Looking for Leafminers on Hazel, Coryllus avellana, in Kent

 

What species might we expect to find?

Bucculatrix demarella doesn't seem very common in Kent, but is said to be widespread if local. Should be able to see the sharp turn in the mine.

Coleophorids

Of the Coleophorids found on Hazel, Coleophora serratella is likely to be the commonest in the UK. 

Small patch mines

Ectodoemia minimella is generally found on Hazel only in the West Country and Ireland, so is unlikely to be found in Kent. It is actually more likely on Betula. Small blotch towards centre of leaf.

Gypsonoma dealbana is quite southern in distribution and said to be common, so it should be quite likely to be found, even by me. It is a small blotch with distributed frass heavily placed through it. May look window-paned.

Small tent mines

Parornix devoniella is described as a small triangular or squarish mine seen first from the underside, brownish initially and then noticeably clear (really??), the larvae then moving to an upwardly (normally, not invariably) rolled up leaf edge to pupate in about October onwards as the leaf falls to the ground? These mines may have dark granules of frass in a long cigar - and then perhaps all over - if I genuinely found one. Larvae should be found in July, then those resulting pupae produce August adults which quickly lay eggs and produce more larval mines for September, then the insects over-winter as pupae in the leaf folds in litter on the ground, eventually producing more adults in May/June.

Phyllonorycter nicellii is on the lower side, and chews more effectively on the margins of the mine allowing the 15 - 20 mm long mine to be seen in outline from the top (but this is also seen in Parornix devoniella). Usually bounded by the veins, but this Phyllonorycter is perhaps more oval than Parornix?. The mines should be found in July, leading to adults in August and a second generation of mines in September followed by pupation until the following spring, The mines should have several creases, and be quite strongly contracted, which may help to distinguish this from Parornix devoniella. The Phyllonorycter mine is said to be 15 - 20 mm long, but nobody seems to measure Parornix devoniella mines, so I just assume them to be shorter. White pupae can sometimes be found in the mine, some frass at the other end.  

Phyllonorycter coryli is on the upper side, often across the veins, very obvious silvery oval patches in the second generation, Often eventually upfolds the margin of the leaf, when it can be confused for the Parornix edge-of-the-leaf folds. This Phyllonorycter leaves its frass in a gathered-together ball and has no windows, any leaf folding being created by the contraction of the tent mine, whereas Parornix leaves its frass in a (spread-out?) cigar, much more dispersed, has windows in the rolled leaf surface and the roll is bound together with silk threads. Also the larva of Parornix devoniella, unlike Phyllonorycter coryli or nicellii, bears four black spots on its pronotum.

Larger mines 

Eriocrania (aka Paracrania) chrysolepidella is a larger whitish blotch mine on the margin of the leaf, with crossing threads of frass, or aggregations of dots, Possibly several larvae share a blotch, mining earlier in the year, April-May.

Cut-outs

Incurveraria pectinea shows as usually numbers of round holes in the leaf, as the larvae tunnel forming blotch mines and then cut out their circular pupation cases. Widespread but tends to be commoner in the north of the UK.

Orchestes avellanae (aka signifer) short tunnel from/along the margin leading to a circular case cut-out. 

Tunnels

Stigmella floslactella. The mines of S. floslactella are generally wider, less angular, less constrained by the veins and contain more scattered frass than those of S. microtheriella. There is quite a wide end section, leaving room on either side of the larvae. Widespread, commoner in Dene Park than Coed Fron Wyllt. Mines found in June-July and August-September.

Stigmella microtheriella. An additional difference then is that even in the very first part of the corridor the frass of microtheriella lies in a narrow line, while the frass of floslactella seems to fill the entire corridor there.

Finally the egg of Stigmella microtheriella may be close to a vein, but floslactella is almost invariably to be found in a vein axil.

Coed Fron Wyllt

Had a couple of really lovely walks along the track in Coed Fron Wyllt, very quiet and no other dog walkers met.

When I checked out the Hazel, Corylus avellana, leaves on the apparently coppiced shrubs growing along the track, Phyllonorycter nicellii could be found (assuming they weren't Parornix devoniella), mostly with live larvae inside, but Phyllonorycter coryli was not as common,  reversing the ratio assumed of finds along the main circular track in December Park. Also there were very few Stigmella mines to be seen. 

Second generation Phyllonorycter coryli and Phyllonorycter nicellii on Hazel.

 

Now we are into September we should be seeing the second generation mines of these two Phyllonorycters. 

I do not intend to try to rear any of these larvae or pupae through to adults as they will be going into diapause and it will be many months before they are supposed to emerge as adults next summer.  

There are plenty of fresh-looking mines of Phyllonorycter coryli, so I am assuming these will all be second generation, and there seem to be even more than I found of the first generation. 

This is a closer view of this leaf. Interesting to speculate what is eating the larger holes in these hazel leaves. It looks like earlier caterpillar damage!

A closer view of two P. coryli mines on a different leaf, the further or upper one being already contracted, has folded the leaf over quite sharply.  

However in contrast I found no obviously fresh mines of Phyllonorycter nicelli, so no direct evidence of a second generation in this species. However I did fine one apparently mature mine still tenanted with a pupa, so this could have been second generation. 

To compensate there is a new arrival on the scene, the mines of a Stigmella species are now very commonly found on the leaves. I am going to assume that this is most likely to be Stigmella floslactella, as the other is said to be a narrow mine.

This is a closer view of the same mine.

The following day I found these feeding marks on a separate couple of leaves reasonably close together  on a hazel bush along the knights wood path. Maybe this is the one of the tracks of two Coleophora larvae, perhaps the result of just one adult female's egg-laying efforts?

This photograph was taken of the upper surface, but the presence of the feeding holes on the underside in each of the mined areas was confirmed later using a hand lens. 

This is a closer view:

This is a useful link about leafminers, from Eakring birds.   

http://www.eakringbirds.com/mothimagescasebearers.htm