Small Striped Flea Beetle Phyllotreta undulata

This is one of a number of similar species of black flea beetles with bold yellow stripes down their elytra. On many the outer edge of the yellow stripes are indented near the middle, whereas the sides of this one (and a couple of other species) are straighter.

I initially experienced some difficulty separating this species from Phyllotetra vittula and my first example initially identified as undulata was, I now believe, Phyllotreta vittula. I think the following individual still stands as undulata - the humeral angle is better-defined (this is more subtle than I expected), the central black elytral stripe broadens towards the rear, the yellowy stripes are shallowly indented along the outer sides and the base of the yellowy stripes lacks the angular extension.

Small Striped Flea Beetle Phyllotreta undulata, Wendling Beck Project (Norfolk, UK), 30th April 2022

This landed on my toilet cistern in front of me while I was going for a pee. Not sure where it came from but I hadn't been outside for a while and the bathroom windows were closed! Anyway, the shape of the dark central bar through the elytra seems to be the easiest character for identifying these, gradually broadening from the base and sharply narrowing (so that the yellow curves inwards) at the apex.

Small Striped Flea Beetle Phyllotreta undulata, North Elmham (Norfolk, UK), 30th April 2022