Knopper galls on a common Oak tree

Knopper galls on a common Oak tree

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Caption: Two knopper galls of acorns of pedunculate oak ( Quercus robur - the common oak ), Norfolk UK. The galls are produced during the asexual stage of the complex lifecycle of the gall wasp Andricus quercuscalicis, a native of Turkey that arrived in Britain in the 1950s. Each contains a larva that will spend the winter inside the fallen acorn, emerging as an asexual female in early spring. These females then fly to a Turkey oak tree, Quercus cerris, and lay eggs into developing male flowers. Male and female wasps emerge from the galled catkins that result. Males emerge first and wait on the surface of female-containing galls for the females to appear. After mating, the fertilised females then lay eggs on the developing acorns of pedunculate oak, to produce knopper galls, as here.

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Keywords: andricus quercuscalicis, common oak, gall, gall wasp, immigrant insect, knopper gall, oak, quercus cerris, quercus robur, turkey oak

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