Philetus Melander

Cumming, Jeffrey M., Brooks, Scott E. & Sinclair, Bradley J., 2016, Review of the little-known western Nearctic fly genus Philetus Melander (Diptera: Empididae), with a discussion of its phylogenetic assignment, Zootaxa 4093 (2), pp. 261-274 : 263

Genus Philetus Melander

Philetus Melander, 1928: 110 . Type species, Philetus memorandus Melander, 1928 (original designation). Melander, 1965: 455; Poole, 1996: 158, 368; Sinclair & Cumming, 2006: 74, 102–105, 107; Yang et al., 2007: 350; Marshall, 2012: 288; Cumming et al., 2014: 171, 205.

Diagnosis. The genus is characterized by the following features: small size (body length 3.0–5.0 mm) brownish grey flies with silvery grey tomentum ( Figs 1 , 4 ); head produced obliquely downwards; ocelli positioned forward on broad V-shaped frons; eyes bare, dichoptic in male and female; inner eye incision present; antenna inserted just below middle of eye ( Figs 5, 6 ); apical stylus slightly tapered with 3 articles including minute terminal hyaline process, subequal to or slightly shorter than length of pyriform postpedicel ( Figs 7, 8 ); proboscis moderately long; epipharyngeal blades movable; palpus straight, directed forward ( Figs 5, 6 ); head and thoracic chaetotaxy dark; mesonotal setae on each side with a few short irregular presutural acrostichal setae, row of 4–6 long dorsocentral and 3–4 intra-alar setae, 1–2 postpronotal setae, 1–2 presutural supra-alar setae, 2 notopleural setae, 1 postalar seta, and 2 (pairs) of long scutellar setae; mesopleuron and laterotergite bare; legs without prominent bristles; wing (Fig. 9) with venation complete (for Eremoneura), including nearly straight Sc reaching C, forked R4+5, cell cua angled apically with CuA curved back towards short evanescent CuA+CuP vein, basal costal bristle present, pterostigma faint, anal lobe developed; male terminalia (Figs 11–20) with median apical hypandrial process, gonocoxal apodeme projecting anteriorly as process from anterodorsal margin of hypandrium, postgonite broad, ejaculatory apodeme lever-like and articulated to base of phallus, phallus tubular with desclerotized apex, epandrium deeply emarginate with left and right lamella connected basally, epandrial lobe present apically, proctiger differentiated into a long ventral and short medial subepandrial lobe attached to prolonged dorsal cercus; female terminalia (Fig. 10) with terminal segments partially telescopic, tergite 10 undivided without acanthophorites, cercus narrow, spermatheca unpigmented and sac-like.

Geographical distribution ( Fig. 21 ). Known from Alaska and the Yukon Territory in the north to California, Nevada and Arizona in the south, including records from British Columbia, Washington, Oregon, Montana, Wyoming and Colorado (with undetermined female specimens listed in the Appendix).

Remarks. In the Nearctic Region, this genus is most similar to Hesperempis Melander and somewhat like Hilara Meigen , but can be most easily distinguished from these empidid genera by the oblique form of the head with forward positioned ocelli and low inserted antennae. Philetus also has straight forward-directed palps and vein Sc nearly straight and joining C at an acute angle unlike Hilara . In addition, Hilara and most members of the Hilarini have vein R1 swollen prior to reaching C and males usually have the first tarsomere of the foreleg expanded (Sinclair & Cumming 2006). In their key to Nearctic genera of Empididae, Steyskal & Knutson (1981, p. 617) refer to a complete lack of thoracic setae in Hesperempis compared with Philetus , but this does not apply to all the included species of Hesperempis (Cumming et al. 2014) . However, the dark setae on the head and thorax of Philetus are diagnostic compared with the pale more inconspicuous chaetotaxy of Hesperempis .

Except for differences in the male and female terminalia, specimens of Philetus also resemble the brachystomatid genus Heleodromia Haliday , although they can be easily separated by the presence of a forked R4+5 wing vein in Philetus . Marshall (2012: 288, fig. 5) provided a good-quality photograph of a live female specimen of Philetus , which is reproduced here with permission ( Fig. 1 ).

Figures

FIGURES 1 − 3. Philetus habitus photograph and habitat. 1. Philetus sp., live female; photograph by S. A. Marshall. 2. Sitka spruce canopy, Upper Carmanah Valley, Vancouver Island, British Columbia. 3. Coastal wet temperate rainforest, Upper Carmanah Valley.

FIGURES 4 − 8. Philetus morphology. 4. P. memorandus, pinned male. 5. P. schizophorus, male head, lateral view. 6. P. schizophorus, male head, anterior view. 7. P. memorandus, female antenna. 8. P. schizophorus, female antenna. Abbreviation: pped—postpedicel.

FIGURES 21 − 23. Distribution of Philetus. 21. Overall distribution of the genus Philetus, including undetermined female specimens. 22. Known distribution of P. memorandus. 23. Known distribution of P. schizophorus.