Longitarsus jacobaeae

Using Duff, these two beetles caught in my garden moth trap within a few days of each other both keyed to Aphthona lutescens. I thought about dissecting them to check the genitalia but then decided not to - after all, separation from the other similar Aphthona species was pretty straightforward. But I did hesitate - because Duff's size range for Aphthona lutescens only goes up to 2.5mm and these seeemed a bit bigger than that. I measured them and sure enough they were 3.25mm and 3.0mm long. So were they just large lutescens, or could they be something else entirely? I remembered that when I'd keyed them to genus I'd noted that the hind tarsus tarsomere 1 was longer than on other Aphthona species - at no more than 0.45 x the length of the hind tibia it wasn't long enough to key to Longitarsus, but it was more than the third of the length that it said it "usually" was for other genera. I turned to Hackston to see if his key supported the ID as Aphthona lutescens and there it became clear that they could not be lutescens (or any Aphthona).

Returning to Duff, and this time the Longitarsus key, they now keyed to either jaobaeaea or flavicornis but according to Duff these two species can only be separated by the male genitalia, so I would need to dissect them after all. They both proved to be females so according to Duff they cannot be determined to species. However, according to Hackston's key (which is based on the German key by Lompe) you can identify females. Indeed the first difference is the fact that hind tarsomere 1 is less than half the length of hind tibia on jacobaeaea which I'd already established was the case. He also says the first two hind tarsomeres broaden towards the apex on jacobaeaea, which they did, and he provides differences in the female spermathecae too, which also supported the ID as being jacobaeaea (a bigger gap between the cornu and nodulus).

So based on all three characters provided by Hackston for separating jacobaeae from flavicornis, these are both jacobaeae. However I don't know why Duff does not include these differences - has he considered them and determined that they are not reliable even in combination? If so I wonder why he doesn't allow for the possibility of Longitarsus having a slightly shorter hind tarsomere 1 as Hackston does (albeit not in his key to genera), but if Duff is right then perhaps these should be left undetermined. I'm happy to take advice on that but in the meantime as they fit jacobaeae according to Hackston I'm labelling them as jacobaeae. Note that I think the nodulus of the first one's spermatheca may have been slightly squashed by my tweezers - it may not have been concave on one side originally.

female Longitarsus jacobaeae showing hind leg, frons, elytral puncturing and microsculpture, humeri and spermatheca, North Elmham (Norfolk, UK), 6th July 2022

female Longitarsus jacobaeae showing hind leg, elytral puncturing and microsculpture, humeri and spermatheca, North Elmham (Norfolk, UK), 11th July 2022