Temnothorax minutissimus

A workerless parasite of Temnothorax curvispinosus.

Identification
Mackay (2000) "It differs from all other species in the subgenus in that the propodeal spines are blunt and are about the same diameter from the base to the tip. It is a small, pale yellow species with an 11-segmented antenna.

This species is .... obviously a member of Myrafant, as the clypeus is convex with a medial carina, but which is not as well developed as in other species in the subgenus. It could be confused with males of Temnothorax curvispinosus or Temnothorax ambiguus. It differs from both in its smaller size (Weber's length 0.7 mm), versus the larger Temnothorax curvispinosus (WL 1.2 mm) and Temnothorax ambiguus (WL 1.1 mm) and in that the eyes are small and round. Eyes of the females of the other two species are larger and oblong. There is little likelihood that this species could be confused with any others in the subgenus. The petiole has a relatively sharp apex, but the worker (if it exists) would be expected to have a blunt petiole, as this pattern of the shape of the petiole between the worker and female is common throughout the subgenus."

Distribution based on Regional Taxon Lists
Nearctic Region: United States.

Known from the District of Columbia, Indiana, Michigan, New York, Ohio, and West Virginia.

Habitat
The type specimens were collected at the edge of a marsh. As a parasite of Temnothorax curvispinosus it is more typically a forest nesting species.

Abundance
Rare.

Biology
The following abstract (Buschinger and Linksvayer 2004) summarizes what is known about the biology of this species:

"Forty-five colonies of Temnothorax curvispinosus containing the rare inquiline ant Temnothorax minutissimus have been collected near Bloomington, Indiana, USA. The colonies were censused and some were kept in laboratory culture. Dealate and alate females of Temnothorax curvispinosus and Temnothorax minutissimus were dissected. The parasite females have a total of six ovarioles. Both, Temnothorax minutissimus and the host species, are facultatively polygynous, and the parasite is host-queen tolerant. Alate males were found in August and September. High numbers of alate and dealate, mated but not yet reproductive, young females of Temnothorax minutissimus were present in colonies collected in early spring, a feature which had been known as "Intranidal Mated Offspring Hibernation" (IMOH). Mated young queens of Temnothorax minutissimus seem to disperse in spring to invade host colonies. Apparently they are accepted quite easily by host colonies. Rearing of colonies collected in the early spring, or hibernated in the laboratory, yielded first a brood of sexuals of Temnothorax curvispinosus, and subsequently considerable numbers of gyne pupae of Temnothorax minutissimus appeared. Only very few males were produced (sex ratio about 0.1 ♂/♀). Intranidal mating attempts were observed, and newly mated young females were detected in colonies having reared gynes and males of Temnothorax minutissimus.

Life history of the species thus is a novel combination of traits found in different other parasitic ant species: Intranidal mating and IMOH as in a few European "degenerate slavemakers" of the genus Myrmoxenus, but the parasite is host-queen tolerant, as is the case in two of the three European inquiline species of Leptothorax (former Doronomyrmex). The development of the parasites after the host species sexuals is a novel trait."

Nomenclature

 *  minutissimus. Leptothorax minutissimus Smith, M.R. 1942a: 59, pl. 6 (q.) U.S.A. Buschinger & Linksvayer, 2004: 71 (m.). Combination in L. (Myrafant): Smith, D.R. 1979: 1393; in Temnothorax: Bolton, 2003: 271. See also: Mackay, 2000: 373.

Worker
Workerless inquiline.

Queen
Dealate female.-Length 3 mm. (with the gaster greatly distended).

Head approximately as broad as long when measured through the eyes, with distinctly emarginate posterior border, rounded posterior corners, and subparallel sides. Ocelli small, but clearly visible. Eye not large, but rather convex, approximately its greatest diameter from base of mandible. Antenna 11-segmented; scape rather robust, not attaining posterior border of head; antennal club 3-segmentecl, longer than remainder of funiculus. Clypeus broader than long, convex, with rounded anterior and posterior borders. Mandible with 2 prominent apical teeth and a number of smaller, indistinct teeth. Thorax short, stout, broadest anteriorly; pronotum with angular humerus posterior to which is a slight lateral concavity; epinotum with a pair of unusually long, bluntly pointed, posteriorly diverging digitiform spines directed slightly dorsad. Petiole with a very high and short node narrower above than below, and with steeply descending anterior and posterior faces; postpetiolar node approximately twice as broad as long, broadest anteriorly, the node narrowed above and short, anterior and posterior faces also steeply descending; superior border of petiole, and postpetiole, slightly emarginate; petiole, in profile, appearing almost nonpedunculate and with the anterior and posterior faces meeting above to form a very sharply defined angle, which is much less than a right angle; postpetiole, in profile, with anterior and posterior faces meeting in a broadly rounded angle.

Dorsal surface of head covered with dense, minute alveoli; cheeks and region between eyes and frontal carinae also with very small longitudinal rugulae. Sculpturing on dorsal surface of thorax more indistinct than on head, the prothorax, however, with a tendency to rugulose-reticulate sculpturing, especially around the humeri. Petiole and postpetiole weakly alveolate except on their anterior faces, which are smooth and shining. Femora, tibiae, and gaster also smooth and shining.

Hairs rather sparse; coarser, longer, and more erect on head and thorax than on gaster.

Light brown or yellowish brown, with edge of mandible, head, sutures on dorsum of thorax, and gaster much darker.

Male
(Buschinger and Linksvayer 2004) Total length ca. 2.15 mm, thorax length 0.76 mm, head width 0.45 mm, scape length 0.24 mm.

Particular characters: Sculpture of head punctate (as in queen); antennal scape comparatively longer than in male of T. curvispinosus; pronotum slowly ascending in comparison with steep ascend in T. curvispinosus; petioles shorter and stouter than in T. curvispinosus; propodeum with or (rarely) without pair of short, acute spines; compound eyes markedly smaller than in males of T. curvispinosus.

Antennomeres: In T. minutissimus males reduced to 9 - 10 - 11 antennomeres (variable), as compared to T. curvispinosus males which have the usual 12 antennomeres.

Color: dark greyish-brownish (as compared to light yellow-brownish, pale males of T. curvispinosus).

Type Material
As reported in Mackay (2000) "Holotype female and three paratype females. USNM. #56210 [seen]."

Type Locality Information
USA. District of Columbia.

Etymology
minutissimus refers to the very small size of queen and male as compared to the host species.