Description of the larvae of Cricotopus festivellus (Kieffer 1906) and Cricotopus diversus (Boesel 1983) with keys to discrimination of larval, pupal and adult stages (Diptera: Chironomidae)

The larva of two very similar Cricotopus species are described for the first time: Cricotopus diversus (Nearctic) and C. festivellus, new description (West Palaearctic). Confusion can arise depending on the source used for identification of Nearctic Cricotopus. The key of LeSage and Harrison (1980) treated adults and exuviae of C. diversus as variants of C. festivellus. Subsequently Boesel (1983) formally described C. diversus and included it in keys to adult Cricotopus of the eastern United States. Adults of these species have been distinguished by consistent differences in the pigmentation on the fourth and fifth abdominal tergites; we also confirmed differences in the structure of the male hypopygium. Keys to larvae, pupal exuviae and adult males are presented. Publicly available DNA barcode records document C. diversus populations in the Mid-Atlantic US and Ontario, Canada, whereas barcode records of C. festivellus were available only for Scandinavia, although this species is widely distributed in Western Europe. These two species are genetically distinct, with 13% mean difference in barcode sequence between species. Both species are reported from rivers and lakes of relatively good water quality.