Owing to the development and spread of
pyrethroid resistance in Anopheles gambiae in Africa there is an urgent need to develop alternative
insecticides to supplement the
pyrethroids.
Chlorfenapyr is a
pyrrole insecticide first commercialized for the control of agricultural pests and termites. Performance against An. gambiae bearing kdr (
pyrethroid and
DDT resistance) or Ace-1(R) insensitive
acetylcholinesterase (
organophosphate and
carbamate resistance) mechanisms was studied using a variety of adult bioassay tests including a simulated-experimental hut system (tunnel tests) that allows uninhibited mosquito behaviour/
insecticide interactions. Strains resistant to
pyrethroids and
organophosphates showed no cross resistance to
chlorfenapyr. In cone bioassays on treated netting the mortality of adult mosquitoes showed an unexpected curvilinear response, with highest mortality occurring at intermediate dosages. Adults expressed irritability to
chlorfenapyr at higher dosages, which might explain the dosage-mortality trend. Toxic activity of
chlorfenapyr was slow compared to conventional neurotoxic
insecticides and additional mortality occurred between 24h and 72 h. In tunnel tests, the dosage-mortality trend showed a more typical sigmoid response and most mortality occurred during the first 24h. Mosquito penetration through the holed, treated netting showed only limited inhibition and blood-feeding was not inhibited. Mortality rates in the kdr strain exposed to
chlorfenapyr treated netting in tunnel tests were much higher than with
permethrin treated netting over the same 100-500 mg/m(2) dosage range.
Chlorfenapyr has potential for
malaria control in treated-net or residual spraying applications in areas where mosquitoes are
pyrethroid resistant. For treated-net applications
chlorfenapyr might be combined with
pyrethroid as a mixture to provide personal protection as well as to give control of resistant mosquitoes.