Black fly spraying: Some things to know about its environmental impact

Written by on June 30, 2021

 Black fly spraying: Some things to know about its environmental impact

By Megan Frank

June 30, 2021

“Blood-sucking black fly (Simuliidae)” by servitude is licensed under CC BY-NC 2.0

Black fly spraying starts June 30 along the Lehigh and Delaware rivers. 

Listen to the story.

The aerial sprays span from Portland, Pa. to Trenton, N.J., and along the Lehigh River from Palmerton to Easton. 

Black flies or biting gnats are considered a pest that can put a damper on outdoor recreation in Pennsylvania. That’s why the state is spraying waterways with Vectobac 12 AS or B.t.i., a thick brown liquid that resembles chocolate milk. It’s also got a fishy odor.

Marten Edwards is a professor of biology at Muhlenberg College. He says the spray is made from bacteria that originates in soil. 

“The bacteria is a very effective way of killing the fly larvae without affecting anything else,” Edwards says, “Because this bacteria, called Bacillus thuringiensis israelensis, is very specific to just those.”

The spray is non-toxic to humans and wildlife, Edwards says, and degrades quickly in the environment. Overall, he says its impact on the environment is minimal. 

“It’s not a general insecticide that would affect fish or other vertebrates or even other insects,” he says, “This is a soil bacterium and it kills certain types of flies. Not all flies, only flies that are related to mosquitos. In terms of the food chain and ability to sustain fish, I would say it would have a minimal impact.”

The helicopter being used is light gray with red and blue stripes. It will circle targeted areas before applications to avoid spraying people.

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