Page Banner

United States Department of Agriculture

Agricultural Research Service


Location: Emerging Pests and Pathogens Research

Title: Fungus gnats and Pythium in the attack on greenhouse plants: conspirators or just cohabitants

item Braun, Sarah
item Wraight, Stephen - Steve
item Castrillo, Louela
item Daughtrey, Margery
item Sanderson, John

Submitted to: Growertalks
Publication Type: Trade Journal
Publication Acceptance Date: 8/26/2012
Publication Date: 9/1/2012
Citation: Braun, S.E., Wraight, S.P., Castrillo, L.A., Daughtrey, M.L., Sanderson, J.P. 2012. Fungus gnats and Pythium in the attack on greenhouse plants: conspirators or just cohabitants. Growertalks. 76(5):98-100.

Interpretive Summary:

Technical Abstract: Research conducted by collaborating Cornell University and USDA-ARS scientists investigated the potential for fungus gnats to vector Pythium root-rot pathogens. Fungus gnat larvae readily consumed Pythium oospores; the spores survived passage through the larval gut and, upon defecation, were able to germinate and infect plants. Fungus gnat larvae, however, are short-lived insects that rarely leave their favored habitats in moist soil or compost. So, they are unlikely to account for transmission of Pythium between greenhouses, between benches within a greenhouse, or even between separated pots on a greenhouse bench. In other experiments, adult fungus gnats failed to pick up infectious Pythium from diseased plants and transmit it to healthy plants. Pythium was never detected in or on the bodies of the adult gnats. A molecular procedure developed to detect Pythium in fungus gnat tissue samples revealed that after Pythium was fed to fungus gnat larvae, large amounts of the pathogen were detectable in the larval guts, and small amounts could be detected in the pupae; however, none was detected in the adults. Thus, even though fungus gnat larvae ingested Pythium, it was not passed to the adult stage, and the adults did not become carriers. Additional experiments showed that adult female fungus gnats are highly attracted to microbial activity associated with diseased and decaying plants. This research indicates that the reason fungus gnats are commonly found on Pythium-infected plants is that the adults are attracted to the diseased roots and stimulated to lay their eggs in the soil: fungus gnats do not transmit the disease to the plants.

Last Modified: 06/26/2017
Footer Content Back to Top of Page