considerably less KT50 (33.4 and 26.3 min) and KT90 (67.5 and 76.27 min). The resistance was high in An. culicifacies to DDT even after the discontinuation of DDT indoor spray 5 years ago. Deltamethrin resistance was induced due to continuous exposure of treated bed nets. Anopheles fluviatilis is still susceptible to both insecticides, probably, due to less insecticidal exposure with anthropophilic and exophilic nature in foothills. Therefore, this study suggests judicious use of adulticides in malaria control specifically in areas infested with multiple vectors.