Mosquito resistance to insecticides remains a major concern for vector control programs based on chemical methods. Hence, a thorough knowledge of vector susceptibility to products recommended for public health is required for effective vector control programs. In this study, we assessed the susceptibility of wild Anopheles gambiae sl and Culex quinquefasciatus populations from N'Djamena (Chad) to four insecticide classes recommended for public health. The study took place from July to October 2014. Following WHO guidelines, bioassays were performed on two- to four-day-old, non-engorged female mosquitoes of both species, collected in the field. The insecticides used were deltamethrin (0.05%), permethrin (1%), DDT (4%), bendiocarb (0.01%), and malathion (5%). Anopheles gambiae sl showed full susceptibility to bendiocarb and malathion but was resistant to pyrethroids; mortality rates were 2% for deltamethrin, 2% for permethrin, and 0% for DDT. Culex quinquefasciatus was susceptible to malathion but resistant to the other insecticides, with a mortality rate of 22% for deltamethrin, 29% for permethrin, 23% for DDT, and 45% bendiocarb. The resistance of Anopheles gambiae sl and of Culex quinquefasciatus may affect the population's adherence to the use of insecticide-treated mosquito nets. Malaria control programs are advised to extend insecticide resistance monitoring to the main culicide species that bite human populations.
Keywords: Africa; Anopheles gambiae sl; Chad; Culex quinquefasciatus; N’Djamena; insecticide; resistance.