Nycterimyia capensis Bezzi, 1924 : 168

Barraclough, David A., 2006, Remarkable sexual dimorphism in the Afrotropical species Nycterimyia capensis Bezzi, 1924 (Diptera: Nemestrinidae), and its taxonomic implications, Zootaxa 1273, pp. 1-7 : 3-6

Nycterimyia capensis Bezzi, 1924: 168 .

Female (only significant differences from male cited):

Dimensions (in mm): Total length 10.3 (includes compensation for abdominal curvature); greatest width of abdomen 3.7; length of wing 10.5; greatest width of wing 3.3.

Body colour: Head pruinosity indistinctly silver to pale yellow, most prominent on and between antennae, on mesofrons and on much of occiput. Thorax mostly yellow­brown; distinctly darker brown as transverse elongate­ovoid areas along medial two­thirds of scutellum posterior to scuto­scutellar suture, and across each postalar callus; pleuron somewhat darker (particularly anteriorly and posteriorly) than mesonotum; pruinosity indistinctly silverish, most evident on pleuron. Legs mostly pale yellow­brown, but femora distinctly darker brown on dorsal surface and/or on apical third. Abdominal dorsum mostly a pale mustard­brown with irregular darker brown blotching, particularly on anterior half; ovipositor glossy dark brown; pruinosity only evident on terga 1–5, here indistinctly silver.

Pilosity ( Fig. 3 ): Entirely pale (i.e. yellow) on head, absent on much of parafrontal, entire parafacial and about posterior half of mesofrons. Ocellar protuberance with pile of similar length over much of surface. Thoracic pleuron with pile entirely yellow, markedly sparser and shorter, largely absent over much of the surface, most noticeably present as a tuft at lower extent of propleuron and over much of posterodorsal section below wing. Mesonotal pilosity much shorter and sparser, very short and recumbent on presutural section, although noticeably denser and more elongate above wing base; largely absent on postsutural section except on postalar callus and posterior half of scutellum, here very short and erect, otherwise a few very short and irregularly scattered hairs evident at high magnification on the remainder. Vestiture on legs greatly reduced, almost entirely yellow except brownish on dorsal section of swollen hind femoral apex; femora with vestiture very short, albeit relatively profuse, some more elongate pile present dorso­apically; tibiae with some irregularly scattered short, sparse hairs. Abdominal pilosity largely absent, very short, recumbent and gold in colour where present; evident only in profile on dorsum, here distributed over posterior half to three quarters of terga 2 to 7, on T3–T7 also evident along much of lateral margins; pilosity almost completely absent on sternum; pruinoity evident only on posterior half of T2, here relatively sparse and silver.

Head: Profile noticeably more slender. Eyes not closely approximated, inner orbits widely separated above, where frons is broadly exposed at vertex; width at vertex slightly more than that of ocellar protuberance, and gradually widening to broadest point just short of antennal bases, where width reaches almost 2.5 times that of ocellar protuberance. Ocellar protuberance only moderately exposed above eye margin in profile, upper extent of frons also just evident in profile. Ocelli smaller in size. Mesofrons somewhat excavate at mid­length. Eye with ommatidia all of similar size. Antenna shorter, style only slightly longer than combined length of first three antennal segments; style noticeably broadened in apical half to two­fifths just short of sharply pointed extremity, distended section with very short serial vestiture along ventral margin, width here about two­fifths that of third antennal segment. Palp longer, subequal in length to style, more obviously swollen apically.

Thorax: Legs very short and particularly stout; hind pair significantly longer than the others; hind femur almost 3.0 times length of fore femur. Fore and mid femora notably short and stumpy. Hind femur significantly swollen in apical two­to three­fifths, but most markedly so in apical two­fifths, maximum width of swollen section almost 3.0 times that of slender basal section.

Wing ( Fig. 2 ): Hind margin only slightly inwardly curved at three places, thus wing appearing significantly broader along much of length. Distance between apex of subcosta and crossvein between first and second longitudinal veins much less than that from crossvein to apices of first and second longitudinal veins (crossvein missing in right wing). Membrane largely an opaque, dark yellow­brown to pale brown, with irregular dark speckling (small spots) evident mainly in apical half of wing. Hyaline wing markings: marking present across much of basal two­thirds (except extreme basal section) of first basal cell (marking absent in male); marking in second basal cell much more extensive, covering much of basal two­thirds to three­quarters (extreme base excepted); small irregular marking in basal two­fifths of fourth posterior cell; irregular marking in basal fifth of fifth posterior cell, this confluent with marking in fourth posterior cell; combined first and second posterior cells without any markings, being a striking difference from the male.

Abdomen: More slender than in male, 1.3 times longer than wide. Unlike male, T6–8 easily evident in dorsal view, and much more slender than preceding terga.

Terminalia ( Fig. 4 ): These not dissected, but studied in situ (only one female available for study). Ovipositor of Bernardi’s type 2; cerci elongate and sabre­shaped; largely a glossy red­brown in colour and completely lacking vestiture; apical section noticeably upcurved in profile.

Material examined: MADAGASCAR: 1 female, Ranomofana [18.95°S: 48.83°E], 22.i.58, F. Keiser (Naturhistorisches Museum Basel). This specimen was collected a day after a single male (also deposited in Basel) was taken at the same locality, both at light. It is certain that they are conspecific. Ranomafana is situated near the coast in eastern Madagascar.

Discussion: The male and female of Nycterimyia capensis are strikingly different ­­ so much so that that if they were collected at different localities and at different times, it is likely that most specialists would consider them to represent different species, or even different genera. The most striking differences between the sexes are the following (female character state in square parentheses):

1. Head profile noticeably more slender in profile in female.

2. Ommatidia significantly larger in upper two­thirds to three­quarters of eye [no differentiation in size of ommatidia].

3. Eyes with inner orbits closely approximated above [widely separated above with frons broadly exposed at vertex].

4. Ocellar protuberance prominent above eye margin in profile [only moderately exposed].

5. Antennal style tapered apically, not here broadened or with short ventral vestiture [noticeably broadened in apical half to two­fifths just short of sharply pointed extremity, distended section with very short serial vestiture along ventral margin].

6. Legs significantly shorter and stouter in female.

7. Thoracic pleuron with dense, elongate pilosity [pile largely absent over much of surface and markedly sparser and shorter when present].

8. Mesonotal pilosity profuse and elongate [largely absent, when present on lateral margin anterior to postalar callus, only of moderate length].

9. Wing markedly inwardly curved at three places along posterior margin [only slightly incurved, thus wing appearing much broader along much of length].

10. First basal cell without a hyaline marking [extensively hyaline over much of basal two­thirds].

11. First/second posterior cell always with transparent marking/s [marking/s absent].

12. Abdomen relatively stout in appearance in dorsal view, with profuse and elongate pile [abdomen more slender, pile almost entirely absent].

There are a number of significant colour characters (body and pile colour) distinguishing the sexes, but these are omitted from consideration, given that colour may be subject to intraspecific variation.

Figures

FIGURES 1 – 4. 1 – 2. Wings of Nycterimyia capensis. 1. Male. 2. Female. 3. Female abdomen, dorsal view, showing lack of vestiture. 4. Female ovipositor, profile.