Pseudomyrmex ultrix

Only known from the type locality in Ecuador.

Identification
Ward (1999) - This species is easily recognized in the worker and queen castes by the very broad petiole such that worker PWI>1.00, worker PWI3 <0.43, queen PWI 0.92–0.99 and queen PWI3 0.40–0.42. The otherwise similar Triplaris-inhabiting species, Pseudomyrmex dendroicus, Pseudomyrmex mordax, Pseudomyrmex triplaridis and Pseudomyrmex triplarinus, have worker PWI <1.00, worker PWI3 0.42–0.59, queen PWI 0.63–0.86 and queen PWI3 0.48–0.62. The angular protuberance on the worker propodeum (at the junction of the dorsal and declivitous faces), the small size of the subpetiolar process, and the densely punctate head sculpture are also distinctive features of P. ultrix.

Distribution
This taxon was described, and is only known, from Ecuador.

Biology
Mature and incipient colonies were found in the type locality, inhabiting Triplaris dugandii trees. Observations made at the time of collection provide evidence that P. ultrix queens compete with, and act as temporary social parasites of, Pseudomyrmex triplaridis queens during colony initiation. In a partially-cut Triplaris tree I found colony-founding, dealate queens of both species occupying internodes of new shoots, together with eggs and pseudococcids. For eight internodes the contents were individually tallied, with the following results. Four internodes housed single P. ultrix queens while the other four internodes contained (i) 7 P. triplaridis queens, (ii) 6 P. triplaridis queens and 1 P. ultrix queen, (iii) 5 P. triplaridis queens and 1 P. ultrix queen, and (iv) 1 P. ultrix queen, 9 P. ultrix workers (nanitics) and 1 P. triplaridis worker (also nanitic). This last nest also had larvae and worker pupae of unknown specific identity. In no case were multiple queens of P. ultrix found within a single internode. The data suggest the hypothesis that P. ultrix queens exploit a pleometrotic tendency in P. triplaridis by temporarily entering into associations with — and presumably mimicking — P. triplaridis queens, while excluding conspecific queens. It is worth noting that P. ultrix queens are considerably larger than those of P. triplaridis: HW 1.43–1.50 (n=6) compared with 1.07–1.25 (n=11) in P. triplaridis.

Nomenclature

 *  ultrix. Pseudomyrmex ultrix Ward, 1999b: 509, figs. 6, 17, 28, 72, 78, 98 (w.q.m.) ECUADOR.

Worker
Measurements (n=8). HL 1.09–1.34, HW 1.04–1.28, MFC 0.112–0.143, LHT 0.77–1.01, CI 0.95–0.97, REL 0.39–0.41, REL2 0.41–0.43, FCI 0.10–0.13, SI 0.44–0.47, FLI 1.55–2.20, FI 0.36–0.39, PLI 0.96–1.05, PWI 1.04–1.14, PPWI 1.55–1.89.

Similar to P. triplarinus except as follows. Median lobe of antennal sclerite better exposed, PFC/ASD 0.60–0.70. Legs shorter, LHT/HL 0.70–0.77. Junction of dorsal and declivitous faces of propodeum marked by slight angular protuberance, laterally on either side. Petiole short and high (PLI »1.00) with broad posterolateral expansion (PWI >1.00, PWI2 0.73–0.80, PWI3 0.38–0.42). Anteroventral petiolar process reduced in size, in the form of a small spine or tooth, directed ventrally. Sculpture on dorsum of head coarser, the punctures 0.010–0.020mm in diameter, and separated by about their diameters or less. Body pilosity common (MSC 47–75, HTC 10–16), with some standing hairs visible in outline on the posterior margin of the head (frontal view). Pubescence on head more conspicuous than in P. triplarinus, the hairs tending to be decumbent, giving the worker a scruffier appearance. Body dark brown, mandibles and anterior third of head a lighter orange-brown, tarsi yellow-brown.

Type Material
Holotype worker. ECUADOR, Napo: 13 km NNE Archidona, 0°48’S, 77°47’W, 960 m, 7.viii.1991, P. S. Ward# 11393. HW 1.19, HL 1.24, EL 0.50, LHT 0.90, PL 0.52, PH 0.52.

Paratypes. Same locality and date as holotype: series of workers, queens and males (to be deposited in, , , MCZC, , , , , , , ).