Effect of elevated water temperature on insect emergence in outdoor experimental channels

Abstract

Emergence of adult aquatic insects was determined weekly with plexiglass traps positioned in two outdoor experimental channels from April through August 1977. One channel was seasonal Mississippi River water temperature and the other maintained at 10°C higher. Maximum water temperatures reached 31·0°C in the ambient and 40·8°C in the heated channel. Chironomids comprised 84% of the insects collected in both channels. Percentage composition differed between the ambient and heated channels for the chironomid taxa while the mayfly, damselfly and caddisfly taxa were more similar. The temperature in the heated channel (10°C above ambient) advanced the emergence of two Chironominae, one Orthocladiinae, one Ceratopogonidae and one Zygopteran species by one to four weeks. Few insects emerged from the heated channel during the period of maximum temperature. Insect emergence was spatially distributed throughout each channel even though dissolved oxygen concentrations were near zero at sunrise and supersaturated at mid-afternoon hours at downstream stations.