Pyrgotidae

McAlpine, David, 2011, Observations on Antennal Morphology in Diptera, with Particular Reference to the Articular Surfaces between Segments 2 and 3 in the Cyclorrhapha, Records of the Australian Museum 63 (2), pp. 113-166 : 153-154

The Pyrgotidae

I have examined antennal structure in the following species: Cardiacera carnei (Paramonov) , Maenomenus ensifer Bezzi , Prodalmannia variabilis Bezzi , Adapsilia sp. (Kuranda, Queensland). The first three of these have fairly uniform antennal structure, but Adapsilia has some unusual features and will be described separately.

In the more typical genera segment 2 has a broad encircling rim, often interrupted by a dorsal notch or incipient cleft. The distal articular surface is more or less concave. The conus is moderately short, not markedly receding dorsally, arising from within a deep cup lined by largely membranous cuticle. This condition apparently confers considerable flexibility on the conus which therefore has the property of an additional articulated antennal segment ( Figs 134–136 ). The foraminal ring is simple, rounded but not quite circular and only slightly tilted dorsally to dorsolaterally; caesti and cusps are absent. The button is located dorsolaterally near or on the annular ridge. This condition somewhat resembles that in the Chloropidae , but there is no chin and the collar is less developed; the chloropids studied have no cleft in the rim. Segment 3 ( Fig. 137 ) is without a typical basal stem, though sometimes it may be more basally prominent dorsally than ventrally. The basal hollow is broad, but only of moderate depth. The basal foramen is located on the lateral wall of the hollow on a slight gibbosity, which is probably flexible. The sacculus of Maenomenus has a relatively large external pore. The external pore could not be detected in the other pyrgotid genera, but a sacculus is presumably present (certainly present in Cardiacera ). The arista in these examples is three-segmented with strongly marked articulation between segments 5 and 6. Segment 4 is relatively large in Cardiacera , in some species almost as long as segment 5; in the other genera it is short but sclerotized.

In Adapsilia sp. ( Fig. 138 ) the antenna is longer than in the above examples. The rim lacks the dorsal notch and the distal articular surface is only partly concave. There is no cup or encircling furrow. The conus is remarkably large, elongate, and apparently flexible over most of its length, but less so basally; its cuticle is thrown into many encircling folds and the surface has finer transverse ridging; the foramen is strongly tilted laterally. This structure is apparently derived from that of Cardiacera etc., but differs markedly in the great prolongation of the conus and extension of the flexibility of the cuticle over much of the length of the conus. Segment 3 has a deep, capacious basal hollow. Segment 4 is reduced to a minute vestige, so that the arista appears to be two-segmented. Korneyev (2004) drew attention to the numbers of aristal segments in the key to Palaearctic genera of Pyrgotidae .

The convergent resemblance in some characters between certain taxa of Conopidae and Pyrgotidae has been mentioned before (e.g., Hennig, 1952: 195). The structure of antennal segment 2 and the conus in Adapsilia provides an additional example (compare Figs 138 and 43 ). As these conditions differ from those in the groundplans of both families, the structural similarities are perhaps to be interpreted as due to similarities in habits of the adult flies.

In addition to the condition of antennal segment 4, possibly useful taxonomic characters in the Pyrgotidae include the structure and position of the prelabrum (“clypeus” in error) and various features of the proboscis.

Figures

Figures 134–138. Antennae of Pyrgotidae. (134) Cardiacera carnei (Paramonov), left seg. 2, distal view, seg. 3 removed. (135) Prodalmannia variabilis Bezzi, left seg. 2, lateral view, seg. 3 removed. (136) P. variabilis, left conus and associated parts, distal view. (137) P. variabilis, left seg. 3, medial view. (138) Adapsilia sp. (Kuranda, Qld), male, part of left seg. 2, lateral view, seg. 3 removed to expose conus. ar, annular ridge; bf, basal foramen of seg. 3; bh, basal hollow; bu, pedicellar button; c, conus; cu, pedicellar cup; fr, foraminal ring of seg. 2; pc, pedicellar cleft; r, pedicellar rim.

Figures 42–44. Antennae of Conopidae. (42) Myopa sp., right antennal seg. 2. (43) Australoconops unicinctus (Kröber), part of right antennal seg.2. (44) The same, right antennal seg.3. bh, basal hollow; bu, pedicellar button; c, conus; da, distal articular surface; m, mouth of postpedicellar pouch; pp, postpedicellar pouch; sc, sacculus (seen superimposed on postpedicellar pouch).