Abstract
Pyrethroid resistance is becoming a major problem for vector control programs, because at present, there are few suitable chemical substitutes for pyrethroids, as when used on bed nets the insecticide must have low mammalian toxicity as well as high activity to mosquitoes. Pyriproxyfen (PPF) is one of the most active chemicals among the juvenile hormone mimic (JHM) group. Sterilizing mosquitoes by using PPF could be a potential control measure for pyrethroid-resistant malaria vectors. We investigated the sterilizing effects of two types of PPF-impregnated bed nets – a 1% PPF-impregnated net and a 1% PPF +2% permethrin-impregnated net (Olyset Duo) – to pyrethroid-resistant wild population of Anopheles gambiae s.s. in western Kenya. High mortality of blood-fed mosquitos was observed 3 days post-collection, in the houses where PPF-impregnated nets were used, indicating the effect of PPF on the longevity of mosquitos that came in contact with the net. Reduction in the number of ovipositing females, number of eggs, and number of progeny per female were also observed in the houses in which both Olyset Duo and PPF-impregnated nets were used. This is the first field study showing the high sterilizing efficacy of PPF against wild pyrethroid-resistant An. gambiae s.s. population. In addition, we recognized the necessity of combined use of permethrin with PPF, in order to reduce the risk of mosquito bites and provide a level of personal protection. Further studies on wild pyrethroid-resistant mosquito populations such as An. arabiensis and An. funestus s.s. would provide more information on the practical use of the PPF-impregnated bed nets.
Highlights
After more than 30 years since the introduction of permethrin, synthetic pyrethroids have emerged as the newest class of insecticides in the vector control program [1]
One hundred and forty-five female An. gambiae s.s. and 5 female An. arabiensis were collected before the intervention, while 153 An. gambiae s.s. and 6 An. arabiensis were collected afterward
Average numbers of An. gambiae s.s. females collected in the houses with Olyset Net, Olyset Duo, and PPF-impregnated net were 1.90, 2.37, and 3.26 per house/day before intervention, and 1.56, 1.55, and 4.70 per house/day after intervention, respectively
Summary
After more than 30 years since the introduction of permethrin, synthetic pyrethroids have emerged as the newest class of insecticides in the vector control program [1]. A causal relationship between the high coverage of LNs due to mass campaigns and the increase in the kdr frequency in An. gambiae s.s. have been reported [3,4,5]. Such kdr mutations do not seem to be common in An. arabiensis [6,7,8], but the metabolic resistance seems to be most common in this species [8,9]. Re-emergence or increase of this species as well as the development of metabolic pyrethroid resistance in eastern and southern Africa have been reported in this species [9,10,11,12,13,14,15]
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