Abstract
The directional selection for insecticide resistance due to indiscriminate use of insecticides in public health and agricultural system favors an increase in the frequency of insecticide-resistant alleles in the natural populations. Similarly, removal of selection pressure generally leads to decay in resistance. Past investigations on the emergence of insecticide resistance in mosquitoes mostly relied on field survey of resistance in vector populations that typically had a complex history of exposure to various public health and agricultural pest control insecticides in nature, and thus the effect of specific insecticides on rate of resistance emergency or resistance decay rate is not known. This study examined the phenotypic, genotypic, and biochemical changes that had occurred during the process of selection for pyrethroid resistance in Anopheles gambiae, the most important malaria vector in Africa. In parallel, we also examined these changes in resistant populations when there is no selection pressure applied. Through repeated deltamethrin selection in adult mosquitoes from a field population collected in western Kenya for 12 generations, we obtained three independent and highly pyrethroid-resistant An. gambiae populations. Three susceptible populations from the same parental population were generated by removing selection pressure. These two lines of mosquito populations differed significantly in monooxygenase and beta-esterase activities, but not in Vgsc gene mutation frequency, suggesting metabolic detoxification mechanism plays a major role in generating moderate-intensity resistance or high-intensity resistance. Pre-exposure to the synergist piperonyl butoxide restored the susceptibility to insecticide among the highly resistant mosquitoes, confirming the role of monooxygenases in pyrethroid resistance. The rate of resistance decay to become fully susceptible from moderate-intensity resistance took 15 generations, supporting at least 2-years interval is needed when the rotational use of insecticides with different modes of action is considered for resistance management.
Highlights
The directional selection for insecticide resistance due to indiscriminate use of insecticides in public health and agricultural system favors an increase in the frequency of insecticide-resistant alleles in the natural populations[1]
The emergence of insecticide resistance shortens the lifespan of the existing vector control tools and undermines the efficacy of novel developed vector control products through cross-resistance or multiple resistance[2,3]. In response to this challenge, the Global Plan for Insecticide Resistance Management (GPIRM)[4] of the World Health Organization (WHO) came up with strategies to preserve the effectiveness of current vector control tools and at the same time develop new and innovative vector control tools for the future, to significantly reduce malaria morbidity and mortalities
Past investigations on the emergence of insecticide resistance in mosquitoes relied on field survey of resistance in vector populations that typically had a complex history of exposure to various types of insecticides[5,6,7] and the effect of specific insecticide selection pressure on the rate of resistance emergency is not known
Summary
The directional selection for insecticide resistance due to indiscriminate use of insecticides in public health and agricultural system favors an increase in the frequency of insecticide-resistant alleles in the natural populations. Past investigations on the emergence of insecticide resistance in mosquitoes mostly relied on field survey of resistance in vector populations that typically had a complex history of exposure to various public health and agricultural pest control insecticides in nature, and the effect of specific insecticides on rate of resistance emergency or resistance decay rate is not known. Past investigations on the emergence of insecticide resistance in mosquitoes relied on field survey of resistance in vector populations that typically had a complex history of exposure to various types of insecticides[5,6,7] and the effect of specific insecticide selection pressure on the rate of resistance emergency is not known. A number of studies have reported the indiscriminate use of other classes of insecticides for agricultural purposes added selection pressure for resistance in mosquito p opulations[2,5,7]
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