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Andricus corruptrix is spreading rapidly and is one of the many species has 2 generations per year, one sexual and one agamic (female only, and capable of laying eggs without mating), and one of the several species that relies on both common oak (Quercus robur) and turkey oak (Q. cerris) for its life cycle.
The sexual generation was previously named A. larshemi before it was realized to be two generations of the same species. The sexual generation bud gall is located on the terminal or lateral buds of turkey oaks (Quercus cerris) and are visible from late january to early february. They are usually found seperatly although occasionally there may be two galls to a bud. The size of the gall can vary from 2.4x1.4mm - 2.6x1.6mm. The galls appearance is of a wide based, shouldered cone with a point. This point differentiates it from A. lignicola which has a rounded tip. The gall has a rough, fibrous surface and there are usually remnabts of the bud scale at the base. The colour of the gall starts as off-white, but during february or march changes to pale green, then becoming tinged with rose pink. This pink flush then spreads across the whole gall and deepens until becoming a warm burnt sienna or orangy brown of the mature gall in late march. The apical ring darkens, becoming inky black, then tones down to leave a darkened ring around the tip, often with a tiny dark mark at the very tip. Occasionally the apical ring may be white, or paler than the surrounding gall. The adult wasps pupate in the gall and start to emerge in mid april.
The female A. corruptrix wasp measures in at 1.7-2mm in length and has a black head with short sparse hairs, the vertex being heavily reticulated. The eyes are black and mid sized with mid brown ocelli. The 13 segmented antennae vary in colour of the flagellum from dark brown to light brown in different insects, with pale hairs present. The pedicel is translucent brown and the scape is black.
The thorax is black with translucent dark brown tegulae. The wings are clear with dark brown veins and short brown hairs. The radial cell is open. The legs have dark brown and hairy coxae and femura, tapering to dirty yellow, although this is variable between insects.
The deeply segmented, almost square shaped gaster (abdomen) is a shiny black-brown with pale edges and a band of pale hairs at the back. There is a long ovipositor sheath but no obvious ploughshare beneath.
The male wasp measures 1.4-2.1mm and has a heavy reticulated black head with short sparse hairs. The eyes are large and black with bright chestnut ocelli. The antennae have 14 tear shaped segments with a very dark brown scape, mid brown pedicel and dark brown flagullum.
The thorax is black with much reticulation and the tegulae are brown. The wings are clear with coarse, short dark hairs and neutral brown veins. The radial cell is open. The legs dark brown coxae and femora with pale joints, the rest being dirty yellow.
The slender and pointed gaster is black and glossy with a single segment and few large hairs at the front.
The bud galls are invaded by 4 Pteromolidae hyperparasites, which are; Mesopolobus dubious, M. fuscipes, M. tibialis, and M. xanthocerus.
The agamic generation lobed gall is found in the buds of common oaks (Quercus robur) from may to july onwards. There are three to five lobed galls found in the buds that have a characteristic shape even when young and upto 8mm across. The gall matures in july and the adult wasps emerge either in october of that year or july to august of the following year.
The agamic generation wasp measures 2.8-4.2mm and has a small orange brown head, which is granulate and has pale hairs. The eyes are black and mid-sized with small mid-brown ocelli. The antennae have 13 segments and are slender and slightly tapered, orange brown and hairy.
The hunched thorax is orange brown with a black propodeum. It is hairy on the side but less so on the top. The legs are orange brown and hairy and the wings are clear with dark brown veins and pale hairs.
The gaster (abdomen) is glossy, fat and orange brown except for a small dark brown blended in spot at the front of the top. It is translucent with faint puntuations on the rear and beneath. It is segmented with bands of pale hairs at the back of each segment. A thin ventral spine with sparse hairs.
The lobed gall is invaded by inquilines and hyperparasites. The inquilines include; Ceroptres arator, Synergus apicalis, S. gallaepomiformis, S. reinhardi, and S. umbraculus.
The hyperparasites include; Cecidostiba fungosa, Eupelmus urozonus, Eurytoma brunniventris, Megastigmus dorsalis, Mesopolobus amaenus, M. dubious, M. fasciiventris, M. fuscipes, M. sericeus, M. tibialis, Ormyrus pomaceus, Sycophila biguttata, S. variegata, Torymus auratus(=nitens), and T. flavipes.
More detailed descriptions and identification keys are available from Robin Williams at the British Plant Gall Society.
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