Pellitory Beauty Cosmopterix pulchrimella

First recorded in the UK in 2001, quickly colonising. It reached Norfolk in 2020 but I'm yet to find it here, my first 3 being in Cornwall. Formerly given the vernacular name Pellitory Cosmet.

I was pretty sure this would prove to be pulchrimella based on the four dashes near the base of the forewings, but retained the specimen just in case this turned out not to be a diagnostic character, although a quick check confirmed none of the other species I was aware of shared this character. I'm glad I did retain it as it turns out that Reed Beauty Cosmopterix scribaiella does indeed share this character (and using MOGBI, published before pulchrimella occurred in the GB&I, it keys to scribaiella). Photos of the two species online appear to show a consistent difference in the form of the apical streak - long and more-or-less evenly narrow in scribaiella and broader but clearly broken (or nearly so) in pulchrimella, the latter matching my specimen. I checked the genitalia, and although I didn't do a very good job of preparing it (so no photos), the signa in the corpus bursae were clearly at different heights within the bursae - this matches the image for pulchrimella in the Moth Dissection website but appears to be wrong for scribaiella where the signa are level with one another.

female Pellitory Beauty Cosmopterix pulchrimella, Porthgwarra (Cornwall, UK), 16th October 2022

I caught two more a couple of nights later, and these proved to be one of each sex. You can see in the photos below the right hand signa in the corpus bursae is much higher than the left hand one, close to top. Judging from the photo on Lepiforum, both signa are just below the middle of the corpus bursae on scribaiella. I'm not sure if there are other differences - possibly in the sclerotised section at the top of the ductus bursae (close to the ostium, or possibly incorporating the ostium?) but without much material to compare I'm not clear if the differences are more to do with how they're positioned. Note in mine this appears to be upside down compared to the image of pulchrimella in the Moth Dissection website - it did seem like it might be flap-like so theoretically flippable - not sure if it is and this happened though.

female Pellitory Beauty Cosmopterix pulchrimella showing genitalia, Porthgwarra (Cornwall, UK), 18th October 2022

As with the female, I'm drawing conclusions about how to separate males on genitalia from a very small number of images, so some caution is needed. However it seems that the upper edge of the valvae is more strongly curved on scribaiella and the smaller flaps (tegumen lobes?) are longer and more even-width on scribaiella. The genitalia broke upon transferring to the microscope slide, so the right valva is detached in the photos below.

male Pellitory Beauty Cosmopterix pulchrimella showing genitalia, Porthgwarra (Cornwall, UK), 18th October 2022