Listron Musetti and Johnson, 2008

Johnson, Norman F., Masner, Lubomír & Musetti, Luciana, 2008, Review of Genera of the Tribe Sparasionini (Hymenoptera: Platygastroidea, Scelionidae), and Description of Two New Genera from the New World, American Museum Novitates 3629 (1), pp. 1-24 : 6-9

Listron Musetti and Johnson , new genus

Figures 7–12

DESCRIPTION: Medium sized, robust, length 2.3–3.2 mm; with abundant, scattered, erect, long hairs on head and body; legs moderately long; head and body black; macropterous.

Head moderately transverse; middle of frons with one (figs. 7, 8) or two (figs. 11, 12) sharp transverse ledges, completely extending between inner orbits; lower frons between ledge and interantennal prominence transversely striate (figs. 8, 12); eye appearing glabrous but with few scattered minute hairs (visible at high magnification); hyperoccipital carina absent; occipital carina well developed, continuous medially, nearly reaching mandible ventrally, crenulate; ocelli rather large, OOL distinctly shorter than LOL (figs. 9, 10), separated from inner orbit by approximately 1 ocellar diameter; inner orbital space subequal to eye height; inner orbits diverging ventrally; frons largely flat, without frontal scrobe; interantennal process moderately developed, overhanging forward, torulus opening ventrally from process; submedian carina absent; orbital carina absent; lower frons without fanlike striae; clypeus relatively small, truncate apically (figs. 8, 12), lateral corners not projecting; not differentiated into anteclypeus, postclypeus; malar sulcus absent; gena smooth, without fanlike striae, moderately expanded; labrum hidden beneath clypeus; mandible clasped, strong, fairly long, gradually tapering in width apically, deeply bidentate, teeth subequal in length, transversely oriented across tip of mandible; maxillary palpus 5-segmented, all segments elongate, cylindrical, not dilated; labial palpus 3- segmented; male antenna rather short, 12- merous; radicle smoothly joined to base of A1, apex parallel to longitudinal axis of A1, Ushaped (figs. 8, 12: U), inserting dorsally into torulus; apex of A1 with moderately broad, transparent lamellae flanking either side of base of A2; A3 longer than A2; female antenna filiform, not noticeably expanded apically; claval formula A12–A5:1-2-2-2-2-2- 2-1; male antenna tyloids on A4–A6 or A4– A8, low, short; male flagellomeres elongate, cylindrical, covered with short, appressed microtrichiae.

Mesosoma (figs. 9–11) robust, rather short, fairly convex dorsally, with abundant long scattered upright pilosity; pronotum in dorsal view rhomboidal in outline, shoulders well developed, subtriangular, anterolateral corners weakly developed; transverse pronotal carina present, delicate; vertical epomial carina present; horizontal epomial carina present; anterior face of pronotum extremely narrow, hidden in dorsal view; lateral face of pronotum moderately concave, predominantly smooth, shining; netrion represented by series of foveolae above forecoxa; anterior margin of pronotum finely crenulate; anterior margin of mesoscutum meeting pronotum dorsally; mesoscutum moderately transverse; admedian lines absent; parapsidal line weakly indicated; notaulus present (figs. 9, 10: no), fine, percurrent, narrow throughout its length, finely foveolate; skaphion absent; transscutal articulation foveolate; scutellum semicircular, without raised axillulae; axilla well developed; metanotum with dorsellum weakly differentiated, unarmed, foveolate; dorsal surface of propodeum with abundant pilosity, with five subparallel longitudinal keels, not medially excavated, posterolateral corners blunt; mesopleuron large, prominent; mesopleural depression rather shallow (fig. 11: dep); mesopleural carina completely absent; sternaulus absent; mesopleural pit not strongly developed; anterior margin of ventral portion of mesepisternum straight, not protruding between forecoxae; episternal foveae absent; dorsal corner of mesepimeron rounded, without posterior tooth; metapleuron (fig. 11: pl 3) considerably convex, almost entirely smooth, nearly glabrous, with few scattered long hairs, not differentiated by keels or carinae (in contrast to sides of propodeum), with complete row of foveolae along anterior margin; anteroventral portion of metapleuron rounded, not separat- ed from lateral face by carina, setose; metapleural pit absent; posterior margin of metapleuron not lamellate; metapleuron separated from propodeum dorsally by change in sculpture; propodeum rugulose laterally, setose throughout, posterolateral corners weakly projecting posteriorly; legs moderately slender; posterior surface of hind coxa smooth; femora not incrassate; trochantellus present on all legs; outer surface of fore tibia with row of strong, large, semierect spines (fig. 9: s); tibial spur formula 1-2-2, inner spurs slightly longer than outer spurs on mid-, hind legs; tarsal formula 5-5-5; tarsomeres cylindrical; pretarsal claws simple; apex of forewing extending slightly beyond tip of metasoma, moderately infuscate, marginal cilia very short; R fairly straight as far as bulla, extending well beyond basal 0.3 of length of forewing, with several stiff, erect, black bristles arising throughout its length, costal portion (marginal vein) very short, punctiform, heavily pigmented; bulla present, very narrow; R beyond bulla extending toward, but not reaching costal margin, strongly widened to form small pseudostigma; R 1 absent or extremely short, therefore without postmarginal vein; r-rs (stigmal vein) very short, strongly downcurved; no other tracheate veins in forewing; hind wing with tubular R reaching half distance to hamuli and costal margin; no strong dark bristles on R; 4 hamuli present.

Metasoma (fig. 7) rather short, considerably depressed, appearing subsessile; female with seven terga, six sterna visible externally; male with eight terga, seven sterna visible externally; basal five tergites subequal in length, broadly transverse; male T7 very narrow, T8 narrow, subcircular; sculpture beyond basal costae with delicate, longitudinal striae; T1 slightly the longest tergite; laterotergites strongly flexed ventrally, remarkably wide, submarginal ridge well developed; no spiracles visible; anterior margin of segment 1 deeply crenulate, margined by anterior carina; anterior margin of T2, S2 simple or finely crenulate; anterior margins of remaining segments simple; S1 weakly compressed laterally, not extending anteriorly between hind coxae; anterior margin of S2 straight, with moderate elevation between acrosternite and sternite; sublateral felt fields absent.

DIAGNOSIS: Most similar to Sceliomorpha with which it shares the U-shaped, fused radicle and the form of the forewing venation. Listron may be distinguished from Sceliomorpha by the arcuate frontal ledges; the convex, smooth, nearly glabrous metapleuron; the presence of foretibial spines; and the extremely short hairs on the compound eyes.

TYPE SPECIES: Listron politum Musetti and Johnson , n. sp.

ETYMOLOGY: An ungrammatical combination of listros, Greek for ‘‘shovel’’, referring to the frontal ledge; and part of the word Sparasion , a related genus. The name is neuter in gender.

GEOGRAPHIC DISTRIBUTION: Chile.

COMMENTS: The two species of Listron that are described below are only known from males. The presence of a frontal ledge and the spines on the femora suggest that the adults are fossorial. The peculiar U-shaped base of the scape appears to be a fairly strong synapomorphy linking Listron with Sceliomorpha .

Listron politum Musetti and Johnson , new species

Figures 7–9

DESCRIPTION: Holotype male: Femora dark brown to black; frons with single transverse ledge (fig. 7); occiput without striae (fig. 9), with only shallowly incised reticulate microsculpture; penultimate maxillary palpomere cylindrical; middle lobe of mesoscutum with widely spaced setigerous punctures, shallowly incised reticulate microsculpture (fig. 9); upper portion of mesopleuron longitudinally rugulose; T1–T4 finely longitudinally rugulose.

Female: Coxae, femora, base of foretibia dark brown; trochanters, tibiae, tarsi brownish yellow; occiput with irregular, weakly developed transverse rugulae; outer surface of fore-, midtibiae with strong spines.

VARIATION: The single paratype male differs most strikingly from the holotype in the yellow femora. More subtly, the lateral portions of the occiput are weakly transversely striate, and the microsculpture of T3 and T4 is coriaceous, lacking any obvious longitudinal elements. In view of the very limited amount of material presently available, we prefer to err on the side of a more inclusive and robust circumscription for this species.

MATERIAL EXAMINED: Holotype male: CHILE: Recinto, Rancho Grande, 36.793 ° S 71.734 ° W, 1-10.I. 2000, MT, DW Webb, DK Yeates; OSUC 162182 ( MEUC). Paratypes: CHILE: Quillota Prov., PN Campanas, Palmas de Ocoa , 2-10.I. 2000, MT, DW Webb, one male, OSUC 162183 ( INHS); Santiago, Cordillera, Reserva Río Clarillos , 1-20.II.1989, R . Miller, L. Stange, Malaise trap, one female, OSUC 186072 ( FSCA) .

Figures

Figs. 7–12. Listron Musetti and Johnson, n. gen. 7, L. politum Musetti and Johnson, n. sp., lateral habitus, holotype male (OSUC 162182). 8, L. politum, n. sp., head, frontal view, holotype male. 9, L. politum, n. sp., head and mesosoma, dorsal view, holotype male. 10, L. bilaminatum Masner, n. sp., head and mesosoma, dorsal view, holotype male (OSUC 174168). 11, L. bilaminatum, n. sp., head and mesosoma, lateral view, holotype male. 12, L. bilaminatum, n. sp., head, frontal view, holotype male. dep, mesopleural depression; no, notaulus; pl3, metapleuron; s, foretibial spur; U, fused antennal radicle. Scale bars in millimeters.