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Cynips divisa has a life cycle which encompasses a sexual generation as well as an agamic (all female with no need to mate) generation which cause different galls in different locations of the common oak trees Quercus robur and Q. petreae.
The sexual generation was previously named C. verrucosa before it was realized to be two generations of the same species. The Red wart gall is the sexual generation gall and can be found in axillary or terminal buds on the twig, and leaf, at the end of the midrib, or on the leaf margin from April to June. It measures about 4x1.8mm in size and slender or barrel shaped. It is brightly coloured yellow, orange to brownish, glossy and hairless and often covered in tiny liquid filled putules. It is inconspicuous and only really shows when mature, which is in may. It contains a single cell and the wasp pupates in the gall usually on the tree, and emerges from the end of may.
The female measures approximatly 2.7mm
Its small head is dark brown and largely smooth with mid sized, dark brown eyes and brown ocelli. The antennae are long, with 14 segments, and tapering and are coloured pale, darkening to the tip.
The thorax is black with a smooth mesoscutum and full length notaulices and a hairy scutellum and a glossy mesopleuron. The wings clear with dark veins and hairs. The legs are bright yellow.
The gaster (abdomen) is not segmented and dark brown, tapering to a pale tip, slightly hairy and dull.
The male measures approximatly 2.2mm
The head is very dark brown and wide with mid sized dark brown eyes. The antennae consist of 14 segments and the third segment is slightly bent.
The thorax is a dark neutral brown, dull and smooth but with some light sculpturing and the notaulices are complete. The wings are clear with conspicuous dark yellow brown veins and hairs. The legs are deep yellow.
The gaster is dark brown, short and square from the side and segmented.
There are no one recorded inquilines or hyperparasite associated with this gall as yet.
The Red pea gall is common on the underside of the oak leaf, from mid summer right through to october. It measure around 5x6mm. It is glossy, flattened slightly and has a very short stalk attaching it to the leaf vein. It starts off green or white, then changes to a noticable flushed red, before finally turning brown as it matures in september. The gall is very thick walled and hard when mature. Each gall has a single cell and the wasp pupates inside the gall, emerging august to december in the same year or occasionally january to march of the following year.
The agamic wasp has a large variation in size and measures 2.2-4mm with an average of 3.4mm.
The head is bright orange brown to dark brown with long, pale hairs. The eyes are neutral brown, contrasting with the rest of the head and the ocelli are translucent pale chestnut. The antennae are slender and long, dark brown and hairy. There are 13 segments.
The thorax varies from bright orange to all dark brown and black beneath, with long, pale hairs. The notaulices are full length. The tegulae are chestnut and the wings are clear with pale yellow to neutral brown veins and brown hairs. The legs are dark chestnut with pale hairs and parts of the coxae are darker.
The gaster (abdomen) is pale to darker chestnut with diagonal darker streaks from top to bottom aong the segments and a tuft of pale hairs at the end of the ventral spine.
Three inquilines, Synergus albipes, S. nervosus, and S. pallicornis, and several hyperparasites of this gall include, Aprostoctus aethiops, Caenacis lauta, Eupelmus urozonus, Eurytoma brunniventris, Mesopolobus dubius, M. fasciiventris, M. sericeus, Sycophila biguttata, Torymus auratus (=nitens), T. cyaneus, T. flavipes and T. geranii.
More detailed descriptions and identification keys are available from Robin Williams at the British Plant Gall Society.
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