Description of the species of Dicoelothorax Ashmead (Chalcidoidea, Eucharitidae) and biology of D. platycerus Ashmead

Abstract Descriptions of the adults of the two species of Dicoelothorax Ashmead, Dicoelothorax parviceps and Dicoelothorax platycerus, and the eggs, planidia and pupae of Dicoelothorax platycerus Ashmead are provided. Females of Dicoelothorax platycerus deposit their eggs on the underside of leaves of Pseudabutilon virgatum (Cav.) Fryxell (Malvaceae). The host of Dicoelothorax platycerus is Ectatomma brunneum Smith (Formicidae: Ectatomminae).


Introduction
Eucharitidae are parasitoids of pupae of Formicidae (Hymenoptera: Aculeata) (Clausen 1940, Heraty 2002, females lay their eggs away from the host within the tissues of certain plants and the active first-instar larva, termed a planidium, must make its way back to the ant nest where it can attack the brood (Heraty and Barber 1990).
Dicoelothorax was established by Ashmead (1899), but without a type species. Ashmead (1904) later designated D. platycerus as the type species. Heraty (2002) provides a detailed diagnosis and description of the genus, and a morphological phylogenetic analysis placing this genus within a Neotropical Kapala clade that are all parasitoids of poneromorph ants. A sister group relationship with Lasiokapala Ashmead, 1899 was proposed based on the broad, angulate postgenal margin and the absence of a postmarginal vein (Heraty 2002).
This genus includes two species distributed in the Neotropical region: D. parviceps Cameron (Argentina, Brazil, Colombia and Guyana) and D. platycerus Ashmead (Argentina, Bolivia and Brazil). The original descriptions of these species are vague and short, and there is no clear differentiation of species. Based on the collections examined and our new material, we were able to differentiate both species. Herein we provide new descriptions and diagnoses. Also, D. platycerus was collected in northwestern Argentina, and information on life history, immature stages, and a new host association are included.

Materials and methods
Dicoelothorax platycerus were collected at San Vicente, Tucumán (26°25'36"S, 65°15'41"W; 740 m altitude) on March 12, 2009 on Pseudabutilon virgatum (Cav.) Fryxell (Malvaceae). Eggs were found on the underside of the leaves. Five females of D. platycerus were collected in the field and provided twigs with leaves, fruits, and flowers of different species of plants in 10 × 3.5 cm plastic tubes to monitor oviposition habits. Leaves of P. virgatum with eggs were placed into a cylindrical glass container of 10 × 10 cm with dampened cotton until emergence of the first instar (planidium). The planidia and some eggs were preserved in ethanol. Planidia were cleared in 10% KOH and both larvae and eggs slide-mounted in Hoyer's medium.
Three nests of Ectatomma brunneum Smith (Formicidae: Ectatomminae) that were in close proximity to the adult collection and oviposition site were excavated. Adults, brood, and debris were collected into plastic containers. Adults and immature stages were then sorted from the debris, examined for parasitism, and subsequently returned to the containers to allow further development of immatures. The immature stages were examined once daily until all parasitoids or ants emerged from the cocoons.
Images were obtained using GT-VISION® ENTO-VISION software operating on a Leica M16 zoom lens linked to a JVC KY-F75U 3-CCD digital video camera; and LEICA APPLICATION SUIT (version 3.5.0) software operating on a Leica MZ12 linked to a Leica DFC295 digital video camera. Images were enhanced with COREL PHOTOPAINT and COREL DRAW (version 15); and some images processed with DEEP FOCUS (Stuart Ball).
Specimens studied are deposited in the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Buenos Aires, Argentina (MACN); Instituto Fundación Miguel Lillo, Tucumán, Argentina (IFML); University of California, Riverside, California, USA (UCRC); and American Museum of Natural History, New York, USA (AMNH). Notes and detailed illustrations of the type material housed at the National Museum of Natural History, Washington (USNM) and the Natural History Museum, London (BMNH) were made available by J. Heraty (UCRC).
Male. Length 3.0-3.8 mm. Similar to female except for following. Antenna brown, frenal processes yellowish with a diffuse black longitudinal band medially and apex black, this band can be extended laterally and covering almost entire surface, or it can be reduced to a narrow medial line (Figs 11, 12, 14); wing venation white, forewing hyaline. Head 1.5-1.6× as long as high. Eyes separated by 2.2-2.4× their height. Malar space 0.7-0.9× as height of eyes. Antenna pectinate; scape shorter than female, 1.8-1.9× as long as broad; basal flagellomere 0.9-1.0× as long as height of head, following flagellomeres with branches progressively decreasing in length (Fig. 13). Mesosoma with striae stronger than female, mesoscutal depression rugose (Fig. 12); axilla and scutellar disc narrower than mesoscutum and with longitudinal striae; scutellum with a small depression anterior to union of processes (Figs 12,14). SSS deeply crenulate dorsally. Frenal processes narrowing toward apex; 3.7-4.4× as long as maximum width, 1.7-2.1× as long as scutellum (Figs 12, 14); in profile, uniformly and slightly curved over gaster. Hind coxa 1.8-2.1× as long as broad. Petiole 3.8-4.3× as long as broad, 1.7-2.1× as long as hind coxa. Gaster smaller than female.
Eggs. Length of egg body 0.18 mm and caudal stalk 0.08 mm (Fig. 19). Undeveloped eggs are whitish and translucent with a smooth chorion, slightly flattened dorsally and convex ventrally, with a caudal stalk that is about half the length of the egg body. The egg is similar to other Eucharitinae as described by Heraty and Darling (1984).
Planidium. As described for other Eucharitinae by Heraty and Darling (1984), but distinguished as follows: length 0.09 mm, width 0.05 mm (Fig. 20); pleurostomal spine not observed; anterior pair of placoid sensilla connected to lateral margin by single line of weakness, dorsal cranial spines absent; ventral transverse process of cranium fingerlike; tergopleural line (Tp) separating pleural and dorsal tergites present on tergites TII-VIII; TI and TII fused dorsally, with two pair of small setae dorsally; TIII with one pair of setae ventrally and one pair dorsally; TV with one pair of stout setae ventrally, reaching to TVII; TVI with one pair of stout setae lateral to Tp; TIX entire and with two long lateral processes ventrally reaching to middle of caudal cerci; TXII with lateral processes reaching to almost the middle of caudal cerci; caudal cerci stout (Fig. 20).
Pupa. Length: 5.4-6.7 mm (Figs 26-31). The pupa are similar to the description by Pérez- Lachaud et al. (2006a) for Kapala izapa Carmichael, but differ as follows: with blunt conical projections on each sidelobe of mesoscutum (Figs 27, 29); one pair of conical and pointed projections in the axilla; undeveloped frenal processes broad and flattened; gaster with raised ridges along metasomal tergites, the first tergite with lateral and ventral projections, and following segments with dorsal, lateral and ventral projections. The larval exuvium was attached to the terminal segments of the gaster (Figs 28,30,31). Pupation occurs inside of the ant cocoon (Fig. 26).
Habitat and location. Specimens were collected in San Vicente (Tucumán, Argentina). In this region it is common to find Aspidosperma quebracho-blanco Schlecht. . This vegetation corresponds to the chaco serrano ecoregion (sensu Digilio and Legname 1966). The host plant, Pseudabutilon virgatum, was widely distributed, but the specimens associated with Dicoelothorax were collected in a forest of Prosopis sp., 12 meters north of the road (Fig. 15).
Host Plant. Pseudabutilon virgatum is a ligneous shrub that grows not more than 1 m in height, persists year round, and blooms in the humid seasons (spring-summer); its leaves are ovate and marginally serrate and last to the beginning of the cold season (May-June) (Fig. 16).
Host ants. Ectatomma brunneum workers were observed and sampled from under the plants with Dicoelothorax. In a radius of about 4m, we found three ant nests (H1-H3). The disposition of chambers and general structure of nests are similiar to those observed by Lapola et al. (2003). Nests had 1 to 3 openings at ground level, without any structure elevated above the surface (Fig. 21). Chambers from which the immature stages were extracted were found at a depth of 10 to 13 cm (Figs 22, 23). In two of those nests we found immature stages of ants and parasitoids; in the other (H3) we only found a chamber with a collection of arthropods suggesting that it was a food cache. Nest H1 contained 17 cocoons and 2 larvae, and nest H2 had 97 larvae and no cocoons.
Life History of D. platycerus. Collections of adults of D. platycerus, P. virgatum, and ant nests were made in 2009 (March 12) and 2010 (March 27 and April 3). Females placed in plastic tubes were observed ovipositing on the undersides of the leaves of P. virgatum (Figs 17,18). A single gravid female oviposited about 40 eggs per 1 mm 2 between the spicules forming the pubescence on the underside of leaves (Figs 17, 18). Numerous mites were observed on the leaves, and oviposition under the dense network of spicules appears to be a protection against egg predators. Eggs hatched within 10 days; however, many of the remaining eggs contained mature planidia that did not hatch. First instars (planidia) are very mobile and have a propensity to jump. Larvae presumably attach phoretically to foraging ants under the host plant and get carried back to the ant nest where they attack the ant larvae (Clausen 1941). Of two pupae of D. platycerus obtained in H1, one male emerged 12 days after the nest was excavated; whereas the other pupa (female) did not emerge (Figs 26 -31). The percentage of parasitism ranged from 6.2% in H2 to 21% in H1. In nest H1, 17 cocoons were recovered, with two pupae of D. platycerus (1 female and 1 male) and 2 ant prepupae parasitized by second instars of D. platycerus (Fig. 24). In nest H2, 97 larvae were recovered with 6 parasitized by planidia (Fig. 25). Discussion. Ectatomma brunneum was reported as the ant host for an unidentified species of Kapala (Eucharitidae: Eucharitini) in French Guiana, (Lachaud et al. 2011). It is noteworthy that the same ant species is the primary host for at least two different eucharitid genera. Similarly, Ectatomma tuberculatum (Olivier) can be attacked by three different eucharitid genera, Dilocantha, Isomerala and Kapala (Pérez- Lachaud et al. 2006b).