Mesopolobus fasciiventris

This Chalcid parasitoid is a member of Pteromalidae and parasitises; Andricus corruptrix agamic, A. curvator sexual, A. kollari agamic, A. lignicola agamic, Cynips divisa agamic, C. longeventris agamic, C. quercusfolii agamic, Neuroterus albipes agamic, N. numismalis sexual and N. quercusbaccarum agamic in Oak and Diplolepis rosae on Rosa canina. This is from one account which is thought to be the first record in Europe, and was from a gall found by Toddy Cooper in Beer, Devon in 2005.

The female measures 2.2-3.7mm, averaging out at 2.6mm.
The head is bright metallic green, hairy and reticulate. The eyes are red brown with very pale red ocelli. The clypeus has a small incision on the margin. The antennae are yellow brown with a long yellow scape and a dark pedicel. There are 2 rings and 6 funicular segments, of which segments 5 and 6 are darker. The club is a paler yellow brown.
The thorax is a metallic bright green or metallic blue green, and hairy. The notaulices are incomplete and the mesepimeron is glossy on top and reticulate below. The tegulae are dark testaceous and lead to the wings which are clear. The veins and hairs are mid coloured and the stigmal and post marginal veins are long. The legs have reticulated metallic green coxae, with the rest of the legs being bright pale yellow. The tarsi have 5 segments.
The gaster (abdomen) is pointed and longer than the head and thorax. It is brilliant blue green in colour with bands of pale hairs at the segment edges. The ovipositor sheaths are not visible.

The male measures in at 1.8mm, with a range of 1.4-2.4mm.
The head is bright metallic green, hairy and reticulate. The eyes are red brown with very pale red ocelli. The antennae are bright yellow with 2 rings and 6 funicular segments.
The thorax is bright metallic green with blue tints and hairy. The notaulices are incomplete and the mesepimeron is glossy on top and reticulate below. The tegulae are pale yellow and lead to the wings which are clear with mid coloured veins and hairs and long stigmal and post marginal veins. The legs have reticulated metallic green coxae, with the rest of the legs being a glowing pale yellow with brown marks near the joints of all the tibiae. The middle tibiae have a highly visible dark, triangular projection at the end. The tarsi have 5 segments.
The gaster has a metallic green front, followed by a narrow band of yellow, which carries on round and below, with the last half of the gaster being brown. These markings are not as definate as the ones on Mesopolobus sericeus.

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

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