The objective of this study was to determine why certain stream insects tend to be found in certain temperature ranges. Many federal, state and local agencies use stream insects to monitor the health of freshwater ecosystems. While the temperature ranges for some insects are often inferred from the temperature of the waters where they were collected, this inference is coarse at best and problematic at worst. Stream temperatures fluctuate a lot during the year and temperature may or may not control where an insect lives. Field insects were collected and sent to a laboratory for testing several temperature endpoints, particularly at higher temperatures. Respiration, breathing rate, and some physical activities were expected to increase, as the insects attempt to deal with elevated temperatures and expected oxygen limitations. Previous research found that oxygen limitation results in the build-up of lactic and uric acids in tissues of insects, but this was not observed over the range of temperatures and types of insects tested for this study. While respiration, breathing rate and, physical behavior such as pumping motions were observed, it did not appear that elevated temperature alone was resulting in oxygen limitation. This was further confirmed with more experiments that looked specifically at low oxygen waters at various temperatures and included an evaluation of the insect’s metabolic waste products; these warm temperature challenges did not suggest an oxygen deficit in these insects. Rather, the experiments suggested a more general elevated metabolic demand where the insects had to work harder to breath, eat, and molt. Further work to try and identify specific macroinvertebrate temperature tolerance values could be used by scientists and resource managers to predict aquatic resources at greatest risk to temperature change.
