Temperature-dependent growth rates of larval midges (Diptera: Chironomidae) from a southeastern US stream

Daily instantaneous growth curves were calculated for larvae within the dipteran family Chironomidae at the tribe (Chironomini and Tanytarsini), subfamily (Chironominae and Orthocladinae), and family levels within along a temperature gradient (15, 20, 25, and 30 degrees C) from egg masses isolated and cultured from gravid adult females. Individual genera were separated and 50 larvae per genus were grown in Petri dishes and in recirculating microcosms, 25 larvae per temperature/container treatment. Growth rates were not significantly different between the Petri dish and microcosm treatments. This overall similarity allowed data from both treatments to be grouped by genus and regressed against temperature to develop growth rate curves for application in secondary production analyses. Growth rates were a function of temperature at all taxonomic levels and fit 2nd-order polynomials with maximum growth rates (0.21-0.26 d(-1)) occurring near 20 degrees C. Growth rates found in this experiment were equal to or slightly higher than those previously found in similar streams. The similarity of growth rates of genera within the Chironomidae representing 3 different subfamilies suggests that higher taxonomic-level growth rate regressions could potentially be used to simplify the estimation of larval chironomid secondary production. Further, the similarity between growth rates observed from the Petri dishes and those in the recirculating streams suggests that only relatively simple experimental conditions are necessary. The shapes of the curves suggest that chironomid communities differing in relative abundance of dominant taxa (i.e., Chironomini vs. Tanytarsini) could have significantly different growth rates, and consequently secondary production, depending on stream temperature/season.