Anopheles gambiae Giles (Diptera: Culicidae) is the most prolific
malaria vector in sub-Saharan Africa, where widespread insecticide resistance has been reported. An. gambiae laboratory strains are commonly used to study the basic biology of this important mosquito vector, and also in new
insecticide discovery programs, where
insecticide-susceptible and -resistant strains are often used to screen new molecules for potency and cross-resistance, respectively. This study investigated the toxicity of
permethrin, a Type-I
pyrethroid insecticide, and
etofenprox, a non-
ester containing
pyrethroid insecticide, against An. gambiae at three life stages. This characterization was performed with susceptible (G3; MRA-112) and resistant (Akdr; MRA-1280) An. gambiae strains; the Akdr strain is known to contain the L1014F mutation in the voltage-sensitive
sodium channel. Surprisingly,
etofenprox displays a lower level of resistance than
permethrin against all stages of mosquitoes, except in a headless larval
paralysis assay designed to minimize penetration factors. In first-instar An. gambiae larvae,
permethrin had significant resistance, determined by the resistance ratio (RR50 = 5), but
etofenprox was not significantly different (RR50 = 3.4) from the wild-type strain. Fourth-instar larvae displayed the highest level of resistance for
permethrin (RR50 = 108) and
etofenprox (RR50 = 35).
Permethrin (PC50 = 2 ppb) and
etofenprox (PC50 = 9 ppb) resulted in headless larval
paralysis (5-h), but resistance, albeit lower, was still present for
permethrin (RR50 = 5) and
etofenprox (RR50 = 6.9). In adult female mosquitoes,
permethrin displayed higher resistance (RR50 = 14) compared to
etofenprox (RR50 = 4.3). The level of
etofenprox resistance was different from that previously reported for a similar Akron An. gambiae laboratory strain (MRA-913). The chemical synergists
piperonyl butoxide (PBO) and
diethyl maleate (DEM) were able to synergize
permethrin, but not
etofenprox in the resistant strain (Akdr). In conclusion, multiple mechanisms are likely involved in
pyrethroid resistance, but resistance profiles are dependent upon selection.
Etofenprox is an effective
insecticide against An. gambiae in the lab but will likely suffer from resistance in the field.