Transstadial transmission of Pythium in Bradysia impatiens (Diptera: Sciaridae) and investigation of fungus gnat vectoring capacity

Studies have provided evidence for transmission of plant pathogenic fungi by greenhouse-inhabiting fungus gnats (Bradysia spp.), and observations have also pointed to a possible correlation between Bradysia fungus gnat infestations and root rot disease outbreaks caused by oomycete pathogens. The goal of this study was to determine if fungus gnats are vectors of Pythium aphanidermatum and to examine the impact of morphological variability in pathogen strains on transmissibility. An additional objective was to determine if P. aphanidermatum could pass from the guts of larval fungus gnats into the pupal and adult stages and ultimately be transmitted by adult gnats. Adult fungus gnats did not pick up infectious propagules of Pythium from diseased plants and transmit them to healthy plants. Species-specific primers and a probe for real-time PCR were developed to detect the presence of P. aphanidermatum DNA in gnat tissue samples. DNA of two strains of P. aphanidermatum was detected in fungus gnat larvae and pupae; however, no DNA of either strain was detected in adult fungus gnats. Experiments in progress are investigating the capacity of fungus gnat larvae to vector Pythium. These findings enhance our understanding of the association between fungus gnats and Pythium spp. in greenhouse floriculture.