Resistance to wheat midge (Diptera: Cecidomyiidae) in winter wheat and the origins of resistance in spring wheat (Poaceae)

Nine winter wheat cultivars ( Triticum aestivum Linnaeus) (Poaceae) were the source of the Sm1 gene for resistance to wheat midge, Sitodiplosis mosellana (Gehin) (Diptera: Cecidomyiidae), in spring wheat. All nine showed antibiosis characteristic of Sm1 , as expected. They also showed oviposition deterrence and reduced hatch, which contributed to overall resistance. The overall level of resistance of the nine winter wheat cultivars was usually lower than that of resistant spring wheat lines in laboratory trials, but equally high in a field trial. Five of seven other North American winter wheat cultivars also showed resistance. Three of these were grown in the 1920s and earlier, before wheat varieties were officially registered. One of these, “Mediterranean”, came from Europe in the 1880s and may be the origin of Sm1 in North America. Two of 11 Chinese winter wheat lines showed resistance to wheat midge but at a lower level than that characteristic of Sm1 . Widespread resistance in North American winter wheat cultivars was unexpected because wheat midge has not been a pest of winter wheat for many decades. North American winter wheat cultivars can provide sources of resistance to wheat midge, particularly high levels of oviposition deterrence as exhibited by “Goens” and “Rawhide”.