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Megastigmus dorsalis Fabricius 1798

A member of the family Torymidae and is a parasitoid of the following gall causers; Andricus aries agamic, A. corruptrix agamic, A. curvator sexual, A. fecundator agamic, A. grossulariae sexual and agamic, A. inflator sexual, A. kollari agamic, A. lignicola agamic, A. quercuscalicis agamic, A. quercusradicis agamic, Aphelonyx cerricola agamic, Biorhiza pallida sexual, Callirhytis erythrocephala sexual, Cynips quercusfolii agamic.

The female wasp measures 1.9-4.1mm which averages out at 3.2mm excluding the ovipositor.
The head is a rich yellow colour with a sharply defined dark metallic green patch on the vertex. The eyes are large and red/brown, sharply contrasting with the rest of the head and the ocelli are large and dark. The antennae are hairy and yellow brown with dark joints, the scape is dark above and testaceous below. There is one ring and 7 funicular segments which have a taper to the long club.
The thorax has varying amounts of well defined dark metallic green on the top and sides and yellow with traces of brown beneath. The notaulices are deep and full length. The tegulae are straw coloured which lead on to the wings which are clear with mid brown hairs. The veins are mid brown and the stigma is dark with a cloud surrounding it that may vary in size considerably. The legs are all yellow with sometimes brown on the rear coxae. 5 tarsel segments are present and darker claws.
The gaster (abdomen) is a rich brown on the top with points running down the yellow sides and yellow underneath. The ovipositor sheaths are hairy and black and is in length about 3/4 the body length.

The male measures in at 1.6-3.5mm with an average of 2.8mm
The head is yellow with a distinct dark patch on the vertex. The eyes are red/brown and large, contrasting with the other colour of the head and the ocelli are also large and chestnut red in colour. The antennae are dirty gold and slender with dark joints and a slight club. There is one ring and 7 funicular segments.
The thorax is dark green metallic, sometimes shading to brown butter yellow below but giving a much darker appearance than with the female. It is sparsly covered with long hairs and the notaulices are deep and full length. The tegulae are straw coloured leading to clear, hairy wings which have a broadly circular stigma. The cloud that encircles the stigma, like in the female, varies considerably in size. The legs are pale yellow with brown tops to the mid and rear coxae. There are 5 tarsel segments and dark claws.
The small gaster is dark chocolate in colour with pale underneath and a yellow bar at the tip.

The flight times for this wasp are all year round apart from february and december.

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

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