Mosquito Map: Resistance Genes and Climate Shift Malaria Vectors in Laos Borderlands

Malaria elimination in Southeast Asia has long been framed as a race between drugs and parasites, but a new study argues that the mosquitoes themselves deserve far closer scrutiny. In research published in the journal Parasites & Vectors, a team led by scientists at Naval Medical University in Shanghai and the Yunnan Institute of Parasitic Diseases set out to answer three deceptively simple questions about the anopheline mosquitoes of the Lao People’s Democratic Republic: which species are actually present at the country’s porous borders, whether they carry mutations conferring resistance to the insecticides used against them, and where climate change might take them next. The answers, drawn from three years of fieldwork and a battery of molecular and computational tools, paint a picture of a vector community that is more diverse, more genetically primed for resistance, and potentially more geographically mobile than many elimination programs have assumed.

The field component of the study took place at four transboundary sampling sites spanning the borders of Laos, Cambodia and Thailand, a region where human movement, trade and seasonal labor constantly shuffle malaria parasites across national boundaries. Between 2017 and 2019, the researchers deployed battery-operated CDC light traps for overnight collections, a method that captures host-seeking mosquitoes without requiring human landing catches and that can be standardized across sites with different ecologies and levels of health infrastructure. In total, 650 Anopheles specimens were gathered. Rather than relying on the wing markings and leg patterns that have traditionally guided morphological identification in Southeast Asia, a region notorious for cryptic species complexes, the team sequenced two molecular markers for each mosquito: the cytochrome c oxidase subunit 2 gene, carried in the mitochondria, and the internal transcribed spacer 2 region, found in the nuclear genome. Using both markers in combination allowed the researchers to resolve species boundaries with far greater confidence than either marker alone, a critical step because misidentified vectors can lead elimination programs to target the wrong insects with the wrong tools.

The molecular inventory revealed fifteen Anopheles species across the four sites, and the composition of these assemblages shifted markedly from location to location. Two species dominated the overall catch: Anopheles kochi, which accounted for 38.46 percent of identified specimens, and Anopheles sinensis, which made up 21.69 percent. This spatial heterogeneity matters operationally. A national malaria control program that assumes a single dominant vector across its territory may find that bed net distribution, indoor residual spraying or larval source management calibrated for one species misses the breeding habits and biting behaviors of another. In the Greater Mekong Subregion, where residual malaria transmission increasingly happens outdoors, among forest goers, and in cattle sheds rather than inside sprayed houses, knowing exactly which anophelines are present at which border crossing is a prerequisite for designing interventions that actually reach them.

Among the collected mosquitoes were eighteen individuals of Anopheles peditaeniatus, a member of the Anopheles hyrcanus group, and it was this species that became the focus of the study’s resistance analysis. The researchers targeted two of the most important known mutations in mosquito insecticide genetics. The first is the knockdown resistance mutation, or kdr, at position L1014F in the voltage-gated sodium channel gene, the classic mechanism by which mosquitoes survive pyrethroid exposure, the chemical class that coats the vast majority of long-lasting insecticide-treated nets distributed worldwide. The second is the G119S substitution in the acetylcholinesterase-1 gene, abbreviated ace-1, which confers resistance to organophosphates and carbamates by altering the very enzyme those insecticides are designed to inhibit. Using targeted sequencing of these two loci, the team genotyped their An. peditaeniatus specimens with single-nucleotide precision.

The results were striking. Not a single kdr L1014F mutation was detected in any of the tested species, a reassuring signal that pyrethroid resistance via this particular mechanism has not yet taken hold in these populations. The ace-1 locus told a very different story. Of the eighteen An. peditaeniatus individuals genotyped, only five, or 27.8 percent, were homozygous for the wild-type susceptible allele, designated GG. Twelve individuals, a full 66.7 percent, were heterozygous carriers of the resistance allele, designated GS, and one individual, 5.6 percent, was homozygous resistant, designated SS. In population genetics terms, this means the resistance allele is already circulating at an allele frequency of roughly 39 percent in this small sample, and the presence of a homozygous resistant individual demonstrates that the allele is viable in the field, not merely an occasional immigrant or laboratory artifact. Because the G119S mutation is known to impose fitness costs on mosquitoes in the absence of insecticide pressure, its high frequency suggests that organophosphate or carbamate exposure, whether from agricultural spraying, public health campaigns or both, has been selecting for it in these border populations.

The authors draw a direct operational conclusion from this finding: insecticide rotation strategies in the region need to be tailored, not generic. If a control program rotates from pyrethroids to organophosphates assuming a clean resistance slate, it may walk directly into a population already carrying ace-1 resistance at meaningful frequency. Conversely, the absence of kdr mutations suggests pyrethroid-based tools such as long-lasting insecticide-treated nets, abbreviated LLINs and central to malaria control across the Greater Mekong Subregion, may retain their efficacy for now, provided resistance is monitored continuously rather than assumed. The study’s genotyping framework, built on targeted sequencing of just two loci, is cheap enough to be folded into routine surveillance, turning each mosquito collection into an early warning system for resistance emergence.

The third pillar of the study looked forward rather than backward, asking where An. peditaeniatus will be able to live as the climate warms. The researchers employed maximum entropy modeling, known as MaxEnt, a widely used ecological niche modeling technique that estimates a species’ potential geographic distribution by relating known occurrence records to environmental variables. The model was trained on 108 occurrence points for the species and 19 bioclimatic variables drawn from the WorldClim version 2.1 database at a spatial resolution of 2.5 arc minutes, roughly 4.6 kilometers at the equator. The baseline climate layer represented the period from 1970 to 2000, while future projections covered 2021 to 2040 under multiple Shared Socioeconomic Pathway scenarios, abbreviated SSPs, which describe different combinations of greenhouse gas trajectories and socioeconomic development. The climate model used to generate these future layers was the Beijing Climate Center Climate System Model version 2-Medium Resolution, or BCC-CSM2-MR, one of the models contributing to the most recent international climate assessments.

The MaxEnt models performed well by the standard area-under-the-curve metric, and they identified three climatic variables as the principal drivers of habitat suitability for An. peditaeniatus. The first is BIO6, the minimum temperature of the coldest month, which essentially defines the thermal floor below which the species cannot survive the winter. The second is BIO18, the precipitation of the warmest quarter, a proxy for the availability of the standing water habitats in which anopheline larvae develop during the hottest part of the year. The third is BIO4, temperature seasonality, which captures the annual amplitude of thermal variation and shapes the timing and duration of breeding seasons. Together, these variables describe a species whose fortunes hinge on the intersection of warmth and wetness, precisely the combination that climate change is reshaping most dramatically across monsoon Asia.

The projected maps diverged sharply depending on the emissions pathway. Under the intermediate SSP245, the pessimistic SSP370 and the high-emission SSP585 scenarios, highly suitable habitat for An. peditaeniatus expanded markedly in the tri-border region where Laos, Cambodia and Thailand meet, suggesting that under most plausible futures, this vector’s operational range will grow rather than shrink in the coming two decades. Under the most ambitious mitigation scenario, SSP126, the pattern reversed: suitable habitat fragmented, with core suitable areas contracting to major wetlands. The contrast is a vivid illustration of how climate policy and malaria policy are entangled. Every fraction of a degree of avoided warming, in this model, translates directly into less contiguous territory for a proven malaria vector, while unmitigated warming hands the mosquito new ground precisely where three national control programs must coordinate their efforts.

The study’s authors argue that these three lines of evidence, species inventories, resistance genotyping and habitat projections, should be integrated into cross-border surveillance systems rather than treated as separate academic exercises. Laos has made remarkable progress against malaria over the past two decades, aided by artemisinin-based combination therapies, insecticide-treated nets and community-level village health workers, yet transmission persists in a heterogeneous pattern fueled by mobile and migrant populations, forest exposure and imported infections from neighboring countries. In that context, a map of where An. peditaeniatus habitat is expanding, overlaid with data on which mosquitoes carry which resistance alleles, becomes a targeting tool: it tells programs where to intensify monitoring, which insecticide classes to deploy or avoid, and where cross-border coordination with Cambodian and Thai counterparts will matter most. As climate change redraws the boundaries of vector habitat across the Greater Mekong Subregion, the study suggests that the countries that treat mosquito genetics and ecological forecasting as routine surveillance infrastructure, rather than occasional research projects, will be the ones that reach elimination first.

Subject of Research: Anopheline species diversity, ace-1 insecticide resistance, and climate-driven habitat suitability modeling of Anopheles peditaeniatus in Lao PDR border regions

Article Title: Anopheline diversity, ace-1 resistance and climate-driven habitat projections for Anopheles peditaeniatus in Lao PDR border regions

Article References: Zhang, J., Zhao, X., Yan, Z., Yang, R., Wu, L., Luo, C., Zhang, C., & Zhang, Y. (2026). Anopheline diversity, ace-1 resistance and climate-driven habitat projections for Anopheles peditaeniatus in Lao PDR border regions. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07592-x

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07592-x

Keywords: Anopheles peditaeniatus, malaria, insecticide resistance, ace-1 G119S, kdr mutation, MaxEnt modeling, climate change, Lao PDR, Greater Mekong Subregion, Anopheles hyrcanus group, habitat suitability, vector surveillance