Oblique-barred Grass-miner Elachista adscitella

Formerly given the vernacular name Oblique-barred Dwarf.

The only previous records of this species in Norfolk are two records of leaf-mines at Foxley Wood in July 2021.

This was netted in flight in a small grassy area at the edge of wet woodland. The identity was suspected from its external appearance. Among the Elachista species that show a single complete straight pale fascia, adscitella normally differs from the others in having pale ochre frons and palps and pale ochre terminal cilia at the apex of the wing. For certain identification the genitalia should be checked and I think this does confirm the identification through a combination of postively matching characteristics to adscitella and elimation of the similar species. Postively first:

• The shape of the valvae are correct, although these are similar in some other species.
• The shape of the aedeagus matches, including the notch on one side at the tip although this is hard to see.
• The shape of the vinculum matches.
• The uncus lobes are about right - MoGBI shows a slightly sharper point at the tip of the incision but photos of adscitella genitalia at the Moth Dissection website match perfectly.
• The juxta processes are basically right, though on mine there appears to be slight projections laterally at the tips which aren't shown in MoGBI. However these projections are apparent on several of the images at the Moth Dissection website.

I think all the other similar species can be elimainated as follows (I have not necessarily listed all of the differences, but the ones I felt were most useful in this case):

• Yellow-barred Grass-miner Elachista gangabella (which I have recorded from the same site, about 150m away) has much shorter, broader juxta processes that are strongly angled outwards. The distal section of the valvae are also only slightly narrower than the basal section. The aedeagus is more shallowly bent.
• Woodland Grass-miner Elachista obliquella has very distinctive juxta processes, sharply angled on the outside towards the base. It also seems to have a deeper indent along the top edge of the valvae.
• Yellow-edged Grass-miner Elachista bisulchella has the tips of the juxta processes produced to a point on the outside; my specimen seemed to show similar projections more than expected on adscitella, but not nearly as obvious as on bisculchella. Also the indent om the top edge of the valvae is deeper and longer, usually with an irregular edge, on bisulchella.
• Millet Grass-miner Elachista cingilella has shorter juxta process with knobbed ends, deeper indents on the valvae and smaller distal portions to the valvae; the aedeagus is also less strongly bent (and is illustrated in MoGBI as having a cornutus though this is not apparent in the image at the Moth Dissection website).
• For completeness as it's listed as a similar species, though I'm not sure why as it has two pale fascias on the wings, Oat-grass Miner Elachista bedella has totally different juxta processes among other things.

There is one other species with quite similar genitalia, Buff Grass-miner Elachista subalbidella, but this species is completely different externally. I was slightly concerned about the shape of the tongue-like processes that extend outwards in front of the sacculus (not sure what they're called - possibly dorsal lobes of the sacculus, or I'm not sure if these are what's referred to as the valvula or if that's something else). These aren't shown at all in MoGBI but in all the photos of adscitella at the Moth Dissection website and the one at Lepiforum, these processes become broader towards the tip before abruptly narrowing and finishing with a long narrow projection. On mine they are quite different, broadening gradually almost to the tip which is broadly rounded. I had a look to see if any European species are similar and most of those I could find were easily eliminated, although there are a lot of species for which I can find neither photos of the moths nor the gentilia. Elachista metella has very similar genitalia, although like the similar British species it doesn't normally have pale frons and palps, judging from the photos on Lepiforum. The first genitalia photo for metella at the Moth Dissection website shows the dorsal lobes of the sacculus (if that's the right term) extremely similar to mine, and other characters are also more-or-less similar. However the aedeagus seems to be slightly more bulged before the bend than mine and the internal edge of the vinculum doesn't seem to be as rounded, so along with the dark frons I think we can rule that out. What became clear while I was investigating this was that on metella at least the shape of those lobes is variable - one was like my moth but another had an apical projection much like the photos of adscitella, while the third was somewhat intermediate. This suggests that the shape of these lobes is not a consistent character, and if that's true for metella then it's probably also the case for other species, and that being the case my concern with calling this one adscitella is eliminated.

The various parts of the genitalia came apart during processing but none of the individual components seemed to get significantly damaged in the process.

male Oblique-barred Grass-miner Elachista adscitella showing left and right valvae, uncus lobnes, vinculum, juxtal processes (2 views) and aedeagus (3 views including close-up of tip), Wendling Beck Environment Project (Norfolk, UK), 14th May 2025