Possible New Controlling Measures for the Pyrethroid-Resistant Malaria Vectors - Abstract
The dramatic success of long-lasting insecticidal nets (LLINs) in African countries has been countered by the rapid development of pyrethroid resistance in vector mosquitoes. The use of excito-repellency chemicals might be bio-rational, since such repellency will not induce physiological resistance. However, little is known about the relationship between the mode of insecticide resistance and excito-repellency in mosquitoes. The goals of our study were to investigate [1] the reactions of vector mosquitos in an area where pyrethroid resistance has developed, [2] the effect of LLINs on these malaria vectors, and [3] the development of new control techniques to supplement LLINs. Laboratory tests showed that resistant species governed by kdr (knockdown resistance) (Anopheles gambiae s.s.) lose repellency to pyrethroids, whereas those lacking kdr (An. arabiensis and An. funestus s.s.) maintain high repellency. LLINs were effective against these pyrethroid-resistant malaria vectors, because they limited feeding on humans during bedtime. However, notable time shifts in human blood feeding activity developed in both An. arabiensis and An. funestus s.s., whereas no such time shift developed in An. gambiae s.s. These time shifts might be partially explained by differences in repellency by pyrethroids for these species. LLINs might not be effective because most blood feeding occurs when people are active outside the bed nets. Screening eaves with pyrethroid-impregnated wide-mesh nets was found to be effective in reducing human exposure to malaria vectors. The excito-repellency of pyrethroids that act as a spatial barrier or reduce feeding motivation of mosquitoes might be another countermeasure.