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Added: 21st May 2011 Description:
Red blisters on the leaves of evergreen oaks (including cork oak [Quercus suber]).
Confidence: It's likely to be this, but I can't be certain. Notes: See Robbins, J. 2007. Plagiotrochus australis (Mayr) and P. coriaceus (Mayr) (Hymenoptera: Cynipidae) new to Britain. Cecidology 22 (1):19-20.
Confidence: I'm as sure as I can be. Notes: Thank you for sending some galls Patrick - having now examined the galls in detail, from which I was able to extract some fragmentary remains of the wasps, I am definite that this is P. quercusilicis. It differs from P. australis in having multilocular galls, i.e. more than one wasp emerging from each gall, also in minute morphological features of the adult wasps. I see these have been reported on the BPGS discussion list from other localities in Cornwall and confirmed by Graham Stone using DNA. For details and similar picture see: http://uk.groups.yahoo.com/group/british_galls/message/1221. They are probably a recent introduction from the Mediterranean, imported with Quercus ilex trees.
No interactions present.