Abstract

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Monson, M.P. 1994. Caddisflies (Insecta: Trichoptera) of the Lake Itasca region, Minnesota; and a preliminary assessment of the conservation status of Minnesota Trichoptera. M.S. Thesis, University of Minnesota. 135 pp.

Abstract:

Objectives of this survey and subsequent study were to prepare an annotated species list of the caddisflies from the Lake Itasca region, to record relative abundance and seasonal distribution for these species, and to compare the diversity and similarity among the caddisfly communities at each site. A companion study was initiated to make a preliminary assessment of the conservation status of all Trichoptera species known from Minnesota at this time.

Annotated records are presented for 126 species of caddisflies representing 37 genera in 13 families. Records are based on 73 light trap collections of over 95,000 adult caddisflies from four sites in the Lake Itasca region of northern Minnesota: LaSalle Creek, Nicollet Creek, Sucker Creek, and Beaver Lake. Caddisflies were collected from June-October 1988, and May-October, 1989. Rank abundance graphs are used to present relative abundance data for the most common species; among these, Cheumatopsyche pettiti, C. oxa, Hydropsyche morosa, H. slossonae (Hydropsychidae), Leptocerus americanus, Ceraclea alagma, C. cancellata, C. excisa, Oecetis inconspicua, O. avara, O. cinerascens, Triaenodes marginatus, T. tardus (Leptoceridae), Lepidostoma bryanti (Lepidostomatidae), and Pycnopsyche guttifer (Limnephilidae), include the five most abundant species from each site. The families Leptoceridae and Hydropsychidae represent 90% of the total individuals reported.

Differences in species richness, relative abundance, and sex ratios are discussed for each site each year. There were generally more species and individuals collected in 1989 than 1988, and among the most common species, females frequently outnumbered males. The Brillouin and Shannon indices and an evenness formula were used to determine that all sites have moderate species diversity. Sorensen's index of similarity is employed to describe beta diversity; based on quantitative information, the degree of similarity is high for Nicollet Creek, Sucker Creek, and Beaver Lake.

Seasonal distribution is recorded for all species for 1988 and 1989. The first flight activity is reported near the end of May for several Cheumatosyche and Hydropsyche (Hydropsychidae) and Oxyethira (Hydroptilidae) species, and for Limnephilus parvulus and Nemotaulius hostilis (Limnephilidae). The last flight activity of the year is recorded during the second week of October for P. guttifer and Neophylax concinnus (Uenoidae). Considering all sites collectively, species found to be most common over the two-year period were generally active over the entire season, from late spring to mid-autumn; C. pettiti, O. inconspicua, O. avara, T. marginatus, and H. morosa are among the species. In comparison, certain species were encountered only for limited periods, such as Fabric inornata (Phryganeidae) and Hesperophylax designatus (Limnephilidae), collected only in June, and Glossosoma intermedium and Protoptila tenebrosa (Glossosomatidae), found only from late July through mid August.

A new species, Oxyethiraitascae Monson and Holzenthal, was discovered at Nicollet Creek during the study; in addition, Oxyethira verna, Hydroptila wyomia, H. xera, Polycentropus clinei, P. iculus, Pycnospyche limbata, Ceraclea vertreesi, Oecetis nocturna, and Triaenodes ignitis, collected during this study, are new records for Minnesota, and O. ecornuta is a new record for Minnesota and the United States. Other new State records were encountered during examination of museum specimens and include Hydroptila angusta, Hydroptila antennopedia, Diplectrona modesta, Oligostomis ocelligera, Micrasema gelidum, Ironoquia lyrata, Onocosmoecus quadrinotatus, Pycnopsyche aglona, Goera stylata, Lepidostoma sackeni, and Ylodes frontalis.

The conservation status of Minnesota Trichoptera is discussed and species are classified as endemic, disjunct, regionally restricted, range limited, or widely distributed. Recommendations are made for future study of the endemic, disjunct, and regionally restricted species. Endemic species are Protoptila talolci (Glossosomatidae), Oxyethira itascae (Hydroptilidae), Polycentropus milaca (Polycentropodidae), Chilostigma itascae (Limnephilidae), and Ceraclea brevis (Leptoceridae); disjunct species are Agapetus tomus (Glossosomatidae), Hydroptila metoeca, H. novicola, H. tortosa (Hydroptilidae), Ceraclea vertreesi, and Setodes guttatus (Leptoceridae); regionally restricted species are Oxyethira ecornuta (Hydroptilidae) and Limnephilus rossi (Limnephilidae). Special emphasis is placed on recommendations for Nicollet Creek, the type locality for both Chilostigma itascae and Oxyethira itascae. An annotated list for all species recorded from Minnesota is presented.

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