Chrysomya albiceps and C. rufifacies (Diptera: Calliphoridae): contribution to an ongoing taxonomic problem

Until recently, the two biologically equivalent blow flies Chrysomya albiceps (Wiedemann) and Chrysomya rufifacies (Macquart) had disjunct distributions outside the Americas; the former was Palaearctic, the latter Australasian and Oriental. The two species are now spreading throughout the Americas and coexist in Argentina. The predatory "hairy" larvae of both species are difficult to separate, which could result in taxonomic errors. New diagnostic characters are presented to differentiate the third instars of the two species. The usefulness of the prostigmatic bristle as a diagnostic taxonomic character in distinguishing adults of these species is questioned.