Strumigenys yasumatsui

The type material was collected from a rotten log in a rainforest.

Identification
Bolton (2000) - A member of the Strumigenys szalayi-group. The lack of the various grooves and impressions in the head that are usually so obvious in this group, coupled with the clavate petiole and reduced sculpture, makes yasumatsui the most distinctive of the bicoloured species and one of the easiest recognised species of the group.

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

Biology
Brown (1971) - The coloration of Strumigenys hemichlaena, Strumigenys tigris and S. yasumatsui, with their broad zonal “striping” of yellow and black, is highly aberrant for dacetine ants. Drab uniform ferruginous, reddish-brown or dark brown, or a weakly bicolorous pattern with the gaster darker than the forebody, is the usual dacetine condition. Bold yellow-and-black “striping” are otherwise found in the Dacetini only in a few Orectognathus (including Arnoldidris) from New Guinea and eastern Australia, and in an as yet undescribed species of Miccostruma from the forests of West Africa.

The adaptive reason for this pattern in the three Strumigenys species is unknown. Such patterns generally are aposematic or “warning” advertisements found in animals with noxious properties, or in the mimics of such animals. It is hard to see what would-be predators would be warned by color patterns, however striking, in an insect only 3-4 mm long. If the color is a warning, then what are the noxious qualities of some or all of these ants (or their common model) that enforce the warning? Despite these questions, these 3 species meet some of the specifications of a mimicry complex. S. hemichlaena occurs widely in the mountains of northern New Guinea at middle elevations, and the other two species are known from a single locality near its upper altitudinal limits. The 3 species are thus sympatric, or nearly so, in the vicinity of Aiyura. They look much alike to the naked human eye. They are so much like Strumigenys szalayi and Strumigenys nidifex in structure that it is hard to imagine that they defend themselves any more aggressively than do these two timid species. Nevertheless. the mandibular “snap-defense” that Strumigenys employ at the nest against arthropod intruders may be more effective than it seems to me, and the color pattern may just be the one most visible to compound eyes with poor resolution. Then, too. some sort of protective allomone could be involved in the situation.Only further observation will tell.

Nomenclature

 *  yasumatsui. Strumigenys yasumatsui Brown, 1971c: 84, figs. 8, 9 (w.q.) NEW GUINEA. See also: Bolton, 2000: 908.

Worker
Bolton (2000) - TL 3.5-3.6, HL 0.91-0.94, HW 0.58-0.64, CI 64-68, ML 0.50-0.52, MI 53-55, SL 0.68-0.70, SI 109-117, PW 0.34-0.36, AL 0.94-0.96 (3 measured).

Preocular impression in ventrolateral margin of head vestigial, the eyes dome-like and very prominent. Side of head without a vertical groove in front of the eye; without an immediately preocular impression that extends round the ventrolateral margin onto the ventral surface. With head in profile ventrolateral margin behind eye without a concavity. Petiole in profile elongate-clavate, without a differentiated node, the dorsal surface forming an uninterrupted single shallow convexity from junction with propodeum to highest point. Entire side of alitrunk, and most or all of dorsum, unsculptured, smooth and shining. Clypeus dark, remainder of head yellow; pronotum and anterior mesonotum black, remainder of alitrunk yellow; waist segments and gaster blackish brown to black.

Queen
Dealate, from type nest series: TL 4.2, HL 1.00, HW 0.71 (CI 71), ML 0.50 (MI 50), scape L 0.68, WL 1.11, greatest diameter of eye 0.15, petiole L (side view) 0.46 mm.

With the usual caste differences from the worker; pterothorax well-developed and bulky. Sculpture better-developed than in worker; vertex rugulose-punctulate around the infuscated ocellar triangle, and 4-5 rugules leading back from ocelli to posterior border of head, but occipital lobes shining as in worker. Pronotum densely reticulate-punctulate, with a smooth shining area on each side wall. Scutum smooth and shining discad, with spaced fine punctures; lateral and anterior faces finely and densely punctulate, subopaque, as are also the upper sides of mesopleura and propodeum, declivity of propodeum, and both petiole and postpetiole. Scutellum rugulose-punctate. Most of mesopleura and sides of propodeum, as well as propodeal disc and all of gaster (except basal costulae), smooth and shining. Pro-meso- and metanota, as well as gaster, brownish-black; rest of body bright ferruginous yellow.

Type Material
Holotype nest series (Taylor Accession No. 2116), 4 workers and a dealate queen collected in a “Zoraptera-stage” rotten log in rain forest at about 1900 m elevation at Aiyura, N. E. New Guinea in June, 1962 by R. W. Taylor. Holotype and paratypes in ; paratypes in.

Bolton (2000) - Holotype worker, paratype workers and queen, PAPUA NEW GUINEA: Aiyura, 1900 m., vi.1962, no. 2116, rotten log, rain forest (R. W. Taylor) [examined].