Piezura nearctica Chillcott, 1961

Moores, Amy & Savage, Jade, 2005, A taxonomic revision of Piezura Rondani (Diptera: Fanniidae), Zootaxa 1096 (1), pp. 41-59 : 50-52

2. Piezura nearctica Chillcott, 1961

Figs. 2A–D

Piezura nearctica Chillcott, 1961: 230

Diagnosis: Distance between eyes 1.7–2.1x width of first flagellomere in male, postpronotum yellow in both sexes, male mesolobus with strongly bifurcate apex ( Fig. 2A ).

Type material examined: Holotype ♂ labeled: Bar Harbour/ Me/ VII.22.1919; Holotype / Piezura / nearctica / Chillcott/ No. 64288 ( USNM).

Other material examined: Over 60 ♂ and ♀ examined. NEARCTIC: Canada: Quebec: Mont St. Hilaire ; Ontario: Ottawa ; USA: Michigan: Dickinson County ; New Hampshire: Benton. ( CNC, LEM, USNM)

Description:

Male: body length 4.5–5.0 mm.

Head: Frons at narrowest point 1.7–2.1x width of first flagellomere; frontal vitta black; anterior fronto­orbital plate with 4–7 medioclinate fr and with a few setulae; 1 reclinate upper orb; parafacial pale grayish­brown pollinose; fronto­orbital plate grayishbrown pollinose; first flagellomere 1.8–2.1x as long as wide; scape, pedicel and base of first flagellomere yellow, distal half of first flagellomere dark grayish­brown; arista short plumose, with longest hair 0.5–0.6x width of first flagellomere.

Thorax: Background color brownish­gray with three distinct dorsal vittae, median one broader than lateral ones; anterior presutural dc 0.7–0.8x length of posterior presutural dc; acr irregularly quadriserial; scutellum with 1 strong ap sctl, 1 weak ds sctl, 2 b sctl, the anterior one weaker and 2–3 accessory setulae; postpronotum reddish­yellow to pale yellow.

Legs: f1 usually infuscated along most of dorsal surface, f2 and f3 infuscated near tip; t3 with 0–1 av on apical third (see Remarks), 1 strong ad on apical half and often with 2–3 erect but much weaker ad on apical third, apical half of pv surface with a few erect setulae; f3 with 1 row of short av, with 1–4 stronger av on apical third, 1 row of ad, stronger towards apex, 1 preapical d, 1 preapical ad and 1 row of short pv with 1–4 stronger pv on apical third.

Wings: Costal spine weak, no more than 1.5x as long as surrounding setulae.

Abdomen: Tergites 3 and 4 variable, with dark lateral patches present or absent and with median vitta present or absent (see Remarks).

Postabdomen: Mesolobus narrow, 2x as high as wide with bifurcate apex ( Fig. 2A ); sternite 5 3x as wide as long ( Fig. 2D ).

Female: body length 4.0–6.0 mm.

Head: As in male except frons at narrowest point 2.6–2.8x width of first flagellomere, 1 lower latero­reclinate orb present; arista with longest hair 0.3–0.4x width of first flagellomere.

Thorax: As in male except anterior presutural dc 0.5x length of posterior presutural dc; scutellum with 2 weak ds sctl.

Legs: Color as in male, but with f1 sometimes completely yellow; t3 with 1 av on apical third, 1–2 ad on apical half and 2 d on apical half.

Wings: As in male

Abdomen: As in male except tergites 3 and 4 always laterally darkened; dark median vitta present on tergites 3 and 4, present or absent on tergite 5.

Postabdomen: See generic description and illustrations ( Figs. 2B, 2C ).

Distribution: NEARCTIC – Canada: Ontario, Quebec; USA: Michigan, New Hampshire, Maine.

Remarks: Prior to this revision, P. nearctica was known only from the male holotype from Maine, USA ( Chillcott 1961). Many additional specimens were discovered in the course of this study and the female is described here for the first time. Upon examination of this additional material, it became clear that a number of anatomical features are more variable than originally described by Chillcott (1961). Piezura nearctica shows variation in the bristle pattern of the hind tibia (anteroventral bristle on apical third present or absent) and in abdominal marking. The absence of an anteroventral bristle on the hind tibia was used by Chillcott (1961) to distinguish P. nearctica from P. pardalina (as P. graminicola ). Since the bristle may be present or absent in P. nearctica , this feature should no longer be used to distinguish the two species. Width of the frons in males and the shape of the mesolobus are much more reliable features to separate the two species.

We also found that no correlation exists between bristle patterns of the hind tibia and abdominal markings. That is, specimens with an anteroventral bristle on the hind tibia may or may not have dark abdominal markings, and those lacking the bristle may or may not have dark abdominal markings. Since all material examined was uniform in most other morphological features (including genitalia), we deemed it unnecessary to erect a new species for those specimens with an anteroventral bristle on the hind tibia.

Figures

FIGURE 2. Piezura nearctica Chillcott. A. Male genitalia external structures, posterior. B. Female spermatheca. C. Female genitalia, ventral. D. Male sternite 5, ventral.