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U.S. Bureau of Reclamation, P.O. Box 1017, Bismarck, ND 58502

Seasonal abundance and life cycles of chironomids (Diptera:Chronomidae) were studied in four wetlands in the Missouri Coteau region of North Dakota in 1983 and 1984. Larval and adult chironomids were collected during ice-free periods using a metal benthos corer and floating emergence traps.

Two species, Chironomus tentans and Glyptotendipes nr. paropes, dominated the fauna of semipermanent wetlands. These species were present in seasonal wetlands but comprised a smaller percentage of the total. Both species have a one-year life cycle with an annual emergence that begins in late May and continues until early June. No larvae or adults were collected from mid-June through early September. Overwintering of larvae occurs in semipermanent wetlands with most larvae in the fourth instar. Seasonal wetlands become dry in July, and chironomids are absent until the following spring when the ponds refill.

Peak chironomid abundance occurred in spring and fall in semipermanent wetlands and in spring in seasonal ponds. Larval density in spring ranged from 2,400/m² in seasonal wetlands to 78,000/m² in semipermanent wetlands. Numbers of emerging adults followed a similar pattern; highest densities occurred in semipermanent ponds (20,000/m²) with fewer (100/m²) in seasonal ponds.