Systenus Loew

Bickel, Daniel J., 2015, The Costa Rican Systenus Loew (Diptera: Dolichopodidae): rich local sympatry in an otherwise rare genus, Zootaxa 4020 (1), pp. 169-182 : 170-171

Genus Systenus Loew

Systenus Loew, 1857: 34 . Type species, Rhaphium adpropinquans Loew, 1857 (= Rhaphium pallipes Roser, 1840 ), des. Foote et al. 1966: 517.

Diagnosis. Head: head almost circular in anterior view; eyes with tiny setulae (ommatrichia) between facets; frontoclypeal suture complete; proboscis projecting anteriorly, keel-like, each labellar lobe with 6 unsclerotized pseudotracheae; single row of postorbitals present; scape without dorsal setae; postpedicel with marked sexual dimorphism: in male lancet shaped, elongate, usually 2-3 times as long as basal width, bearing short apical arista; in female subovate, about as long as wide, bearing long apical arista; postcranium dorsally concave. Thorax: often with bronze medial stripe over ac band; posterior mesonotum distinctly flattened; ac biserial, posteriormost pair larger and laterally offset; 6 strong pairs dc; anterior slope of mesonotum laterad of dc rows with field of short setulae; 1 postalar, 2 postsutural and 2 presutural supraalars, 2 notopleurals, 1 humeral, and 1 posthumeral present per side;. 2 pairs scutellar setae per side, lateral setae less than less half length of medians; strong ventrally projecting white propleural seta present above base of CI. Legs: coxa III with strong lateral seta; femora lacking anterior preapical setae; femora mostly bare of major setae; tibia I mostly bare; tibiae II and III variously with dorsal, and ventral, usually with ad-pd setal pair near ¼. Wing: R4+5 and M subparallel but bowed subapically; flexion (bosse alaire) present in distal sector of M; A1 present. Male postabdomen: segment 7 forming an elongate peduncle, with tergite and sternite 7 incompletely fused, separated by partially sclerotized pleural membrane; hypopygial peduncle, formed of tergite and sternite 7 often held withdrawn between sternites 5 and 6 at rest, and sternite 7 is glabrous while tergite 7 is setose ( Fig. 1 b); hypopygial foramen left lateral; hypandrium fused to epandrium, immovable; two seta-bearing epandrial lobes separate but short, each with only one strong seta present; surstylus usually bifurcate; cercus various. Female oviscapt: fused tergites 9+10 divided medially into 2 hemitergites, each bearing 4 spine-like acanthophorites.

Remarks. Including the nine new species described here, 36 species are currently placed in the genus Systenus: Afrotropical (1 sp.), Australasian (2 spp.), Nearctic (6 spp.), Neotropical (16 spp.), Oriental (1 sp.), and Palearctic (10 spp.) ( Yang et al. 2006; Grichanov & Mostovski 2009). In addition, I have seen a female Systenus in amber from Chiapas, Mexico (Bickel & Solórzano Kraemer, in press), suggesting the genus has been part of the Mesoamerican fauna since at least the Middle Miocene.

The general morphology and taxonomic placement of Systenus within the Medeterinae were discussed in Bickel (1986). An additional observation on the male postabdomen of Systenus should be noted. The hypopygial peduncle, formed of tergite and sternite 7 is often held withdrawn between sternites 5 and 6 at rest, leaving only tergite 7 and the genital capsule exposed. Correspondingly, sternite 7 is glabrous to facilitate retraction within the preabdomen, while tergite 7 is setose, like the adjoining tergite 6, as clearly shown in Figure 1 b.

The Costa Rican Systenus species treated here appear similar in overall hypopygial structure and variation to the six Brazilian Amazonas species as described and figured by Naglis (2000). The following species of Systenus are known from Costa Rica, with the Province and collection month noted.

S. divericatus Bickel. sp. nov., Costa Rica: Guanacaste, February.

S. eboritibia Bickel sp. nov., Costa Rica: Guanacaste, August.

S. emusorum Bickel sp. nov., Costa Rica: Guanacaste, March.

S. flavifemoratus Bickel sp. nov., Costa Rica: Guanacaste, January. S. maculipennis Bickel sp. nov., Costa Rica: Guanacaste, April, July. S. naranjensis Bickel sp. nov., Costa Rica: Guanacaste, February.

S. parkeri Bickel sp. nov., Costa Rica: Guanacaste, November & January. S. tenorio Bickel sp. nov., Costa Rica: Guanacaste, May.

S. zurqui Bickel sp. nov., Costa Rica: San José, August; Puntarenas, December.

Figures

FIGURE 1. Systenus tenorio sp. nov. (holotype): a. male habitus, left lateral (terminalia removed); b. hypopygium, left lateral. S. flavifemoratus sp. nov. (holotype): c. male habitus, right lateral; d. hypopygium, left lateral. S. maculipennis sp. nov.: e. male habitus, left lateral (terminalia removed); f. hypopygium, left lateral. Abbreviations: cer, cercus; epan, epandrium; hyp, hypandrium; ph, phallus; st, sternite; sur, surstylus; tg, tergite; 6, 7, 8, abdominal segments.