Soybean aphid and cereal aphid (Hemiptera: Aphididae) flight activity and abundance were monitored over three years by suction air traps (SATs) and field observations at various locations across south-western Ontario. Rhopalosiphum padi (L.) was the most abundant cereal aphid species detected by trapping and field observations. In 2004 and 2005, field populations of R. padi were low in the autumn; were found in late May and peaked in early June and July. Field populations of R. padi were observed in south-western Ontario in 2005 before alatae were captured by SATs. Low numbers of Sitobion avenae (F.) were observed in SATs and in field monitoring; Rhopalosiphum maidis (Fitch) were captured abundantly in SATs, but found rarely in winter wheat. In 2004, Aphis glycines were not captured in SATs before September. Two dispersal peaks of A. glycines were observed by SATs in 2005, these occurred during the first weeks of August and September. Whereas the phenology of cereal aphid populations described by SATs and field counts was relatively consistent year to year, soybean aphid populations varied considerably.