Illinois Natural History Survey - University of Illinois

Mayflies, Stoneflies, and Caddisflies Help Researchers Track Water Quality


Summertime evening strolls along the banks of Illinois rivers and streams provide an opportunity for Illinoisans to encounter aquatic insect adults. The adults of mayflies (Ephemeroptera) and caddisflies (Trichoptera) are the most frequently encountered groups, but the lucky observer may find the more ecologically sensitive stonefly (Plecoptera). Fishermen know these insect orders as the "hatch to match" when choosing or making artificial "flies" to catch a trout or other gamefish. The immatures of these insects live inconspicuously in gravel, on logs, and buried in the mud of large rivers, streams, and lakes. The life cycles of some species last for only several months, but other species must live in the stream for up to several years before changing to the winged adult stage. It is the immature stages of these insects that aquatic biologists use to monitor changes in water quality of streams.

Monitoring of the entire aquatic invertebrate community has been an effective tool for documenting changes in stream health. Recent studies suggest that a subset of sensitive aquatic insects may actually provide information more quickly (and cheaply) than the entire community. The EPT index (number of Ephemeroptera, Plecoptera, and Trichoptera species in a sample) is one of the most efficient indices of stream health due to its ease of use and low variability. Its usefulness in monitoring stressed ecosystems has been tested by the addition of insecticides to experimental and control watersheds in the North Carolina Piedmont. Researchers found that EPT values in samples displayed low variability, showed different effects in different stream habitats (leaf packs, moss, sand bottoms), and correlated well with other more costly measures of ecosystem function such as rates of nutrient processing, total invertebrate diversity and biomass, and with the calculation of a biotic index specific to the region.

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The Illinois Natural History Survey has been a hotbed of research in the taxonomy, distribution, and ecology of mayflies, stoneflies, and caddisflies throughout the century. Survey entomologists including Barnard D. Burks (mayflies), Theodore H. Frison (stoneflies), and Herbert H. Ross (caddisflies) wrote a large proportion of the original descriptions for North American species during the early and middle part of this century. The original specimens, or types, used to describe those species, and all material collected throughout the careers of Frison, Burks, and Ross, reside in the Survey Insect Collection. Researchers collected the majority of the specimens before the most severe environmental degradation took place. Consequently, they represent irreplaceable and irrefutable proof that species occurred in areas throughout the state and region. Efforts are currently under way to database all these specimen records to make the data more accessible for aquatic entomologists, pollution biologists, and other government agencies needing this type of information. A database containing records of all stoneflies (>17,000 records) in the Survey collection facilitated Dr. Donald W. Webb's efforts to establish imperilment status for several rare Illinois species. These and other databases may be visited at the Survey homepage.

A new statewide monitoring effort, the Critical Trends Assessment Project (CTAP), has begun to monitor the quality and biodiversity of streams, forest patches, prairie remnants, and wetlands in the state. The author is presently monitoring trends in stream health by using EPT species, water chemistry, and habitat quality characteristics. CTAP randomly chose 30 sites this year from across the state to provide an average look at water quality of wadable streams. The fieldwork is complete, with identification and data analysis to follow. At least 120 randomly chosen sites will be sampled over the next four-year period. Resurvey efforts follow a five-year rotation. Some streams drain several landowner partnerships in the state. Landowners in these partnerships institute some best management practices with the help of local and state agencies. Hopefully, these practices will lead to a healthier environment. The ability to make comparisons with historical collections (using insect collections databases) will add another dimension to this project.

The author and his colleagues currently work on several other Survey projects involving EPT species. Reassessment of Illinois summer-emerging stoneflies is a priority. Many large species no longer occur in locations where they historically resided. Ultraviolet light trap collections of adult EPT species, a project funded by the U.S. Geological Survey, provide information on water quality in the lower Illinois River basin. Additionally, The Nature Conservancy funds a search for an Illinois endemic stonefly not collected since 1860.

R. Edward DeWalt, Center for Biodiversity

Charlie Warwick, editor

Illinois Natural History Survey

1816 South Oak Street, MC 652
Champaign, IL 61820

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