The susceptible strain of An. gambiae,
Kisumu in Kenya (KIS), has been analyzed for many years and found to be free from any detectable insecticide resistance mechanism. The resistant strain of An. gambiae (VKPR) originating from Burkina Faso was already highly resistant to permethrin when col- lected in the field and has subsequently been main- tained under constant permethrin selection at each generation (Darriet et al., 1997). This strain was homo- zygous for the knockdown resistance (kdr) gene with a resistance factor (by topical application with per- methrin) of about 40 fold compared to the KIS strain (Chandre et al., 2000).