The research team, led by Xiao Pan and Nuo Xu, joint first authors, together with corresponding author Hongmei Liu of Shandong First Medical University and the Shandong Institute of Parasitic Diseases, analyzed mosquitoes collected from twelve geographic populations spanning the tropical, subtropical, and temperate climatic zones of China. This transect, stretching from the humid tropics of Yunnan Province to the cooler northern temperate regions, offered a natural laboratory for asking a fundamental question in vector biology: to what extent does climate drive the genetic differentiation of mosquito populations, and how does that differentiation interact with the evolution of insecticide resistance?

To answer it, the researchers sequenced two genetic regions with complementary roles. The mitochondrial cytochrome c oxidase subunit I gene, or COI, served as a marker of maternal lineage, population history, and gene flow, with 743 sequences analyzed across the twelve populations. The voltage-gated sodium channel gene, VGSC, the molecular target of pyrethroid insecticides, was sequenced in 546 individuals to detect knockdown resistance, or kdr, mutations, the point substitutions in the sodium channel that reduce the binding efficiency of the insecticide and allow mosquitoes to survive exposure that would kill susceptible insects.

The COI data revealed a moderately diverse but clearly structured picture. Thirty-four haplotypes were identified across the sampled mosquitoes, with overall haplotype diversity of 0.6566 and nucleotide diversity of 0.00172. Notably, the tropical populations, and particularly the population from Xishuangbanna in Yunnan Province, displayed the highest genetic diversity and the richest complement of haplotypes. This pattern is consistent with the idea that tropical southern China may act as a reservoir of genetic variation for the species, a source from which diversity has been funneled northward during range expansion. Populations at the leading edge of an expansion typically carry only a subset of the genetic variation present in the ancestral source, and the reduced diversity observed in temperate populations fits that expectation.

Bayesian clustering analysis using STRUCTURE identified three genetic clusters, K = 3, as the optimal partition of the data. The tropical populations formed a distinct, well-separated genetic cluster of their own, while the temperate and subtropical populations showed extensively admixed compositions, sharing ancestry across cluster boundaries. This admixture is not merely a curiosity of population genetics; it is a direct signal of mosquito movement. Gene flow estimates derived from LAMARC analyses quantified the point dramatically: the exchange rate between subtropical and temperate regions reached 166.56, an exceptionally high value indicating that mosquitoes, and whatever genetic cargo they carry, are moving across the operational boundaries that separate provincial and municipal vector control jurisdictions.

Environmental analysis added the climatic dimension. Among the variables tested, mean annual temperature and annual precipitation emerged as the significant predictors of genetic differentiation among populations. In other words, the genetic distances separating mosquito populations were not explained by geography alone; they tracked the climatic gradients that define China’s major biomes. Warmer, wetter environments appear to sustain larger, more connected mosquito populations, while cooler regions impose ecological filters that shape which lineages establish and persist. The authors suggest that temperature may influence both population connectivity and the geographic distribution of resistance-associated variants, effectively coupling the epidemiology of vector competence to the physics of the atmosphere.

The most consequential result concerns the kdr mutations themselves. Significant differences in mutation frequencies were detected among the three climatic zones, and one relationship stood out with particular clarity: mutation frequency at codon 1532 of the sodium channel gene was negatively correlated with mean annual temperature, with a correlation coefficient of r = −0.766 and a statistically significant P value below 0.05. Counterintuitively, the resistance-associated variant was more common in cooler regions. The authors propose several non-exclusive explanations, including differences in insecticide selection pressure across regions, demographic history, and the possibility that the mutation carries fitness costs in hot climates or benefits under certain local conditions. Whatever the mechanism, the spatial heterogeneity of kdr frequencies means that a single national resistance management strategy is unlikely to succeed; surveillance and intervention must be tailored to climatic context.

Haplotype network analyses of the VGSC sequences added a further layer of insight. Haplotypes carrying kdr mutations were scattered across different branches of the network rather than concentrated in a single lineage. This scattered distribution suggests that the mutations have arisen on multiple genetic backgrounds, or have been spread by gene flow into diverse lineages, rather than emerging once and sweeping through a single clone. Multiple independent origins, or repeated introduction through movement, complicate resistance management because the same mutation can reappear even after local suppression, seeded from neighboring populations.

The practical implications of the study are stark. The combination of high gene flow between subtropical and temperate regions and the documented expansion of subtropical mosquito populations into temperate China creates a corridor for the spatial spread of pyrethroid resistance markers. Warmer areas, where kdr frequencies are already elevated in certain codons, may serve as sources of resistant genotypes that disperse northward with the mosquitoes themselves, aided by trade, transport, and a warming climate that extends the season and the latitude over which Aedes albopictus can survive and reproduce. The authors emphasize that climate-responsive vector management, meaning surveillance systems that anticipate shifts in population structure and resistance distribution as temperatures change, is now essential rather than optional.

For a species that thrives in human-modified landscapes, lays desiccation-resistant eggs in artificial containers, and rides global commerce across continents, Aedes albopictus has always been a moving target. What this study adds is a genetic map of that movement within China, and a demonstration that climate is not a passive backdrop but an active architect of vector population structure and resistance evolution. As mean annual temperatures continue to climb, the genetic boundaries documented here are likely to blur further, and the resistance mutations cataloged at codon 1532 and elsewhere in the sodium channel gene will not respect the climatic zones in which they first appeared. The study, funded by the National Natural Science Foundation of China and several Shandong provincial programs, provides both the baseline data and the conceptual framework that Chinese vector control authorities, and their counterparts across the mosquito’s vast invasive range, will need to stay ahead of a resistance problem that is quite literally on the move.

Subject of Research: Spatial genetic structure and climatic drivers of kdr mutation distribution in Aedes albopictus across China's climatic zones

Article Title: Spatial genetic structure and distribution of knockdown resistance (kdr) mutations in Aedes albopictus across different climatic zones of China

Article References: Spatial genetic structure and distribution of knockdown resistance (kdr) mutations in Aedes albopictus across different climatic zones of China. (n.d.). https://doi.org/10.1186/s13071-026-07701-w

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07701-w

Keywords: Aedes albopictus, kdr mutations, insecticide resistance, population genetics, climatic zones, vector control, VGSC gene, COI haplotypes, gene flow, pyrethroid resistance, dengue, China