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

Abstract

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.

Insecticide Resistance Allele Frequencies in Anopheles gambiae before and after Anti-Vector Interventions in Continental Equatorial Guinea

“…46 For this dataset, sample sizes ranged from 36 to 93, with averages of 57, 50, and 82, respectively. The average change in frequency for all microsatellite alleles was 0.040, 0.055, and 0.038, respectively.…”

“…45 To explore a possible explanation for HW disequilibria in the kdr locus in some populations, microsatellite data for 16 loci for the M form (Ukomba, n = 93) and the S form (Yengue, n = 62) collected in 2007 were used to perform a Bayesian clustering analysis implemented in STRUCTURE version 2.3.3. 46,47 Each STRUCTURE analysis was run for 500,000 generations, with a burn-in period of 100,000 generations by using correlated allele frequencies with no a priori population information. The number of potential distinct genetic clusters (K) examined ranged from 1 to 5 and 5 replicates were run for each K value.…”

Genomic insights into adaptive divergence and speciation among malaria vectors of theAnopheles niligroup

“…Moreover, recent malaria control efforts affect interspecific gene flow, genetic differentiation, population demography and natural selection in mosquitoes (Athrey et al, 2012;Barnes et al, 2017;Clarkson et al, 2014;Kamdem et al, 2017;Norris et al, 2015). Deciphering the signatures of these processes across mosquito genomes is important to minimize their negative impacts on vector control.…”

Pollutants and insecticides drive local adaptation in African malaria mosquitoes

“…gambiae s.l. after introduction of long-lasting insecticidetreated nets (Athrey et al 2012 Insecticide resistance, involving both multiple alleles of kdr and significant levels of metabolic resistance, is widespread Kamdem et al . doi:10.1093/molbev/msx087 MBE among An.…”