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We studied aquatic insect production in three cold desert streams in southeastern Washington. The Size-Frequency (SF) and P/B methods were used to assess production, which is expressed by taxon, functional group, and trophic level.

Dipterans (midges and black flies) were the most productive taxa, accounting for 40-70% of the total insect production. Production by collectors and detritivores was the greatest of all functional groups and trophic levels, respectively, in all study streams.

Insects with rapid development times and multiple cohorts are very important in cold desert streams; they were major contributors to the total insect production. Total insect production rates in our study streams (14-23 g DW.m-2.yr-1) were greater than those found in Deep Creek, Idaho (1.2 g DW.m-2.yr-1), the only other cold desert stream for which production data are available. Our values also were generally greater than published data for most cold/mesic (3-27 g DW.m-2.yr-1) and humid/mesic (3-25 g DW.m-2.yr-1) streams, but lower than in Sonoran Desert Streams (> 120 g DW.m-2.yr-1) or New Zealand streams (approximately 40 g DW.m-2.yr-1).

Our data support the contention of others that production, rather than density or biomass, is the most accurate and meaningful way to assess the role of these organisms in lotic ecosystems.