The African malaria mosquito, Anopheles gambiae, is the primary vector of malaria in sub-Saharan Africa, and is responsible for the disproportionately high burden of global malaria. Pyrethroid insecticides are commonly used to control mosquito populations, and therefore disrupt the transmission of mosquito-borne diseases. However, the widespread use of chemical insecticides has resulted in resistance. Two An. gambiae laboratory strains, G3 (pyrethroid-susceptible) and Akron-kdr (pyrethroid-resistant), are commonly used to evaluate the efficacy of synthetic and natural insecticides. The presented research will focus on investigating the level of resistance to permethrin and etofenprox by comparing resistance ratios (RR) of three life stages (first instar, fourth instar, and adult female mosquitoes) of these two strains. First instar Akron-kdr larvae displayed moderate resistance to permethrin (RR=5) along with etofenprox (RR=3.4). Fourth instar larvae of the Akron-kdr strain displayed stronger resistance to permethrin (RR=108) that was 3-fold higher than resistance observed with Etofenprox (RR=38). Topical application of adult female mosquitoes (Akron-kdr) with permethrin (RR=14.1) was 3-fold more resistant compared to etofenprox (RR=4.3). Pretreatment (4 hr) of adult female Akron-kdr mosquitoes with piperonyl butoxide (PBO; 100 ng) had modest effects on the synergism of permethrin (synergistic ratio (SR)=4.9) and etofenprox (SR=2.7). Pretreatment (4 hr) with 100 ng of diethyl maleate (DEM) synergized permethrin (SR=8.7), but had no synergistic effect with etofenprox (SR=1.3) in Akron-kdr adult female mosquitos. The results of this study indicate that the An. gambiae Akron-kdr strain displays less resistance to etofenprox, in the laboratory, compared to permethrin. Further, our studies indicate that metabolism, in addition to previously identified target site modification of the voltage-sensitive sodium channel (kdr), results in mosquito resistance to permethrin.

Characterizing permethrin and etofenprox resistance in two laboratory strains of Anopheles gambiae

256th National Meeting (2018)

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