Mesostoinae

Subfamily Mesostoinae van Achterberg 1975

Mesostoinae van Achterberg 1975: 158; Quicke & Huddleston 1989: 1310 Avigini (in part) Belokobylskij 1993: 157; van Achterberg 1995: 53 Canberrini Belokobylskij 1993: 156

Austrohormiini Belokobylskij 1993: 159

Hydrangeocolini Whitfield 1992: 275

Diagnosis. Small body with surface mostly smooth and glabrous. Hypoclypeal depression present with labrum glabrous; malar suture present; ocelli minute; occipital carina reaching base of mandible or not, but generally complete; hypostomal carina weak or indistinct; pronotal collar very short, or relatively long with two flanges separated by high transverse carina; mesocutum sometimes protruding over pronotal collar; mesocutum with short notauli, present only anteriorly and somewhat directed toward midpit; midpit of mesoscutum frequently present, posterior region of mesoscutum otherwise smooth; epicnemial carina completely absent to present, frequently weak and sinuate ventrally when complete, commonly present only laterally; propodeum short, with longitudinal carina present at least basally, areola present or not; petiole short with large flat lateral areas and frequently with a pair of lateral carinae converging over median convex area, but not meeting; metasoma beyong petiole smooth and polished, sclerotization weak to almost membranose; spiracle on TII on laterotergite; ovipositor sheaths covered with long setae, ovipositor relatively long (about as long as hind tibia or longer); fore wing with stigma narrow, never globose; 2nd submarginal cell relatively large or r-m absent; vein m-cu widely distad to vein 2RS, interstitial to weakly basad in Andesipolis, rarely distinctly basad; vein 2a present or not; hind wing vein m-cu absent.

Biology. Mesostoinae s.s. and Hydrangeocolini genera are all associated with galls, whether inducing cecidogenesis cecidogenesis (i.e. Mesostoa) or parasitizing Cecydomyiidae (i.e. Aspilodemon). Other genera included in this subfamily are associated with semi-concealed (e.g. leaf-miners, leaf-rollers) Lepidoptera (Andesipolis, Neptihormius).

Included genera. Mesostoa van Achterberg; Praonopterus Tobias (Mesostoinae s.s.); Aspilodemon Fischer, Hydrangeocola Brèthes, Opiopterus Szépligeti (Hydrangeocolini); Austrohormius Belokobylskij (Austrohormiini); Proavga Belokobylskij, Andesipolis Whitfield & Choi, Canberria Belokobylskij, Hormiitis van Achterberg, Neptihormius van Achterberg & Berry, Apoavga van Achterberg; Doryctomorpha * Ashmead.

*Although supported by phylogeny this genus was not transferred to Mesostoinae by Zaldívar-Riverón (2006). Belokobylskij (2009) preferred a classification within Rhyssalinae, based on morphology. Quicke (2014) rejected this later classification. Here we follow the classification proposed by Quicke.

Distribution. Neotropical and Australasian Regions.

Discussion. The weakly sclerotized metasoma beyond petiole has linked the genera in this subfamily to the Hormiinae, and it is still a helpful character to separate Mesostoinae from Rhyssalinae. Position of fore wing vein m-cu, distinctly distad to 2RS, has also been traditionally used as a diagnostic character, and is useful for most genera except Andesipolis. Inclusion of Andesipolis in this subfamily reinforces a close relationship within Rhyssalinae and Mesostoinae, as well as the idea of a more plesiomorphic biology (suggested by Quicke 2014) and morphology. For instance, the Rhyssalinae found in Costa Rica (i.e. Oncophanes Förster 1862, Rhyssalus Haliday 1833, Dolopsidea Hincks 1944) have diagnostic character in common with Andesipolis: 1. propodeal areola well defined with a transverse ridge plus two pairs of lateral oblique carinae (this character is variable in Andesipolis, also found in Proavga and Neptihormius); 2. pronotal collar with two flanges, one posterior longer and flat and the anterior with a crenulate sulcus (most Mesostoinae have the pronotal collar very short, sometimes entirely concealed by mesoscutum); 3. vein 2a of fore wing present, sometimes only weakly indicated (although some Mesostoinae have this vein present, it is absent in most genera); 4. Rhyssalinae genus Oncophanes, as well as Andesipolis and Neptihormius, are gregarious parasitoids of leaf-miner, -tyers, -rollers, while Mesostoinae s.s. and Hydrangeocolini are gall-associated.

Besides phylogenetic evidence (Zaldivar-Riverón et al. 2006; Sharanowski et al. 2011), the inclusion of Andesipolis in Mesostoinae, rather than Rhyssalinae is justified by the following synapomorphies: 1. vein m-cu of hind wing absent (a synapomorphy of Mesostoinae, in Rhyssalinae the vein m-cu is present); 2. hypostomal carina weak or absent (another synapomorphy of Mesostoinae; in Rhyssalinae the carina is distinct and conects with the occipital); 3. epicnemial carina weak or absent ventrally, when present it is sinuate and weak (in Rhyssalinae and also in Rhysipolinae the carina is strong and straight ventrally); 4. metasomal TI short with convex median area and large flat lateral areas (the flat lateral areas are absent in Rhyssalinae).