Myopias delta

Colonies contain about 30 individuals and have a single queen. They appear to be specialized predators of other ants.

Identification
Willey and Brown (1983) - Worker and queen: A modest-sized species, completely distinct from all congeners in possessing down-curved triangular mandibles with distinct basal and masticatory borders meeting at a dentiform basal angle. Head oblong, with convex sides and straight posterior border. and broadly rounded posterior corners. Worker eyes reduced to dots. Frontal lobes and median clypeal lobe large; clypeal lobe squarely truncate. Antennae very robust; scapes overreaching posterior border of head; funiculus dominated by a long. thick, 4-merous apical club. Trunk compact, weakly convex, separated into two subequal parts by a distinct but not sunken metanotal groove. Petiolar node short and high. summit posterior and acutely rounded. posterior face vertical and feebly concave. Gaster constricted behind first segment. Integument smooth and shining, with separated minute punctures. Color dark yellowish brown.

This species cannot easily be placed to species group, and the mandibular form (triangular) even puts generic assignment into doubt. The 3-merous palpi (both sets) and the upturned tooth on each labral lobe probably are derived characters shared with the tenuis group, so the triangular mandibular shape may well be secondarily derived from the Myopias plan; it seems, indeed, that the dentition of M. delta is more easily homologized with that of various Myopias species than it is with the run of Pachycondyla groups. It thus becomes doubly important to find again the larvae of M. delta.

Distribution based on Regional Taxon Lists
Australasian Region: Australia. Indo-Australian Region: New Guinea.

Biology
Willey and Brown (1983) - Wilson’s notes on the type colony, slightly modified: “A colony of one queen and about 30 workers, with brood at all stages, none preponderant; in a crumbling small Passalus-stage log, diameter about 5 inches, held in shape by intact bark. Ants relatively fast, nervous, similar to other [Myopias] species. Workers and brood scattered through a number of indistinct galleries and chambers in the crumbling wood. In one chamber near larvae was a fresh, decapitated worker of a small Leptogenys species. Around another, large chamber was the kitchen midden, consisting of discarded [Myopias] cocoons and numerous remains of ants, mostly or entirely myrmicines, including at least two genera (q.v.).” The “q.v.” refers to the vial containing the whole colony. Unfortunately, the Myopias brood and the midden remains, left in alcohol after an adult sample had been mounted from the vial, was lost in transit by a colleague who had borrowed Wilson's and Brown's Myopias collection residues for study.

From the circumstances of the collection as noted by Wilson, it seems likely that M. delta is an ant predator specializing on Myrmicinae, but perhaps occasionally accepting ponerines or other subfamilies. We need further collections and field and laboratory observations to confirm this interesting possibility and to learn the details of the M. delta behavior and ecology.

Nomenclature

 *  delta. Myopias delta Willey & Brown, 1983: 281, figs. 8, 21 (w.q.) NEW GUINEA.

Worker
Holotype: TL 4.1. HL 0.79. HW 0.70 (CI 89). ML 0.30 (MI 38). MLO 0.54, SL 0.66 (SI 94), EL 0.04, WL 1.27. hind femur L 0.68, hind tibia L 0.61 mm.

Worker paratypes (15 from type nest series) range downward from size of holotype to smallest individual. TL 3.9, HL 0.75, HW 0.68 (CI 91), ML 0.29 (MI 39), MLO 0.49, SL 0.62 (SI 91), EL 0.04, WL 1.20 mm.

Head a little longer than broad. with parallel gently convex sides. straight posterior border. and rounded posterior corners. Frontal lobes broad, median clypeal lobe thick and wide (CLL 0.07. CLW 0.14), squarely truncate at apex, sides slightly convergent towards apex. Median frontal sulcus very short, not extending rearward past constricted ends of frontal carinae.

Mandibles basically of the ordinary ponerine. rather than Myopias-like, form, triangular and strongly down-curved, with distinct basal and oblique masticatory margins, each furnished with five coarse, spaced teeth, the most basal of which, corresponding to the basal angle, is subacutely dentiform; apical tooth the largest and most acute; masticatory margins crossing over one another at full closure. Basal oblique groove and its lateral extension (strix) strongly developed.

Eyes small. round and dot-like, with indistinct facets, only 0.03-0.04 mm long, and distant from mandibular insertions by about 0.20 mm. Antenna massive, scape thick, especially toward apex, and overreaching posterior border of head (when held straight back in full-face view) by more than half apical scape width; funiculus with 4-merous club (which takes up more than 0.6 of funicular length) following six short, transverse ring segments (II through VII); pedicel (funiculus I) about 5X length of II.

Labrum without a median tooth, but each of its two lobes bears a delicate, upturned apical tooth. Palpi segmented 3,3.

Trunk compact; aside from the rounded declivities of pronotum and propodeum, the dorsal profile in side view is only weakly convex, with moderate interruptions at premesonotal suture (movable) and metanotal groove; latter is moderately wide and distinctly, but not very strongly, impressed, and it divides the trunk into approximately equal anterior (promesonotal) and posterior (propodeal) halves. Dorsum of propodeum gently convex, about twice as long as mesonotum; declivity of propodeum steeply sloping, its outline convex in side view, but the surface feebly concave, and weakly submarginate above and laterally, as seen fr.om above.

Petiolar node short and high, highest and widest behind at narrowly rounded summit, after which the posterior face drops off sharply and almost vertically. Anterior face nearly as steeply sloping upward, shorter, meeting sloping dorsal face at an obtusely rounded angle. Sternal keel prominent, with a thick, obliquely truncate anterior process, pointed behind, then diminishing convexly caudad (see fig. 21). In holotype and two of the paratypes, the posterior convex portion bears an additional low point or tubercle, but shape of keel is variable in any case.

Gaster robust, distinctly constricted after first segment; segment II about as high as I, and only very slightly wider. Sting long, sharp, upcurved, capable of at least 0.4 mm extension. Seen from above, anterior border of gaster I transverse, straight.

Body smooth and polished, with well-spaced, small (mostly 0.01 mm diameter or less), piligerous punctures, most numerous on dorsum of head and gaster. Antennae, frontal lobes, tibiae and tarsi densely and finely punctulate. Bullae of metapleural glands obscurely striate.

Longer pilosity abundant on body, sparse on antennae and mandibles, and almost lacking on legs; mostly 0.03 to about 0.20 mm long, appressed to erect, but mainly decumbent to suberect on propodeum, node, and first two gastric segments; longest on clypeal lobe, propodeum, node and gastric apex. Pubescence mostly appressed to decumbent, inconspicuous and mesally inclined on anterior half of head, more abundant and conspicuous on antennae and legs.

Color dark yellowish brown or orange brown; legs, mandibles, antennal scapes slightly more yellowish.

Queen
Dealate, from holotype nest series: TL 4.7, HL 0.80, HW 0.71 (CI 89), ML 0.34 (MI 43), MLO 0.57, SL 0.70 (SI 99), EL 0.18, WL 1.47 mm.

Showing the usual ponerine differences of caste, and darker, deep brownish red, in color; scutum yellowish brown, with a broad, V- or Y -shaped median fascia of deep reddish brown; mandibles, antennae, legs, and indefinite patches on lateral areas of pronotum and upper mesopleura obscure yellowish brown. Punctures a little coarser and more conspicuous than in workers. An additional dealate queen apparently belonging to this species, taken in 1901 by L. Biro (Hungarian Natural History Museum), comes from Friedrich-Wilhelmshafen (now Madang, Papua New Guinea); it is notably smaller (HL 0.62, HW 0.50 mm.) than either workers or queen from the type colony; and was found in the Hungarian collection placed with the M. tenuis.

Type Material
Holotype (MCZ) and paratypes (MCZ, BMNH, ANIC) from a colony collected in rain forest just west of the lower Busu River; near Lae, Papua New Guinea on 9 May 1955, by Wilson (No. 983).



Etymology
The name delta refers to the triangular mandibles.