Researchers found high abundance of Aedes mosquito larvae in microhabitats such as discarded grinding stones in Bengaluru. Credit: Farah Ishtiaq

An outdoor surveillance study in Bengaluru has found high abundance of Aedes mosquito larvae in microhabitats such as discarded grinding stone, coconut shells and man-made containers1.

Such unplanned waste disposal contributes to localised dengue outbreaks in the city, says a research team at the Tata Institute for Genetics and Society.

The scientists examined the prevalence of mosquito larvae and the abundance of mosquito species during four seasons – dry, pre-monsoon, monsoon and post-monsoon – across various habitats.

They surveyed microhabitats including plant axils, tree holes, coconut shells, discarded plastic containers, grinding stones and tyres, plant pots and stagnant water, and macrohabitats such as barren land, lakes, plantations, and high and low density areas.

The team, led by Farah Ishtiaq, collected 1,619 mosquito larvae that represented 16 mosquito species. Aedes aegypti was the dominant species, followed by Aedes albopictus, Culex quinquefasciatus and Anopheles stephensi.

Both Aedes species were prevalent in discarded grinding stones but showed negative association with stagnant water. Discarded tyres only showed the presence of A. aegypti larvae.

Larval prevalence was not affected by the type of macrohabitat or water pH, but decreased with an increase in temperature. Among microhabitats, discarded containers had the most abundant larvae, followed by coconut shells and plant pots. The least abundant were plant axils and tree holes.

Mosquitoes that emerged from the grinding stones were larger than the ones from plastic containers or coconut shells. Larger females can fly farther; smaller ones which require multiple meals can only fly short distances.

The study shows that neighbourhood surveillance in public places can help real-time forecasting of dengue outbreaks in urban areas, the researchers say.