Dicoelothorax platycerus Ashmead

Torrens, Javier & Heraty, John M., 2012, Description of the species of Dicoelothorax Ashmead (Chalcidoidea, Eucharitidae) and biology of D. platycerus Ashmead, ZooKeys 165, pp. 33-46 : 37-41

Dicoelothorax platycerus Ashmead Figs 6-31

Dicoelothorax platycerus Ashmead 1904: 470-471; De Santis 1979: 107; De Santis 1980: 211; Heraty 2002: 130, figs 113-119 (lectotype and paralectotype). Type females in USNM, http://www.chalcidtypes.com/default.asp?Action=Show_Types&Single_Type=True&TypeID=878 [examined]

Description.

Distinguished from Dicoelothorax parviceps by the mesosoma and frenal processes having fine closely-spaced longitudinal striae, closer and more slightly raised in female (Figs 8, 9, 12, 14); dorsal concavity of mesoscutum and scutellum smooth or weakly striate medially (Figs 8, 9); frenal processes in dorsal view widened medially and narrowing only slightly to apex, which is almost the same width as their base and broadly rounded (Figs 8, 9); venation brown; scutellar processes of male yellowish with diffuse black longitudinal band medially and apex black, slightly curved in lateral view, and almost twice as long as scutellum (Figs 12, 14).

Female. Length 3.0-4.5 mm. Head, mesosoma, coxae, petiole and Gt1 except distal part black; flagellum, basal ¾ of femora, frenal process, distal part of Gt1 and rest of terga brown but with processes sometimes completely black; scape, pedicel and rest of legs and distal limits of terga yellowish (Figs 6, 8, 9). Wings slightly infuscate, venation brown.

Head 1.4 –1.5× as broad as high. Frons and face granulate, weakly strigose, with small and scattered setae or without setae (Fig. 7). Eyes separated by 2.3 –2.7× their height. Malar space 0.8 –1.2× as long as height of eyes. Antenna with 8 segments; scape 2.4 –2.8× as long as broad, slightly broader apically, smooth, with a few scattered setae. Length of flagellum 0.7 –0.9× height of head, basal flagellomere 0.8 –1.2× as long as scape, basal flagellomere ranging from serrate to clavate, following flagellomeres serrate, clava rounded (Fig. 7).

Mesosoma. Midlobe of mesoscutum elevated anteriorly, with short, thin, decumbent and scattered setae; striate-rugose on anterior face, sidelobes longitudinally striate, modlobe dorsally smooth or weakly striate and concave (Figs 6, 10). Axilla and scutellar disc smooth and concave dorsally, scutellar disc longitudinally striate laterally. SSS weakly crenulate dorsally and deeply invaginated and smooth laterally (Figs 8, 9). In dorsal view, frenal processes widened medially and tapering only slightly to apex, apically almost the same width as their base and broadly rounded, with longitudinal striae slightly marked and closely spaced; processes 3.1 –3.5× as long as maximum width and 2.4 –2.7× as long as scutellum (Figs 6, 8, 9); in profile, curved over gaster. Upper half of mesepisternum and mesepimeron longitudinally striate. Hind coxa semiglobose and elongate, 1.7 –2.1× as long as broad; with weak longitudinal striae and scattered, thin setae (Fig. 10). Hind femur densely setose. Forewing 2.3 –2.5× as long as broad; stigmal vein slender and perpendicular to wing margin, 1.9 –2.2× as long as broad; postmarginal vein indistinct and less than half as long as stigmal vein (Fig. 8).

Metasoma. Petiole 3.6 –4.1× as long as broad, 1.7 –2.0× as long as hind coxa and 1.2 –1.3× as long as hind femur; Gt1 smooth and without setae (Figs 6, 10).

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.(Quebracho blanco), Cassia , Cercidium sp. (Brea), Cereus validus Haworth, Harrisia pomanensis (F.A.C.Weber) Britton & Rose, Jodina rhombifolia Hooker et Arnott (Sombra de toro), Opuntia sp. (Tuna, Quimilo), and Prosopis sp. (Algarrobo). 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 Dicoelothorax platycerus .

Collections of adults of Dicoelothorax platycerus , Pseudabutilon 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 Pseudabutilon virgatum (Figs 17, 18). A single gravid female oviposited about 40 eggs per 1 mm2 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 Dicoelothorax 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 Dicoelothorax platycerus (1 female and 1 male) and 2 ant prepupae parasitized by second instars of Dicoelothorax 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).

Material examined.

ARGENTINA. Salta, Tartagal, xii.1971, UCRC_ENT 305490 and UCRC_ENT 305491 (2 males, AMNH). Salta, Güemes, 7.ii.1983, UCRC_ENT 305492 (1 female, AMNH); same location and data, UCRC_ENT 305493 (1 male, AMNH). Salta, Cabeza de Buey, 24°47'36"S, 64°01'57"W, 15-16.iii.2007, J.&J. Heraty & J. Torréns, UCRC_ENT 305494 (1 female, UCRC); same location and data, UCRC_ENT 305495 and UCRC_ENT 305496 (2 males, UCRC); same location and data, UCRC_ENT 305497, UCRC_ENT 305498 and UCRC_ENT 305499 (3 males, IFML). Salta, Cabeza de Buey, 24°47'36"S, 64°01'57"W, 19.ii.2008, P. Fidalgo, UCRC_ENT 305500 (1 female, MACN); same location and data, UCRC_ENT 305501 (1 male, MACN). Salta, Lumbreras, 25°12'19"S, 64°54'34"W, 14.iii.2009, J. Torréns, UCRC_ENT 305502 (1 female, IFML). Tucumán, San Vicente, 26°25'36"S, 65°15'41"W, 12.iii.2009, J. Torréns, UCRC_ENT 305503 and UCRC_ENT 305504 (2 females, IFML); same location, 27.iii.2010, J. Torréns, ex. Pupa of Ectatomma brunneum UCRC_ENT 305505 (1 female, IFML); same location and data, UCRC_ENT 305506 (1 male, IFML); same location, 03.iv.2010, J. Torréns, ex. pupa of Ectatomma brunneum , UCRC_ENT 305507 (1 male, IFML).