The Effective Population Size of Malaria Mosquitoes: Large Impact of Vector Control

Malaria vectors in sub-Saharan Africa have proven themselves very difficult adversaries in the global struggle against malaria. Decades of anti-vector interventions have yielded mixed results—with successful reductions in transmission in some areas and limited impacts in others. These varying successes can be ascribed to a lack of universally effective vector control tools, as well as the development of insecticide resistance in mosquito populations. Understanding the impact of vector control on mosquito populations is crucial for planning new interventions and evaluating existing ones. However, estimates of population size changes in response to control efforts are often inaccurate because of limitations and biases in collection methods. Attempts to evaluate the impact of vector control on mosquito effective population size (Ne) have produced inconclusive results thus far. Therefore, we obtained data for 13–15 microsatellite markers for more than 1,500 mosquitoes representing multiple time points for seven populations of three important vector species—Anopheles gambiae, An. melas, and An. moucheti—in Equatorial Guinea. These populations were exposed to indoor residual spraying or long-lasting insecticidal nets in recent years. For comparison, we also analyzed data from two populations that have no history of organized vector control. We used Approximate Bayesian Computation to reconstruct their demographic history, allowing us to evaluate the impact of these interventions on the effective population size. In six of the seven study populations, vector control had a dramatic impact on the effective population size, reducing Ne between 55%–87%, the exception being a single An. melas population. In contrast, the two negative control populations did not experience a reduction in effective population size. This study is the first to conclusively link anti-vector intervention programs in Africa to sharply reduced effective population sizes of malaria vectors.撒哈拉以南非洲的疟疾传播媒介，在全球抗疟斗争中已被证实是极为棘手的防控对手。数十年来的媒介防制干预措施收效参差不齐：部分地区成功实现了疟疾传播的有效削减，而另一些地区则收效甚微。这种成效差异可归因于两方面因素：一是缺乏普适高效的媒介控制工具，二是蚊虫种群逐渐产生了杀虫剂抗药性。明确媒介控制对蚊虫种群的影响，对于规划新型干预方案与评估现有防控措施均至关重要。然而，由于采集方法存在局限性与系统性偏倚，针对防控措施引发的种群规模变化的估算往往精度不足。迄今为止，旨在评估媒介控制对蚊虫有效种群大小（effective population size, Ne）影响的相关研究，尚未得出确定性结论。为此，我们收集了赤道几内亚境内3种重要疟疾媒介——冈比亚按蚊（*Anopheles gambiae*）、梅尔氏按蚊（*An. melas*）与穆氏按蚊（*An. moucheti*）的7个种群的样本数据，共涵盖1500余只蚊虫，覆盖多个采样时间点，涉及13至15个微卫星标记（microsatellite markers）位点。近年来，这些种群均暴露于室内残留喷洒（indoor residual spraying, IRS）或长效杀虫剂蚊帐（long-lasting insecticidal nets, LLINs）的防控措施之下。为进行对照，我们同时分析了2个无系统化媒介防制历史的种群的数据。我们采用近似贝叶斯计算（Approximate Bayesian Computation, ABC）方法重构了这些种群的种群动态历史，以此评估上述干预措施对有效种群大小的影响。结果显示，在7个研究种群中的6个，媒介防制措施对有效种群大小产生了显著影响：有效种群规模缩减了55%至87%，仅1个梅尔氏按蚊种群未出现该变化。与之形成鲜明对比的是，2个阴性对照种群的有效种群大小均未发生缩减。本研究首次明确将非洲的媒介防制干预项目与疟疾媒介有效种群规模的大幅缩减建立了直接因果关联。