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Mosquitoes Add Bacteria to Water to Help Larvae Grow: Preprint

Natalia Mesa, PhD

11 Apr 2022

Pregnant mosquito females deploy the microbe Elizabethkingia to speed larval growth; the larvae, in turn, help the bacteria outcompete other strains - image by: the

Aedes aegypti mosquitoes, carriers of many devastating diseases including dengue, Zika, and yellow fever, thrive in a variety of environments. While particularly pesky in jungles and forests, they even flourish in cities, laying eggs in nutrient-poor pools of standing rainwater. This has left scientists wondering: how is it that they survive so well in urban areas?

A preprint published on February 23 in bioRxiv shows that female mosquitoes might be able to sculpt the environment where they lay their eggs, depositing growth-boosting bacteria in the water alongside their young. The researchers say that the findings might help us develop new ways to control the disease-bearing pests. 

“We’ve always wondered how mosquitoes manage to get enough nutrients from such a poor environment,” says study author Marcelo Lorenzo, a biologist at the René Rachou Institute in Minas Gerais, Brazil

Previous research has shown that adult mosquitoes have a symbiotic relationship with some types of bacteria, which help the insects digest sugars and produce more eggs. Pregnant females are also choosy about the pools in which they deposit their young—they lay their eggs in water that smells like certain bacteria, indicating that some strains might help the young survive. Lorenzo and his colleagues thought mosquitoes might be able to transfer these helpful bacteria into water sources that don’t have them, which Lorenzo likens to “preparing a place where the kids will grow.” 

“It’s a really cool study and . . . an important topic,” says Jeff Riffell, a neuroecologist at the University of Washington who was not involved in the work. It raises another question, he adds: “Is there intergenerational transmission in the microbes that could really impact [mosquitoes’] natural history lifespan?” 

Mosquito moms’ bacteria of choice

The researchers first tested if pregnant female Aedes aegypti mosquitoes could deposit the bacteria they already carried on their bodies onto other substrates by having the insects land on sterilized food plates. Mosquitoes transferred bacteria primarily from three genuses: Bacillus, Elizabethkingia, and Serratia.

The team then wanted to test which bacterial strains, if any, mosquitoes deposited into the water alongside eggs. To do this, the researchers placed a cup of water filled with fish food inside a sterile cardboard box. They then ran four different experiments: they introduced either sterilized eggs or unsterilized eggs into the water, or a lone, hungry female mosquito that was either pregnant or not into the box. When they cultured and genetically sequenced the bacteria in the water, they found that bacteria grew in all conditions but the diversity of the bacteria decreased significantly after pregnant females laid their eggs in the water (the diversity was similar in the other conditions). They saw that this decrease in bacterial diversity correlated with the presence of Elizabethkingia.

“This Elizabethkingia was a bacteria that we found in our . . . transmission experiments. And we also found that it is an indicator species” of egg laying, Katherine Mosquera, a molecular biologist at the René Rachou Institute and a coauthor of the study, tells The Scientist. 

By extracting Elizabethkingia from the guts of mosquitoes collected in the field in Rio de Janeiro and then growing eggs in its presence, the researchers found that the bacteria speed up larval development, decreasing the time it takes mosquitoes to hatch and reach adulthood from 180 hours to 171 hours. By hastening larval growth, the bacteria could accelerate mosquitoes’ life cycles and allow populations to grow faster. 

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