INTERACTIVE EFFECTS OF DIET AND THERMAL REGIME ON GROWTH OF THE MIDGEPSEUDOCHIRONOMUS-RICHARDSONI MALLOCH

1. Larvae of Pseudochironomus richardsoni were reared to pupation in i ndividual enclosures, in one of three thermal habitats in a northern C alifornia stream. The average temperature range in cold seeps was 15-2 1 degrees C, while the main channel ranged from 20 to 27 degrees C, an d side pools ranged from 18 to 33 degrees C. Diet consisted of either diatoms or algal detritus. 2. Specific growth rate ranged from 0.057 t o 0.267 day(-1). Specific growth and developmental rates were highest on a diatom diet, and increased with temperature. Regressions of growt h rate on mean microsite temperature were also significantly altered b y diet. Differences in specific growth rate due to diet are magnified at higher temperatures. 3. Pupae reared on diatoms were larger than th ose reared on detritus. The mass of pupae reared on detritus decreased with increasing temperature. However, there was no significant relati onship between pupal mass and temperature for larvae reared on diatoms . 4. The combined effects of food quality and thermal environment on g rowth of the midge P. richardsoni are significantly different from the independent effects of diet and temperature. Interactive effects of f ood quality and temperature may influence the contribution of certain aquatic habitats (algal mats) to invertebrate secondary production.