ARS | Publication request: Lack of Pythium aphanidermatum transmission by adult fungus gnats (Bradysia impatiens) and investigation of larval vectoring capacity

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 16, 2009
Publication Date: June 1, 2009
Citation: Braun, S.A., Castrillo, L.A., Sanderson, J.P., Daughtrey, M.L., Wraight, S.P. 2009. Lack of Pythium aphanidermatum transmission by adult fungus gnats (Bradysia impatiens) and investigation of larval vectoring capacity. Phytopathology (Supplement). 99:S16.

Technical Abstract: Studies have provided evidence for transmission of plant pathogens by greenhouse-inhabiting fungus gnats (Bradysia spp.). The goal of this study was to determine if fungus gnats are vectors of Pythium aphanidermatum. In the first of a series of laboratory experiment, 10 adult gnats were released into small chambers containing two P. aphanidermatum-infected and two healthy geranium seedlings. None of the healthy plants became infected after 7 days. In a second experiment, adult gnats were dragged across Pythium culture plates and immersed in solidifying water agar or released into a dish with solidified agar. Pythium colonies developed in 11% of the plates with gnats immersed in agar, but in only 1% of plates where gnats moved freely on an agar surface. In a third experiment, 50 adult female gnats were placed in containers with potting mix and 35 either infected or healthy seedlings. After 24 hours, 20 of the 50 gnats were transferred to a new container with 35 healthy seedlings and 10 were immersed in water agar. None of the seedlings became infected, and no Pythium colonies formed in the agar dishes. Extensive replication of these experiments demonstrated that adult fungus gnats are unlikely aerial vectors of P. aphanidermatum. Experiments are being conducted to correlate levels of inoculum pick-up by adult gnats with real-time PCR. Molecular assays are also being conducted to determine the potential of larvae to vector the pathogen directly or transtadially.