Natural occurrence of Fusarium graminearum on adult wheat midge and transmission to wheat spikes

To determine the presence of Fusarium graminearum on wheat midges (Sitodiplosis mosellana), adult females were captured from a spring wheat (Triticum aestivum) field near Quebec City (Canada) and plated on potato dextrose agar. A mouth aspirator was used to capture live midges in sterile vials. F. graminearum was isolated from 2.1, 5.3 and 0.6% of midges captured in 1997, 1998 and 1999, respectively whereas other Fusarium spp. were isolated from 2.5% of the midges in 1999 and from none in 1997 and 1998. To verify that wheat midges can effectively transmit Fusarium spores to wheat spikes, glasshouse-grown wheat plants were exposed for five days to adult female wheat midges previously inoculated in the laboratory with F. graminearum macroconidia and also to uninoculated control wheat midges. At dough stage, the fungus was recovered from 29% of the spikes of plants that had been exposed to inoculated midges, and from none of the other plants. This is the first report of the natural occurrence of F. graminearum, and other Fusarium spp., on female adult wheat midges and of its transmission to wheat spikes by the midge.