Now, at the start of July, there are quite a few of the first generation Phyllonorycter coryli (Nicelli) leaf mines in their early flat silvery stage are appearing on the upper side of the Hazel leaves. Sometimes there are multiple mines per leaf. The caterpillars seem quite small, a couple of mm long at this stage. It would probably be better to wait a couple of weeks to see if we can find some pupal cocoons in order to breed through. There may be some up-folding of the leaves already, and that somewhat darker more contracted stage of the mine surface is the one to wait for. These should fairly quickly metamorphose into the adult moths. Sadly I had no luck getting any adult moths out of these mines.
The caterpillars mine July and September-October, while the two generations of adult moths are May and August. By implication there should be a resting pupal stage from October through April. Presumably this is in the decaying leaves and then the litter on the forest floor. There should also be a brief pupal stage between July and August that is our target stage for collection. The pupae should be in cocoons in the opposite corner of the mines to the piles of frass.
There is also the significant possibility of accidentally collecting numbers of parasitoids instead of unparasitised pupae. It will be interesting to keep an eye out for Braconid and Ichneumonid wasps.
and a closer view:
and I did find just one possible example of Phyllonorycter nicellii (Stainton), the Red Hazel Midget, which mines the underside of the leaf. I think I was lucky to spot it, as I just saw the darkness of the leaf fold. I didn't think that it was necessarily typical, but it did clearly have the "nibbling" around the edge of the mine clearly visible on the upper surface of the leaf, so I doubt it was N. coryli. The species appears to have a similar life cycle timing to Phyllonorycter coryli, and I found a few more over the following weeks, but this is still very much the minority species in this particular wood.
The NBN atlas claims that "the mine [of Phyllonorycter nicelli] is usually between two side veins. The pupa is formed in a white cocoon in a corner of the mine. It is attached to both the roof and the floor of the mine. The frass is deposited in an opposite corner." This mine was on the edge of the leaf, so that the margin of the leaf rolled down and in, unlike the common depictions of the mine as arching up between two leaf veins, with the axis of the mine leading away from the midvein. Almost all the other mines I detected were of the more typical form described.
Again there are multiple Chalcid and Ichneumonid parasitoids recorded.
This is a more typically shaped mine for Phyllonorycter nicellii, photographed a few days later on the 5th. Note that the tent is in great condition, with multiple browner creases, typical of the Phyllonorycter genus and of this species, so I am fairly confident about the ID.
