Pseudomyrmex opaciceps Ward, 1993

Ward, Philip S., 1993, Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae), Journal of Hymenoptera Research 2, pp. 117-168 : 159-160

Pseudomyrmex opaciceps Ward , sp. nov.

(Fig. 5)

Holotype worker. - GUATEMALA Retalhuleu: Puente Samala, 3.8 mi. NE San Felipe , 24.vii. 1966, D. H. Janzen W006724966 ( LACM). HW 1.43, HL 1.42, EL 0.85, PL 0.89, PH 0.39 .

Paratypes, - Series of 11 workers with same data as holotype; large series of ca. 60 workers and 10 males with the same locality and collector as holotype but the following dates and collection numbers: 18. vii. 1966 M 002718966 (possibly mis-labelled - see below), 18. vii. 1966 W 002718966 , 18. vii. 1966 W 004718966 , 18. vii. 1966 W 005718966 (possibly mis-labelled - see below), 23. vii. 1966 W 002723966 , 24. vii. 1966 W 001724966 , 24. vii. 1966 W 003724966 ( BMNH, LACM, MCZC, MZSP, PSWC, UCDC, USNM) .

Additional non-type material. - Series of workers, queens, and males from six additional localities. MEXICO Chiapas: 94.5 mi. SE Tonola (D. H. Janzen) . GUATEMALA Retalhuleu: 2 mi. N Puente Samala, 3.8 mi. NE San Felipe (D. H. Janzen) ; 3 mi. N Puente Samala, 3.8 mi. NE San Felipe (D. H. Janzen) ; 5 mi. W Retalhuleu, Hwy. CA- 2 at Rio Nil (D. H. Janzen) ; Guatemala: Ciudad de Guatemala (D. H. Janzen) . EL SALVADOR La Libertad: Quezaltepeque (M. Irwin & D. Cavagnaro) ( LACM, MCZC, PSWC) .

Worker measurements (n=14). - HL 1.30-1.42, HW 1.33-1.43, MFC 0.040-0.058, Cl 0.99-1.04, REL 0.57-0.61, REL2 0.56-0.61, OOI 0.14-0.68, VI 0.65-0.71, FCI 0.029-0.042, SI 0.46-0.50, SI2 0.77-0.88, FI 0.36-0.39, PDI 1.12-1.37, MPI 0.059- 0.076, NI 0.65-0.70, PLI 0.42-0.47, PWI 0.38-0.43, PPWI 0.92-1.16.

Worker diagnosis. - With the traits of the P. gracilis group (see couplet 6 of key) and the following more specific features. Head about as broad as long; anterior margin of median clypeal lobe straight to weakly convex; pronotum with blunt dorsolateral margination; mesonotum more steeply inclined than basal face of propodeum; petiole long and slender (see PLI and PWI values) with a distinct anterior peduncle (Fig. 6); head densely punctulate-coriarious and matte; standing pilosity abundant, pale silvery-white, not black. Color: head and mesosoma dark brown to black, mandibles and appendages lighter brown; petiole, postpetiole and gaster a contrasting pale luteous brown or orange-brown. Portions of the fronto-clypeal complex, malar area, and mandibles may also be luteous brown.

Taxonomic comments. - This species is distinguished from the closely related and sympatric P. gracilis by a modest but consistent difference in head sculpture. In workers and queens of P. opaciceps the punctulate-coriarious sculpture and associated dense pubescence obscure the sheen of the head, producing a matte appearance under soft light, while in P. gracilis the head remains at least weakly shining. In addition the workers and queens of P. opaciceps average smaller in size than those of P. gracilis and they have a more slender petiole (PLI <0.48; see Figs. 5,6,53). Finally, P. opaciceps has a distinctive and largely invariant color pattern: the pale yellow or orange-brown petiole, postpetiole and gaster contrast with the much darker head and mesosoma. This is not observed in Central American P. gracilis , although a similar color pattern occurs in some Colombian populations of P. gracilis , and it also seen in some individuals of the more distantly related South American species P. venustus (F. Smith) .

Among the P. opaciceps paratypes in LACM, the pinned specimens with Janzen collection numbers M002718966 and W005718966 appear to have been mis-labelled. In the Janzen alcohol collection samples M002718966 and W005718966 contain colony series of two quite different species (in the P. ferrugineus and P. pallidus groups, respectively); but there are two other alcohol samples from the same date and locality (W 002718966 and W 004718966) which are of P. opaciceps . I conclude that a frame-shift occurred in the process of labelling the pinned series of specimens, producing the labelling error (this has happened to a substantial number of P. ferrugineus group collections - see "Materials and Methods" section). The remaining paratype (and non-type) material of P. opaciceps appears to be correctly labelled.

Biology. - P. opaciceps is evidently a generalist twig-nesting Pseudomyrmex , but Janzen also collected it from an Acacia cornigera tree overgrown by vines and unoccupied by the P. ferrugineus group (5 mi. W Retalhuleu, Guatemala, collection numbers M 010714966- A and M 010716966- D).