Horismenus myrmecophagus, Hansson, Christer, Lachaud, Jean-Paul & Perez-Lachaud, Gabriela, 2011

Hansson, Christer, Lachaud, Jean-Paul & Perez-Lachaud, Gabriela, 2011, Entedoninae wasps (Hymenoptera, Chalcidoidea, Eulophidae) associated with ants (Hymenoptera, Formicidae) in tropical America, with new species and notes on their biology, ZooKeys 134, pp. 65-82 : 67-69

Horismenus myrmecophagus sp. n. Figures 12-617, 2123-24

Material.

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.

Diagnosis.

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 myrmecophagus has 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).

Description.

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.

Ratios.

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.

Etymology.

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

Distribution.

Mexico (Chiapas).

Biology.

Horismenus myrmecophagus is 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.

Remarks.

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 myrmecophagus it is possible that Horismenus alienus is also a parasitoid of ants.