Leafcutter Bees Using Plastic Might Not Be As Good as Previously Thought

With the mounting problem of plastics getting everywhere in the environment, people have been quick to jump at any possible solution - including the use of leafcutter bees. However, a new study suggests that the leafcutter bee solution may not be as good as previously thought.

Efforts to manage plastic waste have ranged from the development of catalysts that break down plastic into its more basic parts to the possibility of insects digesting them. In 2019, a team of researchers from Argentina submitted the first global report of a bee making its nest with plastic.

Now, a recent study from Utah State University finds additional evidence of leafcutter bees using plastic to construct its nest. Additionally, it examines the possible adverse effects of plastic use, especially for solitary bees in this species.

Easily Recognizable

The team, composed of evolutionary ecologist Joseph Wilson, undergrad researcher Sussy Jones, naturalist and former math teacher Scott McCleve, and National Bee Services scientist Olivia Carril, published their report in the journal Science Matters.

"Leaf-cutter bees are among the most recognizable of solitary bees, because of their habit of cutting circles out of leaves to build their cylindrical nests," Wilson explains. He added that they began investigating after receiving reports of leafcutters using plastic materials, especially plastic flagging used mostly in agriculture and construction.

Wilson, a biology associate professor at USU-Tooele, adds that these bees using plastic could affect the "dynamics and environment" of the nest cells constructed since plastic does not "breathe" like the natural materials previously used, like leaves. He also shared that back in the 1970s, a researcher allowed leafcutter bees to nest among plastic straws. It resulted in ninety percent of the bees' offspring dying because of fungal growth. Wilson explained that the plastic did not allow gas exchange and trapped moisture, encouraging fungal growth.

Wilson suggests using fabric ribbons, made from natural fibers, instead of plastic flagging. The use of biodegradable material will make for a natural and breathable nest cell and spare the bees from the moisture-trapping traits of plastic.

Finding Round Cuts in Leaves and Plastic Flags

Researchers report that most bee species are solitary, building their nests in cavities in the ground or inside tunnels in wood. Specifically, leafcutter bees, members of the genus Megachile, are known for cutting circular pieces of leaves as nest cells.

Researchers reported yellow and orange plastic flaggings found in Douglas, Arizona that had the circular cuts consistent with those made by leafcutter bees in leaves. They reported the first observation made in July 2009, with a following observation recorded in September 2019.

A previous study suggested that the bees' increasing plastic use might be an "ecologically adaptive trait" in response to increasing plastic wastes from human-related activity. However, the USU team does not entirely concur with this conclusion, arguing that an ecological adaptation should serve to increase the fitness of the species exhibiting the new trait. Without further studies to confirm the positive or negative effect of plastics on leafcutter bees, researchers say that calling the plastic use of the bees an ecological adaptation might be too early.