With deforestation malaria mosquitoes shifting to rice fields in Meghalaya

Malaria-carrying mosquitoes in India are shifting from forests to rice fields, impacting the battle against the disease. Traditionally, mosquitoes like Anopheles baimaii and An. minimus, linked to forests, were major malaria vectors in the northeastern region. With deforestation, increased rice cultivation, and the use of insecticide-treated nets, new species are becoming dominant.

Mosquitoes shift from forests to fields

A study conducted in the northeastern state of Meghalaya has revealed that the composition of these malaria-spreading Anopheles mosquitoes is changing. This shift is believed to be linked to deforestation, increased rice cultivation, and the widespread use of mosquito nets.

In Meghalaya state, where malaria is sporadic, a study found that species like An. maculatus and An. pseudowillmori are now prevalent, thriving in rice fields. This shift highlights the importance of adapting malaria control strategies to changing mosquito habitats.

Researchers collected mosquitoes from three regions in Meghalaya, near Nonglang in the West Khasi Hills (WKH), and Barato and Nartiang in the West Jaintia Hills (WJH). They used CDC miniature light traps set near houses and also made collections in cattle sheds. Larvae were opportunistically collected from various habitats, mainly in rice fields.

The study, conducted between August 2018 and April 2021, involved 1,389 adult mosquito collections and 144 larval collections. Morphological identification was applied to the specimens before storing them for later DNA extraction and molecular identification. Relevant Institutional Review Boards approved the study.

Study reveals malaria mosquitoes’ habitat shift

The research team included the study as part of a larger project on malaria, which focuses on the disease’s spread, the types of mosquito species in the state, and the link between people’s behaviours and the disease.

In Meghalaya, there are more than 24 species of Anopheles mosquitoes. People usually find two species, Anopheles baimaii and Anopheles minimus, in forests and consider them the main carriers of malaria in the northeast.

However, the study found that these two species were rare, while four other species were common and found in rice fields. This suggests that rice fields might be creating conditions that allow Anopheles maculatus and Anopheles pseudowillmori to thrive and potentially spread malaria.

When the researchers started the study, malaria rates in Meghalaya were high, but they dropped significantly during the research. This led the researchers to shift their focus to understanding if the main carriers were decreasing and what other carriers might be playing a role in spreading the disease.

The researchers identified 19 species from 2,575 Anopheles samples collected from two districts. Ten of these species were breeding in rice fields. They found large numbers of Anopheles maculatus, Anopheles pseudowillmori, and Anopheles jeyporiensis breeding in rice fields. Given the large area of rice fields in Meghalaya, they could be important breeding grounds for mosquitoes.

Study identifies mosquito species in Meghalaya

The researchers developed a reliable method for identifying mosquito species in Meghalaya using molecular techniques. They faced challenges with misidentifications in public databases and established a comprehensive approach using COI DNA barcoding and maximum-likelihood trees for species identification.

The study focused on Anopheles mosquitoes in different taxonomic groups. For instance, An. annularis from Meghalaya grouped with sequences from Pakistan, Sri Lanka, and Northern India. An. maculatus from Meghalaya was conspecific with counterparts in Southeast Asia.

The study identified distinct clades within species, suggesting possible new species. The researchers used GenBank and BOLD databases for comparisons, addressing issues of misidentification and confirming species identities.

The study identified various mosquito species in Meghalaya, focusing on Anopheles mosquitoes.We employed molecular methods for reliable species identification, which revealed distinct genetic clusters. For example, An. jeyporiensis from Meghalaya differed from its counterparts in Odisha, indicating distinct species.

An. culicifacies from Meghalaya was genetically close to Odisha, suggesting possible regional variations. The An. hyrcanus group exhibited two distinct clades, confirming species identity. Overall, we identified 19 Anopheles species, with some unique to specific regions.

Notably, 10 out of 19 species were found breeding in rice fields. Genetic diversity analysis highlighted variations among species, providing insights into their populations and potential implications for malaria transmission.

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