Phyllotreta ochripes

This is one of a number of similar species of black flea beetles with bold yellow stripes down their elytra. The different species differ in the precise shape of the stripes, in this case the yellow extending up to the side margin behind the humeri and then much narrowed by a rounded indentation from the side before broadening out again towards the apex.

Both of these (taken together off Garlic Mustard) were sexed as females by the shape of the 5th antennal segment - this segment is clearly longer than the adjacent segments and, although paler on one than the other, not darker than the 6th segment; on males this segment is thickened and usually darker than segment 6. The spermathecae of this genus aren't illustrated in Duff so I'm not sure they differ much between species, but as I had these I might as well include them...

2x female Phyllotreta ochripes showing their spermathecae (first 3 photos are the same insect with the spermatheca on the left), North Elmham Cathedral Meadows (Norfolk, UK), 16th May 2021