The locust gall midge, Obolodiplosis robiniae (Haldemann) (Diptera: Cecidomyiidae) was first discovered in 2006 as a new important invasive alien insect pest in China (Yang et al., 2006). It is native to the North America and attacks leaves of black locust tree, Robinia pseudoacacia, now it hasoutbroken in Hebei, Liaoning, Shandong, Beijing and Tianjin in China, only feeds on leaves of the black locust tree. In some areas, all the trees are damaged by the pest, its attacking rate is up to 100%, and infested leaves roll up. The alien species remarkably threaten the health of R. pseudoacacia which has been planted in large areas as an important species for road and courtyard greening in China. Further it can beget secondary insects to outbreak and result to tree dying. So it is very important thing to control the pest insect.

Now we found a hymenopterious parasitic wasp, Systasis obolodiplosis Yao et Yang, sp. nov., which parasitizes the larvae-pupae of O. robiniae. It is surprised that the natural enemy was found after its host was discovered about half year as a new invasive species in China, also the enemy is a group specially parasitizing the gall-making Cecidomyiids (Diptera). Did it introduce accompanied with its host? Or it is indigenous? Maybe the alien pest already existed in China long time ago, just had not been found. And so far, there is not a chalcid parasitoid of the pest was recorded in the world. These and its biology will have been done in the future. We expect it can be a good natural enemy for bio-control of the locust gall midge.

The new species belongs to the genus Systasis of the family Pteromalidae (Hymenoptera). Main characters of the genus as follows: head and mesosoma scattered with areolates; mesosoma distinctly convex; notauli complete and deep; antennal formula 11253; fore wing with a row of setae under marginal vein in the lower side, speculum large and its hind margin up to stigmal vein.

The genus Systasis Walker was erected in 1834. So far, it contains 54 species in the world. There are 24 species in Australia, 14 species in Palearctic region, 18 Oriental species and 5 species in North America, among them there are 7 species occur both Palearctic and Oriental faunal regions (Dzhanokmen, 1996; Farooqi et al., 1972; Graham, 1969; Heydon, 1995; Huang et al., 2005; Noyes, 2005; Sureshan, 2002; Xiao et al., 2001). In China, there are 9 species have been recorded (Xiao et al., 2001; Huang et al., 2005).

Some species of the genus feed on grass seeds, but most species are associated with gall-making insects, mainly Cecidomyiidae (Diptera), such as Asphondylia sesame Felt, Contarinia salbergiae Mani, Dasineura ericina (Loew), D. amaramarjarae Grover (Xiao et al., 2001). The new species parasitizes the larvae-pupae of O.robiniae (Haldemann) (Diptera: Cecidomyiidae).

Systasis obolodiplosis Yao et Yang, sp. nov. (Plate Ⅰ, 1-10) Type-specimens

Holotype:♀, Oct. 2006, Shanghe County, Shandong Province, Yan J-H col. Ex: larvae and pupae of O. robiniae (Haldemann). Paratypes: 3♂, with same data as holotype.

Diagnosis

The new species, S.obolodiplosis Yao et Yang, sp.nov., can be recognized for the following characters: 1)Body blue-green. 2)Scape with proximal 1/3 testaceous, and distad 2/3 and pedicel blue, flagellum brown with blue metallic tint. 3)Body sculptured coarsely. 4)Female body length 2.1 mm; male body length 1.3 mm. 5)Female eye height 2 times as long as marlar space; male's eye height 2.8 times as long as marlar space. 6)Female with scape just reaching up to vertex. 7)Female with basal cell open below and basal vein bare; fore wing having several hairs in distally triangle area formed by stigmal vein and postmarginal vein. 8)Female 1.9 times as long as wide.

Description

1) Female Body length 2.1 mm.

Color Body colored blue-green. Antennae with scape proximally 1/3 testaceous, and distally 2/3 blue. Pedicel is concolored with body. Flagellum colored brown with blue metallic tint. Eye is reddish brown. Ocelli colored amber. Metasoma is blue-green with purple metallic tint. Legs with coxae, trochant and femur concolored with body, but tip of femur, tibiae and tarsi except tip yellow. Tip of tarsi and claw dark brown. Wings hyaline. Tegula with proximal half dirty white, and distal half black.

Head Head stout, areolate and with piliferous punctures. In the dorsal view head 2.2 times as wide as long. POL is 4.9 times as long as OOL. Three ocelli formed an acute triangle. Eye large. Temple 1/4 of eyes width. Vertex scattered with sparse piliferous punctures, while face, especially lower face, with dense piliferous punctures. Head 1.4 times as wide as high in the front view. Eye height 0.6 times of head height, 1.8 times of eye space, 1.4 as high as wide. Marlar sulcus distinct. Malar space 0.5 times of eye height. Clypeus emarginate medially. Antennae lies on the ventral line of eyes, slightly clavate; scape just reaching up to vertex, stout, 2.6 times as long as wide; combination length of pedicel and flagellum as long as head width; pedicel longer than combinated length of anelli and the first funicular segment, 1.9 times as long as wide; two anelli transverse slice; each funicular segment longer than wide, the length ratio of them as F1: F2: F3: F4: F5 = 3: 3.5: 3.5: 3.5: 3, the width ratio as: F1: F2: F3: F4: F5 = 2.8: 2.5: 2.8: 2.8: 2.8. The last funicular longer than the first club segment; club with tip round, slightly clavate, 1.7 times as long as wide; antennae with a row or two rows sparse longitudinal sensilla.

Mesosoma Mesosoma convex and swollen, as wide as head, areolate on the surface, with sparse hairs. Pronotum short, collar with posterior margin incised medially deeply connected with anterior margin, so in dorsal view only two sides are visible. Mesoscutum 0.7 times as wide as long, mid lob protruding forward and scattered with several hairs on the surface, and lateral lobs convex. Notauli complete and deep. Scutellum slightly shorter than mesoscutum, longer than wide (12:10), with a small longitudinal split at anterior margin medially, and hind margin hang over dorsellum, dorsellum covered and invisible in dorsal view. Propodeum areolate, short, only 1/6 of scutellum in length, and its hind corner round; media carina present and ridged, with hind 1/3 divided into two subcarina and divergent; plicae carinate strongly; media area 5 times as long as wide; nucha evanescent; spiracle oval, upper edge just connected with hind margin of dorsellum; callus with several hairs. Pleura of mesosoma sculptured, subalar area and upper mesepimeron with reticulations, metapleuron areolate.

Legs Coxae sculptured, and hind coxae areolate, hind leg with the first tarsus 1.5 times as long as the spur of tibia.

Wings Fore wing with proximally more than 1/3 bare under submarginal vein, basal vein bare and below open; costal cell bare in upper side, but with a line of hairs in lower side medially; speculum big, hind edge reaching up to stigma, but lower side with a row of seven long setae admarginal vein; behind speculum hairs sparse, the triangle area with only several hairs in distal margin, a line of hairs arising from uncus of stigma and coming into outer margin of wing; submarginal vein with eight setae; marginal vein 1.8 times as long as postmarginal vein, and postmarginal vein 1.5 times as long as stigmal vein. Hind wing long and narrow, with sparse and short hairs.

Metasoma Metasoma shorter than mesosoma (11.4:12.3), acuminate, imbricate on the surface, 1.9 times as long as wide. Each tergite is straight in posterior margin. The first tergite occupied about 1/3 of metasoma. Ovipositor inserted in distal 1/3 of metasoma, projecting part in length equal to the last tergite.

2) Male

Body length 1.3 mm, blue-green. It is similar to female, except legs with trochanter and tips of fore, mid-femur dirt yellow; hind femur concolored with body. Antennae with scape 4 times as long as wide; pedicel nearly spherical, combinated length of pedicel and flagellum 1.3 times of head width; each funicular segment longer than wide, the length ratio of them as: F1:F2:F3:F4:F5 = 2.5:2.2: 1.8:2.1:2, the width as F1:F2:F3:F4:F5=1.1:1.1:1.3:1.3:1.6. Metasoma only 0.6 times of that of female, distinctly shorter than combination of head and mesosoma.

Etymology

The specimens are reared from the locust gall midge O.robiniae, so it is named from its host genus.

Recognition

The new species is similar to S. longula Bouček, : but its metasom:a 1.9 times as long as broad, shorter than mesosoma, fore wing with marginal vein 1.2 times as long as stigmal vein and basal vein without hairs; while S. longula metasoma 2.4 times as long as broad, longer than head an:d: thorax together, fore wing with marginal vein 1.7 times as long as stigmal vein and basal vein with several hairs. Actually, the new species can be easily recognized from other species of the genus because its antennae colored blue with metallic tint, distal 2/3 of scape and pedicel strongly blue, especially flagellum with blue metallic tint which has not been found in other known species of the genus.