I LLINI S UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN
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University of Illinois at Urbana-Champaign Library Large-scale Digitization Project, 2007.
Natural History Sirvey Library 199?8 19)
SUMMER EPHEMEROPTERA, PLECOPTERA, AND TRICHOPTERA (EPT) SPECIES RICHNESS AND HILSENHOFF BIOTIC INDEX AT EIGHT STREAM SEGMENTS IN THE LOWER ILLINOIS RIVER BASIN
Dr. R. Edward DeWalt and Dr. Donald W. Webb Center for Biodiversity Illinois Natural History Survey 607 East Peabody Drive Champaign, IL 61820
TECHNICAL REPORT 1998 (9) ILLINOIS NATURAL HISTORY SURVEY CENTER FOR BIODIVERSITY 11 May 1998
PREPARED FOR
United States Geological Survey National Water Quality Program Urbana, IL 61801
ABSTRACT
Adult Ephemeroptera, Plecoptera, and Trichoptera (EPT) species were collected from eight lower Illinois River basin streams sites during June, July, and August 1997. A total of 17,889 specimens were collected, comprising 67 species in 17 families. Caddisflies, or Trichoptera, were dominant both in the number of species (40 species) and in abundance (88.3% of all individuals). Mayflies (Ephemeroptera) contributed far less to species richness and abundance, while most streams were nearly devoid of stoneflies (Plecoptera). Log 0oEPT species richness differed significantly across stream sites (ANOVA, F=12.61, p=0.0001), and peak in July (ANOVA,
F=67.69, p=0.0001). Hilsenhoff Biotic Index (HBI) was not significantly different across stream sites (Fig. 5, ANOVA, F=0.89, p=0.53). However, mean monthly HBI scores were highly significantly different (ANOVA, F=4.99, p=0.008), with July being closest in score to the HBI calculated over all species collected for the summer. All basin sites rated as at least "fair", based on Hilsenhoff's scale. Virtually no difference in mean total HBI values existed between large and small streams (4.86 and 4.71, respectively). Several weaknesses exist in using a taxonomic richness metric or a biotic index alone. We suggest that both be used in concert to assess stream health. Where ever possible, multiple light traps samples over a season should be used to encompassed more variation in the metrics. If only one can be taken, early in July seems to be the time frame to produce results closest to season-long investigations. INTRODUCTION Monitoring stream ecosystems using aquatic macroinvertebrates has been an effective tool for documenting changes in community health (Plafkin et al. 1989). Some macroinvertebrate indices of stream health have been identified as most useful and efficacious. These include the EPT index (sum of Ephemeroptera + Plecoptera + Trichoptera species richnesses, Lenat and Penrose 1996), total macroinvertebrate taxa richness (Plafkin, et al. 1989), and several numerical biotic indices (Hilsenhoff Biotic Index, or HBI of Hilsenhoff 1987, and the North Carolina Biotic Index, or NCBI of Lenat 1993). Wallace et al. (1996) recently endorsed the EPT index as possibly the most efficient of the macroinvertebrate indices. Similarly, Barbour et al. (1992)
2 compared a large number of macroinvertebrate indices and found that simple species counts, especially those of sensitive taxa, were most effective at determining impairment of streams.
Aquatic stages of EPT taxa are most often used for stream monitoring. However, this leads to underestimates of the EPT assemblage in a stream segment since immature stages are often identified only to the generic level. Most identification keys to the species level focus on the adult stage.
Illinois is fortunate to have published, statewide monographs on their EPT fauna. Frison
(1935) published a classic treatment of the stoneflies (Plecoptera) of Illinois. Shortly thereafter, Ross (1944) presented his "Caddisflies (Trichoptera) of Illinois." The mayflies (Ephemeroptera) of the Illinois was published by Burks (1953). The information gathered by Illinois Natural
History Survey (INHS) researchers on these EPT taxa is unsurpassed in any region of the country. Despite this vast knowledge, the number of EPT taxa cannot be reliably estimated for any particular stream reach in Illinois since these studies were for the purposes of gathering specimens for taxonomic treatment of the orders not for ecological purposes. The Illinois River basin drains much of what was the wet-prairie region of central Illinois. Lack of detailed benthic studies in the central and western part of the state precludes knowledge of "typical" EPT composition there. However, Ross (1944), Burks (1953), and Frison (1935) generalize about the fauna of large and small rivers in Illinois.
The USGS- National Water Quality Assessment (NAWQA) program has targeted the Illinois River system for study. The long-term goals of this program are to describe the status and trends in the quality of a large, representative part of the Nation's surface- and ground-water resources, and to provide a sound, scientific understanding of the primary factors affecting the quality of these resources. Several sampling stations in the lower Illinois basin have been established, benthic macroinvertebrate samples collected and are now being processed. Results of these studies are expected to require much time to compile. Collection of the adult EPT species at these sites would provide a rapid view of local river health and provide a species list to guide identifications of the immature stages found in benthic samples. Our objectives were to use summer-emerging EPT species to characterize the biotic integrity of eight NAWQA sites in the lower Illinois River basin. Use of a second measure of biotic integrity, the HBI, allows for direct comparison of the performance of both indices.
Questions asked were 1) How do the EPT and HBI indices vary throughout the summer months? 2) Do EPT and HBI vary significantly with the number of individuals sampled? 3) Are there differences in EPT and HBI between sites?, and 4) Do EPT and HBI say the same things about the streams in which they are used. These collections will also aid in the identification of immature insects taken in benthic samples. A search of Frison (1935), Ross (1944), Burks (1953) and databases at the INHS will also provide a historical assemblage for sites in the Illinois River basin.
METHODOLOGY
Eight existing NAWQA sites were chosen in the lower Illinois River basin to survey for EPT species (Fig. 1, Table 1). These sites correspond with local benthic macroinvertebrate sampling efforts. Adult EPT were trapped from areas adjacent to the stream using a BioquipTM
AC/DC 12 volt ultraviolet collecting light during June, July, and August of 1997. This apparatus was suspended 1 m above the ground so as to reflect off a vertically hung white sheet. Two 20 cm X 30 cm white plastic trays placed below the sheet trapped insects in a pool of 80% EtOH. The light trap ran for 1 hr beginning at sunset. Air temperature was monitored at most sites at the beginning and end of the 1 hr period. Caddisflies struck the sheet several times and fell to the trays below. However, mayflies and stoneflies required some additional care to obtain high quality specimens. Mayfly sub-adults (subimagoes) were collected directly off the sheet and placed into styrofoam cups, where they were held until they had transformed to the imago, a terminal stage of development. They were then preserved in 80% EtOH. Several species of male stoneflies require eversion of internal genitalia before they can be successfully identified. Males of Perlestasp. and Isoperla sp. were picked from the sheet and their lower abdomens squeezed gently until their genitalia extruded. The entire insect was then immersed in 80% EtOH, maintaining extrusion of the genitalia, until the insect no longer
4 struggled. These males were stored in separate vials. The trays of insects were then poured into a 11 container for transport back to the laboratory.
Adults were subsampled, where appropriate, and sorted into vials. Specimens were identified to species in most cases. Females could not be identified to species in some cases. All data was entered into an ExcelT database and analyzed using the Statistical Analysis System (SAS
1985). The dataset was sorted by location and month, the percentages for each taxon calculated, and the total numbers of EPT taxa counted. The HBI is a Midwest index of stream organic pollution (Hilsenhoff 1987). Tolerance values have been assigned to many taxa that range from 0 to 10, with higher numbers indicating a greater tolerance for organic pollution. Tolerance values were only available at the genus level for some species, e.g. caddisfly genera Cheumatopsyche and Hydroptila. Tolerance values were absent for some species entirely, necessitating removal of those species from the HBI calculations. All taxa encountered and their assigned tolerance values, are provided Table 2. The influence of month and site upon EPT and HBI values was investigated using the General Linear Models (GLM) approach of Analysis of Variance (ANOVA, SAS 1985).
Logio transformations of data eliminated the discrete nature of the EPT count. A Duncan's Multiple Range Test (SAS 1985) was used to determine relationships between sites and months for EPT and HBI parameters. The ANOVA was an exploratory analysis and its conclusions should be accepted with care. Small sample size (degrees of freedom = 32, 8 sites and four "month" levels including total, June, July, and August EPT and HBI) may pose a problem with interpretation.
We used the Spearman Rank Correlation (SAS 1985) to investigate the relationships untransformed HBI values to that of the EPT and its components. Most specimens were accessioned into the INHS collections as vouchers for the study. All specimen-level data from voucher specimens (species, location, numbers, etc.) have been added to searchable Ephemeroptera, Plecoptera, and Trichoptera databases maintained by the INHS. RESULTS
Dates of collection, times, temperatures, and total counts corrected for subsample rates are presented in Table 3. Ultraviolet black light traps yielded 17,889 subsampled EPT adults and 67
5 species over the summer, 1997 sampling period (Table 4). Trichoptera contributed 61.2% (41 species) of this total, while mayflies provided another 34.3% (25 species). Stoneflies were a relatively minor component of the EPT fauna, contributing only 4.5% (3) of the total.
Abundance: Abundances, standardized for subsampling effort and to a 1 hr collection period were extremely variable across sites sampled (Table 3). Mean values of log 0o adjusted abundance were not significantly different across sites (ANOVA, F=1.23, p=0.35). It is probable that a low degrees of freedom obscured abundance relationships. However, larger rivers (Sangamon River at Oakford, Mackinaw River, Illinois River at Starved Rock) accounted for three of the top four mean abundances. Smaller streams either supported lower densities or provided less visible area around the ultraviolet light trap. Significant logl0 abundance differences were found across months (ANOVA, F=6.10, p=0.01). A Duncan's MRT produced the following relationships :
Duncan Grouping Mean N Month A 3.40 8 July AB 3.03 8 August B 2.57 8 June
June and July were the only months with different abundances. July and August mean air temperatures, taken during sample visits, were 14-15% warmer than during June. This would reduce the numbers of insects flying in June. Additionally, most of Illinois had experienced a cooler-than-normal spring which delayed the development of adults until July. Dominant taxa: Three of four large stream sites (Illinois River sites, Sangamon R. at Oakford, Mackinaw River near Green Valley) were dominated by species of net-spinning caddisflies in the family Hydropsychidae (Fig. 2). Chief among these was Potamyiaflava (Hagen) whose percent contribution over the entire summer ranged from 16 to nearly 55%. Ross (1942) characterizes this species as a large river inhabitant, often of great abundance. We have personally witnessed this tawny species emerging in large numbers from the shores of the Mississippi and other large rivers in the state. Hydropsyche bidens Ross was common at three of the four sites. Ross (1944) found no definite association with stream size for this species. Cheumatopsyche sp. was an abundant
6 taxon at all stream sites. Most of the individuals were females whose identity was impossible to ascertain. Males were identified as Cheumatopsyche lasia Ross, C. campyla Ross, and C. pettiti (Banks). Ross (1944) found that C. lasia and C. pettiti most often occurred in small streams, but could be found in large rivers as well. Cheumatopsyche campyla has a preference for large rivers. Small-to-medium streams demonstrated much less overlap in dominant taxa than did large streams (Fig. 3). Cheumatopsyche sp. was found at three of the four sites. Again, most were unidentifiable females. Sometimes all three species found in large rivers were also present in the smaller ones. However, C. pettiti was often the most common of the three. Nectopsyche sp. were commonly taken in these streams. Females were unidentifiable to species and were most often the bulk of the individuals. When males were present, N. candida Ross and N. diarina Ross were the abundant species. Ceraclea sp. were dominant at three of four sites, and were almost exclusively composed of C. tarsipunctataand C. transversa. Both species have been collected throughout the state in a wide variety of stream sizes (Ross 1944; Moulton and Stewart 1996).
Species Richness: Log 0oEPT species richness (Fig. 4) differed significantly across stream sites
(ANOVA, F=12.61, p=0.0001). A Duncan's MRT (a=0.05) found the following relationships:
Logl0 Duncan Grouping Mean EPT N Site A 2.39 4 Indian A 2.36 4 Mackinaw AB 2.31 4 Sangamon-Monticello AB 2.31 4 Panther BC 2.25 4 La Moine BC 2.24 4 Illinois-Starved Rock CD 2.16 4 Illinois-Florence D 2.10_ 4 Sangamon-Oakford
Generally, small and medium-sized streams had the highest EPT values. Indian Creek displayed the highest overall richness at 38 species, while the medium-sized La Moine River tallied only 21 total EPT (Fig. 4). The Mackinaw River was the most diverse large river. It produced 41.9%
7 more EPT than the Sangamon River at Oakford, which had the lowest EPT richness of the large rivers (Fig. 4).
LogD0 of EPT species richness was also different across months (ANOVA, F=67.69, p=0.0001). A Duncan's MRT demonstrated three distinct groupings (a=0.05) with the following relationships:
Duncan Grouping Log 0o N Month Mean EPT A 2.45 8 Total B 2.30 8 July B 2.24 8 August C 2.07 8 June
The month "Total" represents a count of all species for a particular site. It is not surprising then that this EPT tally forms a distinct grouping. July and August values were not significantly different, but June EPT totals were significantly different from both months. Most EPT species were cued to emerge in July this particular year--the cool spring delaying transformation of larval stages to adults until that time. Hilsenhoff's Biotic Index: There were no significant differences in mean HBI scores across stream sites (Fig. 5, ANOVA, F=0.89, p=0.53). However, mean monthly HBI scores were highly significantly different (ANOVA, F=4.99, p=0.008). A Duncan's MRT produced the following relationships among monthly means:
Duncan Grouping Mean N Month A 5.33 8 August AB 4.78 8 Total B 4.53 8 July B 4.23 8 June
This is a complex relationship, but the most obvious outcome is that June had a significantly lower (greater health/quality) HBI score than did August. All other relationships cannot be clarified at this time; however, it appeared that HBI scores increased as the summer waned. Late season dominance by such species as P.flava and the several Cheumatopsyche species produced higher values in August. Species with lower tolerance values dominated in June. Total HBI values are the most appropriate ones on which to base decisions, since they represent the average tolerance of the whole community. Given a similar thermal regime, July might be the best month to estimate tolerance of the entire community if only one monthly sample could be collected. Hilsenhoff
(1987) presented the following ranges and quality designations.
HBI Ranges Quality Rating 0.00-3.50 Excellent 3.51-4.50 Very Good 4.51-5.50 Good 5.51-6.50 Fair 6.51-7.50 Fairly Poor 7.51-8.50 Poor 8.51-10.00 Very Poor
Total HBI values are the most appropriate measures of biotic integrity since they encompass the entire------summer- fauna.------These are provided along with tentative ratings from Hilsenhoff (1987). Total HBI --Qua----Quality Site Score Rating Medium-to-Large Rivers Mackinaw 4.87 Good Illinois -Starved Rock 4.63 Good Illinois-Florence 5.52 Fair Sangamon-Oakford 4.40 Very Good Small-to-Medium Rivers Sangamon-Monticello 4.93 Good La Moine-Colmar 4.07 Very Good Indian 5.14 Good Panther 4.69 Good
All sites were rated as at least "fair", having scored 5.50 or below. Virtually no difference in mean total HBI values existed between large and small streams (4.86 and 4.71, respectively). The
Sangamon River at Oakford and the La Moine River at Colmar were rated at "very good" by the HBI. This is disturbing since these sites demonstrated low EPT taxa richness. Relationships of HBI, EPT and its Components: A Spearman Rank Correlation (n=32) found very low correlations of HBI and EPT values: Variables HBI EPT EPHEM PLEC TRICH ADJABUND HBI 1 FmPT 1 EPHEM 0.33 1 PLEC -0.39 -0.154 1 TRICH 0.26 0.45 0.06 1 ADJABUND 0.10 0.39 0.37 0.24 1
Additionally, no components of the EPT index were found to have a predictable (inverse) relationship with the HBI. This was possibly due to the heavy weighting of abundant species in the calculation of the HBI and the fact that a large percentage of EPT taxa were represented by relatively few individuals. Trichoptera and Ephemeroptera richnesses were highly correlated with the EPT index. Plecoptera were not abundant in most streams and usually were represented by only one or two species. This accounted for its low correlation to the EPT index. The variable "adjabund" is abundance adjusted for subsampling effort. It showed a positive, but small relationship to any of the HBI and EPT indices, demonstrating that the number of individuals had only a minor effect on these indices of stream health.
Notes on Species Encountered: Only 6 of the 31 baetid mayflies known from Illinois (Burks 1953, McCafferty website: www.entm.purdue.edu/entomology/mayfly/mayfly.html) were collected or historically known from the sample locations. Species records in Burks (1953) and in about 4000 database records of Ephemeroptera at the INHS showed that only Callibaetisfluctuans(Walsh) had been previously reported from the area. We recorded five species at four of eight sites in medium- to-small rivers and streams (Table 4). Three of the six caenid mayflies known to occur in Illinois were taken from these silty prairie streams. Some species, such as Caenis hilaris (Say) and C. latipennis Banks were dominant inhabitants across all stream sizes. The Sangamon River at Monticello produced huge numbers of C. latipennis during August. Heptageniid mayflies accounted for 10 species (26 known from Illinois, Burks 1953, Bednarik and McCafferty 1979), the most common of which being Stenacron interpunctatum (Say). This species occurred in both large and small streams and is tolerant of siltation and low dissolved oxygen (Hilsenhoff 1987,
10 Lenat 1993). Isonychia rufa McDunnough, one of five Isonychia to occur in Illinois and an inhabitant of the swifter portions of streams, was documented at several sites across all stream sizes. Only the males of this species can be identified. Female specimens identified to Isonychia were probably this species. Burks (1953) and Kondratieff and Voshell (1984) characterize the genus Isonychia as a common inhabitant of prairie streams in the Mississippi River drainage. Species richness of stoneflies was very low for the study area. Seven summer-emerging (perlids and perlodids) species are historically known from the drainage (Table 4), but only Perlestadecipiens (Walsh) and Isoperla bilineata (Say) widely occur in the region during summer. Snellen and Stewart (1979) reported a lengthy egg diapause in P. decipiens (as P. placida (Hagen). Hynes (1961) postulated that this type of diapause may permit drought resistance and avoidance of competition for food and space. It may also allow for avoidance of high summer water temperatures and the concomitant low dissolved oxygen concentrations. No such study had been conducted for L bilineata. It is disturbing that no specimens of Acroneuria,Agnetina, or
Neoperla were collected. Species in these genera may have experienced drastic declines in Illinois during the last several decades. Three families contributed the largest number of caddisfly species during the study. These were the hydropsychids, hydroptilids, and the leptocerids. Twelve species of hydropsychids were collected or have been known to occur at or near the sites sampled. Ceratopsyche bronta (Ross) was a dominant species at the two smallest streams, Indian and Panther Creeks. Ross (1944) and Schefter and Wiggins (1986) report this species frequents cool, headwater streams and is tolerant of moderate organic enrichment. Although Ross (1944) discusses some preferences of Cheumatopsyche species for large or small streams, our data suggests that the three species encountered have wide ranges of stream size preference. Cheumatopsyche lasia Ross has been noted to be abundant in heavily silted streams throughout the central prairie of North America (Ross 1944, Moulton and Stewart 1996). Hydropsyche betteni Ross occurred only in small-to- medium-sized streams, where it was occasionally dominant. Schuster and Etnier (1978) and Hilsenhoff (1987) found it to be highly tolerant of organic enrichment. Hydropsyche bidens Ross
11 was collected from all sites except Panther Creek. It appeared to prefer larger rivers (Moulton and Stewart 1996), where it was often abundant.
Eleven species of hydroptilid, or micro-, caddisflies were taken from or known to occur in the lower Illinois River basin near the stream sites. Two species were abundant, Hydroptila ajax Ross and H. angusta Ross. The greatest abundance of H. ajax occurred in Indian Creek, a small, open stream. Hydroptila angusta inhabited small stream and large rivers and has been found in abundance in light trap samples from the Ohio River (DeWalt, 1998). Another micro-caddisfly,
Mayatrichiaayama Mosely, was taken only at the Illinois River near Florence. Ross (1944) and
Moulton and Stewart (1996) describe its habitat preference as being for small-to-medium-sized, rapid, clear streams. Although several specimens were taken at Florence, some doubt exists that this was their origin. Small brooks run out of the bluff above this site nearby. Leptocerid caddisflies, with 17 species, contribute the greatest species richness for caddisflies in this study. A significant finding was that of several females of the rarely collected, N. pavida (Hagen) at the Sangamon River, Monticello site. Ross (1944) reported this from two collections, Monticello and Herod (southern Illinois). Oecetis inconspicua (Walker) was present at all sites. It is perhaps the most widely distributed caddisfly species in Illinois due to its ability to live in both lotic and lentic environments (Ross 1944). Small populations of five other Oecetis species were take during the study. A large number of female Triaenodes melacus Ross were taken from Panther Creek. To date this species has only been recorded from two other location in the state, Cooper Creek near Mill Creek and it type locality of Blackman Creek near Rudement, both in the Shawnee Hills of southern Illinois. It has been taken in low numbers from scattered locations in AL, IN, KS, KY, MO, MS, and OH. Cyrnellusfraterus (Banks) was the only other widespread and abundant caddisfly species.
Ross (1944) and Moulton and Stewart (1996) report it principally from large rivers, but it has been found in smaller streams and at the shores of lakes (DeWalt, pers. obs.). Hilsenhoff (1987) rates it as being highly tolerant of organic enrichment.
12 CONCLUSIONS
Inspection of 17,889 specimens from this Illinois River basin study has demonstrated that its EPT assemblage, as represented by light trap collections, was overwhelmingly dominated by caddisflies. Sixty-one percent of all species and 88.3% of all individuals were caddisflies. Three caddisfly families contributed 40 of the 67 EPT species encountered. These were the Hydroptilidae (11 species), Hydropsychidae (12), and the Leptoceridae (17). These same families also dominated abundance. Hydropsychid caddisflies contributed 56.6% of all individuals, while the leptocerids added 19.4%, and the hydroptilids provided 7.9%. Moulton et al. (1993) studied the caddisfly fauna of the Brazos River in Texas. They found 42 species occurring over an equivalent time period. The same three families that were diverse and abundant in our study were found to be diverse and abundant in the Brazos River. The species P.flava, H. bidens, and several Cheumatopsyche sp. were dominant at several sites, the former two mostly in medium-to- large rivers. Mayflies contributed 34.3% of the EPT species collected, but only 11.3% of individuals. Caenids provided three species and 6.6% of the abundance. Heptageniids provided 11 species and 2.9% of abundance. Stoneflies provided only 4.5% of all species (3 total) and only 0.4% of abundance. Species richness was greatest in Indian Creek (38 taxa). Lowest richness was found in the La Moine River (21). Small-to-medium-sized streams tended to have more species than the largest rivers. Richness peaked in July at nearly all sites, followed by August and June. Low richness in June was most likely due to lower air and water temperature that prevented emergence early in that month. EPT richness values were not significantly correlated with HBI values. The predicted relationship would be inverse since low HBI numbers indicate greater stream health/biotic integrity. In fact, the La Moine River at Colmar had the lowest overall EPT richness of any site, but had one of the lowest (best) HBI scores. Several reasons may account for this lack of relationship. EPT richness is counts every species encountered equally, so rare species have a great impact upon it. Whereas, the HBI weights the tolerance values of taxa by their abundance.
13 Additionally, for several abundant taxa (Cheumatopsyche sp., Hydroptila sp. and others) we were forced to assign tolerance value for the genus, as no species-level tolerance values exist. Some species within a genus may well have biologically significant differences in ecological tolerance. These weaknesses demonstrate the need to use both taxonomic richness and a biotic index for monitoring of stream health.
Both EPT and HBI values, calculated on adult data, should be focused on the entire community within an emergence season. This can best occur when light trap samples are available for several months. If this is not possible, then an early July light trap sample would be the next best choice. We have found that an HBI score based solely on July light trap collections best mimicked the HBI score taken across June, July, and August. Similarly, the number of EPT found in July samples was much closer to the summer-long EPT list.
14 ACKNOWLEDGMENTS
We wish to thank the INHS for providing facilities and time relief for this project. Mitch
A. Harris, of the USGS, helped secure funding and aided in the design of collection protocols.
We wish to thank D. L. Adolphson, P. J. Terrio, and K. Gao, of the USGS, and L. J. Peraino, of the INHS, for help with light trapping of insects. The University of Illinois through the Federal WorkStudy program provided student workers who helped collect, sort, label, and database specimens. These students were P. Li, M. Lavin , D. Duong, B. Lopez, and L. Hernandez. Without their help, this project would not have been feasible.
15 LITERATURE CITED
Barbour, M. T., J. L. Plafkin, B. P. Bradley, C. G. Graves, and R. W. Wisseman. 1992.
Evaluation of EPA's rapid bioassessment benthic metrics: metric redundancy and variability
among reference stream sites. Environmental Toxicology and Chemistry 11: 437-449.
Bednarik, A. F., and W. P. McCafferty. 1979. Biosystematic revision of the genus Stenonema (Ephemeroptera: Heptageniidae). Canadian Bulletin Fisheries Aquatic Sciences 201: 73 p.
Burks, B. D. 1953. The mayflies, or Ephemeroptera, of Illinois. Bulletin Illinois Natural History Survey 26: 216 pp.
Frison, T. H. 1935. The stoneflies, or Plecoptera, of Illinois. Bulletin Illinois Natural History Survey 20: 471 pp. DeWalt, R. E., B. P. Stark, and M. A. Harris. 1998. Perlesta golconda, a new stonefly species from Illinois (Plecoptera: Perlidae). Entomological News 109: ? pp.
Hilsenhoff, W. L. 1987. An improved biotic index of organic stream pollution. Great Lakes Entomologist 20: 31-39.
Hynes, H. B. N. 1961. The invertebrate fauna of a Welsh mountain stream. Archives fur Hydrobiologia 57: 344-388. Kondratieff, B. C., and J. R. Voshell, Jr. 1984. The North and Central American species of Isonychia (Ephemeroptera: Oligoneuriidae). Transactions American Entomological Society, 110: 129-244. Lenat, D. R. 1993. A biotic index for the southeastern United States: derivation and list of tolerance values, with criteria for assigning water-quality ratings. Journal North American Benthological Society 12: 279-290. Lenat D. R., and D. L. Penrose. 1996. History of the EPT taxa richness metric. Bulletin North
American Benthological Society 13: 305-307. Moulton, S. R. II, and K. W. Stewart. 1996. Caddisflies (Trichoptera) of the Interior Highlands
of North America. Memoirs American Entomological Institute 56: 313 pp.
16 Moulton, S. R. II, Daniel Petr, and K. W. Stewart. 1993. Caddisflies (Insecta: Trichoptera) of the Brazos River drainage in north-central Texas. Southwestern Naturalist 38: 19-23. Plafkin, J. L., M. T. Barbour, K. D. Porter, S. K. Gross, R. M. Hughes. 1989. Rapid Bioassessment Protocols for Use in Streams and Rivers: Benthic Macroinvertebrates and Fish. USEPA, EPA/44/4-89-001.
Ross, H. H. 1944. The caddis flies, or Trichoptera, of Illinois. Bulletin Illinois Natural History Survey 23: 326 pp.
SAS. 1985. SAS User's Guide: Statistics, 5th ed. Statistical Analysis Institute. Cary, North Carolina. 956 pp.
Schuster, G. A., and D. A. Etnier. 1978. A manual for the identification of the larvae of the
caddisfly genera Hydropsyche Pictet and Symphitopsyche Ulmer in eastern and central North America (Trichoptera: Hydropsychidae). USEPA, EPA 600/4-78-060. Snellen, R. K., and K. W. Stewart. 1979. The life cycle of Perlestaplacida (Plecoptera: Perlidae) in an intermittent stream in northern Texas. Annals Entomological Society of America 72: 659-666.
Wallace, J. B., J. W. Grubaugh, and M. R. Whiles. 1996. Biotic indices and stream ecosystem processes: results from an experimental study. Ecological Applications 6:140-151.
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2 Table 2. Hilsenhoff Biotic Index (HBI) values and brief discussion of tolerance values for EPT species collected during summer 1997 at eight lower Illinois River basin sites.
Taxon HBI Discussion Acentrella ampla No HBI available Baetis intercalaris 6 Fallceon quilleri No HBI available Labiobaetispropinquus 6 Paracloeodesminutus No HBI available Caenis amica 7 for genus Caenis, none for species given Caenis hilaris 7 Caenis latipennis 7 Hexagenia bilineata 6 for genus Hexagenia, none for species given Hexagenia limbata 6 Pentageniavittigera 6 Heptageniadiabasia 3 Heptageniaflavescens No HBI available Leucrocuta aphrodite No HBI available Leucrocuta maculipennis No HBI available Nixe inconspicua _No HBI available Stenacron interpunctatum 7 Stenonema mexicanum 4 S. integrum is a synonym of S. mexicanum Stenonema luteum No HBI available Stenonema prob. pulchellum 3_ Stenonema terminatum 4 Isonychia rufa 2 for genus Isonychia, none for species given Ephoron album 2 for genus Ephoron, none for species given Ephoron leukon 2 Anthopotamus myops 4 Perlesta decipiens 5 as Perlestaplacida, a complex, containing P. decipiens, the most common species in the region. Perlinelladrymo 1 Isoperla bilineata 4 Helicopsyche borealis 3 Ceratopsyche bronta 5 Cheumatopsyche aphanta 5 for genus Cheumatopsyche, none for species given Cheumatopsyche campyla 5 Cheumatopsyche lasia 5 Cheumatopsyche pettiti 5 Hydropsyche betteni 6 Hydropsyche bidens 3 Hydropsyche simulans 7 Potamyiaflava 5 Hydroptilaajax 6 for genus Hydroptila, none for species given Hydroptilaalbicornis 6 ______Hydroptilaangusta 6 Hydroptila consimilis 6_____.. Hydroptilaperdita 6____ Hydroptilawaubesiana 6
19 Table 2. Hilsenhoff Biotic Index (HBI) values and brief discussion of tolerance values for EPT species collected during summer 1997 at eight lower Illinois River basin sites. Taxon HBI Discussion Mayatrichiaayama No HBI available Orthotrichiacristata No HBI available Oxyethira pallida 3 for genus Oxyethira, none for species given Ceracleapunctata 3 for genus Ceraclea, none for species given Ceracleatarsipunctata 3 Ceraclea transversa 3 Leptocerus americanus No HBI available Nectopsyche candida 3 for genus Nectopsyche, none for species given Nectopsyche diarina 3 Oecetis avara 8 for genus Oecetis, none for species given Oecetis cinerascens 8 Oecetis inconspicua 8 Oecetis persimilis 8 Triaenodesmarginatus 6 for genus Triaenodes, none for species given Triaenodes tardus 6 Anabolia consocia 5 for genus Anabolia, none for species given Chimarraobscura 4 for genus Chimarra, none for species given Phryganeasayi 8 for genus Phryganea, none for species given Cyrellusfraternus 8 Neureclipsis crepuscularis 7 for genus Neureclipsis, none for species given Paranyctiophylaxaffinis 5 for genus Paranyctiophylax, none for species given Polycentropus sp. 6 for genus Polycentropus, none for species given
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