Dayomyia, 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

Dayomyia n.gen.

Type species D. molens n.sp.

Description. Male (female unknown). Medium-sized dark flies of moderate to rather stout build with partly infuscated wing.

Head. Parafacial broad; face deeply and extensively concave, so that median facial carina is not visible in profile; outer vertical bristle situated behind and below vertex; no other cephalic bristles differentiated from scattered fine setulae. Antenna of moderate proportions for Platystomatinae , with large, elongate segment 3; arista with minute pubescence less than 0.2 of its maximum diameter in length. Prelabrum reduced, flattened on ventral surface of head (perhaps sexually dimorphic).

Thorax with only the following major bristles differentiated: long posterior notopleural, one small dorsocentral, apical scutellar. Legs of moderate length; femora not incrassate; fore femur (but not other femora) with spinescent posteroventral bristles. Wing: stem vein (base of R) setulose dorsally only beyond level of humeral crossvein; veins 3 and 4 not strongly convergent towards apex; anterior crossvein meeting vein 4 well beyond mid-length of discal cell; alula moderately large; squama (lower calypter) forming moderately short lobe, no larger than axillary lobe (upper calypter).

Abdomen broadly ovate. Aedeagus of basic platystomatine structure, with pair of short terminal filaments.

Distribution New Caledonia: far north of Grande Terre.

Notes

The great reduction in chaetotaxy sets Dayomyia apart from most other platystomatid genera. The nearest approach to this condition is in Angitula Walker , but that genus and its probable sister-group Terzia McAlpine form a distinctive clade unlikely to be closely related to Dayomyia . Dayomyia is distinguished from Angitula s.l. by the robust habitus and relatively stout legs, by the short, unmodified prothorax, the extensive covering of many short setulae on the mesoscutum, the absence of the metathoracic postcoxal bridge, and the large alula. The resemblance in chaetotaxy is due to convergence.

The wing venation of Dayomyia shows points of resemblance to Brea Walker and Pseudorichardia Hendel , particularly in the unusually long second basal and anal cells, and there is some resemblance in general features of wing pattern. The course of the subcosta distally is more like that of Brea , but I am unable to find enough distinctive character states on which to base a hypothesis of close relationship.

Several features of Dayomyia suggest relationship to Rhytidortalis Hendel and through this genus to possibly related genera such as Microepicausta Hendel and Scotinosoma Loew. In the antenna, the strong armature of setulae on the dorsomedial surface of segment 2, and the bulky segment 3 with dorsal convexity basad of the insertion of the arista are reminiscent of males of Rhytidortalis averni McAlpine and some other Rhytidortalis species (see McAlpine, 2000). These characters are all subject to sexual dimorphism in at least some Rhytidortalis species, but female conditions in Dayomyia are unknown. The extent of the basal swelling of antennal segment 6 in Dayomyia is more like that of Rhytidortalis than that of Brea and Pseudorichardia , as is the minute decumbent pubescence towards the base of that segment. The males of R. averni and to some extent those of other Rhytidortalis species have the prelabrum reduced in depth and its anterior surface receding, a condition approaching that of D. molens . The males of Brea and Pseudorichardia do not have the prelabrum thus reduced. The aedeagus of Dayomyia resembles that of Rhytidortalis , but is of such a generalized type for the Platystomatinae that no particular synapomorphy can be inferred. Dayomyia shows substantial difference from Rhytidortalis in venation, chaetotaxy, and facial structure, but these differences mostly involve autapomorphies for the former.

From these observations I put forward the hypothesis of closer relationship of Dayomyia to Rhytidortalis and related genera than to other (or most other) platystomatine genera, but this view cannot, without further knowledge, be based on well supported synapomorphies, uniquely derived within the Platystomatinae .

The generic name refers to Barry James Day who, over many years, has made significant collections of Diptera , including many new taxa, for the Australian Museum. Most recently these have included New Caledonian platystomatids. The generic name is treated as a feminine noun in the nominative case.