Iridomyrmex viridigaster Clark

Heterick, Brian E. & Shattuck, Steve, 2011, Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae) 2845, Zootaxa 2845 (1), pp. 1-174 : 156-158

Iridomyrmex viridigaster Clark

( Figs 84, 86 )

Iridomyrmex viridigaster Clark, 1941: 87 , pl. 13, fig. 18.

Iridomyrmex mimulus Shattuck, 1993b: 1317 , figs 14, 15, 36. New synonym.

Types. Iridomyrmex viridigaster Clark : Holotype worker from Patho, Victoria (MVMA). Paratypes: same data as holotype (ANIC, 2 workers, examined). Iridomyrmex mimulus Shattuck : Holotype worker from Lake Eyre (South), South Australia (ANIC, ANIC32-000079 , examined).

Worker Description. Head. Posterior margin of head weakly concave; erect setae on posterior margin in fullface view set in a row, or present in small aggregations on one or both sides of posterior margin of head; sides of head noticeably convex; erect genal setae present on sides of head in full-face view, or 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 asymmetrical, curvature of inner eye margin more pronounced than that of its outer margin. Frontal carinae concave; antennal scape barely attaining posterior margin of head, or surpassing it by less than 1 x its diameter. Erect setae on scape absent, except at tip; prominence on anteromedial clypeal margin present as an indistinct swelling or undulation; mandible elongate triangular with oblique basal margin; long, curved setae on venter of head capsule present. Mesosoma. Pronotum moderately and evenly curved over its length. Erect pronotal setae numerous (12 or more), short and bristly. Mesonotum sinuous, or straight. Erect mesonotal setae numerous (12 or more), short and bristly. Mesothoracic spiracles always prominent as small, vertical protuberances; propodeal dorsum protuberant; placement of propodeal spiracle posteriad and near propodeal declivity; propodeal angle present as a bluntly defined right angle, the dorsal and declivitous propodeal faces never separated by a carina. Erect propodeal setae numerous (12 or more), short and bristly. Petiole. Dorsum of node acuminate, or convex; node thin, scale-like, orientation more-or-less vertical. Gaster. Non-marginal erect setae of gaster present on first gastral tergite; marginal erect setae of gaster present on first tergite. General characters. Allometric differences between workers of same nest absent. Colour sides of head and usually mesosoma orange to brick-red (mesonotum and propodeum may have cloudy brownish infuscation), frons, legs and gaster brown. Colour of erect setae depigmented, whitish.

Measurements. Worker (n = 13) — CI 93–99; EI 24–27; EL 0.30–0.33; EW 0.15–0.19; HL 1.23–1.38; HW 1.16–1.33; ML 0.47–0.65; PpH 0.18–0.22; PpL 0.66–0.76; SI 75–80; SL 0.93–1.01.

Comments. Although it is by no means very common, I. viridigaster is the most frequently encountered member of the species complex that bears its name. As understood here, this taxon incorporates I. mimulus , erected by Shattuck (1993b) , as a junior synonym. Further investigation could reveal that I. anderseni also belongs to this species. In terms of its critical measurements (e.g., lengths and indices pertaining to the scape and eyes), the I. mimulus holotype also satisfies the requirements for belonging to the species I. viridigaster , although its overall dimensions are rather on the small side. Additional workers of I. viridigaster , not recognised in the earlier study as they were among unsorted accessions, form a size-based continuum that now includes I. mimulus . Iridomyrmex viridigaster is a relatively variable member of the complex that bears its name, and the ground colour of the anterior mesosoma can vary from a rich red in the large workers that belong to populations in south-eastern Australia, to a yellowishbrown in workers from populations in the Flinders Ranges. The latter ants also tend to be hairier with erect setae on the sides of the head capsule, but such setae are usually sparse or absent in the redder south-eastern specimens. Ecological data are lacking for this species.

Figures

FIGURE 86. Scape length versus head width for I. hesperus and I. viridigaster.