THE NEARCTIC SPECIES OF DUTA NIXON (HYMENOPTERA: SCELIONIDAE), EGG PARASITOIDS OF GROUND CRICKETS (ORTHOPTERA: GRYLLIDAE)

Abstract The Nearctic species of the genus Duta are revised. Two new species are described: D. foveolata (Canada, USA) and D. policeps (Canada, USA). Duta virginiensis (Ashmead), new combination, is shown to be widely distributed in the Western Hemisphere, extending to the New World tropics. A diagnosis of Duta and a key to the Nearctic species are given. The impact of environmental degradation on the frequency of Duta species in North America is discussed. Résumé Les espèces néarctiques du genre Duta ont fait l’objet d’une révision. Deux nouvelles espèces sont décrites : D. foveolata (Canada, É.-U.) et D. policeps (Canada, É.-U.). Duta virginiensis (Ashmead), nouvelle combinaison, s’est avéré très répandu dans l’hémisphère occidental et atteint même les tropiques du Nouveau Monde. On trouvera ici la diagnose de Duta ainsi qu’une clé d’identification des espèces néarctiques. L’impact de la dégradation de l’environnement sur la fréquence des espèces de Duta en Amérique du Nord est évalué. [Traduit par la rédaction]


INTRODUCTION
The name Duta was proposed by Nixon (1933) for Holoteleia tenuicornis Dodd, an Oriental species. Nixon also described a new subspecies of D. tenuicornis from South Africa. Szab6 (1957Szab6 ( , 1966 described one species from Europe and two species from Argentina. Mineo (1979) treated D. longimarginata Szab6 as a junior synonym of D. tenuicornis. Galloway (1976) transferred two Australian species from Leptoteleia Kieffer to Duta. Masner (1976) summarized the world distribution of Duta, gave a new generic diagnosis, and discussed the synonymy and relationships. Muesebeck (1979) reported, without names, several species of Duta from America north of Mexico. Galloway and Austin (1984) revised Duta in Australia, recognizing four species.
Until very recently (Muesebeck 1979) the genus Duta was not properly recognized in North America. The only described species, D . virginiensis (Ashmead), was previously placed in Anteris Foerster (Ashmead 1893), in Prosanteris Kieffer (Kieffer 1926;Muesebeck and Walkley 195 I), in Ceratoteleia Kieffer (Muesebeck 1958), or in Calotelea Westwood (Muesebeck and Masner 1967;Masner and Muesebeck 1968). Kozlov (1970) and Masner (1976) placed Duta in the tribe Psilanteridini of the subfamily Scelioninae. In North America the members of Duta may be distinguished from Holoteleia Kieffer and Harringtonia Masner principally by the presence of a skaphion, from Spiniteleia Masner by the unarmed scutellum, and from Opisthacantha Ashmead by the unarmed metanotum. In contrast to some Nearctic species of Holoteleia all three Nearctic species of Duta have wings fully developed, reaching to or surpassing the tip of the metasoma.
The geographic distribution of Duta is nearly worldwide with only the Chilean and New Zealand subregions without recorded species (Masner 1976). The centre of diversity is in both the New and Old World tropics, but only a fragment of this fauna has been described. A few species have penetrated into temperate zones. The three Nearctic species are widely distributed in the eastern part of the continent (cf. Figs. 1-3) with only a few individuals recorded west of the Mississippi River and with no records west of the Rocky Mountains and none from the boreal or arctic part of North America. This pattern corresponds in principle with the geographic distribution of ground crickets (Gryllidae, Nemobiinae) in North America (Daniel Otte, personal communication).
The biology and behaviour of species of Duta are little known. The wasps are presumed to attack eggs of various ground crickets (Gryllidae, Nemobiinae) with one wasp hatching from an egg. Even though no Nearctic species has been reared from eggs of ground crickets, all three species were frequently caught in pan traps together with nymphal or adult ground crickets especially during the late summer and fall. I also examined an undescribed Oriental species of Duta reared from the egg of a ground cricket. Severin (1935) described the biology of a closely related scelionid wasp, Calliscelio marlattii (Ashmead), an egg parasitoid of Gryllus assirnilis Fabricius, a serious pest of agricultural crops in South Dakota. Up to 50% of all eggs of the pest were reportedly parasitized by the wasp. Adults of Duta are encountered in both open and forest habitats, in grasslands, on the ground, among herbaceous plants, and occasionally also in detritus. Pan trapping is the most productive collecting method. The three Nearctic species have a distinct late summerearly autumnal peak of frequency.
All three species were frequent in pan traps, sweep samples, and to a lesser degree in Malaise traps over the period of 2 decades of my exploration of North America . However, a steady decline in frequencies in all three species, especially in the past 5 years, may indicate a serious environmental problem. Traps operated in 10 locations around Ottawa, Ontario, and representing at least four major ecosystems (grassland, forest, marsh, sands) yielded gradually fewer individuals of Duta. A near total crash in populations occurred in [1989][1990]. A similar decline in the frequencies, with several cases of possible extirpation, was monitored on 48 other species of local scelionid wasps with hosts which develop on or in the soil; thousands of specimens were examined. The severe reduction in populations of these species may be attributed to major physical or chemical changes in the soil such as the increased acidity due to aerial pollution. It is interesting to note that in Europe species of Duta and other ground scelionids, that occupy the same soil niche, were already very rare before and during the previous decades of my work in Central Europe (1948-1968. The advanced environmental destruction in Europe is a possible explanation of this phenomenon. Almost all of the 1089 specimens of Duta examined in this study are deposited in the Canadian National Collection (CNCI) and were collected in the past 2 decades. In a few exceptional cases the deposition of specimens other than in the CNCI is clearly stated. clava and sensillar formula 1-2-2-2-1-0 in female, thread-like in male, with antennomere 5 modified (sex segment). Mesosoma in dorsal view longer than wide; skaphion well developed; notaulus percurrent; transscutal suture with foveolae at side, deep at meson; scutellar disc convex, unarmed; dorsellum unarmed, with smooth ventral lip; propodeum unarmed, considerably reduced medially; mesosoma in lateral view with netrion well developed; mesopleural carina complete; fore wing with submarginal vein adjacent to fore margin of wing, with erect bristles along its length; marginal vein either shorter or longer than stigmal vein, always shorter than postmarginal vein; basal vein absent or nebulose in some species; hind wing with distinct and complete submarginal vein; legs slender, with tarsal formula 5-5-5.
Description. Female (Holotype). Length 1.7 mm. Colour light chestnut brown; head dark brown to black, side of pronotum and pleura yellowish-brown; TI golden brown, mandible (except darker tips), palpi, labrum, radicle, and base of Al yellow; upper half of A1 light brown, A2-A12 dark brown to black; legs including coxae bright yellow; wings clear.
Mesosoma in dorsal view longer than wide (50:40); cervical part of pronotum distinctly foveolate; skaphion smooth and glabrous; mesoscutum with dense coriaceous sculpture and dense decumbent pilosity, sculpture becoming finer to indistinct in front of transscutal suture on posterior margin of midlobe; notaulus deep and broad, percurrent; humeral and suprahumeral sulci deep, distinctly foveolate (Fig. 15); scutellum anterolaterally with 4 major foveolae and with very broad and deep transscutal suture medially, anterior half of scutellum with fine, coriaceous sculpture, posterior half smooth, posterior margin of scutellum (in front of scutellar rim) distinctly foveolate; ventral lip of dorsellum narrow, smooth; propodeum medially very narrow but still developed, propodeum at sides smooth medially, with deep foveolae along posterior margin; mesosoma in lateral view convex, slightly longer than high (50:43); side of pronotum predominantly smooth and glabrous, with distinct row of foveolae along upper margin between tegula and cervix with circular patch of fine, dense sculpture in front of spiracle and with irregular sculpture along anterior margin; netrion deeply foveolate along anterior margin, foveolae as large as one-half width of netrion; mesopleural depression smooth and glabrous; mesopleural carina complete, sharp, flanked ventrally by row of deep foveolae (Fig. 16); mesepisternum below mesopleural carina with a few scattered hairs and with delicate patch of microcoriaceous sculpture near acetabular carina; mesepimeron divided from mesepisternum by row of deep foveolae; acetabular carina crenulate ventrally; metapleuron smooth and glabrous with row of foveolae along anterior margin and with deep sulcus dorsomedially, sulcus foveolate in upper half; fore wing ( Fig. 9) relatively short and narrow, not exceeding tip of metasoma, with 8-9 long, semierect bristles on submarginal vein, marginal vein moderately elongate but shorter than stigmal vein (7: lo), stigmal vein considerably slanted, postmarginal vein long, clearly defined, distinctly longer than marginal vein (25:7); basal and median veins nonpigmented, spectral.
Duta policeps sp.nov. (Figs. 2,7,8,10,14,17) Diagnosis and Recognition ( 9 6). Upper frons, ocellar triangle, and most of vertex smooth, small patch of fine coriaceous sculpture behind posterior ocellus; vertex in lateral view with semierect hairs; marginal vein in fore wing distinctly longer than stigma1 vein; frons above interantennal process without keel. Duta policeps can be distinguished from both D. foveolata and D. virginiensis by the smooth vertex in the ocellar triangle and by having the longest marginal vein of all three Nearctic species. From D. foveolata it also differs by the lack of foveolae under the mesopleural carina and nonfoveolate humeral and suprahumeral sulci. From D. virginiensis it also differs by the absence of a keel above the interantennal process and by the distinctly semierect hairs on the vertex (lateral view). Description. Female (Holotype). Length 1.6 mm. Colour light chestnut brown; head and A3-A12 dark brown to black; scutellum, T2 posteriorly, T3-T7 brown; pronotum, skaphion, mesoscutum, TI, T2 anteriorly, S1, S2 anteriorly, and side of pronotum yellowish brown; radicle, mandibles, palpi, anterior half of Al, and legs including coxae bright yellow; wings clear.
Metasoma in dorsal view longer than wide (85:39); T1 only slightly wider than long (17:14), with strong longitudinal costae and with 4 long erect bristles at side; T2 wider than long (45:20) with strong longitudinal costae in anterior three-quarters; rest of tergite smooth with a few long scattered hairs at sides; T3 slightly wider than long (39:32), smooth and glabrous, with only a few, short hairs along side and with patch of only 3 cells of microcoriaceous sculpture posterolaterally; T4 smooth with ony a few, short hairs; T5-T7 smooth with fine, setigerous punctures and denser pilosity particularly at sides.
Mesosoma in dorsal view slightly longer than wide (45:40); cervical part of pronotum nonfoveolate; skaphion smooth and glabrous, with 2 shallow, parallel longitudinal lines medially and with few delicate transverse wrinkles between 2 lines; entire mesoscutum with dense, coriaceous sculpture and dense decumbent pilosity; notaulus deep but fine, percurrent; humeral and suprahumeral sulci deep, nonfoveolate; scutellum anteriorly with 4 major foveolae and a broad deep transscutal suture medially; anterior third of scutellum with fine, coriaceous sculpture, posterior part smooth with long, semidecumbent, scattered hairs, posterior margin of scutellum (in front of scutellar rim) distinctly foveolate; ventral lip of dorsellum broad, smooth; propodeum medially in dorsal view almost concealed under lower margin of dorsellar lip, propodeum at sides (posterior to spiracle) partly smooth, with posterolateral comers moderately projecting; mesosoma in lateral view (Fig. 18) highly convex, slightly longer than high (40:45); side of pronotum partly smooth and glabrous, with row of irregular foveolae along upper margin between tegula and cervix, with circular patch of fine dense sculpture; netrion with fine foveolae along anterior margin, foveolae as large as 113 width of netrion; mesopleural depression smooth and glabrous; mesopleural carina complete, sharp, without foveolae ventrally; row of fine foveolae connecting acetabular carina with anterior end of mesopleural carina; mesepisternum below mesopleural carina with few scattered hairs and with delicate patch of microcoriaceous sculpture near acetabular carina; acetabular carina crenulate ventrally; mesepimeron divided from mesepistemum by row of deep foveolae; metapleuron smooth and glabrous, with row of minute foveolae along anterior margin and with deep sulcus dorsomedially, sulcus foveolate only in upper extreme part; fore wing ( Fig. 11) relatively