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Mesopolobus xanthocerus (Thompson 1878)

Mesopolobus xanthocerus is a parasitoid of the family Pteromalidae. As such it parasitises many members of the gall forming family of Cynapidae such as; Andricus corruptrix sexual, A. fecundator sexual, A. grossulariae sexual, A. kollari sexual and agamic, A. lignicola sexual and agamic, A. quadrilineatus agamic, A. quercuscalicis sexual, Biorhiza pallida sexual and Neuroterus anthracinus sexual galls. The flight times of this wasp are january and february then from april through to august.

The female measures from 1.9-2.5mm with an average of 2.1mm head and body.
The head is a dull metallic golden green and reticulated. The eyes medium to large and are a dull red brown in colour and the ocelli are tiny and brown. The antennae are brassy yellow and distinctly tapered with a long plae yellow scape and pedicel. There 3 rings and 5 funicular segments.
The thorax is dull metallic golden green. The notaulices are incomplete and the tegulae are dull straw coloured leading to the wings which are clear with pale yellow hairs and veins and longish stigmal and post marginal veins. The legs have reticulated metallic coxae with a large brown femur tapering to paler below. There are 5 tarsel segments with darker claws.
The gaster (abdomen) is pointed and is deep green shot dark bronze green with a shiney first segment and light sculpture on the remainder. The ovipositor sheaths are not visable.

The male measures 1.5-1.8mm averaging out at 1.7mm
The reticulated head is metallic bright green. The eyes are neutral brown. The antennae have 3 rings and 5 funicular segments that are deep yellow brown with a taper to a dark club, a long, pale yellow scape and pedicel.
The thorax is metallic bright green with the notaulices incomplete. The tegulae are dull straw coloured and lead to the wings which are clear with very pale hairs and veins and a longish stigmal vein and post marginal vein. The legs have reticulated metallic coxae with a large brown femur tapering to paler below. The middle tibia are enlarged with a black process on the outside edge near the apex. There are 5 tarsel segments with darker claws.
The gaster is metallic with a yellow band across the middle of the broad top. The gaster looks broad from above but thin from the side.

More detailed descriptions and identification keys are available from Robin Williams at the British Plant Gall Society.

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