Monday, 17 August 2009

More Gall

Following on from the Oak galls a couple of days ago, two more are in evidence, one on the Oak Trees and one on the Thistle plants.
The Artichoke Gall is formed within the leaf axils of Oak trees by the Gall Wasp 'Andricus fecundatrix'.
As with the other Gall Wasps, they have two generations each year, one Asexual and one sexual. The first, asexual generation lays eggs on the Oak catkins, these develop into the second generation which mate lay eggs on the leaf buds of the Oak. These develop into these Artichoke Galls.
The insects emerge from these galls when they have fallen to the ground in the Autumn, ready to repeat the cycle the following Spring.
This Thistle Gall, was growing in the stem of a Creeping Thistle.
Caused by the eggs (up to 30 of them) of the fly 'Urophora cardui' a small Fruit Fly. Hatching into grubs, they burrow into the stems and cause the swelling. The larvae pupate and turn into adults still inside the gall and emerge as adults through small 'tunnels' in the late Summer.
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