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Andricus lignicola, like many other Andricus species, has 2 generations per year. The first of which is sexual, whereas the second is agamic (all female, and needs no male to reproduce). This wasp also needs two species of Oak in which to breed. The sexual Gall is found on the buds of the Turkey Oak (Quercus cerris), whereas the agamic galls are found in the buds of various species of Quercus including the Common oak (Quercus robur), as well as Q. petraea, Q. pubescens. The sexual generation was previously named A. vanherni before it was realized to be two generations of the same species.
The sexual gall is widespread across the country, on the buds of the turkey Oak and measures about 1.5x3mm. It is difficult to spot and share some similarities with some of the other closley related gall wasps. There are several galls in a bud and each one is a single cell containing a single larva. In contrast with the other similar galls, which do not become visible until spring, they reach half size in late September to early October.
The colour of the gall changes from bright green to pink which then deepens to a blood blister purple and remains this colour throughout the winter. In early February, as the gall matures, the colour changes again to the characteristic fawn brown of the mature gall. Its shape is conical, although there are often flat side where the galls touch each other with a rounded tip. The height of the galls is generally very similar, with the tops being all level with each other. The gall is closely attached to the bud segments, which may well cover the lower half of the gall.
The larva pupates in the gall on the tree and the adults start to emerge from February, to seek out a mate, with the females then searching for a common Oak in which to lay there eggs in the buds and create a new generation of, this time, agamic females. The flight period for these wasps begins in February and lasts through to June, with another in September for the galls that had not already emerged that spring.
The wasps that emerge from the sexual gall are difficult to tell from other sexual gall wasps in that the male has a black body at 1.5-2mm in length, with dirty yellow legs and brown antennae which comprises of 14 segments. The female is about the same length with a black head and thorax and a black- brown gaster (abdomen). Tapered brown to yellow legs and dark brown antennae with 13 segments.
Parasites of this gall includes;
Mesopolobus dubius,, M. Fuscipes, M. tibialis, M. xanthocerus, and Aulogymnus skianeuros
The agamic generation gall is known as a Cola gall and is found on the buds of Common Oaks. It is spherical in shape like the marble gall but is smaller (upto 10mm across) and with a rough surface. It can be seen from July onwards and matures in October, with the wasp pupating inside the gall and emerging in November to December of the 1st year or April to July of the following year.
The adult agamic female is again very similar to other Andricus species with basically a yellow/brown or biege colouration all over and 13 antennae segments.
Inquilines of this gall include;
Ceroptres arator, Saphonecrus cannatus, Synergus albipes, S. apicalis, S. crassicornis, S. gallaepomiformis, S. reinhardi, S. umbraculus, Periclistus brandtii.
Parasite species of the cola gall include;
Eurytoma brunniventris, Sycophila biguttata, Megastigmus dorsalis, Torymus auratus (=nitens), T. geranii, Ormyrus nitidulus, Mesopolobus amaenus, M. fasciiventris, M. fuscipes, M. sericeus, M. xanthocerus, Eupelmus urozonus, Aulogymnus skianeuros.
More detailed descriptions and identification keys are available from Robin Williams at the British Plant Gall Society.
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