Mesopolobus sericeus

This Chalcid parasitoid is a member of Pteromalidae and was peviously known as Mesopolobus jucunus. It is normally associated with Cynipidae galls on Oak were it has a succession of three or four generations per year and over winters as fully grown larva inside a gall. It is also a rare parasitoid of Diplolepis rosae with three records to date from Oxford in 1923, Northumberland in 1958 and County Durham in 1970. All three of these wasps from D. rosae were larger than the ones usually associated with Oak galls, but it is not thought that they are a new species.

It parasitises; Andricus callidoma, A corruptrix agamic, A. curvator sexual, A. grossulariae agamic, A. inflator agamic, A. kollari agamic, A. lignicola agamic, A. lucidus agamic, A. quercuscalicis agamic, A. quercusramuli agamic, A. solitarius agamic, Aphelonyx cerricola agamic, Biorhiza pallida sexual, Cynips disticha agamic, C. divisa agamic, C. longeventris agamic, C. quercusfolii agamic, Neuroterus anthracinus (=Andricus anthracinus) agamic, N. numismalis sexual and N. quercusbaccarum sexual in Oak and Diplolepis rosae on Rosa canina.

The female wasp measures in length 2.2-4mm averaging 3.1mm
The head is bright metalllic green and reticulated. The clypeus has a large marginal notch in the centre. The eyes are bright red with a latticework of darker patches inside and the ocelli are small and dark brown in colour. The antennae are brassy olive with darker joints and longitudinal sensillae, the long scape and pedicel are deep yellow with pale yellow hairs. The antennae have 2 rings and 6 funicular segments which are tapered to a slight but definate club.
The thorax is bright metallic green with the notaulices being three quarters length from the front. The tegulae are pale yellow and lead to the wings which are clear with pale veins and neutral hairs. The stigmal and post marginal veins are longish and the basel cell is bare. The legs have reticulated metallic green coxae, more or less brown on pale femora with the rest being smooth yellow, There are 5 tarsel segments and the claws are dark.
The gaster (abdomen) appears triangular from the side and is from metallic glossy green bronze throught to brilliant gold in colour. The ovipositor sheaths are not visible.

The male wasp averages 2.1mm with a range of 1.4-3mm in length
The head is reticulated and green/red metallic in colour. The clypeus has a large marginal notch in the centre. The eyes are red and the ocelli are small and red. The antennae are bright pale yellow with some tiny darker brown spots, There are 2 rings and 6 funicular segments which are angled and tapering and there is a distinctive hooked tip to the club.
The thorax is punctate and reticulated. It is coloured metallic green, golden green or purple and blue. It is hairless except at the side and rear. The notaulices are incomplete. The tegulae are pale yellow and lead to the wings which are clear with pale hairs and veins. The stigmal vein is long and the basel cell is bare. The legs have reticulated metallic coxae with the rest being bright pale yellow. There are 5 tarsel segments.
The gaster is brown bronze and largely hairless but with a distinctive yellow shuttle mark on the back.

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

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