Insecticide resistance status of Anopheles gambiae s.l. and Anopheles stephensi populations to existing and some candidate insecticide formulations

Abstract

Malaria control in Ethiopia mainly relied on case management and vector control using long-lasting insecticidal nets (LLINs) and indoor residual sprayings (IRS). Anopheles arabiensis, a member species of An. gambiae s.l is the major malaria vector in Ethiopia, and An. stephensi is an invasive species detected in recent years mainly in the eastern part of Ethiopia. Insecticide resistance in malaria vectors is a huge challenge to the national malaria elimination programe. This study was conducted to investigate the insecticide resistance status and mechanisms of resistance in An. gambiae s.l. and An. stephensi in Ethiopia. Anopheles gambiae s.l. (from Jimma, Oromia) and An. stephensi (from Awash Sebat Kilo, Afar region) were reared from larvae and pupae. Three to five days-old female adults were tested with WHO-impregnated papers (deltamethrin (0.05%), alphacypermethrin (0.05%), pirimiphos-methyl (0.25%), bendiocarb (0.1%), propoxur (0.1%), and clothianidin (2%)) as per WHO standard procedure. Clothianidin (10µg/ml), chlorfenapyr (100µg/ml) and a potential candidate insecticide broflanilide were tested using CDC bottle bioassays. Anopheles gambiae s.l. member species mosquitoes were identified by speciesspecific polymerase chain reaction (PCR) and screened for the presence of target site mutations L1014F and L1014S in the voltage-gated sodium channel (VGSC) gene using allele-specific PCR. The data were analysed using SPSS version 20.The results of the study showed that An. gambiae s.l. populations were susceptible to propoxur and pirimiphos methyl but resistant against the other existing insecticides (bendiocarb, alpha cypermethrin and deltamethrin, clothianidin. Anopheles stephensi population from Awash 7 kilo was resistant to almost all tested insecticides, with probable resistance to clothianidin (97%). Anopheles gambiae s.l. and An. stephensi were fully susceptible to chlorfenapyr (100μg/ml) and clothianidin (10μg/ml). Moreover, both An. gambiae s.l. and An. stephensi were susceptible to broflanilide at doses of 50μg/ml, 25 μg/ml, 12.5 μg/ml, 6.25 μg/ml, 3.125 μg/ml 1.562 μg/ml and 0.78 μg/ml. Of 120 An. gambiae.s.l. specimens tested for species identification (ID PCR), 117(97.5%) were An. arabiensis. The L1014F kdr mutation was detected in An. arabiensis with frequencies of 22.8%. No L1014S mutation was detected in An. arabiensis at the study sites. This study provides information on the insecticide resistance status of An. arabiensis and An. stephensi. Anopheles stephensi was resistant to multiple insecticides. Anopheles arabiensis were susceptible to pirimiphos methyl and propoxur but resistant to the other insecticides. The West African kdr mutation (L1014F) was detected at low frequency, and the L1014S kdr was not detected in An. arabiensis. Therefore, the observed resistance in An. arabiensis and An. stephensi to multiple insecticides is a big concern and could deeply affect the sustainability of insecticide-based interventions strategies in Ethiopia.