Although best known because of their importance as agricultural pests, Tephritidae are also worthy of attention as generally attractive flies with intricate wing patterns and interesting mating and defensive behaviours. The taxonomy of the North American species is relatively well known, and the entire North American fauna was recently reviewed by Foote et al. (1993), who included distributional data and maps showing 42 species and 19 genera ranging into Ontario. We here review the Ontario fauna, primarily on the basis of specimens in the University of Guelph Insect Collection (DEBU), the Canadian National Collection (CNCI), the Lyman Entomological Museum (LEM), and the Royal Ontario Museum (ROME). The Ontario records in Foote et al. (1993) represent only about 60% of the fauna; we now recognise 67 species and 30 genera in the province, significantly more than previously thought but still a manageable number compared to the roughly 4550 valid species within almost 500 genera of Tephritidae described worldwide.

The keys in Foote et al. (1993) are thorough and richly illustrated, but are necessarily complex because they cover all 300 North American tephritid species. The keys herein are relatively simple because they are limited to the 73 species that occur, or are likely to occur, in the province of Ontario. More than 700 colour photographs are used to support a technical key adapted from Foote et al. (1993), as well as a field key designed for the identification of genera using a hand lens or macro photographs.

Although the keys included in this paper use a variety of characters, wing patterns are particularly important, and colour wing photos are included for all species. Whole specimen photographs are also included, since many species have a distinctive habitus that can confirm identifications. Host data has been included wherever possible, as host information can often expedite speedy and reliable identification.

DNA barcoding (Hebert et al. 2003), a recently developed approach to animal identification, is of potential value to the rapid detection of pest tephritid species, especially immature life stages that may be difficult to identify using morphological characters. DNA barcodes (standardised cytochrome c oxidase 1 sequences) are provided here for 40 of the the 67 Ontario tephritid species as an adjunct to traditional morphological tools for tephritid identification. In order to identify any unknown specimen, barcoding requires a reference database of known DNA sequences for comparison; the barcodes included herein contribute to that reference database for the Tephritidae.