Barley Flea Beetle Phyllotreta vittula

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 have experienced some difficulty separting these from Phyllotetra undulata.

I initially thought this was going to be undulata, the only member of this pair that I had previously identified. The humeral angles seemed well-enough defined, with the elytral base appearing broader than the pronotal base which, using Duff, I thought pointed to undulata. The central narrowing of the yellowish stripes wasn't evident though, and the black central stripe seemed pretty even-width, both more suggestive of vittula. But in both of those respects it wasn't so different from one of the undulata I had previously identified, so at this point I was still leaning towards undulata. But the size of the beetle (1.9mm) was within the range given for vittula and smaller than undulata, and this strengthened my doubt. A perusal of images of undulata and vittula online revealed that I was over-interpreting the differences in humeral angles given in Duff and in fact this was probably ok, or even better, for vittula. At this point I checked Mike Hackston's key and he provided an additional feature for vittula (vittata actually, but I think this is a synonym): "The yellowish bands form an angular extension on or behind the shoulder swelling." My insect showed this feature, so all things considered I think it must be vittula.

Duff provides diagrams of the male aedeagus for each Phyllotreta but not the female spermathecae. I'm not clear if that's because the spermatheca isn't useful for ID, but in case it is, I include a photo of this.

female Phyllotreta vittula showing spermatheca, Ling Plantation, North Elmham (Norfolk, UK), 10th May 2022

After going through the identification process described above I re-examined my records of undulata. Unfortunately one wasn't supported by either a specimen or a photo so I've binned that record, but the other two (specimens examined at the time but not retained) appear to involve one of each. This one (below) is the first example of either species that I found, and like the one above it appears to show the elytral pattern of vittula. Now armed with a better understanding of the differences in humeral angle I think it fits vittula better on that character too.

Phyllotreta vittula, North Elmham Cathedral Meadows (Norfolk, UK), 19th April 2021

The next two were caught together and although there were differences in the shapes of the elytral stripes, both seemed to fit vittula best. On the first one the stripes showed the angular extension at the shoulder more clearly than appears in the photo. This one was a female:

female Phyllotreta vittula showing spermatheca, Wendling Beck Environment Project (Norfolk, UK), 30th April 2023

The other one was a male - and reassuring that the aedeagus checked out against the illustrations in Duff removing any nagging doubt that I might have been getting these wrong.

male Phyllotreta vittula showing aedeagus from side and flat (with close-up of tip), Wendling Beck Environment Project (Norfolk, UK), 30th April 2023

Another male...

male Phyllotreta vittula showing aedeagus from side and flat, Wendling Beck Environment Project (Norfolk, UK), 29th April 2023