Green Islands at Dene Park

Wow, today has been a bit of a revelation! Firstly a more careful check of some of the leaves on the Beech hedge in the front garden have revealed two old mines of a Stigmella, which must be Stigmella hemargyrella.

I had no idea that either of the Stigmella species was in the locality, nor that this species was present here, in our own front garden. The only time I've identified this leaf-miner before has been at Oldbury Hill on the Lower Greensand Ridge some distance to the North, where I photographed it on the 13th of September. What a turn-up for the books! Perhaps I've missed it at other sites as well, I just can't be sure!

In both pictures below the mine appears to start from near the margin of the leaf, and travels towards the mibrib where it ends, which is the main diagnostic characteristic of Stigmella hemargyrella as opposed to Stigmella tityrella. This is perhaps clearest in the second picture. In both cases you can also see the white spotting of the feeding marks of the Beech Leafhopper on the upper leaf surface.

The major leaf miner found in the hedge, much commoner than the two Stigmella I found today, is the ubiquitous Phyllonorycter maestingella, at least as identified according to the characteristics of the mine. This insect is specific to Beech. Ideally the adults would be raised in order to definitively separate it from Phyllonorycter messianella, which is found on a range of trees, also including Beech. However the ID to species can still be made fairly confidently I think, because of the long tubular mine which is well made within the boundaries of the main ribs of the leaf. P. messianella should be a more oval shaped mine.

Here in the picture below on the underside of a leaf you can see two old Phyllonorycter maestingella mines, both fairly decrepit. The one on the left is as found, but I had opened the one on the right to look for its contents.

Looking closer at the opened mine, I found some aphids sheltering in the old mine. Insects that use the structures of others are referred to as inquilines. I have no information on which species these may be or whether they have been noted by other observers.

Once I'd got over the enjoyable shock of locating Stigmella hemargyrella so close to home, I got Monty into the car and I struggled to get my bandaged foot into my walking boots. We headed off to Dene Park, not really hoping to do anything more than confirm previous sightings of the leaf mines and galls seen there previously, as I thought I was getting to know the Beech trees there quite well by now. The paths were clearly autumnal now, and the overall appearance of the woods has changed significantly since I was last here a week ago.

As quite a few of the Beech leaves have now turned colour, some of the branches are still mainly green, but others are already mainly golden or russet.

Amongst such concentrations of leaves that have already turned, a very few of them have either remained green entirely or remained green in obvious sections, sometimes clearly delineated by their veins. I have heard that this is a sign of hormonal interference from leafminers - and wow - that's exactly what is happening! In the picture below we can see an old Phyllonorycter maestingella mine on the top side of the midrib, which is having some, but little, effect, and two Stigmella tityrella mines on the lower side, which are very clearly causing the lamina all around them to remain bright green, and are likely to be at least recently, if not currently active. The caterpillar on the right (at least) seems to be still within the mine, visible at the end of the tunnel. These Stigmella mines must be Stigmella tityrella because the mines start next to the midrib, and generally travels outward the margin of the leaf, weaving sharply from side to side and each staying with their own segment created by two adjacent major veins.

This was fantastic! The very first time I had identified this insect was in North Wales last weekend, and I've not seen it in Kent at all before, despite the fact that it must have been there, and I'd been looking for it. And yet, I found these two almost as soon as I looked at the Beech trees, by noticing the green island - and there were these two mines!! Its going to be very easy to find some more, if they are actually present here, and they form such clear green islands!

And here is another, again Stigmella tityrella and again very obvious from the green island effect, and again found very quickly. Clearly Stigmella tityrella has been here in Dene Park all along during my autumn visits, just as Stigmella hemargyrella has been present in the garden hedge since at least earlier in the autumn!

Now that I had my eye in, and knew the patterns to look for I found half a dozen other S. tityrella mines, including this one on a leaf that was still completely green. The occupant may have only recently left, leaving the "flap-door" open!

The effect is however not confined just to Stigmella, as seen in this Phyllonorycter maestingella mine found further down the side track. Could this be an example of convergent evolution?

And here we go again, the midge Hartigiola annulipes, a very common gall former on Beech, also seems to have a very effective mechanism of keeping the majority of, if not the whole of the leaf, green. Here is a fairly clear example of the effect, of which I saw many examples.

Here is the gall again, a rather better pair of specimens perhaps, again on a green, quite fresh-looking, leaf

and here that same photo is again, this time in close-up. Note that there was a third gall, but it has been knocked off, just leaving its base.

Some of the leaves have been subject to a fungus leaf spot, which seems to appear on particular clusters of leaves, perhaps due to inoculum potential!

I've seen this damage below illustrated somewhere before, but I cannot remember for the life of me which insect causes this bizarre, if not unique, damage. Its the first time I've ever seen it in real life, but I know I've seen this picture in a book somewhere!

I spent most of our visit today in amongst the various compartments of Beech - they do look great with their russet carpet of leaves and clean woodland floors where the dense foliage of beech has inhibited the development of any significant undergrowth.