Iridomyrmex victorianus Forel

Heterick, Brian E. & Shattuck, Steve, 2011, Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae) 2845, Zootaxa 2845 (1), pp. 1-174 : 153-155

Iridomyrmex victorianus Forel , stat. n.

( Figs 82 , 96 )

Iridomyrmex rufoniger victorianus Forel, 1902: 466 .

Iridomyrmex mattiroloi parcens Forel, 1907b: 27 . New synonym.

Iridomyrmex emeryi Crawley, 1918: 90 . New synonym.

Types. Iridomyrmex rufoniger victorianus Forel : Lectotype worker (here designated) from Ballarat, Victoria, Froggatt (MHNG, ANIC32-032053 ). Paralectotypes, same data as lectotype (MHNG, 2 workers (damaged), examined; MCZC, 4 workers (1 damaged), examined; NHMB, 1 worker (without locality data)). Iridomyrmex mattiroloi parcens Forel : Neotype worker (top specimen, here designated) from Wentworth Falls near Valley of the Waters , west end of Fletcher St. , 33°24’S 150°51’E, New South Wales, 21 December 1988, S. O. Shattuck , wet sclerophyll, foraging in column on ground, ANIC Ants Vial 76.98 (ANIC, ANIC32-036181 ). Iridomyrmex emeryi Crawley : Syntypes from Healesville, Victoria (not located during study, apparently lost).

Worker Description. Head. Posterior margin of head weakly concave, or strongly concave; erect setae on posterior margin in full-face view, present in small aggregations on one or both sides of posterior margin of head; sides of head noticeably convex; erect genal setae absent from sides of head in full-face view (one to a few small setae may be present near mandibular insertion). Ocelli absent; in full-face view, eyes set at about midpoint of head capsule; in profile, eye set anteriad of head capsule; eye semi-circular, or asymmetrical, curvature of inner eye margin more pronounced than that of its outer margin. Frontal carinae convex; antennal scape surpassing posterior margin of head by approximately 2 x its diameter. Erect setae on scape absent, except at tip; prominence on anteromedial clypeal margin present as an indistinct swelling or undulation; mandible regularly triangular with oblique basal margin; long, curved setae on venter of head capsule absent. Pronotum strongly inclined anteriorly, or moderately and evenly curved over its length. Erect pronotal setae moderate in number (6–12), longest setae elongate, flexuous and/or curved, or moderate in number (6–12), short and bristly. Mesonotum straight. Erect mesonotal setae sparse to absent. Mesothoracic spiracles always inconspicuous; propodeal dorsum protuberant, or smoothly and evenly convex; placement of propodeal spiracle posteriad and near propodeal declivity, or mesad, more than its diameter away from propodeal declivity; propodeal angle weakly present or absent, the confluence of the dorsal and declivitous propodeal faces indicated, if at all, by an undulation. Erect propodeal setae sparse to absent. Petiole. Dorsum of node convex; node thin, scale-like, orientation more-or-less vertical. Gaster. Non-marginal erect setae of gaster present or absent on first gastral tergite; marginal erect setae of gaster absent on first tergite. General characters. Allometric differences between workers of same nest absent. Colour ants of different populations variable in colour from light brownish-orange to black; gaster with weak to moderately strong bluish-green iridescence. Colour of erect setae pale to light brownish.

Measurements. Worker (n = 12)—CI 89–93; EI 25–27; EL 0.16–0.22; EW 0.12–0.16; HFL 0.77–1.03; HL 0.66–0.91; HW 0.60–0.83; ML 0.82–1.12; MTL 0.53–0.76; PpH 0.13–0.18; PpL 0.34–0.51; SI 91–104; SL 0.60– 0.80.

Comments. In appearance, workers of I. victorianus resemble small I. rufoniger workers, the two species being closely related. However, the hind tibiae of I. victorianus lack genuine erect setae (tiny appressed setae may accidentally be forced into a more vertical position in some specimens). The antennal scape is also slightly longer and the posterior margin of the head generally less concave (see ‘Comments’ under I. rufoniger ). Dark morphs may also be confused with eastern populations of I. splendens , but iridescence is confined to the gaster in the former, the posterior margin of the head in the latter is broadly if gently concave in most specimens, and the propodeum is typically more truncate and protuberant in I. victorianus . Iridomyrmex victorianus is fairly morphologically uniform throughout its range, but can vary considerably in size and colour. Most variation is seen along the New South Wales coast, and workers collected at Bateman’s Bay and Lake Cowell may be almost twice the size of the very small workers found in populations in the Armidale area. Colour can vary from light brown with a slightly darker gaster to a uniform blackish. The description of I. emeryi by Crawley is entirely consistent with the dark form of I. victorianus , and CSIRO material identified as the latter includes specimens taken from within 40–50 km of where the I. emeryi syntype worker was collected. As discussed above, I. emeryi becomes a junior synonym of I. victorianus in this work.

The range of I. victorianus is limited to the east coast of mainland Australia, and mainly to the more humid coastal areas. It extends from Kangaroo Island and the Fleurieu Peninsula, South Australia eastwards, through Victoria and New South Wales and north into Queensland about as far as Eungella NP. Label data indicates that the ant will occupy a variety of habitats, although generally wet or dry sclerophyll forest is preferred, and will nest under bark or in fallen timber as well as under stones or directly in the soil. Foragers will move up tree trunks, and have been collected in malaise traps. As with many other Iridomyrmex , this species tends caterpillars of blue butterflies such as Jalmenus evagoras . These ants may opportunistically use the nests or nest mounds of much larger species, rather than excavate virgin soil: one series, collected at Yango creek, New South Wales, was found in the mound of a bulldog ant, Myrmecia pyriformis . Another observation from label data is that workers exhibit a death-like state (thanatosis) to evade capture. However, despite the relative wealth of observations recorded on labels attached to pins, there is no recorded evidence of association with human dwellings for this very common species.

Iridomyrmex mattiroloi parcens Forel is here treated as a synonym of I. victorianus . Although Forel (1907) established this name as a subspecies of I. mattiroloi , I. mattiroloi is now considered as being restricted to Tasmania. Of the Iridomyrmex species known to occur in the Blue Mountains, I. victorianus is most similar to I. mattiroloi , and the most likely to be confused with it. Based on this, and the above mentioned similarities, I. parcens is here considered to represent the same taxon as I. victorianus , and therefore becomes a synonym of that species in this work. Since there is a strong likelihood that the original type material for I. mattiroloi parcens was destroyed during WWII, a neotype is here designated (top ant on a pin containing three worker ants) to give stability to the name. The neotype was collected within 20 km of Forel’s original collection site (Mt. Victoria, New South Wales), and the neotype worker and its two associates correspond well with that author’s original description of the species. The physical resemblance of this morph of I. victorianus to I. mattiroloi , apart from the differences mentioned in the key, is quite strong, and Forel’s association of the two taxa (i.e., as subspecies and species) is perfectly comprehensible given the taxonomic reasoning of his day.

Iridomyrmex emeryi Crawley is also considered a synonym of I. victorianus . Crawley (1918) cites Healesville as the type locality of this species. However, this material could not be located during this study, and may have been lost. Nonetheless, the worker description and figure found in Crawley’s article are sufficiently detailed to exclude other possibilities. As we have not conducted an exhaustive search for the types it does not seem appropriate to designate a neotype at this time.

Figures

FIGURE 82. Iridomyrmex victorianus (Eden Burning Study Area, NSW, ANIC32-047708): A. Front of head; B. Side of body; C. Top of body; D. Distribution of material examined.

FIGURE 96. Scape length versus head width for I. meridianus, I. mjobergi, I. neocaledonica, I. splendens and I. victorianus.