Plesioaxymyia vespertina, Sinclair, Bradley J., 2013

Sinclair, Bradley J., 2013, Rediscovered at last: a new enigmatic genus of Axymyiidae (Diptera) from western North America, Zootaxa 3682 (1), pp. 143-150 : 146

Plesioaxymyia vespertina sp. nov.

(Figs 1–3)

Material examined. HOLOTYPE Ƥ, labelled: “ USA: WA: Mt Rainier NP/ Narada Falls to Reflection Lk/ trail; N46°46' W121°44' / 1400 m, 17.vii.2012 / B.J. Sinclair”; “ HOLOTYPE / Plesioaxymyia / vespertina / Sinclair [red label]” ( CNC). PARATYPE: USA. Alaska: Isabel Pass, mi 206 Richardson Hwy., 2900', 13.vii.1962, P.J. Skitsko (1 Ƥ, CNC).

Etymology. The species name is from the Latin vespertinus (western), in reference to its distribution in North America.

Description. Female. Body length: 3.7 mm (not including antenna). Head: Antenna longer than width of head; scape and pedicel somewhat paler than dark brown flagellum; pedicel slightly longer than scape. Frons with setulae along inner eye margin and above antennal bases. Thorax: Scutum dark brown, concolorous, clothed in fine pruinescence and short setulae; lacking prominent setae. Pleura somewhat paler than scutum, subshiny. Coxae concolorous with pleura; femora pale brown, darker towards apices; tibiae pale brown with proximal and distal portions darker; tarsomeres dark brown; mediolobus and pulvilli bright white. Wing: Length: 3.8 mm, subequal to body length, excluding antenna; pterostigma distinct, brown, otherwise wing unmarked; M1+2 with long stem, longer than M2. Halter stem with 2–3 scattered setulae, lacking dense cluster of setae. Abdomen: Basal segment dark; segments 2–6 pale brown; segment 7 with anterior half pale brown and posterior half dark brown; pleural region dark brown. Male and immatures. Unknown.

Remarks. This species was collected by sweep net while walking along the Woodland hiking trail from the base of Narada Falls to Reflection Lake in Mt. Rainier National Park. This trail runs below Hwy 706, through mid-elevation conifer forests at approximately 1400 m. The season appeared to be early spring, with many small snowmelt streamlets and broad, major streams often retaining thick snow caps. However the daytime air temperatures reached 27–29°C and spring flowers were in full bloom.

The immature stages of P. vespertina are assumed to occur in saturated logs and branches as recorded for the other three extant axymyiid genera. But given the unsuccessful attempts to collect the immature stages at the Alaskan locality, perhaps the immature stages reside in wet leaf litter or decomposing fungi. Larvae of the family Perissommatidae , which has been suggested as closely related to Axymyiidae (see following section), have been found in decomposing fungi ( Colless 1962).