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It's the leaf damage done by a fly, not a fungus. You might like to move the observation to invertebrates.
This is different to most of the other 60 posts. It does not show traditional mining but interconnected galleries.
Do you have thoughts about this ian (thistle)?
THREE MARINE PROJECTS
I thought that this could be rather older damage with the leaf having died around the old mine.
OK, I have recently unearthed all of the posts to look them over. This one is different and may not show the normal pattern of feeding by the larvae. Looking as closely as we can, it seems that some of the galleries here are not interconnected - down at 4 o'clock say. Notice that the feeding areas do not cross the main leaf-vein and, in some places stop at intermediate veins, as in the 4 o'clock. In nearly all records and web pics the intermediate veins do not act as barriers to mining and, in a good many, the main vein doesn't either - there are notable exceptions of course!
We read that Phytomyza ilicis feeds solely on holly (that may not be true of course) what we don't read is that other larvae are hosted by holly.
On the face of it, this looks like feeding on both the upper and lower tissue layers - leaving the near transparent surface tissue. As I understand it all so far (from personal observation), the miner larvae may progress upside down, eating the ceilings of the tunnels.
All this may seem trivial but I am trying to grasp some of the detail of miners - I am going to hit them as hard as I can next year..
Lastly, I'd be interested in your opinion regarding whether this is a gall or not and what differentiates it in that resect from say, the Birch Miner seen in my post here http://www.ispotnature.org/node/438364. And see my note here http://www.ispotnature.org/node/331248
It looks different from Phytomyza damage. I don't know what has done it, but I see the leaf below has a small amount of similar damage but only on the area exposed - that is, not on the area shaded by the top leaf. So I'm wondering if they have just had a bash that has caused damage sufficient to kill some leaf parts, or whether a particularly caustic bird dropping might have hit them.
Thanks for coming (from the Library?) John. Wisdom as always.
I have a small VERY slow growing holly in the garden - this morning I found possible remains of several mines. in a few leaves. Summer 2015 then might bring my record of its furthest north sighting.
Lat/Lng: 51.8, -0.9
OS grid ref: SP8112