Mexon Masner 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 : 10-13

Mexon Masner and Johnson , new genus

Figures 13–18

DESCRIPTION: Medium sized, length 2.1– 2.4 mm; body moderately elongate, with relatively elongate appendages; head and body dark brown or black; legs and antennae much lighter in color, yellow to yellowish brown; males macropterous, females unknown.

Head distinctly transverse (figs. 15, 16), foramen magnum very high (figs. 13, 18); hyperoccipital carina absent; occipital carina well developed, sharply raised, continuous medially, descending to mandibular condyle, finely crenulate; ocelli clustered into small triangle (fig. 15), OOL several times longer than LOL, LOL # 1 ocellar diameter; OOL longer than POL; compound eye (figs. 13, 18) oval, glabrous, inner orbits subparallel, only slightly diverging ventrally; frons moderately convex, without scrobe, with fairly long, semierect hairs; interantennal process moderately projecting, torulus opening laterally from process; submedian carina absent; orbital carina absent; lower frons without fanlike striae; interocular space distinctly broader than height of eye; clypeus projecting, subtruncate, without sharp posterolateral corners, no differentiation into anteclypeus and postclypeus; malar sulcus absent; gena (malar space) about half length of eye, broad, sculpture variable; labrum hidden beneath clypeus; mandible strong, elongate, deeply bidentate, with lower tooth slightly longer than upper, clasped, i.e., with right overlapping left; palpal formula 4-2, all segments more or less cylindrical; basal labial palpomere short, apical palpomere bulbous; male antenna long, slender, 12-merous; radicle inserted at angle into base of scape (figs. 14, 18: r); A1 only slightly longer than A3; A3 several times longer than A2; all antennomeres distinctly elongate, 2–2.5 times longer than wide, with short, appressed hairs; male antenna keels on A4–A5.

Mesosoma only slightly longer than high (fig. 13), fairly convex dorsally, generally roughly sculptured; pronotum in dorsal view with abundant setae, with anterior margin angulate, distinct surface posterior to transverse dorsal carina, lateral shoulders short, broad, heavily rugulose, frontal plate of pronotum well developed, nearly vertical; transverse pronotal carina sharp or partly obscured by neighboring rugulosity; vertical epomial carina weakly developed; horizontal epomial carina moderately to distinctly developed, angularly joining transverse pronotal carina; anterior margin of pronotum above forecoxa crenulate; lateral face of pronotum moderately concave, facing anterolaterally, without scrobe for reception of foreleg, predominantly smooth, shining, glabrous; netrion indicated as fusiform row of rough foveolae, open above coxa, fairly broad; anterior margin of mesoscutum meeting pronotum dorsally; mesoscutum convex, wider than long; admedian lines absent; parapsidal lines moderately to shallowly impressed; notaulus either present or absent, when present broad, almost percurrent, dilated posteriorly, roughly rugulose; skaphion absent; transscutal articulation deep, foveate; scutellum wider than long, semicircular, unarmed; axillulae sharp, almost bladelike; axilla deeply excavated, subtriangular; metanotum narrow, dorsellum moderately differentiated, unarmed; dorsal surface of propodeum deeply excavated medially, posterolateral corners acute, spikelike projecting, nearly glabrous; keels, plicae of propodeum not developed; mesopleuron large, prominent, ventral portion with scattered setae; mesopleural depression well developed (fig. 13: dep), deep, glabrous; mesopleural carina absent (fig. 18) or present (fig. 13: mpc) on anterior, upper half; sternaulus absent; mesopleural pit present, fairly deep; anterior margin of ventral portion of mesepisternum straight, not protruding between forecoxae; acetabular carina well developed; posterior margin of mesopleuron with row of well-developed, deep foveae; episternal foveae absent; posterodorsal corner of mesepimeron rounded, without posterior tooth; metapleuron with scattered, silvery pilosity, with deep diagonal foveolate groove; anteroventral portion of metapleuron rounded, not separated from lateral face by carina; metapleural pit absent; posterior margin of metapleuron not lamellate; propodeum laterally with fine pilosity, propodeal spiracle well developed; legs long, slender (fig. 17); hind coxa large, posterior surface of hind coxa smooth; femora not incrassate; trochantellus present on all legs; outer surface of fore-, midtibia without spines; tibial spur formula 1- 2-2, spurs subequal in length on midtibia; in type species hind inner spur distinctly longer than outer; tarsal formula 5-5-5; tarsomeres elongate, tapering in width apically; pretarsal claws fairly large, simple; forewing rather long, distinctly surpassing apex of metasoma, slightly infuscate; marginal cilia moderately long; R fairly straight, long, extending to midlength of forewing, running distinctly away from costal margin, with numerous, upright, stiff black bristles arising throughout its length, bulla clearly indicated, costal portion (marginal vein) thick, stigmalike, with proximal edge slanting backward; R 1 (postmarginal vein) very short; stublike r-rs (stigmal vein) long, gently arcuate, downcurved, dilated apically, arising from lower margin of marginal vein; no other tracheate veins in forewing; basal vein nebulous, well demarked, pigmented, forming strongly acute angle with R; Rs, M, Cu nebulous, indicated by long, pigmented lines; hind wing with proximal third of R tracheate, distal two-thirds not developed; no strong dark bristles on R; three hamuli present.

Metasoma (fig. 17) moderately elongate, uniformly segmented, with predominantly longitudinal costae; subcylindrical; T1 slightly the longest tergite, anteromedially slightly to moderately produced; anterior margins of T2– T5 distinctly impressed, foveolate; T7 narrow, subvertical; male with seven terga, six sterna visible externally; submarginal ridge well developed, defined by narrow laterotergites to form deep submarginal rim; no spiracles visible; no cerci visible; anterior margin of segment 1 deeply crenulate; S1, anterior margin of S2 hidden by hind coxae; narrow sublateral felt fields present on S2.

DIAGNOSIS: Distinguished from Sparasion by the absence of a transverse ledge on the frons, the medially clustered ocelli, and the convex frons. Distinguished from Sceliomorpha by the presence of a well-developed radicle, the presence of a short postmarginal vein, and the glabrous compound eyes.

TYPE SPECIES: Mexon adelphos Masner and Johnson , n. sp .

ETYMOLOGY: A combination of México, from where the two species were collected, and part of the name Sparasion , a closely related genus. The name is neuter in gender.

GEOGRAPHIC DISTRIBUTION: México: Michoacán (type) , Oaxaca.

COMMENTS: In overall appearance, this scelionid genus is vaguely reminiscent of a small male ant, mainly because of its small eyes, clustered ocelli, and dorsal position of the foramen magnum. This last character suggests that the hypostomal bridge in these species is remarkably long. The unknown female will probably be distinguished by a long horn on T1, judging by the excavated propodeum and projections of T 1 in the male sex.

Mexon adelphos Masner and Johnson , new species

Figures 13–15

DESCRIPTION: Holotype male: Length: 2.15 mm. Head and body brown; legs, including coxae, yellowish brown; antenna slightly darker than legs; wings slightly infuscate, with darker nebulous Rs+M, Rs, M, Cu; stigma (marginal vein), R 1 dark brown. Interocellar space, occiput behind with rough rugulosity (fig. 15); upper frons, OOL space, postgena almost smooth; lower frons rugose punctate; antenna with segments elongate, length of A4 2.9 times width, length of A5 2.6 times width; A1 relatively short, length 1.3 times length of A3; transverse carina on pronotum weakly developed (fig. 15), hidden by rough rugulosity of dorsal pronotum; anterior two-thirds of mesoscutum with rough rugulosity; notaulus present, almost percurrent, dilated posteriorly, rugulose foveolate; parapsidal lines absent, posterolateral scapula almost smooth; posterolateral edge of scapula sharply upraised; parapsidal line well developed; mesopleural carina entirely absent; anteromedian margin of T1 distinctly elevated.

MATERIAL EXAMINED: Holotype male: MEXICO: Michoacán, Carapan , July 10, 1981, J. LaSalle, OSUC 174166 ( CNCI).

DIAGNOSIS: Most easily distinguished from M. consors by the presence of notauli on the mesoscutum and the presence of coarse rugulae on the posterior portion of the head.

Mexon consors Masner and Johnson , new species

Figures 16–18

DESCRIPTION: Holotype male: Length: 2.4 mm. Head and body black; legs, including coxae, contrastingly golden yellow; antenna dark brown; wings slightly infuscate, with darker nebulose Rs+M, Rs, M, Cu; stigma dark brown. Interocellar space, occiput (fig. 16), entire frons smooth, with scattered setigerous punctures; antenna with segments shorter, length of A4 2.5 times width, length of A5 2.3 times width; A1 longer, length 1.6 times length of A3; transverse carina on pronotum entire, sharply defined; mesoscutum generally smooth, with scattered setigerous punctures; notaulus absent; parapsidal lines weakly developed; posterolateral margin of scapula without raised edge; mesopleural carina developed in upper half, weakly crenulate; anteromedian margin of T1 only slightly elevated.

MATERIAL EXAMINED: Holotype male: MEX- ICO: Oaxaca, 1.4 miles NE La Cumbre, July 18, 1985, Jones, Schaffner; OSUC 174167 ( TAMU).

DIAGNOSIS: Most easily distinguished from M. adelphos by the absence of notauli on the mesoscutum and the lack of coarse rugulae on the posterior portion of the head.

Figures

Figs. 13–18. Mexon Masner and Johnson, n. gen. 13, M. adelphos Masner and Johnson, n. sp., head and mesosoma, lateral view, holotype male (OSUC 174166). 14, M. adelphos, n. sp., head, frontal view, holotype male. 15, M. adelphos, n. sp., head and mesosoma, dorsal view, holotype male. 16, M. consors Masner and Johnson, n. sp., head and mesosoma, dorsal view, holotype male (OSUC 174167). 17, M. consors, n. sp., lateral habitus, holotype male. 18, M. consors, n. sp., head, lateral view, holotype male. dep, mesopleural depression; mpc, mesopleural carina; r, radicle. Scale bars in millimeters.