Roederiodes Coquillett 1901

Roederiodes Coquillett

Roederiodes Coquillett, 1901: 585. Type species, R. junctus Coquillett (original designation).

Roederioides (error).

Recognition. Adult Roederiodes are distinguished from other clinocerine genera by the broad gena and long, slender labrum, small labium and geniculate female cercus. Pupae are readily identified by the long and elevated face and labral sheath and U-shaped labellar sheath. Larvae are characterized by four elongate caudal processes. The genus name is masculine.

Redescription. See Sinclair (1995).

Remarks. This genus occurs in all geographical regions except Australasia and now includes 25 described species (Appendix). Sinclair & Harkrider (2004) removed and transferred five species to Clinocerella Engel, but this decision was subsequently revised and now only the following three former species of Roederiodes are assigned to Clinocerella: gereckei (Wagner & Horvat, 1993), siveci (Wagner & Horvat, 1993), wagneri (Pusch, 1996). The other two species, Roederiodes macedonicus Wagner & Horvat, 1993 and R. montenegrinus Wagner & Horvat, 1993 remain in Roederiodes on the basis of mouthparts and male terminalia.

Distribution. In the New World, the genus is rather widespread from the Northwest Territories of Canada, south to Costa Rica. In North America, the genus is surprisingly absent from the Pacific Northwest (British Columbia, Idaho, Oregon, Washington), Alberta and Montana, despite focussed collections of aquatic associated empidids by a number of Dipterists over the past 100 years.

Biology. The immature stages of Roederiodes were first illustrated, described and reared by Needham & Betten (1901) from larvae collected among black fly (Simuliidae) pupal cases in rapids in New York State, whereas pupae were collected from within empty black fly pupal cases. The larvae and pupae were later described in detail by Sinclair & Harkrider (2004). Adults are usually observed in small clusters on branches and boards positioned above fast flowing water, often in spray zones (Needham & Betten 1901; Sinclair & Harkrider 2004; pers. obs.). Needham & Betten (1901) reported that these clusters of male and female flies remained, even if the wood was lifted and were readily collected for closer study. The substrate below these clusters was wet with a thin gelatinous mass of minute eggs. Sinclair & Harkrider (2004) found R. wirthi Chillcott eggs among simuliid eggs scraped from rocks, which were observed when brought into the lab. Upon hatching, the empidid larvae readily feed on newly emerging black fly larvae. In the lab, R. wirthi larvae were mostly fed with chironomid larvae. Adults have been collected among swarming black flies, and it is assumed that both larvae and adults are predators of simuliids (Chillcott 1961).

Adults of Roederiodes are believed to overwinter. This is based on the observation of males and females of R. distinctus Chillcott in Colorado (S.J. Fitzgerald 2020, pers. comm.). Adults were collected from November to February from depressions which formed air pockets on the bottom of medium-sized emergent rocks above the water surface in a small shallow creek. Adults were found clustered in the air pockets in groups of about three to fifteen. In October, May and July, when Colorado temperatures are still mild, these clusters were not observed and adults were collected in the splash zone of mid-creek rocks (S.J. Fitzgerald 2020, pers. comm.). These winter clusters are believed to be a behaviour in response to low air temperatures. The author has collected adult specimens of R. recurvatus Chillcott in streams in Quebec in mid-April. These adults were only collected by dip-net in early spring conditions and no adults were observed in flight. Based on the observations from populations in Colorado, it is hypothesized these early spring collections in Quebec represent overwintering adults. Elsewhere in Quebec, adults have been trapped in emergence traps from June to September (Harper 1980; Landry & Harper 1985).