Ptychoptera alexanderi Hancock, sp. nov.

Ptychoptera alexanderi Hancock sp. nov.

Diagnosis. This species of Ptychoptera shares the general morphological characters of other known species but exhibits a unique combination of a number of features. The most obvious is the slender male antennae being nearly the same length as the body. This is achieved by the basal flagellomere being twice the length of each of the three or four following flagellomeres, which are about 10 times as long as wide. By comparison, the Nearctic species have these same flagellomeres only two to three times their own width. The clypeus of both sexes is swollen. As in the majority of western Nearctic species, this new species has cross vein r-m meeting R4 + R5, whereas in the two eastern species, P. quadrifasciata Say and P. osceola Alexander, r-m meets Rs before the fork. The wing is strongly patterned with three dark curved bands and a short apical band that marks the upper internal edge of the apical patch. The central pair of bands is curved in opposing directions, having the effect of leaving an almost circular clear area in the middle of the wing centred over the base of the radial cells. There is no pigmentation proximally in the basal cells. Macrotrichia are extensive in all the radial cells (Fig. 1). A marked pattern on the dorsum is provided by a blackish outline to the deep mesonotal suture continued around the dorsal edge to above the wing base, giving a strong blackish W-shaped mark to the dorsum against a paler yellowish brown background. The black shiny anepimeron contrasting with the other pleurae is marked. There is no obvious pruinosity on the thorax; many other species of Ptychoptera have silvery patterns changing with different viewing angles. There is no auxiliary copulatory organ on the third (visible) abdominal sternite, as in some Palaearctic species. In the male, the extreme length of the lateral arms of the ninth tergite, extending nearly the same distance as the gonostyles is noticeable. Another notable difference in the male genitalia of the Nearctic species P. quadrifasciata and P. osceola is the enlarged ninth sternite that accommodates the large spherical sperm pump. This character is not so strongly developed in P. alexanderi sp. nov.

Holotype male. Body length 8.0 mm, wing 8.8 mm, antenna 7.0 mm. Head: vertex shining black; occipital region and face brown; clypeus convex and same shade of brown as are palp, scape, pedicel, and basal flagellomere plus extreme base of second flagellomere, remainder of antenna brownish-black; 1st flagellomere twice length of succeeding flagellomere. Antennae of male elongated, nearly equal to body length. Thorax: shining and mainly yellowish-brown. Blackish in prescutellar area of dorsum, more obviously so when viewed from behind; black border to dorsal suture, joining anteriorly with broader black lateral markings that originate above wing base; poorly defined medial stripe visible within suture when viewed anteriorly. Anepimeron distinctly black, contrasting with remaining yellow pleurae. Halteres yellow in basal quarter, otherwise black. Scutellum yellow; mediotergite black. Mid and hind coxae with illdefined darker streaks of brown; femora yellowish-brown except for narrow apical ring; remaining leg segments brownish-black. Wing with partial black bands and apically darkened; typical wing fold rather obvious, extending from base of anal vein to bend in second cubital (Fig. 1). Abdomen: shiny blackish-brown; laterobasal half of tergite 2, basal 3rd of tergite 3, and laterobasal corner of tergite 4 yellowish; sternites yellow. Genitalia with greatly extended lateral arms to tergite 9, as long as gonostyli (Fig. 2). Caudal margin of ninth sternite bearing clasper-like structure that protrudes dorsally (Fig. 3).

Female. body length 8.0 mm, wing 9.0 mm, antennae 2.5 mm. General appearance same as male except for short antennae and abdomen more broadly yellowish about base of tergites 3, 4, and 5; downcurved cerci totally yellow. Lighter wing markings may be due to specimen being recently emerged when collected, but degree of change from teneral condition to full pigmentation is unknown (Fig. 4).

Material examined. Holotype male: MEXICO, Chiapas, Sierra Madre Mountains, El Triunfo (Biosfera Reserva): 1900-2000m, 5º39’26”N 92º48’32”W, E.G. Hancock, collected by sweeping, 30.vii.2003, (holotype male deposited in the Hunterian Museum (Zoology), Glasgow, Scotland bearing registration number GLAHM: 127118. Paratype: female: same data (also deposited in Hunterian Museum (Zoology), registration number GLAHM: 127119). Both specimens were micropinned in the field and are staged on a polythene foam strip.

Etymology. Ptychoptera alexanderi sp. nov. is named in memory of Charles Paul Alexander (1889-1982), the much admired and prolific New World nematoceran systematist, who included this family in his research.

Biology. The adults of Ptychoptera alexanderi sp. nov. were swept from fairly rank streamside vegetation, where the stream margin comprised coarse sand grading to mud. Adult ptychopterids are generally found near running water or in marshy areas, and rest in dense waterside vegetation (Stubbs 1993). The larvae are associated with saturated mud or soils near water (Brindle 1962). They are considerably elongated caudally, presenting a superficial resemblance to the long-tailed larvae of the Eristalinae (Syrphidae). To cope with respiration after pupation, the right thoracic breathing horn is greatly elongated, up to twice the length of the pupa, whereas the other horn is atrophied. These and other observations (Alexander 1920, 1981; Brindle 1962; Hodkinson 1973; Stubbs1993) support the idea that this new species was found in a typical situation and probably was breeding in the stream margins near where the adults were found. Notwithstanding these conditions, no other specimens could be collected despite considerable effort.