Orasema stramineipes

Burks, Roger A., Heraty, John M., Dominguez, Chrysalyn & Mottern, Jason L., 2018, Complex diversity in a mainly tropical group of ant parasitoids: Revision of the Orasema stramineipes species group (Hymenoptera: Chalcidoidea: Eucharitidae), Zootaxa 4401 (1), pp. 1-107 : 12-15

Orasema stramineipes species group

Diagnosis. Both sexes. Labrum with 4 ( Fig. 12) or very rarely up to 6 digits. Flagellum with 8 funiculars ( Fig. 13). Head width:head height 1.0–1.3. Either axillula with a set of strong subparallel carinae ( Fig. 73) or axillular groove anteriorly narrowed ( Fig. 167), anteriorly absent ( Fig. 257), or apparently entirely absent (hardly distinguishable from neighboring sculpture: Fig. 119). Posterior portion of axillular groove represented by large sculpture ( Fig. 35). Fore wing basal cell bare, speculum present as a small bare area ( Fig. 16). Lateral margin of petiole without complete carina ( Fig. 28). Female. First (ventral) valvula of ovipositor with 3–5 strong, widely separated teeth, second (dorsal) valvula with 6–10 annuli ( Fig. 85). Male. Petiole at least 5.1× as long as broad.

Description. Scape yellow in females, yellow or brown in males, not reaching median ocellus; pedicel globose, as broad or broader than F2; flagellum with 8 funiculars, anellus disc-shaped to stout (variable within species), clava subcylindrical. Labrum with 4 (rarely up to 6) digits. Mandible large, yellow with brown margins, mandibular formula 3:2; maxilla and labium yellow to pale brown, of normal size, palpal formula 3:3. Scrobal depression weak, laterally rounded, with transverse striae and finely reticulate sculpture; dorsal scrobal depressions absent. Epistomal sulcus vaguely defined; anterior tentorial pit strongly impressed; anteclypeus distinct or indistinct, broadly rounded to straight (variable within species). Occiput strigate, weakly emarginate in dorsal view, dorsal margin abrupt posterior to ocellar triangle, rounded lateral to it; temples present, rounded. Malar depression weakly impressed between mouth and eye margin.

Notauli narrow to deep. Axilla dorsally rounded, on roughly same plane as mesoscutellum; scutoscutellar sulcus narrow, regularly foveate, reaching transscutal articulation; mesoscutellar disc slightly longer than broad; axillular groove sometimes with an incomplete carina laterally, but if axillular groove with complete carina then axillula with additional subparallel carinae. Prepectus triangular dorsally, strongly narrowed ventrally, sculpture of prepectus areolate-reticulate. Propleuron convex, reticulate. Postpectal carina weak. Propodeal disc broadly rounded; median furrow, if present, flanking a median carina. Hind coxa reticulate dorsally, becoming smooth ventrally; hind femur with uniform cover of short, dense setae; tibiae yellow, hind tibia densely setose. Fore wing basal cell bare, speculum dorsally bare but ventrally with some setae near basal cell, wing disc densely setose; marginal fringe relatively long; submarginal vein with small setae; marginal vein with minute setae; stigmal vein straight to slightly angled, slightly longer to 2.0× as long as broad, uncus present; postmarginal vein 2–5× as long as stigmal vein (tip of postmarginal vein translucent and difficult to assess in many specimens).

Petiole cylindrical, linear in profile, lateral margin without carina, ventral sulcus present with margins narrowly separated; in males petiole long, 5.1–7.9× as long as broad. Apical setae of hypopygium with one pair of setae much longer than the others. Ovipositor slightly curved cephalad; subapical carina present; first (ventral) valvula with 3–5 strong, widely separated teeth, second (dorsal) valvula with 6–10 annuli that are broadly separated dorsally by smooth area.

Discussion of diagnostic features. The stramineipes -group contains several species that are highly variable in body size, likely because of host size. The list of variable features includes many that are commonly used for species-level and even genus-level taxonomy in other Chalcidoidea ( Bouček 1988; Graham 1969, 1987, 1991), such as face sculpture, propodeal sculpture, antennal flagellomere shape, and number of rows of longitudinal sensilla. The stigmal vein and propodeal sculpture are illustrated for all species, but these features are also highly variable in many (but not all) stramineipes -group species. This variation was not accompanied by any apparent restriction in variation in other features. Morphological identification of the stramineipes -group species can therefore be highly reliant on subtle and variable features of color and sculpture of the mesoscutum and mesoscutellum, making this a difficult group to identify. Because of this difficulty, species diagnoses are made more lengthy, including comparisons with similar species.

In the stramineipes -group, some or all of the funiculars may be subapically constricted (vase-shaped), which is a distinctive feature within Orasema , but is variable within species. The femora in the stramineipes -group may be irregular in shape, but this too is highly variable intraspecifically, occurring more often in smaller specimens. Propodeal sculpture is highly variable, and it is possible that no sculptural features are reliable as diagnostic features in this group. Despite that possibility, we rely upon sculpture of the mesoscutum and mesoscutellum for species diagnosis, because of a shortage of alternatives.

Biology. Species are larval parasitoids of myrmicine ants belonging to the genera Pheidole and Wasmannia, and possibly Solenopsis (Myrmicinae). Eggs are deposited singly into incisions made into either fruit or leaves. Immature stages and morphology of the host ant pupal stages are summarized in Figure 4. Larvae, including planidia, are very uniform in structure across the clade, with greater detail on immature stages described under descriptions of O. evansi and O. minutissima . Three instars have been identified: the planidium (first instar), which occurs in both an unfed active form ( Fig. 4 B, C) and the feeding and expanded form that is found both internally on the host larva ( Fig. 4 D) and externally on the host pupa ( Fig. 4 E), the second instar ( Fig. 4 F) found nestled between the legs of the ant pupa, the mature tuberculate third instar ( Fig. 4 G), and a prepupal stage that is free of the ant pupa ( Fig. 4 H). The pupa lacks any prominent lateral or dorsal tuberculate processes on the metasoma, but otherwise are similar to other Orasema (Heraty 1990, 2000).

Distribution. Widespread across the southeastern United States and as far south as northern Argentina ( Fig. 3).