Science for All newsletter: Human activity has shaped the genetic diversity of dengue mosquitoes in India

From its roots in Africa, the dengue-spreading mosquito, Aedes aegypti, expanded its range in the 15th century, across the world, aided by the transatlantic slave trade between Africa, America and Europe. And by the late 19th century the insect, with its great environmental adaptability, reached India: in 2024 the country recorded around 2,50,000 dengue cases.

Today, Aedes aegypti, the main vector of chikungunya, yellow fever and Zika too, has spread to almost every environment in India: deserts, tropical forests, urban jungles, and recently, in certain rural areas where they were never found before.

Now for the first time, scientists scoured the country, sampled 126 mosquitoes from 13 regions, to better understand the evolution of this mosquito’s genetic diversity. An understanding of this heterogeneity is vital, said a paper published in Acta Tropica, as genetic diversity also influences the ability of mosquitoes in spreading disease or resisting insecticides.

The authors, from ICMR-National Institute for Research in Environmental Health in Bhopal, also offered surveillance and control strategies across India’s diverse eco-climatic landscape.

As a marker of genetic connection, they used a little part of the insect’s mitochondrial DNA, or the cytochrome c oxidase subunit I (COI). They found that in India, these mosquitoes contained several genetic lineages separated by relatively few DNA changes.

But the biggest contributor in shaping the genetic structure of Aedes aegypti populations has been human-mediated: “the mosquito’s close association with human environments… largely driven by anthropogenic factors, such as urbanization, transport infrastructure, trade, and increased human mobility,” said the paper.

For instance, mosquitoes in highly connected urban centres show greater gene flow compared to those where human movement is restricted.

Interestingly, urban landscapes can both facilitate and constrain mosquito movement. “Certain anthropogenic features, particularly major roads and highways, may function as physical or ecological barriers that limit dispersal [spatially].” The genetic structure in Aedes aegypti vary considerably across geographic regions, reflecting the combined influence of human-assisted dispersal and localised anthropogenic barriers, noted the paper.

Aedes aegypti populations in diverse ecological settings show much variation in morphology, physiology, behaviour, and genetics. Specimens were collected from ecologically diverse regions: Jodhpur, Kota, Sri Ganganagar, Srinagar, Kullu, Hoshiarpur, Lucknow, Nagpur, Raipur, Kolkata, Visakhapatnam, Guwahati, Shillong, Itanagar, and Thiruvananthapuram. The scientists found that genetic differences were significant in certain population pairs collected from Itanagar, Kota and Thiruvananthapuram.

Strains from deserts indicated a shorter lifespan compared to those in coastal areas, and they exhibit significant wing morphological differences in disparate geographies. The paper stated that this investigation of the genetic structure of Aedes aegypti populations could inform future vector surveillance, population genetics studies, and targeted vector control strategies, especially in the context of expanding urbanization and changing climatic conditions.