Department of Entomology and Nematology, College of Agriculture and Environmental Sciences, University of California, Davis, CA, USA.
University of Florida-Florida Medical Entomology Laboratory, Vero Beach, FL, USA.
Parasit Vectors. 2021 Mar 6;14(1):141. doi: 10.1186/s13071-021-04627-3.
Since their detection in 2013, Aedes aegypti has become a widespread urban pest in California. The availability of cryptic larval breeding sites in residential areas and resistance to insecticides pose significant challenges to control efforts. Resistance to pyrethroids is largely attributed to mutations in the voltage gated sodium channels (VGSC), the pyrethroid site of action. However, past studies have indicated that VGSC mutations may not be entirely predictive of the observed resistance phenotype.
To investigate the frequencies of VGSC mutations and the relationship with pyrethroid insecticide resistance in California, we sampled Ae. aegypti from four locations in the Central Valley, and the Greater Los Angeles area. Mosquitoes from each location were subjected to an individual pyrethrum bottle bioassay to determine knockdown times. A subset of assayed mosquitoes from each location was then analyzed to determine the composition of 5 single nucleotide polymorphism (SNP) loci within the VGSC gene.
The distribution of knockdown times for each of the five Californian populations sampled was non-parametric with potentially bimodal distributions. One group succumbs to insecticidal effects around 35-45 min and the second group lasts up to and beyond the termination of the assay (120+ min). We detected 5 polymorphic VGSC SNPs within the sampled California populations. One is potentially new and alternatively spliced (I915K), and four are documented and associated with resistance: F1534C, V1016I, V410L and S723T. The Central Valley populations (Clovis, Dinuba, Sanger and Kingsburg) are fairly homogenous with only 5% of the mosquitoes showing heterozygosity at any given position. In the Greater LA mosquitoes, 55% had at least one susceptible allele at any of the five SNP loci. The known resistance allele F1534C was detected in almost all sampled mosquitoes (99.4%). We also observe significant heterogeneity in the knockdown phenotypes of individuals with the identical VGSC haplotypes suggesting the presence of additional undefined resistance mechanisms.
Resistance associated VGSC SNPs are prevalent, particularly in the Central Valley. Interestingly, among mosquitoes carrying all 4 resistance associated SNPs, we observe significant heterogeneity in bottle bioassay profiles suggesting that other mechanisms are important to the individual resistance of Ae. aegypti in California.
自 2013 年发现以来，埃及伊蚊已成为加利福尼亚州广泛存在的城市害虫。居民区隐匿的幼虫滋生地以及对杀虫剂的抗性给防治工作带来了巨大挑战。对拟除虫菊酯的抗性主要归因于电压门控钠离子通道（VGSC）的突变，这是拟除虫菊酯的作用部位。然而，过去的研究表明，VGSC 突变可能不完全预测观察到的抗性表型。
为了研究加利福尼亚州埃及伊蚊的 VGSC 突变频率及其与拟除虫菊酯杀虫剂抗性的关系，我们从加利福尼亚州中央山谷和大洛杉矶地区的四个地点采集了埃及伊蚊。每个地点的蚊子都进行了单独的拟除虫菊酯瓶生物测定，以确定击倒时间。然后，从每个地点的部分测定蚊子中分析了 VGSC 基因中 5 个单核苷酸多态性（SNP）位点的组成。
五个加利福尼亚种群的击倒时间分布是非参数的，可能具有双峰分布。一组在 35-45 分钟左右屈服于杀虫作用，而另一组持续到甚至超过测定的终止时间（120+分钟）。我们在采样的加利福尼亚种群中检测到 5 个 VGSC SNP 多态性。一个可能是新的和可变剪接的（I915K），而四个是有文件记载并与抗性相关的：F1534C、V1016I、V410L 和 S723T。中央山谷种群（克洛维斯、迪纳布、桑格和金斯堡）相当同质，任何给定位置只有 5%的蚊子表现出杂合性。在大洛杉矶的蚊子中，55%的蚊子在五个 SNP 位点中的任何一个都至少有一个易感等位基因。在几乎所有采样的蚊子中都检测到了已知的抗性等位基因 F1534C（99.4%）。我们还观察到具有相同 VGSC 单倍型的个体的击倒表型存在显著异质性，这表明存在其他未定义的抗性机制。
与抗性相关的 VGSC SNP 很普遍，尤其是在中央山谷。有趣的是，在携带所有 4 个抗性相关 SNP 的蚊子中，我们观察到瓶生物测定谱的显著异质性，这表明其他机制对加利福尼亚埃及伊蚊的个体抗性很重要。
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