Drive up to a mushroom farm, open the car door, and you’ll understand why facilities like this one operate in rural areas. An overwhelming odor of manure emanates from compost piles scattered around the farm and from inside mushroom houses — the long, squat, wood and concrete structures where mushrooms are grown.
“If there was a steak in that house, we wouldn’t be able to smell it, because all we would smell is poop,” says Kevin Cloonan, a doctoral student in Tom Baker’s lab. “But the fungus gnat’s sense of smell is so precise they can sort it all out.”
Fungus gnats, Lycoriella ingenua, are small enough to squeeze into a mushroom house through the tiniest of crevices. Although adult gnats don’t damage the crop directly, they can transfer a devastating fungal pathogen that lays waste to the tender young mushrooms. Even if a female isn’t carrying this pathogen, she spawns about 200 larvae that devour belowground mushroom parts and gobble up compost nutrients that the mushrooms need to grow. An infestation of fungus gnats can cut a mushroom harvest by 70 percent — a huge hit to an industry that contributes $2 billion to the Pennsylvania economy each year.
Insecticides that easily controlled these pests have been banned one by one over the years. “Now we’re starting to see a reemergence of these gnats, but we don’t know much about them,” says Cloonan. He is looking for a way to turn their acute sense of smell against them — to prevent their entry into mushroom houses or capture them if they do sneak in.