Andricus foecundatrix, Oak Artichoke Gall

Common Name: Oak Artichoke Gall

The oak artichoke gall is an abnormal growth on oak trees, primarily on pedunculate (Quercus robur) and sessile (Quercus petraea) oaks, caused by the gall wasp Andricus foecundatrix. The gall resembles an artichoke or a hop cone and forms in the oak's terminal or axillary leaf buds. This gall is the result of the asexual generation of the wasp, which emerges in the spring, lays eggs in catkins, and produces the subsequent sexual generation of wasps.

The wasps emerging from the oak artichoke galls will be female; and these females will go on to lay a solitary egg in the male flowers of the oaks, which will cause the formation of the 'hairy catkin galls.' The flies that arise form these galls are of both sexes and the cycle then starts again after they have mated and eggs are laid in the oak buds. Once the oak artichoke gall has fallen to the ground the imago may leave the gall in the following spring, or may delay the emergence for 2–3 years. Galls may persist and exhibit opened scales curving outwards.

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