HOLOTYPE female (BMNH), glued to a card, labelled “MEXICO: Chiapas, Tuxtla Chico, Rosario Izapa, 14°58'25"N, 92°09'19"W, 430 m, 25.ii.2010, G. Pérez-Lachaud & J.-P. Lachaud, reared from Camponotus sp. ca. textor pupa, nest no. 2, on mandarine (Citrus reticulata)”.PARATYPES. 1♀ with same label data as holotype (BMNH); 29♀ with same label and host data as holotype but collected from nest #3 28.ii.2010 (22♀ in BMNH, 2 ♀ in CH, 5♀ in ECO-CH-AR). Several paratypes have opaque and somewhat distorted wings due to premature killing in alcohol, i.e. before the wing membranes had hardened.

Frons with interscrobal area protruding and carinate (Fig. 2); scutellum entirely reticulate, without median groove and lateral mesh–rows (Fig. 4); fore wing speculum small and closed below (Fig. 21); all coxae white; propodeum with submedian grooves strongly reticulate and with anterolateral foveae weakly indicated anteriorly (Fig. 5); propodeal callus with five setae.

The species is very similar to Horismenus alienus Hansson, but differs mainly in the shape of the petiole which in Horismenus alienus has a strongly raised transverse carina dorsally, but Horismenus myrmecophagushas two strong and rounded projections dorsolaterally (Fig. 5); it differs also in sculpture of median propodeum: smooth in Horismenus alienus, but strongly reticulate in Horismenus myrmecophagus(Fig. 5).

Female. Length of body 1.1–1.4 mm. Scape white; pedicel and flagellum pale brown. Frons golden–green with purple tinges (Fig. 23). Vertex metallic bluish–green. Mesoscutum metallic bluish–green (Fig. 24). Scutellum dark golden–purple with green tinges (Fig. 24). Propodeum dark golden–purple (Fig. 24). Legs white. Wings hyaline. Petiole dark golden–purple. Gaster dark brown with metallic purple tinges.

Antenna as in Fig. 17. Frons (Fig. 2) with part just above frontal suture with raised and weak reticulation, remaining parts with raised and strong reticulation; frontal suture V–shaped, incomplete and not reaching eyes; antennal scrobes joining frontal suture separately. Vertex (Fig. 3) with raised and strong reticulation; without a median groove. Occipital margin rounded.

Mesoscutum with raised and strong reticulation (Fig. 4); notauli indistinct. Scutellum with raised and strong reticulation (Fig. 4), without median groove and lateral mesh–rows. Dorsellum slightly concave and with raised and strong reticulation. Propodeum with raised and strong reticulation (Fig. 5); propodeal callus with five setae. Coxae with raised and weak reticulation. Fore wing speculum small and closed below (Fig. 21); with 12 admarginal setae.

Gaster (Fig. 6) with first tergite with very weak reticulation posteriorly and laterally, otherwise smooth.

DE/DO 6.9; WH/DE 1.9; HE/MS/WM 2.4/1.0/2.0; POL/OOL/POO 2.5/1.0/1.1; WH/WT 1.2; LW/LM/HW 1.8/1.0/1.0; PM/ST 1.4; LC/WC 1.4; WG/WC 2.0; LS/LT 0.22; MM/LG 1.0.

Male. Unknown.

Named after the feeding habits of the larva (from the Greek myrmecophagus = ant eater).

Mexico (Chiapas).

Horismenus myrmecophagusis a gregarious endoparasitoid of the larvae of Camponotus sp. ca. textor, a neotropical weaver ant. Parasitized host larvae spin a cocoon before their development is arrested, but no pupation occurs. Parasitized ant larvae are not modified in external form or color by the developing parasitoids, but changes in appearance were observed in the host at the end of the wasp larval development. In material preserved in alcohol, late instar larvae, pupae and teneral adults of the wasps can be readily observed inside ant larvae, within the host cocoon, but earlier developmental stages of the parasitoids could not be detected. The wasp larvae pupate inside the host larva. Horismenus individuals occupy almost the entire body of the host. Wasp pupae were found aligned on either part of the middle of the body of the host, their heads converging to the center, while the cephalic and caudal portions of the host larva were occupied by the host remains and the parasitoids meconia (Fig. 1). An average of 6.7 individuals developed per host (range: 4–12, mode: 7, n=27 parasitized cocoons examined). Adults emerge from the host cocoon through a unique, common hole pierced in the host larval cuticle and through the cocoon wall, but it is unknown whether adult wasps leave the nests to mate. Only females have been observed to date (all broods examined, where the sex of the parasitoid could be ascertained, were constituted by females (n=10 parasitized hosts)). The facts that only single sex broods parasitize any one host, and that only females are known, suggest that Horismenus myrmecophagus is a thelythokous species. Large ant larvae (presumably queens) have never been observed to be parasitized.

Camponotus sp. ca. textor (until now referred to in the literature as Camponotus senex textor Forel) is a common, dominant ant in shade coffee plantations in the Soconusco Region of Chiapas, Mexico (Philpott 2005). This species builds aerial nests on various native and introduced trees (Inga sp., Citrus reticulata, Camponotus sinensis) with the silk of their larvae. Nests measure up to 40 cm in diameter, and colonies may comprise up to 30.000 individuals (Pérez-Lachaud and Lachaud, unpublished data).

The host range of Horismenus myrmecophagus is unknown. It is possible that this species may attack other ant species occupying similar niches, given that certain species of Horismenus are known to be polyphagous (e.g. Horismenus aeneicollis, Horismenus apantelivorus, Horismenus opsiphanis or Horismenus sardus, see Hansson 2009a), and that other ants are known to be parasitized by eulophids in the type locality (e.g. Pachycondyla crenata (Roger), A. de la Mora personal comment), and in French Guiana (e.g. Camponotus (Dendromyrmex)sp., G. Pérez-Lachaud and J.-P. Lachaud, unpublished data), though their identity has not been confirmed yet.

The similar species Horismenus alienus is known only from the female and its host/biology is unknown, but due to its morphological similarity to Horismenus myrmecophagusit is possible that Horismenus alienus is also a parasitoid of ants.

HOLOTYPE female (BMNH) glued to a card, labelled “MEXICO: Chiapas, Tuxtla, Chico, Rosario Izapa, 14°58'25"N, 92°09'19"W, 430 m, 28.ii.2010, G. Pérez-Lachaud & J.-P. Lachaud, reared from larva of Microdon sp., predator inside Camponotus sp. ca. textor, nest no. 3”. PARATYPES. 10 ♀ 2♂ with same label data as holotype (4 ♀ 1♂ in BMNH, 1♀ in CH, 5♀ 1♂ in ECO-CH-AR).

Fore wing speculum covered with setae (Fig. 22); scutellum transverse, 0.75X as long as wide, entirely reticulate with raised and strong reticulation and with a narrow median groove in anterior half (Fig. 9); propodeum with a median carina but without submedian grooves (Fig. 10). This species is easy to recognize through these diagnostic features.

Female. Length 2.0 mm. Scape yellowish–brown, pedicel pale brown, flagellum dark brown. Frons dark golden–green (Fig. 25). Vertex golden–red. Mesoscutum golden–red with posterior 2/3 of midlobe metallic bluish–green (Fig. 26), to predominantly metallic bluish–green or golden–green. Scutellum golden with a median spot metallic bluish–green (Fig. 26), to predominantly metallic bluish–green. Propodeum metallic purple (Fig. 26). Coxae black to dark brown with golden–green tinges; femora, tibiae and tarsi yellowish–brown. Wings hyaline. Petiole black, shiny. Gaster metallic dark purple.

Antenna as in Fig. 18. Frons (Fig. 7) with interscrobal and clypeal areas and part just above frontal suture smooth, remaining parts with raised and strong reticulation with small meshes; frontal suture V–shaped, incomplete not reaching eyes; antennal scrobes join with frontal suture separately. Vertex (Fig. 8) with raised and strong reticulation, areas just behind posterior ocelli smooth; posterior part without median groove. Occipital margin rounded (Fig. 8).

Mesoscutum and scutellum with raised and strong reticulation (Fig. 9); notauli as indistinct impressions, forming posterior part of midlobe to an indistinct triangle. Dorsellum concave with raised and strong reticulation. Propodeum smooth (Fig. 10) or with raised and weak reticulation; median carina narrow and weak; propodeal callus with 5–7 setae and with 2–3 additional setae on median part of propodeum. Coxae smooth. Fore wing speculum absent or very small, obliterated by setae (Fig. 22); with 15 admarginal setae.

Gaster (Fig. 11) with first tergite smooth and shiny with a very weak reticulate band close to posterior margin.

DE/DO 4.2; WH/DE 2.4; HE/MS/WM 2.7/1.0/1.4; POL/OOL/POO 3.1/1.0/1.6; WH/WT 0.9; LW/LM/HW 1.9/1.2/1.0; PM/ST 1.7; LC/WC 4.0; WG/WC 1.5; LS/LT 0.32; LP/WP 1.5; MM/LG 1.3–1.4.

Male. Length 1.6 mm. The male is similar to the female except: scape inflated (Fig. 19) and dark brown, slightly longer petiole and shorter gaster.

HE/MS/WM 2.4/1.0/1.2; LP/WP 1.6; MM/LG 1.6.

Named after the feeding habits of larvae (from the Greek microdonophagus = eater of Microdon).

Mexico (Chiapas).

Horismenus microdonophagus is a gregarious endoparasitoid of Microdon larvae (Diptera: Syrphidae), a predator on the brood of Camponotus sp. ca. textor. One Microdon sp. larva that was about to pupate was found inside a Camponotus nest. From this single host 79 females and 6 males of Horismenus microdonophagus emerged.

One of the two males has the flagellum of both antennae missing, as have also some of the female paratypes, and the other male has the entire right flagellum and apical two flagellomeres of the left antenna missing. Only specimens in fair condition were included in the description, i.e. are type material. The remaining specimens were too fragmented to be included.

HOLOTYPE female (BMNH) glued to a card, labelled “COSTA RICA, Puntarenas, Parque Nacional Corcovado, Mosokha, Quebrada Hedionda, 15.iii–15.iv.2003, Khanaki.”

This species is similar to Microdonophagus levis Hansson (Hansson 2009b) in its smooth and shiny thoracic dorsum but differs from the latter in several characters: scutellum without median groove (Fig. 14); propodeum with a narrow median carina and with distinct anterolateral foveae (Fig. 15); lower mesepimeron enlarged (Fig. 28) but not as enlarged as in Microdonophagus levis (Fig. 29).

Female. Length 2.0 mm. Scape yellowish–brown, pedicel and flagellum pale brown. Head and body including gaster dark brown and shiny. Coxae pale brown; femora, tibiae and tarsi yellowish–brown. Wings hyaline.

Flagellum without anelli, with three funicular segments and a two-segmented clava (Fig. 20). Frons smooth and shiny (Fig. 12), without antennal scrobes and frontal suture, with a narrow and sharp process (an interantennal crest) between toruli. Vertex smooth and shiny (Fig. 13). Occipital margin sharp (Fig. 13). Eyes with scattered long hairs (longer than in Microdonophagus levis).

Mesoscutum smooth and shiny (Fig. 14); midlobe with two pairs of setae; notauli as distinct grooves throughout. Scutellum smooth and shiny (Fig. 14); with one pair of setae; with sublateral grooves in posterior half. Propodeum with a narrow median carina (Fig. 15); with wide sublateral grooves; with distinct anterolateral foveae; propodeal callus with about eight setae; propodeal surface smooth. Fore wing with four setae (right fore wing) and six setae (left fore wing) respectively on dorsal surface of submarginal vein; costal cell bare; speculum small and closed below; postmarginal vein not visible.

Petiole hidden behind inflated gaster but appears to be about as long as wide, dorsal surface with strong sculpture. Gaster circular; gastral tergites smooth (Fig. 16).

HE/MS/WM 1.7/1.0/1.3; POL/OOL/POO 6.0/4.4/1.0; WH/WT 1.0; LW/LM/HW 1.7/1.0/1.0; LP/WP ca 1; MM/LG 1.0.

Male. Unknown.

From the Latin tertius = third. Named for this being the third species described in the genus.

Costa Rica.

Unknown, but possibly associated with ants, as is the type species of Microdonophagus, Microdonophagus woodleyi.

Brazil (new record, 1♀ from Santa Catarina, Nova Teutonia, 7.iv.1938, F. Plaumann, in BMNH), Colombia (Hansson 2002), Panama (Schauff 1986).