Composition and phenology of Chironomidae (Diptera) from an intermittent stream in Kansas

Abstract

Taxonomic composition and emergence phenologies of Chironomidae inhabiting an intermittent stream in eastern Kansas were determined over a three year period using collections of surface-floating pupal exuviae. Duration of surface flows varied substantially over the period of study, ranging from 266 days in 1993-1994 to 215 days in 1994-1995 and 137 days in 1995-1996. The stream bed dried completely during summer and/or fall in all three years. Fifty-five species emerged from the stream during the study, with Orthocladiinae having the greatest species richness (26 taxa), followed by Chironomini (14), Tanytarsini (10) and Tanypodinae (5). No Diamesinae, Prodiamesinae, Podonominae nor Pseudochironomini were present. Annual emergence varied considerably with 29 species in 1993-1994, 49 species in 1994-1995 and only 6 species in 1995-1996. During the first two years the phenological patterns resembled those expected for small, cooler-water streams, with winter and early spring emergence dominated by Orthocladiinae. The peak in emergence of Orthocladiinae was followed by a small but distinct increase in Tanytarsini in early spring, then Chironomini became more common as water temperatures increased and surface discharge declined. The timing of emergence was strongly influenced by the date at which surface discharge began, and resulted in about a 2 month shift between 1993-1994 and 1994-1995. Averaged over the three years of the study, emergence was dominated by seven species: Corynoneura sp. 1, Corynoneura sp. 2, Orthocladius lapponicus, Parametriocnemus cf. lundbecki, Thienemanniella sp., Larsia decolorata, and Zavrelimyia sinuosa. The remaining species consisted of a mixture of species common in perennial streams plus (1) winter/early spring emerging species that likely persist in the stream in desiccation-resistant stages or in the hyporheic during periods of intermittency, (2) semiaquatic or semiterrestrial species, and (3) species of genera in which larvae are known to produce cocoons and diapause, or occur in moist sediments. We estimate that as many as 60 % of the species of Chironomidae are facultative or specialist species that characterize this intermittent stream.