ORIGINAL RESEARCH HIGH LEVEL OF DDT RESISTANCE IN THE MALARIA MOSQUITO: ANOPHELES GAMBIAE S.L. FROM RURAL, SEMI URBAN AND URBAN COMMUNITIES IN NIGERIA

Objective: To investigate the susceptibility status of the major malaria mosquito in selected rural, semi-urban and urban areas of Nigeria to DDT and Permethrin based insecticides used in vector control. Methods: Two to three day old unfed adult female Anopheles mosquitoes raised from larvae collected across three ecological zones in Nigeria were exposed to 4 % DDT impregnated papers. To find out the possibility of DDT – pyrethroid cross-resistance, susceptibility tests were carried out using 0.75% Permethrin. Mosquitoes tested were identified to species level using PCR assays. Knockdown resistance assays were also carried out on all specimens. Results: At all three locations, the principal species was A. gambiae s.s constituting more than 80% of mosquitoes analysed. The 24 hour post-exposure mortality for Permethrin ranged from 51.7 to 100% with resistance observed in five out of the 19 communities tested. DDT resistance was observed at all of the 12 communities tested with mortality ranging from 9.8% to 80%. Incidence of Permethrin resistance was associated with urban communities compared to DDT resistance which was widespread in all the communities. Resistance was recorded in the A. gambiae s.s, however DDT resistance was observed in A. arabiensis from five study communities. Conclusions: Indications of differential susceptibility to Permethrin and high frequency of DDT resistance in A. gambiae was observed which highlights the need for baseline information prior to the use of DDT for indoor residual spray in Nigeria. It also highlights the need for an effective insecticide resistance management programme.