Production of Corydalus cornutus (Megaloptera) in Four Streams Differing in Size, Flow, and Temperature

Estimates of annual production for the predaceous aquatic insect Corydalus cornutus (Megaloptera) revealed considerable variation among four Texas streams with similar water quality characteristics but differing in size, flow, and temperature. Values of production varied from 1.62 g dry mass m-2 yr-1 to 13.19 g dry mass m-2 yr-1. This variation was largely due to differences in growth and development which occurred as a result of differences in thermal regime. At three of the streams, C. cornutus appeared to be univoltine with a cohort production interval (CPI) of 333 days. At a fourth site with higher summer temperatures, development from egg to mature larva occurred in 6-7 months or less, leading to a CPI of 210 days and suggesting bivoltinism (not previously reported for this group). Of the factors thought to control secondary production, including habitat, temperature, food quality and quantity, and biological interactions, temperature seems to be the most important. In addition, a direct relationship was found between production and stream width. This effect could result from limited primary production in canopied, narrow streams which might reduce prey species production and thus lower prey availability to C. cornutus. Permanency of flow appeared not to strongly influence production because the highest production was found in an intermittent stream. Our estimates of production for C. cornutus are among the highest yet reported for a predaceous species and approach the values obtained for primary consumer species in desert streams.