Morphological and Phenological delimitation ofChironomus prior sp.n. andc. tardussp. n. (Diptera: Chironomidae), sibling species from arctic Alaska

Two discrete periods of adult emergence indicated that an unknown Chironomus population consisted of a pair of sibling species. Morphometric analysis of all life history stages confirmed this hypothesis. The new species Chironomus prior and C. tardus can be distinguished as larvae, pupae, and male and female adults, although many traditional taxonomic characters are of little use. Populations of both species in several ponds emerged with high intraspecific synchrony and consistent seasonal phenology over four summers, and protandrous emergence was often detected. Sexual dimorphism in weight is of the same magnitude as the size difference between these species, and life cycles of sympatric populations appear to differ primarily in the timing of prepupal development and emergence.