Dayomyia molens, McAlpine, 2007

McAlpine, D. K., 2007, New Taxa of Signal Flies (Diptera: Platystomatidae) of New Caledonia, Records of the Australian Museum 59 (1), pp. 65-77 : 68-70

Dayomyia molens n.sp.

Figs 1–4

Types. HOLOTYPE?, New Caledonia: 1 km SW of Mandjelia , 750 m, 20°24'S 164°32'E, 5.i.2005, G.B.M, MV light, rainforest ( PM) . PARATYPE?, Mandjelia —lower creek, 580 m, 20°24'S 164°31'E, 4.i.2005, G.B.M. ( QM) .

Description. Male.

Coloration. Head predominantly tawny-brown; cuticle largely pruinescent or finely sculptured and not shining; parafacial with zone of coarser, dense whitish pruinescence next to eye; face densely white-pruinescent except along summit of median carina and on lower margin; postgenal region and part of occiput with coarse greyish pruinescence. Antenna orange-tawny. Thorax black, largely shining; mesoscutum with small lateral marginal zone of yellowishgrey pruinescence both before and behind notopleural bristle, former extending mesad of humeral callus; posterior parts of pleura and much of postscutellum greyish-pruinescent. Legs largely black to brown-black; apices of all femora and bases of all tibiae narrowly tawny. Wing with brown markings partly diffuse as in Fig. 4 ; much of membrane on central and basal part of wing suffused with yellow; axillary lobe and squama creamy-white. Halter yellow. Abdomen black; tergites largely shining and with bluish reflections, except for a transverse stripe of grey-brown pruinescence near junction of tergites 1 and 2; sternite 1 largely glossy blackish, with grey-pruinescent zone on each lateral margin.

Head as wide as mesoscutum and c. 1.3× as wide as high; postfrons narrowest near vertex, where its width is c. 0.4 that of head, rather sparsely finely setulose; parafacial without setulae except towards upper and lower extremities; frontal lunule shortly exposed, with few fine setulae; facial carina extending for almost full height of face, very narrow, but slightly dilated at lower extremity; cheek almost half as high as eye; occiput flattened on c. upper third, strongly swollen on rest of extent except for central depression containing occipital foramen. Antenna: segment 1 short, but prominent in profile; segment 2 moderately short, with many setulae, including field of numerous short, stout setulae (often damaged) on medial surface; segment 3 almost as long as face; arista apparently slightly shorter than segment 3, perhaps slightly damaged apically in all examples; segment 4 visible but extremely reduced; segment 5 separated from segment 6 by membranous ring; segment 6 swollen on basal part, with very inconspicuous pubescence. Palpus of moderate proportions, compressed, setulose; proboscis moderately short and stout; prementum broader than long, with distal margin almost straight.

Thorax stout; mesoscutum almost as broad as long, with many non-seriate setulae; humeral callus with numerous setulae; scutellum rather short, convex, subtriangular but rounded apically; subscutellum small and recessed; mesopleuron, pteropleuron, and sternopleuron finely setulose; prosternum broad, with short setulae and rudimentary precoxal bridge; metapleural sclerite extending narrowly between hind coxa and abdominal segment 1, but not forming postcoxal bridge. Legs without differentiated bristles, except for the posteroventral series of fore femur; posterior bridge of hind coxa without setulae; mid tibia with one rather short stout apical ventral spur and several stout setulae on each side of it. Wing: venation as in Fig. 4 ; subcosta not fading distally, meeting costa at acute angle; cell-4 index = 0.76–0.81; membrane, including that of alula, largely microtrichose; pale basal areas of first basal, second basal and anal cells, and zone behind mid-length of anal cell almost bare; squama of moderate size, slightly broader than a semicircle.

Abdomen. Tergites 2 to 5 with numerous, generally distributed small setulae; tergite 2 showing narrow membranous zone along much of posterior margin except at sides; tergite 5 almost as long as tergite 4, without enlarged setulae; at least sternites 1 and 2 with fine setulae. Postabdomen: aedeagus with small terminal tuft of pubescence on stipe; preglans well differentiated from stipe, short, asymmetrical; glans ovoid-cylindrical; bulb short, inconspicuous; paired terminal filaments broadly fused basally, each much shorter than glans.

Dimensions. Total length (abdomen variably flexed) 5.5–7.1 mm; length of thorax 2.7 mm; length of wing 5.9–6.1 mm; length of glans of aedeagus 0.25 mm.

Notes

The male of D. molens has a field of short, strong setulae on the dorsomedial surface of antennal segment 2. In both the available specimens there is damage to these setulae which is very unlikely to be the result of collecting or subsequent handling, because this surface of the antennae is less freely exposed than other parts. On the holotype at least eight of these setulae on the right antenna have been snapped off or ground off at or just beyond their bases, while on the left antenna five setulae are similarly damaged. In the paratype about 28 setulae on the right antenna and 26 on the left are damaged, i.e. most of the setulae on this part of the segment. On each antenna the setulae on the rest of the surface of segment 2 are intact.

I have commented on damage to setulae, which appear to be a specialized development on the medial surface of antennal segment 2, in the canacid (or tethinid) Tethinosoma fulvifrons Malloch and the platystomatid Rhytidortalis averni McAlpine ( McAlpine, 2007 [this volume]). I hypothesized that, in these flies of sandy (beach or dune) habitats, the antennae may play a role in digging or extrication from loose sand. I have no information to suggest that any such activity is likely for Dayomyia , but the data seem to indicate that some unknown activity of the fly involves abrasion of these setulae.

The specific epithet is a Latin participle, grinding, in reference to the abraded antennal setulae.

Figures

Figs 1–4. Dayomyia molens. (1) Head. (2) Scutellum, dorsal view. (3) Distal part of aedeagus, scale = 0.2 mm. (4) Wing.