Bendiocarb, a potential alternative against pyrethroid resistant Anopheles gambiae in Benin, West Africa.
BACKGROUND
Anopheles gambiae, the main malaria vector in Benin has developed high level of resistance to pyrethroid insecticides, which is a serious concern to the future use of long-lasting insecticidal nets (LLIN) and indoor residual spraying (IRS). In this context, one of the pathways available for malaria vector control would be to investigate alternative classes of insecticides with different mode of action than that of pyrethroids. The goal of this study was to evaluate under field conditions the efficacy of a carbamate (bendiocarb) and an organophosphate (fenitrothion) against pyrethroid-resistant An. gambiae s.s.


METHODS
Wild populations and females from laboratory colonies of five days old An. gambiae were bio-assayed during this study. Two pyrethroids (deltamethrin and alphacypermethrin), an organophosphate (fenitrothion), a carbamate (bendiocarb) and a mixture of an organophosphate (chlorpyriphos + a pyrethroid deltamethrin) were compared in experimental huts as IRS treatments. Insecticides were applied in the huts using a hand-operated compression sprayer. The deterrency, exophily, blood feeding rate and mortality induced by these insecticides against An. gambiae were compared to the untreated control huts.


RESULTS
Deltamethrin, alphacypermethrin and bendiocarb treatment significantly reduced mosquito entry into the huts (p < 0.05) compared to untreated huts. Blood feeding rates in huts treated with fenitrothion and the mixture chlorpyriphos/deltamethrin were reduced from 10.95% respectively to 3.7% and 4.47% three months after treatment and from 10.20% to 4.4% and 2.04% four months after treatment. Exophily rates in huts with deltamethrin, alphacypermethrin and the mixture chlorpyriphos/deltamethrin were significantly higher than in the huts with fenitrothion. Deltamethrin and alphacypermethrin had the lowest mortality rate while fenitrothion killed 100% of An. gambiae (in the first month) and 77.8% (in the fourth month). Bendiocarb and the mixture chlorpyriphos/deltamethrin mortality rates ranged from 97.9 to 100% the first month and 77.7-88% the third month respectively.


CONCLUSIONS
After four months, fenitrothion, bendiocarb and the mixture chlorpyriphos/deltamethrin performed effectively against pyrethroid-resistant Anopheles. These results showed that bendiocarb could be recommended as an effective insecticide for use in IRS operations in Benin, particularly as the mixture chlorpyriphos/deltamethrin does not have WHOPES authorization and complaints were mentioned by the sleepers about the safety and smell of fenitrothion.
Akogbéto
Martin C
MC
Centre de Recherche Entomologique de Cotonou (CREC), Cotonou, Bénin 06 BP: 2604.
Padonou
Gil Germain
GG
Gbénou
Dina
D
Irish
Seth
S
Yadouleton
Anges
A
D000818:Animals; D000852:Anopheles / Q000187:drug effects*; D001541:Benin; D001681:Biological Assay; D005260:Female; D005278:Fenitrothion / Q000494:pharmacology*; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D008288:Malaria / Q000517:prevention & control; D009032:Mosquito Control / Q000379:methods; D048448:Phenylcarbamates / Q000494:pharmacology*; D011722:Pyrethrins / Q000494:pharmacology*
D007306:Insecticides; D048448:Phenylcarbamates; D011722:Pyrethrins; C007725:bendiocarb; D005278:Fenitrothion