Caddisflies: O’Brien rhyacophilan caddisfly
Rhyacophila colonus

(Trichoptera: Rhyacophilidae: Rhyacophilinae)
Profile prepared by Sarah Foltz, The Xerces Society for Invertebrate Conservation

This species lives in running water habitat of streams and torrents in dense forest, and is known from a collection of nine adults in 1965 at the Oregon type locality (in the vicinity of O’Brien, Josephine Co.), and from a relatively recent (1993) collection of one adult male in California (Trinity County, Little Bidden Creek). Despite extensive, targeted surveys at the type locality in 1998 and 1999, this species has not been recovered, and it is possible that it is now extirpated from the area. Housing development and stream-water diversions have been occurring in the vicinity of O’Brien, Oregon (on both private and USFS land) during the forty-three year time-span since this species was originally collected, and the risk of local extirpation due to these habitat-altering activities appears to be high. Riparian habitat protection, including maintenance of water quality, substrate conditions, and canopy cover, would likely benefit and help maintain this species.

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conservation status

Global Status (2008): G1
Rounded Global Status: G1- Critically Imperiled
National Status (United States): N1
State Statuses: California: not ranked, Oregon: SH (Possibly Extirpated: species occurred historically in the state and there is some possibility that it may be rediscovered, but efforts to relocate occurrences have not been successful).
IUCN Red List Category: NE – Not evaluated

Note that the recent California record resulted in a global status change from GH/NH to G1/N1. This change is not yet apparent on the public NatureServe website. (NatureServe 2008, Cordeiro 2008, pers. comm.)

identification

Adult: The adults of this species are small, moth-like insects, 1.2 cm (0.5 in) in length. Species identification is based on the male genitalia (Schmid, 1970).

Immature: Although the larval stage of this species is unknown, all members of the family are free-living (case-less) until the end of the final larval stage when a pupal chamber is made. Pupal enclosures of most Rhyacophila species are constructed of rock fragments and fastened to the underside of a stable rock on the benthos surface (Wisseman 2008, pers. comm.). In North America, Rhyacophila pupal chambers range in length up to 25 mm (1 in.), and may be quite obvious on the undersurface of rocks (Wiggins 2004).

life history
The larval behavior and diet of this species are probably similar to others in the genus. Rhyacophila larvae are generally predaceous, feeding on simuliid (black fly) larvae, chironomid (midge) larvae and pupae, and the pupae of other caddisflies (Thut 1969, reviewed in Wiggins 2004). Rhyacophila gut content analysis has also revealed small proportions of mites, oligochaetes (segmented worms), and copepods (microcrustaceans) (Thut 1969). The flight period of this species is unknown, but the known records in both Oregon and California were in June. Little is known about the adult emergence, sexual maturation, mating, oviposition, dispersal, and life span of this species.
distribution

This species is known from a collection of nine adults at the Oregon type locality (in the vicinity of O’Brien, Josephine Co., 1965), and from a collection of one adult male in California (Trinity County, Little Bidden Creek @ Highway 299, 1993) (Burdick 1999). Darren Borgias with The Nature Conservancy conducted extensive surveys for this species in 1998 and 1999. (Borgias and Wisseman 1999). Surveys took place between May and August, across twenty-one days in total, and included overnight ultraviolet light trapping, sweep netting, and benthic searches for larvae at thirteen Siskiyou National Forest streams in the vicinity of the type locality. A Nature Conservancy report details the dates and locations of the survey, including maps (Borgias and Wisseman 1999). Although five Rhacophila species were collected (identification by Robert Wisseman), this species was not among them, and it is possible that the species is now extirpated from the area.

Forest Service/BLM Lands: The only known documented Oregon occurrence is in the vicinity of the Siskiyou National Forest.

habitat associations
The entire Rhyacophila genus, whose name is derived from the Greek roots rhyaco (stream or torrent) and philia (fondness), is confined to running water. Within the genus, larvae of the Sibirica subgroup are typically found in small to mid-size streams in forested, montane areas (Wisseman 2006, pers. comm.). The adults of this species were collected along streams and torrents in dense forest. Larvae of the congeneric R. arnoudi forage for prey in interstitial spaces between gravels and are found in stream runs with a deep layer of gravel and coarse sand substrates that are not smothered with silt or algae (Wisseman 2008, pers. comm.).
threats

Housing development and stream-water diversions have been occurring in the vicinity of O’Brien, Oregon (on both private and USFS land) during the forty-three year time-span since this species was originally collected (Borgias and Wisseman 1999). Since subsequent collection effort has not revealed this species, the risk of local extirpation due to these habitat-altering activities appears to be high.

conservation needs

Inventory: Although this rare species appears to be extirpated from the 1965 type locality in Oregon (Borgias and Wisseman 1999), the recent record (1993) in California (Burdick 1999) suggests the continued existence of this species, and has resulted in a global status change from GH (possible extirpated) to G1 (critically imperiled) (Cordeiro 2008, pers. comm.). Conduct follow-up surveys at the California site and adjacent habitat in an effort to collect a voucher series and establish the current status of this species at the site (Wisseman 2008, pers. comm.). Since the larvae of this species are unknown, collect as many life stages as possible and rear out some individuals in order unambiguously associate immature stages with adults (see Survey Protocol, attached). Further documentation of this rare species’ range and habitat is especially critical for advancing our understanding of its needs and taking the appropriate conservation measures.

Management: Protect all new and known sites and their associated watersheds from practices that would adversely affect any aspect of this species’ life cycle. Riparian habitat protection, including maintenance of water quality, substrate conditions, and canopy cover, would likely benefit and help maintain this species.

references

Borgias, D. and Wisseman R.W. 1999. Report on the 1998 and 1999 survey for Rhyacophila colonus, in forested torrents near O’Brien, Oregon. The Nature Conservancy of Oregon. Prepared for Diane Perez, Siskiyou National Forest.

Burdick, D.J. 1999. Trichoptera of California. Listing of records in the Donald G. Denning collection of Trichoptera at the California Academy of Sciences, San Francisco, California. Posted at a web site in 1999. Department of Biology, California State University, Fresno, California. Reference obtained via personal communication with R. Wisseman, 2008.

Cordeiro, Jay. 2008. Personal communication with Sarah Foltz.

NatureServe. 2008. “Rhyacophila colonus.” NatureServe Explorer: An online encyclopedia of life [web application]. Feb. 2008. Version 7.0. NatureServe, Arlington, Virginia. 6 Oct. 2008 .

Schmid, F. 1970. Le genre Rhyacophila et la famille Rhyacophilidae (Trichoptera). Memoirs of the Society of Entomology of Canada. 66:1-230.

Thut, R.N. 1969. Feeding habits of larvae of seven Rhyacophila (Trichoptera: Rhyacophilidae) species with notes on other life history features. Annals of the Entomological Society of America 62: 894–898.

Wiggins, G.B. 2004. Caddisflies: the underwater architects. University of Toronto Press, Toronto. 292pp.

Wisseman, Robert W. 2006. Personal communication with Eric Scheuering.

Wisseman, Robert W. 2008. Personal communication with Sarah Foltz.

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