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gnats coming out of commercial office AC ducts

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From: Kimberly Weber
San Diego, AZ
As a Property Manager for Commercial Office buildings, one of the Office Suites has dead gnats (black, very small with wings) coming out of the AC duct-work and dropping on desks. There is no food or garbage in the Suite and no floor drains or water source. Any ideas where the gnats might be coming from? I have not seen water leaks on the drop ceiling tiles or around the AC units that are also above the drop ceiling tiles. Pest Control Company has not found the source of the problem. Any suggestions?

Extension Message
From: Richard Hentschel
Extension Educator, Horticulture
DuPage/Kane/Kendall Unit
These are likely to be a kind of fungus gnat. Fungus gnats as the name implies they feed on fungus found in the system. They do not need standing water, just enough moisture to allow fungus to grow and which the larvae feed upon. Depending on the species they can go from egg to adult in 8 to 12 days. Duct work that has settled and allows for moisture to remain and grow fungus is enough. Systems that no longer drain completely can also be a problem.

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