Long-term use of permethrin-impregnated nets does not increase Anopheles gambiae permethrin tolerance.
Previous use of permethrin-impregnated bednets (mosquito nets) and curtains in four Kenyan villages for one year, 1990-91, raised the permethrin LT50 of Anopheles gambiae to 2.4-fold above its baseline value, designated permethrin tolerance (PT), as measured by exposure to 0.25% permethrin-impregnated papers in W.H.O. test-kits. During 1992-93, with ongoing use of permethrin-impregnated nets and curtains, PT regressed slightly compared with the contemporary susceptibility level of An.gambiae from non-intervention villages, to 1.8-fold in 1992 and only 1.6-fold in 1993. Thus the selection pressure of impregnated nets for PT in An.gambiae appears to be minimal in our study villages, although the impact of permethrin was demonstrated by a significantly lower parous-rate of An.gambiae females in the intervention (63-66%) than in non-intervention (79%) villages, and by reduced malaria transmission (reported elsewhere). In a selected stock of An.gambiae from the study area, PT did not affect the susceptibility to deltamethrin, fenitrothion, propoxur or DDT. Bioassays described herein provide easy procedures for field-monitoring of mosquito susceptibility/tolerance/resistance to insecticides used for net impregnation in operational programmes.
Vulule
J M
JM
Vector Biology and Control Research Centre (Kenya Medical Research Institute), Kisumu, Kenya.
Beach
R F
RF
Atieli
F K
FK
Mount
D L
DL
Roberts
J M
JM
Mwangi
R W
RW
D000818:Animals; D000852:Anopheles / Q000145:classification; D001512:Bedding and Linens; D005260:Female; D007305:Insecticide Resistance; D009032:Mosquito Control / Q000379:methods*; D026023:Permethrin; D011722:Pyrethrins
D011722:Pyrethrins; D026023:Permethrin