Malaria Entomology Research Unit, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
Malar J. 2010 Dec 14;9:360. doi: 10.1186/1475-2875-9-360.
Anopheles gambiae is a major vector of malaria in the West African region. Resistance to multiple insecticides has been recorded in An. gambiae S form in the Ahafo region of Ghana. A laboratory population (GAH) established using wild material from this locality has enabled a mechanistic characterization of each resistance phenotype as well as an analysis of another adaptive characteristic - staggered larval time-to-hatch.
Individual egg batches obtained from wild caught females collected from Ghana and the Republic of the Congo were monitored for staggered larval time-to-hatch. In addition, early and late larval time-to-hatch sub-colonies were selected from GAH. These selected sub-colonies were cross-mated and their hybrid progeny were subsequently intercrossed and back-crossed to the parental strains. The insecticide susceptibilities of the GAH base colony and the time-to-hatch selected sub-colonies were quantified for four insecticide classes using insecticide bioassays. Resistance phenotypes were mechanistically characterized using insecticide-synergist bioassays and diagnostic molecular assays for known reduced target-site sensitivity mutations.
Anopheles gambiae GAH showed varying levels of resistance to all insecticide classes. Metabolic detoxification and reduced target-site sensitivity mechanisms were implicated. Most wild-caught families showed staggered larval time-to-hatch. However, some families were either exclusively early hatching or late hatching. Most GAH larvae hatched early but many egg batches contained a proportion of late hatching larvae. Crosses between the time-to-hatch selected sub-colonies yielded ambiguous results that did not fit any hypothetical models based on single-locus Mendelian inheritance. There was significant variation in the expression of insecticide resistance between the time-to-hatch phenotypes.
An adaptive response to the presence of multiple insecticide classes necessarily involves the development of multiple resistance mechanisms whose effectiveness may be enhanced by intra-population variation in the expression of resistance phenotypes. The variation in the expression of insecticide resistance in association with selection for larval time-to-hatch may induce this kind of enhanced adaptive plasticity as a consequence of pleiotropy, whereby mosquitoes are able to complete their aquatic life stages in a variable breeding environment using staggered larval time-to-hatch, giving rise to an adult population with enhanced variation in the expression of insecticide resistance.
冈比亚按蚊是西非地区疟疾的主要传播媒介。在加纳的阿哈福地区，已经记录到冈比亚按蚊 S 型对多种杀虫剂的抗性。使用来自该地点的野生材料建立的实验室种群 (GAH) 使每种抗性表型的机制特征以及另一种适应性特征 - 孵化时间错开的幼虫得以实现。
从加纳和刚果共和国捕获的野生雌性个体中获得的单个卵批，监测孵化时间错开的幼虫。此外，从 GAH 中选择了早期和晚期孵化时间错开的幼虫亚群。这些选定的亚群进行杂交，然后将其杂种后代回交和交叉交配到亲本品系中。使用杀虫剂生物测定法，对 GAH 基础种群和孵化时间错开的选择亚群的四种杀虫剂类别的杀虫剂敏感性进行了量化。使用杀虫剂增效生物测定法和针对已知靶标敏感性降低突变的诊断分子测定法，对抗性表型进行了机制特征描述。
冈比亚按蚊 GAH 对所有杀虫剂类别的抗性水平不同。涉及代谢解毒和靶标敏感性降低的机制。大多数野生捕获的家系表现出孵化时间错开的幼虫。然而，一些家系要么是早期孵化，要么是晚期孵化。大多数 GAH 幼虫孵化较早，但许多卵批中含有一定比例的晚期孵化幼虫。时间错开的选择亚群之间的杂交产生了不适合基于单基因孟德尔遗传的任何假设模型的模糊结果。在孵化时间错开的表型之间，杀虫剂抗性的表达存在显著差异。
对多种杀虫剂类别的存在的一种适应性反应必然涉及多种抗性机制的发展，其有效性可能会因抗性表型表达的种群内变异而增强。与幼虫孵化时间错开选择相关的杀虫剂抗性表达的变化可能会诱导这种增强的适应性可塑性，这是由于多效性，即蚊子能够在可变的繁殖环境中完成其水生生活阶段，使用孵化时间错开的幼虫，从而产生成虫种群对杀虫剂抗性的表达增强。
