Mushroom phorid flies are an annoying problem for growers of one of Pennsylvania’s most valuable crops.

The tiny insects damage mushrooms, limit yields and make harvesting a hassle.


Penn State photos courtesy of Michael Wolfin Mush 1 This simple screen over a mushroom growing room window is loaded with an environmentally friendly pesticide that kills mushroom phorid flies by the millions.

The swarming flies also irk the neighbors, entering homes by the thousands as they leave mushroom houses in search of mates.

Mushrooms aren’t going to leave Chester County, which produces more than two-thirds of the nation’s mushrooms, worth $550 million last year. But something has to be done about phorid flies.

The answer could be low-tech and inexpensive, as Penn State entomologist Tom Baker explained during a Jan. 11 video meeting as part of the Pennsylvania Farm Show (above).

Baker spoke during the session “Cultivating Innovation,” which was in keeping with the 2021 Farm Show’s overall theme, “Cultivating Tomorrow.”

The answer to the phorid fly problem begins not in Kennett Square but in rural African villages where mosquitoes transmit malaria from person to person.

Scientists at Penn State’s Huck Institutes of the Life Sciences were part of an international search for a way to combat the mosquitoes.

The technology they came up with is astoundingly effective and astoundingly cheap. It is a short tube with an insecticide-laden mesh that kills mosquitoes before they can draw blood from a sleeping human.

The tubes are placed high in the interior walls of villagers’ homes. The tubes pass through the walls and exit the home just under the eaves of the structure. They are called eave tubes, and they are spaced 2 or 3 feet apart.

Air circulates through a home and is heated by the bodies of its inhabitants as they go about their lives. The heated air rises and exits through the eave tubes, carrying with it the scent of humans. Mosquitoes are attracted to this scent, enter the tubes, encounter the insecticidal mesh, and die.

In some villages, eave tubes have been responsible for a 90% drop in mosquito population. This story is told online in a couple of informative videos. 

Phorid flies, of course, are a less dramatic story than killer mosquitoes. Their threat is to human comfort rather than human health.

They really weren’t a problem in the U.S. until 2012, when the use of the insecticide diazinon in mushrooms was disallowed. The flies flourished, feeding on mycelium, which is the mushrooms’ “root” system.

The Penn State study was performed at SherRockee Mushroom Farms, which has 34 growing rooms at its Lincoln University location in Chester County.

Each growing room has a window, which is where the magic happens. We contacted Baker for details, and he referred us to Michael Wolfin, one of the scientists who helped conduct the study,

Here’s what Wolfin had to say:

“We’re not exactly using eave tube technology, though we are trying to achieve the same effect. Our concept is similar; we use the fly’s natural behaviors against it.

“Newly emerged flies inside the mushroom growing rooms want to go outside to mate, and flies that have mated outside the growing rooms want to go inside to lay eggs. SherRockee Farms has a vent window in each growing room. Flies moved into and out of the rooms through the windows.

“The inside flies try to go through the window because they are attracted to the sunlight, and the outside flies try to go through the window because they are following the odor from inside the growing rooms. We covered these windows with electrostatic screening to serve as a barrier. The screening is, I believe, a kind of plastic that our pesticide sticks to.

“We used a wettable dust pesticide that consists of a mix of essential oils — mostly thyme oil, I think — and silica as the pesticide. This material is deemed generally safe under federal pesticide regulations and doesn’t require labeling. Anyway, because it’s applied only to the screens, it doesn’t go onto the crop.”

Wolfin said the study began in September, and the screens’ effect was immediate. The primary goal of the screens was to keep flies from exiting the growing rooms. Two weeks after the first screens were installed, there were millions of dead flies under each window inside the growing rooms. Any mated females that would have tried to get back into the rooms to lay their eggs were killed as well.

As the study progressed, fewer and fewer fly corpses accumulated under the windows. By the time of the Farm Show webinar, Baker felt confident enough to call the study a “proof of concept.”

The research will continue as the Penn State team experiments with different techniques and pesticides. Wolfin and Baker are confident Penn State’s window treatments will at least be considered by other growers.

Lancaster Farming


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