Eupelmus (Merostenus) excavatus, Dalman

Gibson, Gary A. P., 2017, Synonymy of Reikosiella Yoshimoto under Merostenus Walker (Hymenoptera: Chalcidoidea: Eupelmidae), with a checklist of world species and a revision of those species with brachypterous females, Zootaxa 4255 (1), pp. 1-65: 28-33

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Eupelmus (Merostenus) excavatus


M. (Merostenus) excavatus (Dalman)  

Figs 39–55 View FIGURES 39 – 48 View FIGURES 49 – 55

Eupelmus excavatus Dalman, 1820: 382   –383. Holotype ♀ ( NHRS, examined). Type data: [ Sweden] Scaniae.  

Merostenus Phedyma Walker, 1837: 355   . Lectotype ♂ ( BMNH, type no. 5.2313, examined), designated by Graham , 1969: 93. Type data: England: nr London. Synonymy by Ruschka, 1921: 309.  

Urocryptus excavatus   ; Westwood, 1839: 72.

Eupelmus (Urocryptus) excavatus   ; Thomson, 1876: 108.

Eupelminus excavatus   ; Dalla Torre, 1898: 272.

Merostenus excavatus   ; Ruschka, 1921: 309; Nikol’skaya, 1952: 487/500 [key]; Erdős, 1960: 204 –205 [key]; Peck, Bouček and Hoffer, 1964: 61 –62 [key]; Askew, 1987: 49 [key]; Trjapitzin, 1978: 235 /426 [key]; Fusu, 2013: 5 [male compared with Reikosiella Yoshimoto   males], 16 [male imaged].

Type material. The holotype of Eupelmus excavatus   is an uncontorted female pinned laterally through the mesosoma such that all features are visible; it has two labels, a tiny blue square piece of paper and a larger white label with “153”, and is entire except both antennae beyond the anelli are missing. The male lectotype of Merostenus Phedyma   has the following four labels: LECTOTYPE [purple-bordered circular label] / Merostenus   | phedyma   | Walker / Eupelminus   | excavatus Dalm.   | Ch   . Ferriere det. ♂ / B.M. TYPE | HYM. | 5.2313. It is entire and glued by its venter to a card rectangle.

Description. FEMALE (habitus: Figs 40, 42 View FIGURES 39 – 48 ). Length = 1.3–2.7 mm. Head ( Fig. 39 View FIGURES 39 – 48 ) dark brown in smallest individuals but usually mostly green with variably distinct and extensive reddish-violaceous to purple lusters on smoother part of frons and within scrobal depression, most commonly at least on dorsal surface of interantennal prominence; in frontal view about 1.2× as wide as high, and in lateral view about 1.6× as high as long with lower face abruptly angled to longer upper face such that anterior and ventral margins subparallel and vertex uniformly rounded; vertex meshlike coriaceous and scrobal depression meshlike reticulate to transversely reticulate-rugose, but frons between about level of posterior ocelli and scrobal depression shiny and much smoother, at most in part with subeffaced coriaceous sculpture, with dorsal surface of interantennal prominence similarly shiny or variably distinctly coriaceous to alutaceous, and lower face distinctly coriaceous to alutaceous; entirely setose with short setae except for bare scrobal depression, with setae on lower face paler compared to dark setae on frontovertex and those on frons separated by distance mostly greater than MPOD and at least in larger females originating from tiny but quite distinct pits; scrobal depression distinct though transversely to high Π-shaped, the broadly arched upper margin usually separated from anterior ocellus by distance about equal to POL though sometimes appearing closer if frons distinctly coriaceous below anterior ocellus, but at least lateral margin outcurved from lateral margin of torulus toward lower inner orbit such that parascrobal region absent; ratio of OOL: POL: LOL: MPOD = 1.5–2.0: 2.6–3.7: 1.4–2.0: 1.0 [larger individuals with smaller ratios]. Antenna ( Fig. 42 View FIGURES 39 – 48 ) dark except for yellow scape ( Figs 39, 42 View FIGURES 39 – 48 ); scape slightly curved and slender, with thin flange on inner surface apically and therefore slightly wider apically, but mostly tubular with length about 5.5–6.3× medial width; pedicel about 1.75–2× as long as apical width; fl1 usually slightly wider than long but at most quadrate, fl2–fl4 all longer than wide and fl5–fl8 decreasing in length such that apical funiculars quadrate to slightly transverse; clava about 1.9–2.8× as long as wide. Labiomaxillary complex yellow to brownish-yellow and mandibles paler, more yellowish basally, and darker, more orangish to reddish apically.

Mesosoma ( Figs 40–42 View FIGURES 39 – 48 ) mostly orangish to orangish-brown but at least larger individuals with following darker brown and sometimes with violaceous to purple lusters: dorsal surface of pronotum except for mediolongitudinal paler band within anterior half ( Fig. 41 View FIGURES 39 – 48 ), scutellar-axillar complex ( Fig. 43 View FIGURES 39 – 48 ), at least convex callar regions of propodeum ( Fig. 43 View FIGURES 39 – 48 ), mesopectus and extreme anterior angle of acropleuron ( Figs 42, 44 View FIGURES 39 – 48 ), and often metapleuron ( Fig. 41 View FIGURES 39 – 48 ). Pronotum completely sclerotized but often with slight indication of mediolongitudinal furrow or slender band of slightly different sculpture mediolongitudinally, and distinctly convex, cone-like produced dorsomedially ( Figs 41, 42 View FIGURES 39 – 48 ) with neck forming anterior portion and collar forming posterior portion, but both similarly meshlike coriaceous; mostly bare dorsally but with a few, short, inconspicuous setae along anterior margin and sides, and transversely over medial ridge on putative collar portion anteriorly. Mesoscutum ( Fig. 41 View FIGURES 39 – 48 ) with lateral lobes strongly ^-like angulate from median, but carinate only posteriorly, and with anterior margin curved up anterior to lateral lobes behind pronotum; variably distinctly meshlike coriaceous but dorsally extensively setose with at least two lines of setae along inclined inner surface and line of setae dorsally and ventrally along outer inclined surface of lateral lobe. Scutellar-axillar complex ( Fig. 43 View FIGURES 39 – 48 ) with scutellum convex, the frenum bare and coriaceous, but anterior to frenum more coarsely sculptured, setose, and tapered anteriorly to acute angle widely separated from transscutal articulation, with angulation carinately margined only apically; axillae comparatively large and long, longitudinally striate-strigose, setose laterally, and anterior to scutellum separated by deep longitudinal depression. Fore wing ( Fig. 43 View FIGURES 39 – 48 ) short, disc only about 1.25–1.5× as long as wide, spatulate with broadly rounded to truncate apical margin extending to level equal with anterior margin of frenal area of scutellum; disc hyaline with submarginal vein extending at least two-thirds length but terminating at least slightly before apex of disc, and with 2 or 3 setae, but membrane otherwise bare except often for inconspicuous marginal fringe along posterior and/or apical margins of disc. Mesopectus entirely setose with white setae; acropleuron ( Fig. 41 View FIGURES 39 – 48 ) posteriorly broadly curved to level of anterior margin of mesocoxa ( Fig. 44 View FIGURES 39 – 48 ), shiny and mostly smooth with distinct sculpture only narrowly along anterior margin and sometimes subeffaced sculpture dorsally and ventrally. Metanotum ( Fig. 43 View FIGURES 39 – 48 ) with dorsellum delineated as laterally carinate, anteriorly V-like incised median region, with median carina at least anteriorly. Metapleuron ( Fig. 44 View FIGURES 39 – 48 ) bare, variably distinctly meshlike coriaceous to coriaceousreticulate, with sinuate anterior margin so as to be widest ventrally and slightly reflexed into slender flange abutting posterior margin of acropleuron, and with ventral margin also reflexed as slender flange continued obliquely toward acropleuron so as to differentiate a triangular region with 1 ( Fig. 44 View FIGURES 39 – 48 : arrow) or 2 setae between acropleuron and anterodorsal angle of metacoxa. Legs ( Figs 40, 42 View FIGURES 39 – 48 ) mostly yellowish-orange to orangish-brown with coxae and apical tarsomeres usually darker brown if mostly light in color; mesotibia with row of up to 8 apical pegs in larger individuals ( Fig. 45 View FIGURES 39 – 48 ); metacoxa setose along outer surface basally and dorso- and ventrolongitudinally. Propodeum ( Fig. 43 View FIGURES 39 – 48 ) superficially quite long, medial length about one-third distance between transscutal articulation and posterior margin of dorsellum, but upcurved posterior margin sinuately incurved toward anterior margin medially to form high ridge with subcontiguous margins posteriorly and fused anteriorly into median carina; callus strongly, cone-like produced ( Fig. 44 View FIGURES 39 – 48 ) with terminal spiracle lateral to furrow differentiating median ridge, shiny and smooth or at most finely coriaceous, and setose laterally and very sparsely posterior of spiracle.

Metasoma with petiole transverse-quadrangular ( Fig. 43 View FIGURES 39 – 48 ). Gaster ( Fig. 46 View FIGURES 39 – 48 ) dark brown with at most slight coppery to violaceous lusters except Gt1 variably extensively green to bluish-green or with some reddishviolaceous lusters; meshlike coriaceous with transverse band of inconspicuous dark setae on all tergites except Gt1 and syntergum uniformly setose without marginal line of setae; syntergum in dorsal view ( Fig. 40 View FIGURES 39 – 48 ) with posterior margin transverse; supra-anal plate sometimes not evident, but often visible as yellowish to brown, transverse sclerite adjacent to posterior margin of syntergum ( Figs 47, 48 View FIGURES 39 – 48 ); ovipositor sheaths brown, projecting only slightly beyond syntergum.

MALE (habitus: Figs 49, 50 View FIGURES 49 – 55 ). Length = 1.0– 1.9 mm. Head ( Fig. 51 View FIGURES 49 – 55 ) sometimes mostly brown with only slight metallic luster in smallest individuals but usually dark with variably conspicuous blue to green lusters and with variably extensive purple, coppery and/or reddish-violaceous lusters; mostly to entirely meshlike-coriaceous but smaller individuals with frons and scrobal depression often with finer sculpture and sometimes virtually smooth and shiny; with white setae on lower face and frons and darker setae on vertex; scrobal depression shallow, transversely oval with indistinct margins, laterally not extending completely to inner orbit such that narrow, setose parascrobal region differentiated along inner orbit, and dorsally smoothly merged with frons, and without or with variably distinct but tiny pit medially above interantennal prominence; OOL: POL: LOL: MPOD = 1.4–2.0: 2.4– 3.0: 1.1–1.6: 1.0; frontovertex about 0.6× head width. Antenna ( Fig. 52 View FIGURES 49 – 55 ) variably dark brown except scape basally often variably extensively paler, more yellowish, and dark part usually with slight greenish luster; scape compressed-tubular with subparallel dorsal and ventral margins, about 5.0–5.8× medial width; pedicel about 1.6– 1.9× as long as broad and much shorter than fl2; combined length of pedicel + flagellum about 2.3–2.5× head width; fl1 strongly transverse, anelliform; fl2 to clava each with short pedicel basally, and with semierect, curved setae somewhat longer than width of flagellomere, and with obscure, very sparse mps apically; fl2–fl8 conspicuously elongate-tubular, all of similar length but apical funiculars somewhat shorter with fl2 about 2.7– 3.3× as long as wide and fl8 about 2.2–2.3× as long as wide excluding basal pedicels; clava about 4.3–4.7× as long as wide with clavomeres separated by distinct sutures. Eye ( Fig. 51 View FIGURES 49 – 55 ) very sparsely and obscurely setose with very short setae; EH about 1.2–1.3× EL and 1.1–1.6× MS. Labiomaxillary complex light brown to brown.

Mesosoma ( Figs 49, 50 View FIGURES 49 – 55 ) similar in color to head, mostly brown in smaller individuals but usually metallic green with some coppery luster to bluish. Pronotum completely sclerotized, meshlike coriaceous, and setose with white setae laterally and along posterior margin. Mesonotum ( Fig. 49 View FIGURES 49 – 55 ) meshlike coriaceous to variably strongly roughened, reticulate-rugulose, and setose with white or at least pale setae anterior to frenum. Fore wing ( Fig. 53 View FIGURES 49 – 55 ) hyaline in smaller individuals but usually with at least slight brownish infuscation on disc basally behind parastigma and sometimes more extensively; length about 2.9–3.3× as long as maximum width and length of marginal vein about 0.9–1.0× width; cc: mv: stv: pmv = 3.9–4.8: 3.1–4.0: 1.0: 2.1–2.3; stigmal vein distinct; costal cell dorsally with line of setae along about apical half of leading margin and ventrally setose along length; basal cell and disc entirely, uniformly setose. Metapleuron ( Fig. 55 View FIGURES 49 – 55 ) bare except usually for 1 or 2 setae anteroventrally ( Fig. 50 View FIGURES 49 – 55 : insert), and meshlike coriaceous to smooth dorsally but more strongly sculptured, usually reticulate, ventrally; extending dorsally only about two-thirds or less distance to anterior margin of propodeum, to level equal with anterior margin of propodeal spiracle ( Figs 50 View FIGURES 49 – 55 : insert, 55), and with posterodorsal margin of acropleuron separated from anterodorsal margin of metapleuron. Propodeum ( Figs 54, 55 View FIGURES 49 – 55 ) with medial length about 0.4–0.5× distance between transscutal articulation and posterior margin of dorsellum; with variably complete median carina and with transverse crenulate furrow along anterior margin lateral to dorsellum, but otherwise meshlike reticulate; callus setose with white setae lateral of spiracle, the spiracle obviously separated by more than own diameter from anterior margin with posterior margin close to mid-length and usually at apex of at least an apparent convexity if not a distinct, cone-like protuberance ( Fig. 55 View FIGURES 49 – 55 ). Leg color highly variable, from entirely yellowish, including coxae, to entirely dark brown with slight metallic luster ( Fig. 50 View FIGURES 49 – 55 ); metacoxa setose with white setae along ventrolateral margin and dorsolongitudinally, and sometimes on outer surface basally.

Metasoma with petiole ( Fig. 54 View FIGURES 49 – 55 ) yellowish to brown, smooth and shiny except sometimes with some fine longitudinal crenulae basally, and trapezoidal with sides divergent posteriorly and with posterior margin wider than anterior margin. Gaster ( Figs 49, 50 View FIGURES 49 – 55 ) dark apically but Gt1 dorsally at least extensively pale, yellowish, and sometimes with up to about basal half of gaster entirely yellow; dorsoventrally flattened to oval in cross-section ( Figs 49, 50 View FIGURES 49 – 55 ); Gt1 smooth, shiny and bare dorsally, but subsequent tergites finely coriaceous to alutaceous and variably extensively setose dorsolaterally, though often at least Gt2 bare medially.

Distribution. PALAEARCTIC: listed by Noyes (2016) from throughout the region as far east as Yaroslavl Oblast in Russia. I examined specimens from Austria ( BMNH), Croatia ( BMNH), Cyprus ( USNM), England and France ( CNC, USNM), Germany, Hungary and Italy ( CNC, UCRC, USNM), Palestine ( BMNH), and Sweden and Switzerland ( CNC). NEARCTIC: Canada (Nova Scotia).

Chamberlin (1924a) stated that 430 males and 471 females of M. excavatus   were released from Europe into Utah, of which voucher material remains in UCRC, but Essig and Michelbacher (1933) stated that it apparently never established. Gibson (1995) did not see any M. excavatus   collected in Utah or elsewhere in the USA and also questioned whether it had established. However, one male collected in 1993 and two other males collected in 2004 ( CNC) in Nova Scotia indicate it was accidentally introduced and has established in eastern Canada   .

Hosts. Hypera postica (Gyllenhal) ( Chamberlin 1924b)   , Hypera punctata (Fabricius) ( Chamberlin 1924b)   , Hypera variabilis Herbst ( Bouček 1977)   ( Coleoptera   : Curculionidae   ).

Chamberlin (1924b) stated that M. excavatus   feeds externally on the egg masses of the alfalfa weevil, H. postica   , and the clover leaf weevil, H. punctata   . Larvae estivate in the stems of alfalfa and adults emerge in the autumn.

Remarks. Merostenus excavatus   is the only excavatus   -group species in the Palaearctic region and its relationships with other species in the species-group and M. ( Merostenus   ) remain unresolved. Females are readily distinguished by their unique scutellar-axillar structure/sculpture pattern ( Fig. 43 View FIGURES 39 – 48 ) and cone-like produced propodeal callar regions that terminate in the spiracle ( Figs 43, 44 View FIGURES 39 – 48 ). Males are perhaps most readily identified by the metapleuron extending dorsally only to a level equal with the anterior margin of the propodeal spiracle ( Fig. 55 View FIGURES 49 – 55 ) rather than distinctly anterior of the spiracle closer to the anterior margin of the propodeum. Most males also have the callus at least noticeably convex, if not more cone-like produced ( Fig. 55 View FIGURES 49 – 55 ), similar to females. Because of these features the males from eastern Canada are confidently identified as M. excavatus   even though females have yet to be collected. As noted in the section on monophyly and relationships of the excavatus   species-group, males often have one or two setae within the anteroventral angle of the metapleuron above the recurved flange that forms the ventral margin of the metapleuron above the metacoxa ( Fig. 50 View FIGURES 49 – 55 : insert). Females have one or two setae in a similar relative position but in a differentiated region below the recurved ventral margin between the acropleuron and metacoxa ( Fig. 44 View FIGURES 39 – 48 : arrow). The setae of males and females likely are in a homologous position because in males the ventrally recurved margin of the metapleuron extends above the base of the metacoxa to its anterior margin, whereas in females the recurved ventral margin extends obliquely from above the posterodorsal angle of the metacoxa toward the acropleuron, thereby differentiating the region with the one or two setae between the acropleuron and anterodorsal angle of the metacoxa.


Swedish Museum of Natural History, Entomology Collections


Smithsonian Institution, National Museum of Natural History


Canadian National Collection of Insects, Arachnids, and Nematodes


University of California, Riverside














Eupelmus (Merostenus) excavatus

Gibson, Gary A. P. 2017

Merostenus excavatus

Fusu 2013: 5
Askew 1987: 49
Trjapitzin 1978: 235
Peck 1964: 61
Erdos 1960: 204
Ruschka 1921: 309

Eupelminus excavatus

Dalla 1898: 272

Eupelmus (Urocryptus) excavatus

Thomson 1876: 108

Urocryptus excavatus

Westwood 1839: 72

Merostenus Phedyma Walker, 1837 : 355

Graham 1969: 93
Ruschka 1921: 309
Walker 1837: 355

Eupelmus excavatus

Dalman 1820: 382