THE NEARCTIC SPECIES OF IDRIS FOERSTER. PART I: THE MELLEUS-GROUP (HYMENOPTERA: SCELIONIDAE)

Abstract The state of taxonomy of Idris, egg parasitoids of spiders, in Nearctic North America is reviewed. The concept of Idris is discussed and Ceralobaeus Ashmead is considered a junior synonym (new synonymy). The melleus-group of Idris is defined and 11 Nearctic species are keyed and described: I. castaneus sp.nov. (south and southeastern USA), I. chrysion sp.nov. (southeastern USA), I. costatus sp.nov. (eastern USA), I. lacunatus (Baja California, Mexico). I. leedsi sp.nov. (midsouthem USA), I. melleus (Ashrnead) (south and southeastern USA and southern Canada), I. onychion sp.nov. (southeastern USA), I. ornatus sp.nov. (eastern USA), I. pulvinus sp.nov. (south and southeastern USA), I. spartinae sp.nov. (southeastern USA), and I. triticola sp.nov. (midwestern USA). Extra-limital Nearctic members of the melleus-group are briefly discussed. Résumé On trouvera ici une révision taxonomique des espèces d’Idris, parasitoïdes des oeufs d’araignées dans la zone néarctique de l’Amérique du Nord. Le concept d’Idris fait l’objet d’une discussion et le genre Ceratobaeus Ashrnead en devient un synonyme récent (nouvelle synonymie). Le groupe melleus d’Idris est défini, 11 espèces néarctiques sont décrites et une clé d’identification permettra de les distinguer : I. castaneus sp.nov. (sud et sud-est des É.-U.), I. chrysion sp.nov. (sud-est des É.-U.), I. costatus sp.nov. (est des É.-U.), I. lacunatus (Basse-Californie, Mexique), I. leedsi sp.nov. (centre sud des É.-U.), I. melleus (Ashmead) (sud et sud-est des É.-U et sud du Canada), I. onychion sp.nov. (sud-est des É.-U.), I. ornatus sp.nov. (est des É.-U.), I. pulvinus sp.nov. (sud et sud-est des É.-U.), I. spartinae sp.nov. (sud-est des É.-U.) et I. triticola sp.nov. (centre-ouest des É.-U.). Les espèces de groupe melleus de l’extérieur de la zone néarctique sont examinées brièvement. [Traduit par la Rédaction]


INTRODUCTION
The genus Idris is worldwide in distribution (Masner 1976) and comprises 159 described species (Johnson 1992). The members are solitary primary parasitoids of eggs of various spiders (Eason et al. 1967;Bradoo 1972;Fitton et al. 1987). The adults may be collected by various methods but most successfully by trapping with pan traps, interception traps, or Malaise traps rather than by sweep net. Rearing from cocoons of spider eggs is the only method of obtaining host data. The habitus and size of individual species are determined by the dimensions and shape of the host egg. Interestingly, eggs of extremely small as well as large spiders are not parasitized. This tendency results in the predominantly uniform size of Idris members varying most frequently between 1 and 2 mm. It is perhaps the small size of these parasitoids that discourages many entomologists from paying more attention to their natural history. And yet the first focus on this genus in North America reveals one of the most fascinating challenges in the study of biodiversity. Indeed, once completed, the revision of Nearctic Idris might serve as a primary example of neglected or underestimated biodiversity in the temperate zone. We also hoped that this study will call attention to the much needed faunal exploration of the North American continent.
The history of taxonomic research on Idris in Nearctic North America is rather brief. The first few species were described by Ashmead (1893) under Acoloides Howard and

MORPHOLOGY AND MEASUREMENTS
Morphological terms follow Masner (1979Masner ( , 1980Masner ( , 1983; those requiring detailed or amended definitions are listed below. Several new terms are being used and they are marked with an asterisk (*). Details on measurements and instructions follow the definition and character states of each term (where applicable).

* BODY STREAMLINE
Course of imaginary lines connecting widest points of head with points of maximal width of metasoma: (a) lines divergent anteriorly (Fig. 20), (b) lines parallel or subparallel, (c) lines convergent anteriorly; seen in dorsal view.

HEAD
Cheek and lower frons-(a) Striae absent or rudimentary, (b) striae short, not reaching lower orbit, (c) striae long, reaching lower orbit or even continuing above along inner orbit; seen in frontal view. Eye height-Maximal distance between upper and lower orbit of eye; measured in frontal view. Eye pilosity-(a) Eye glabrous or with rudimentary pilosity, if hairs absent or shorter than 1 OD (see below), (b) hairy if hairs subequal to 1 OD, (c) strongly hairy if hairs longer' than 1 OD. Frontal keel-Longitudinal median keel on frons running from interantennal process toward anterior ocellus: (a) keel absent or rudimentary, (b) keel incomplete, fine or strong but not reaching anterior ocellus, (c) keel complete if reaching anterior ocellus; seen in frontal view.
Occipital carina-Carina bordering posterior margin of gena: (a) joining hyperoccipital carina, (b) separated from hyperoccipital carina; posterior view, preferably with head severed. Head height-Maximal distance between lower margin of clypeus and top of vertex; measured in frontal view. Head length-Maximal distance between frons and postgena; measured in lateral view. Head width-Maximal distance between outer margins of eyes; measured in dorsal view. Hyperoccipital carina-Transverse carina on vertex of head: (a) joining occipital carina, (b) separated from occipital carina, (c) merging into eye orbit, ( d ) carina absent; seen in posterior view, preferably with head severed. Hypostomal carina-Carina on hypostoma of back of head; seen in posterior view, only with head severed. Interantennal process-Raised process between antennal toruli; seen in frontal and lateral view, preferably with antenna and radicle removed. Interorbital space-Shortest distance on frons between inner orbits; measured in frontal view. Malar space-Distance between lower orbit of eye and mandibular condyle; measured in frontal view.
* OD-Diameter of lateral ocellus: (a) as scale to measure length of temple behind eye (view diagonally from behind, e.g. Fig. 7), (b) as scale to measure length of hairs on eye, (c) as scale to measure distance of lateral ocellus from eye margin (OOL).
* Speculum-Smooth, shining area on lower frons right above interantennal process: (a) speculum not defined if entire frons sculptured, or frons entirely smooth, (b) speculum not abrupt with irregular margin, (c) speculum abrupt with sharp margin; seen in frontal view.
ANTENNA Clava (A7) in female-Maximal length in relation to maximal width; measured in lateral view. Female A2-A6/A7-Relative lengths; measured in lateral view. Female A2lA31A4-Relative lengths; measured in lateral view. Male A3-AlO-Relative lengths; measured in lateral view.

MESOSOMA
* Axillar crenulae-Several crenulae in anterolateral comer of scutellum; seen in dorsal view. Crenulae-Series of pits arranged in chain; if pits distinctly transverse (Fig. 18,pronotum) crenulae termed lacunae. Epomium-Vertical carina along anterior margin of pronotal side; seen in lateral view, epomium best visible if head severed. Humeral sulcus-Sulcus in posterolateral comer of mesoscutum medial to tegula: (a) sulcus absent, (b) sulcus non-crenulate, (c) sulcus crenulate; seen in dorsal view. Lacunae -See crenulae. Mesosoma height-Maximal distance between top of mesoscutum and lowermost point of mesopleuron; measured in lateral view. Mesosoma length-Maximal distance between anterior margin of pronotum and posterior margin of nucha; measured in dorsal view. Mesosoma width-Maximal distance between posterolateral comers of pronotum in front of tegulae; measured in dorsal view. Notauli-Pair of longitudinal grooves on mesoscutum: (a) notaulus absent, (b) notaulus rudimentary, indicated only in front of transscutal articulation; seen in dorsal view.
Nucha-Posteromedian projection of propodeum housing articulation with condyle on T1 and S1 of metasoma; crenulae on nucha and posterior wall of propodeum visible only if metasoma severed. Pronotal crenulae-Chain of crenulae in lower comer of pronotum (above fore coxa, cf. Fig. 10 Microsculpture, body pilosity, and the general habitus of the body (including body streamline) appear particularly valuable as characters in species recognition. The above characters display the least amount of intraspecific variation and are therefore of primary importance in Idris taxonomy. For proper evaluation of both the microsculpture and the pilosity, the use of a light disperser (Mylar* tracing paper) is indispensable, especially in yellow species. Needless to say, the specimens must be clean, free of body oil, and mounted on points to permit different angles of observation. For some character states it is necessary to detach the head and metasoma and tagmount them separately on the point. Fine differences in general habitus (such as convexity of mesosoma in profile) can be accentuated by the superimposition of line drawings of two or several closely related species.
Body colour as well as the extent and configuration of colour patterns appear to be surprisingly constant character states in Idris. Similarly, infuscation of wings and their patterns are quite constant in all species examined.
Mesosoma short, moderately to highly convex dorsally, rarely flattened; pronotum in dorsal view usually very short medially, pronotal shoulders rarely prominent; side of pronotum often with arc of crenulae in netrion area, sometimes with irregular sculpture or smooth; epomium developed or not; mesoscutum semicircular; skaphion not developed; notaulus at most indicated posteriorly; humeral and suprahumeral sulci often well developed, rarely crenulate; scutellum semicircular, usually with strong posterior rim crenulate inwardly; mesopleuron slightly concave medially, often with rows of crenulae in front of mesepimeron; dorsellum unarmed; propodeum often longitudinally canaliculate or with fine irregular sculpture, rarely almost smooth; median keels of propodeum usually low, rarely projecting in sharp spikes or transformed into flattened lamellae flanking apex of horn on T1; wings relatively short and broad, not exceeding much tip of metasoma ( Q Q ), or longer ( 0 cr), rarely wings shortened or reduced to stumps ( Q Q ); submarginal vein in fore wing distinctly remote from fore margin of wing, often with long erect bristles, vein reaching almost to middle of wing length; marginal vein short, almost point-like, rarely slightly enlarged; stigmal vein moderately to distinctly long, slanted subdiagonally, moderately knobbed apically; postmarginal vein at most rudimentary, not tracheate apically, shorter than stigmal vein; basal vein at most nebulous, no other veins present; hind wing usually with submarginal vein tracheate; legs relatively short, tarsal formula 5-5-5.
Metasoma usually short, subcircular, less frequently broadly spindle-like, rarely elongate, with seven visible tergites in female, tergite 7 fully external, strongly sclerotized, usually sharply triangular, not extruded with ovipositor; metasoma with eight visible tergites in male; T1 in female often humped medially, or with short or long horn, horn circular in cross section, not compressed from sides; T1 and T2 often longitudinally costate; T3 almost always largest and widest of all tergites, rarely subequal to T2; laterotergites narrow, sharply flexed and deeply incised in corresponding sternites; laterostemites well developed (seen only in dissection).
The following brief key will distinguish members of Idris from other genera of Baeini in America north of Mexico. Diagnosis. Head in dorsal and lateral views moderately to remarkably large relative to mesosoma and metasoma, head in dorsal view broadly transverse, always wider than mesosoma and especially metasoma, thereby creating streamline of body diverging forward (Fig. 20); female head in lateral view moderately to markedly higher than mesosoma; eye relatively small, with dense fine to long hairs; eye height subequal to malar space; temple behind eye usually wide, ranging from slightly less than 1 OD (I. onychion) to 3.5 OD (I. spartinae); female head in frontal view subcircular, as high as wide [in I. ornatus and I. sparinae slightly higher than wide (Fig. 12), in I. lacunatus slightly wider than high ( Fig. 16)], male head wider than high; interorbital space distinctly larger than eye height (except in I. ornatus); vertex usually distinctly arched in females, less distinctly in males; cheek and lower frons with fan of long strong striae, striae reaching at least to lower orbit of eye, usually higher; speculum not defined, sculpture of frons laterad frontal keel usually finer (entirely smooth in I. leedsi) than on upper frons and entire area glabrous; frontal keel strongly developed, reaching to anterior ocellus (except in I. onychion and I. ornatus); head in posterior view with hyperoccipital carina smoothly continuous with occipital carina (junction slightly sinuate in I. lacunatus); hypostomal carina absent (weakly developed in I. lacunatus); radicle usually distinctly elongate, about one-third of A1 length (shorter in I. lacunatus); female clava relatively long and slender, spindle-shaped, usually shorter than A2-A6 (except in I. chrysion); male antenna with A3-A11 bead-like, All-A12 fused in one segment.
Mesosoma in dorsal view with notaulus not developed (rudimentary in I. ornatus); humeral sulcus shallow (except in I. onychion and I. leedsi), not crenulate; suprahumeral sulcus not developed; scutellum semicircular (subtriangular in I. onychion and I. pulvinus), with axillar crenulae developed, with rim present, entirely crenulate (only partly crenulate in I. onychion and I. pulvinus); propodeum canaliculate (except in I. pulvinus), with median keels only moderately developed, and posterior margin usually with moderate rim, posterolateral comers of rim usually not projecting (except in I. lacunatus); mesosoma in lateral view relatively high, with pronotum anteromedially relatively long relative to cervical opening (except in I. pulvinus); side of pronotum usually with row of crenulae in lower part, crenulae reduced in some species; mesopleuron with deep crenulae (lacunae) in upper part, often evenly granular in lower part; mesopleural carina not developed (except in I. ornatus); mesopleural depression usually granular (except in I. lacunatus, I. onychion, and I. triticola); metapleuron predominantly to entirely granular (except in I. leedsi), with crenulae along margins; fore wing relatively narrow, lengthtwidth ratio approximately 3: 1, rounded apically, surpassing tip of metasoma; submarginal vein with row of long semierect bristles distinctly surpassing fore margin of wing.
Metasoma in dorsal view relatively small and narrow compared with rest of body; T1 in female without hump, subtrapezoidal to broadly transverse with strong longitudinal costae (costae incomplete in I. pulvinus); T2 trapezoidal, with longitudinal costae anteriorly, rest of tergite predominantly granular (except in I. leedsi); T1 and T2 combined longer than or subequal in length to T3 (T3 slightly longer in I. chrysion); T3 transverse, with even granular sculpture (in I. ornatus with weak longitudinal rugulae anteromedially, in I. leedsi smooth medially); metasoma in lateral view with depression along anterior margin of T2.
Discussion. Because no species-group has been formally defined among the Nearctic Idris (and for that matter anywhere in the world) it is difficult to compare the melleus-group with its nearest relatives. Members of the melleus-group could be characterized best by the following cephalic synapomorphies. The head is remarkably large in relation to the rest of the body, especially the diminutive metasoma, therefore if viewed from above the body streamline is diverging forward (Fig. 20). The hyperoccipital carina joins the occipital carina in a gentle arc, the eye is relatively small, with its height subequal to the interorbital space and the radicle is distinctly elongate. Some of the cephalic characters mentioned above occur also in members of two small undescribed species-groups of Idris intended for Part I1 of our project. However, the shared character states of these two groups do not exist in the unique combination that is diagnostic for members of the melleus-group.
Zdris castaneus sp.nov. (Figs. 15,21) Diagnosis. Body chestnut brown; temple wide, 2.5 OD; head in frontal view as high as wide, interorbital space distinctly larger than eye height; side of pronotum with only weak crenulae in lower comer; propodeum at meson shorter than half length of TI; T2 with longitudinal sculpture exceeding basal half of tergite as in I. melleus.

Etymology. Castaneus (Latin) referring to the chestnut brown colour of the body.
Remarks. Idris castaneus is probably the most widely distributed Nearctic species of the group, but rarely collected.
Description. HOLOTYPE Q . Length 0.90 mm, body colour golden yellow, except eye and ocelli darker; wings clear.

Biology. Unknown.
Variation. The specimen from North Carolina is larger (length 1.10 mm), and slightly darker. The epomium is usually not developed but is rudimentary in one specimen.
Etymology. Chrysion (Greek) meaning gold (diminutive) and refemng to the yellow body colour; here as a noun in apposition.

Biology. Unknown.
Variation. The single female paratype is slightly lighter than the holotype.
Etymology. Costatus (Latin) in reference to the strong, short costae on T2.

Biology. Unknown.
Variation. Scutellum in one paratype (Las Barracas) with smooth part on posterior third. Etymology. Lacunatus (Latin) referring to the large transverse crenulae (lacunae) on the side of the pronotum and mesopleuron that give the structure a 'washboard' effect.

Remarks.
Although zoogeographically from the Neotropical region (Baja California), this species is more closely related to the Nearctic species of the melleus-group (principally in cephalic characters) than to 10 undescribed Neotropical species of this group examined in CNCI.
Zdris leedsi sp.nov. (Fig. 24) Diagnosis. Body light brown; temples wide, 2.5 OD; T2 with strong short costae reaching on to basal third of tergite; metapleuron without microsculpture, smooth and highly shining; posterior two-thirds of T1 and median part of T3 almost smooth, shining, with extremely delicate coriaceous microsculpture; posterior side of propodeum (below posterior margin) smooth and shining; frons laterad keel smooth; closely related to I. costatus, especially in the shape of T1.
Mesosoma in dorsal view slightly wider than long (5652); mesoscutum strongly transverse, much wider than long (56:30), with scattered decumbent yellowish hairs, fine granular sculpturing; humeral sulcus well developed; scutellum semicircular, wider than long (44:20),with same pilosity and sculpturing as mesoscutum; propodeum canaliculate; posterolateral comers not projecting, posterior margin of propdeum weakly raised, median keels weakly developed, not raised, part of propodeum below posterior margin smooth and shining, apical margin of nucha crenulate; mesosoma in lateral view longer than high (52:48). moderately convex; scutellar rim projecting slightly, overlapping dorsellum; side of pronotum with fine granular sculpture in upper part, with short crenulae and fine transverse ridges and no microsculpture in lower part; epomium sharply developed; mesopleuron generally with microsculpture in upper two-thirds, with five strong transverse ridges below tegula, middle part of mesopleural depression smooth and shining, lower part of mesopleuron with very fine granular microsculpture; mesopleural carina indicated in anterior part as sulcus; metapleuron without microsculpture, smooth and highly shining; side of propodeum sparsely h a j s posterolateral comers not projecting.
Metasoma in dorsal view longer than wide (7550); TI broadly transverse subtrapezoidal, with anterior margin slightly upcurved (33:15), with strong longitudinal costae, anterolateral comers not angular; T2 trapezoidal, wider than long (48:24), with strong longitudinal costae in anterior third, costae ending abruptly, entire remaining surface of tergite almost smooth and highly shining with inconspicuous delicate coriaceous microsculpture and with few weak longitudinal elements medially visible only under high magnification; T1 and T2 combined distinctly longer than T3 (38:27); T3 wider than long (50:27), surface generally smooth and highly shining with delicate granular microsculpture especially at sides, median part almost smooth; metasoma in lateral view distinctly convex, depression between T1 and T2 deep; S 1 and S2 with costae similar to corresponding tergites.
Male. Unknown. Biology. Host and habits unknown. Adults occur in a variety of habitats in late summer and fall (August-October).

Biology. Unknown.
Variation. The middle tooth of the mandible in some specimens can be smaller than the upper and lower teeth.
Etymology. Onychion (Greek) meaning a finger nail (diminutive), referring to the protruded apex of the scutellar rim; here as a noun in apposition.
Description. HOLOTYPE Q . Length 1.60 mm, body colour dark chestnut brown, except legs, mandible, and antenna light brown; wings slightly infuscate.
Male. Unknown. Etymology. Omatus (Latin) in reference to the rich decorative sculpture on both the mesosoma and metasoma.

Remarks.
Idris ornatus is not closely related to any of the Nearctic members of the group, but is related to one undescribed species from Mesoamerica (Mexico, Costa Rica).
Male. Unknown. We examined two males from St. Catherines Island (GA) caught along with several females of I . pulvinus that might represent the opposite sex. However, structural differences other than sexual dimorphism (e.g. shape and sculpture of the scutellum) between these males and the known females of I. pulvinus compel us not to make the formal sex association.

Biology. Unknown.
Variation. Microsculpture of the propodeum varies from partly smooth to entirely rugulose; anterior half of TI with predominantly fine granular sculpturing; metapleuron with varying sculpture, from partly smooth to distinctly granular.
Etymology. Pulvinus (Latin) meaning a pillow or cushion in reference to the shape of segment 1 of the metasoma; here as a noun in apposition.
Description. HOLOTYPE Q . Length 1.10 mm, body colour chestnut brown except antenna and coxae light brown, rest of legs lighter yellow; fore wing with dark spot below marginal-stigma1 vein, and generally infuscate in posterior half.

Material
Etymology. The specific name is derived from Spartina, a plant dominating the type locality.
Material Examined. 2 Q I .
Biology. Unknown; two females were found in wheat fields.
Etymology. Triticola (Latin) in reference to the presumed association of this species with wheat (Triticum\.
Remarks. Although the main difference between 1. triticola and I. spartinae is in the body colour, we prefer to treat these as distinct species largely because of disjunct distribution and profound differences in their choice of habitats.

USA)
ornatus sp.nov. (Fig. 14) Q -Sides of pronotum with only weak crenulae in lower comer; propodeum at meson shorter than half length of T1 (Fig. 15); temple wide, 2.5 OD; head in frontal view as high as wide; body length 1.1 mm; interorbital space distinctly larger than eye height (south and southeastern USA)

ACKNOWLEDGMENTS
We sincerely thank the curators and staff from various North American museums (listed in Materials and Methods) who have kindly loaned us specimens of Idris. Henry Robison (University of Arkansas, Magnolia) and Gene Leeds (US Forestry Service, Arkansas) operated yellow pan traps in the Ozark Mountains and donated valuable material. Staff of the Centre for Land and Biological Resources Research (Agriculture and Agri-Food Canada, Ottawa, ON) provided assistance in the preparation of this manuscript: S. Rigby prepared the ink drawings, Michael Sharkey and Jean-Frangois Landry reviewed the manuscript and made valuable comments. We also gratefully acknowledge the two anonymous external reviewers for their comments and criticism.