Mosquito larvae that grow up in water contaminated with plastic accumulate the litter in their bodies – and some of it remains there even after the larvae emerge as adult flies. The mosquitoes may exacerbate the problem of plastic contamination when they are eaten by animals living on land.
Plastic pollution is ubiquitous in the environment, particularly in water. Birds, fish and other animals living around aquatic systems can ingest small plastic pieces by accident. These microplastics, with a diameter under 5 millimetres, pose a huge threat to the health of marine and freshwater ecosystems as they enter the food web.
But their impact may be spread by animals with a lifecycle that involves living both in water and on land. Many insects, such as mosquitoes and dragonflies, spend their juvenile stages in water but move to land once they become adults. Amanda Callaghan at the University of Reading, UK, and her colleagues suspected these organisms could be vehicles that transport plastics into uncontaminated environments.
To test their idea, Callaghan’s team fed 150 aquatic mosquito larvae with a mixture of food and microplastic beads of different sizes. They examined 15 individuals selected at random while the animals were still in the larval stage, and they looked at another 15 individuals when the animals had turned into flying adult mosquitoes.
The team found microplastics in all 30 individuals. On average, a larva contained over 3000 2-micrometre-wide beads. As the animals matured they gradually stopped consuming microplastics and excreted most of them. Even so, Callaghan still counted about 40 beads on average in adults.
She says the work suggests a new pathway for the dispersal of plastic. For instance, mosquitoes might act as a vector for transferring aquatic microplastics into the guts of the birds and bats that eat insects. “Any organism that feeds on terrestrial life phases of freshwater insects could be impacted by microplastics found in aquatic ecosystems,” she says.