How Mosquitoes Spread Microplastics

Mosquitoes may spread more than just diseases; they may be unwittingly contaminating ecosystems with microplastics. khlungcenter/Shutterstock

There's little escaping plastic, no matter what kind of creature you are — even a mosquito.

A study published in Biology Letters found mosquito larvae that grow up in water contaminated with microplastics will take the plastics into their bodies and carry it with them as adults.

The findings point to a new way for microplastics to enter ecosystems, worsening an already serious problem.

Plastic vectors

Microplastics, as their name states, are small pieces of plastic that are less than 5 millimeters long. They're sometimes difficult to spot and are the result of either larger pieces of plastic breaking down again and again over time, or they're tiny pieces of polyethylene plastic called microbeads. Regardless, the buildup of microplastics pose a threat to waterways and marine life, and managing them is vital to cleaning our oceans.

The risk posed by microplastics isn't just in the sea, however. Freshwater systems are also at risk, and that's where the mosquitoes come into play.

Mosquitoes spend a portion of their life cycle in water, first as eggs in an egg raft, then as larvae and pupae, before becoming adult mosquitoes capable of flight. As a result, they can take in microplastic thinking its food. Researchers decided to find out if these microplastics persist into adulthood.

The researchers fed 150 mosquito larvae microplastic of different colors and sizes. One group of mosquitoes received fluorescent yellow-green microplastics that were 2 micrometers long, while another group was fed fluorescent dragon green microplastics that were 15 micrometers long. The microplastics were mixed with other legitimate sources of food in two instances, while a third group received a 1:1 mix of both types of plastics. A final group received no microplastics at all.

Mosquito larvae underneath water
Mosquito larvae consume microplastics under the assumption that it's food. James Gathany/CDC/Wikimedia Commons

"Larvae are filter feeders that waft little combs towards their mouths, so they can't actually distinguish between a bit of plastic and a bit of food," Amanda Callaghan at the University of Reading and one of the researchers for the study, told The Guardian. "They eat algae, which are more or less the same size as these microplastics."

Naturally, the group that didn't receive any microplastics showed no occurrences of microplastics when analyzed later. But the other three groups all showed varying levels of microplastics in the equivalent of the mosquito kidney when they reached adulthood. Larvae did eventually stop eating microplastics at a certain age. The size of the microplastics made a difference in how much was retained by an adult, with the 15-micrometer beads more likely to be expelled over time than the 2-micrometer beads.

These findings indicate that mosquitoes can be carriers of plastic pollution. When consumed by predators like birds or bats, not to mention other predatory insects, the microplastics in the mosquitoes transfer to the predators, keeping the plastic pollution alive and well in ecosystems like rivers and lakes.

"This is a new pathway to get plastics up in the air and expose animals that are not normally exposed," said Callaghan. "We don't know what the impact will be."