Macrostomus occidentalis Rafael & Cumming

(Fig. 9)

Macrostomus occidentalis Rafael & Cumming 2006: 55, figs. 20–22, 40; Yang et al. 2007: 145 (catalogued).

Diagnosis. Thorax, abdomen and legs predominantly yellow; postcranium black dorsally, moderately yellow ventrally; fore tarsomeres 1–3 not whitish distally; first hind tarsomere with seven slender dorsal setae; male tergite 8 with distal projection truncated.

This species was described and figured by Rafael & Cumming (2006). The female is unknown. It has a distribution west of the Andes in Colombia (Cauca departament) (Fig. 9). The type-specimen is deposited at CAS.

Discussion. Macrostomus occidentalis appears most closely related to M. fulvithorax on the basis of the truncate male tergite 8 projection, the bifid posterior lobe of the male cercus and the hypandrium without ventral setae. It differs from M. fulvithorax by having a more acute apical protuberance on the hypandrium and a less sclerotized ventral surface of the hypandrium.

Biogeographical pattern. According to Amorim & Pires (1996), Amorim & Silva (2002) and Amorim (2009) the continental northern Neotropical region is divided in two components. The NW Neotropical component is northwest of the Amazonas-Madeira-Mamoré Rivers and extends as far as tropical Mexico. The other component is southeast of these rivers, called the SE Neotropical component. The NW Neotropical component is further subdivided into the transandean area, Chocó-Central America (Chocó-CA), and the Northwest Amazonia (NWAm) area. The NWAm is further subdivided into the North Amazonia (NAm) and the Southwest Amazonia (SWAm) (Fig. 7). The NAm area runs from Japurá-Caquetá Rivers to the coast (Atlantic Ocean) with its eastern and southern limits extending along the Parnaiba River, between the states of Maranhão and Piauí, to the south several hundred kilometres and west crossing the Tocantins River to the Xingu River, before running north to the Amazon River. The SWAm area includes a portion south of the Caquetá-Japurá rivers, as well as west of the Madeira River and south along the Mamoré River to Bolivia and Peru. The SE Neotropical component is also subdivided in two areas: the Southeast Amazonia (SEAm) and the Atlantic Forest (Fig. 7). The relationships of these regions to one another have been presented in an area cladogram (Fig. 7) by Amorim (2009).

All species of the M. ferrugineus species-group occur in the three areas of the NW Neotropical component (Fig. 8). In the Chocó-CA area, M. occidentalis occurs in Cauca, Buenaventura, located west of the Andes and M. fulvithorax occurs in Panama. In the NWAm area (NAm + SWAm), all the remaining species occur, namely M. fuscithorax, M. fusciventris, M. melanothorax, M. ferrugineus, M. longipennis, M. furcatus and M. flavus. In the SWAm area, three species occur that are also recorded from NAm, namely, M. fusciventris, M. melanothorax and M. longipennis. The only record from the SEAm area is that of M. ferrugineus from Alter do Chão in Pará state (Rafael & Cumming 2004). This locality is near the southern border of the NAm area, separated only by the Amazon River and the presence of M. ferrugineus in this site on the southern side of the Amazon is probably due to dispersal. Virtual confinement of the M. ferrugineus species-group to NW Neotropical component, with two potentially closely related species, M. fulvithorax and M. occidentalis, restricted to the Chocó-CA area is highly suggestive of an evolutionary history for the entire species-group that is largely in agreement with the area cladogram (Fig. 7) presented by Amorim (2009).