Pseudomyrmex particeps Ward, 1993

Ward, Philip S., 1993, Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae), Journal of Hymenoptera Research 2, pp. 117-168 : 146

Pseudomyrmex particeps Ward , sp. nov.

(Figs. 14, 23, 54, 57, 72)

Holotype worker. - COSTA RICA, Puntarenas: Rincon, Peninsula Osa , 3.iii. 1965, D.H. Janzen #111 ( LACM). HW 0.83, HL 1.10, EL 0.50, PL 0.50, PH 0.31 .

Paratypes. - Same data as holotype: series of 82 workers, 14 males, one queen ( AMNH, BMNH, CASC, GBFM, INBC, JTLC, LACM, MCZC, MZSP, PSWC, UCDC, USNM). Additional non-type material listed below .

Worker measurements (n = 12). - HL 0.93 - 1.10, HW 0.77 - 0.83, MFC 0.037 - 0.050, Cl 0.75 - 0.84, REL 0.44 - 0.48, REL 2 0.55 - 0.60, OOI 1.47 - 1.96, VI 0.65 - 0.75, FCI 0.048 - 0.062, SI 0.45 - 0.49, SI 2 0.78 - 0.83, NI 0.53 - 0.62, PLI 0.58 - 0.66, PWI 0.55 - 0.60, PPWI 1.03 - 1.26.

Worker diagnosis. - Very similar to P. nigrocinctus (q. v.) except as follows. Eyes longer (REL 2 0.55 - 0.60, EL / LHT 0.59 - 0.64) (Figs. 14, 42, 43). Front of head more strongly shining. Medium to dark brown; gaster uniformly dark brown or black; mandibles, fronto-clypeal complex, and appendages lighter brown.

Comments. - P. particeps is obviously a very close relative of the allopatric P. nigrocinctus , but there are consistent differences between the two in eye size and color which exceed the limits of variation seen throughout the much wider range of P. nigrocinctus . Workers in the type series of P. particeps also have more elongate heads than those of P. nigrocinctus but this distinction is not seen in other samples. Differences between queens of the two species are more striking with the two known queens of P. particeps having more elongate heads (Cl ≈ 0.61, compared with 0.67 - 0.72 in a sample of 13 P. nigrocinctus queens) and longer metatibiae relative to head width (LHT / HW ≈ 1.12 versus 0.97 - 1.07 in P. nigrocinctus ). Additional alates of P. particeps are needed to confirm these differences and the apparent distinctions in male genitalia (see male key).

Distribution and biology. - P. particeps is a rare species known only from the Osa Peninsula and one adjacent locality, in Costa Rica (Fig. 72). It appears to be associated exclusively with Acacia allenii , a forest species (see Janzen, 1974 for more information aboutthehostplant). In contrast, P. nigrocinctus is found farther north in more open habitats where it typically inhabits Acacia collinsii . The differences in worker morphology between P. particeps and P. nigrocinctus (darker color and more elongate head and / or eyes in the former) parallel those observed between populations of P. spinicola from the same areas (see below under P. spinicola ), suggesting similar selection pressures associated with more forested habitats and partial ( P. spinicola ) or exclusive ( P. particeps ) occupancy of a different Acacia species.

Material examined. Type material listed above, plus the following ( JTLC, LACM, PSWC). - COSTA RICA Puntarenas: 4 mi S Rincon (D. H. Janzen) ; Bahia Drake, Osa Penin . (FJoyce) ; Corcovado Natl. Pk., Sirena , 50 m (J. T. Longino) ; Rincon (A. R. Moldenke) ; San Jose: 16.7 mi SW San Isidro on Hwy. 22, 160 m (D. H. Janzen) .