Friday, 15 February 2008

More on Holly

As Gill observed yesterday, the edges of the mine made by the mining fly Phytomyza ilicis on Holly leaves are currently very sharp:I spent a couple of years fretting over the problem that only one single species of insect mines Holly leaves. Holly must be a wonderful place to have a mine: hard leaves and sharp points are great protection. The answer to the dilemma is stranger than the solutions that readily come to mind. All leaves attempt to heal themselves, and Holly is no exception. Holly has a very hard exterior surface, and when it heals itself, it does so with great strength. That means that any insect close to the healing point would be liable to be squashed by the leaf surfaces. Phytomyza ilicis is the only miner that can move faster than the leaf heals, so that's why it's the only miner in Holly. At this time of year the sunlight is weak and the healing process is slow, so the edges of the mine are sharper than they are in summer.

Eagle-eyed observers will notice that this unfortunate individual hasn't made it. Even thick Holly leaves don't make you completely immune to the attentions of parasitic wasps.

And this is typical damage caused by the Vine Weevil - Otiorhynchus sulcatus .
Otiorhynchus sulcatus also feeds on Rhododendron and I expect you'll find similar damage on vine leaves, although I don't get to see too many of those in Donegal....

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