Longitarsus jacobaeae (?)

I judged hind tarsomere 1 to be marginally shorter than the hind tibia, and as such, using Duff, these two beetles caught in my garden moth trap within a few days of each other both keyed to Aphthona lutescens (I find it hard to judge the position of the hind tibial spur which would have countered this). But 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 - it hadn't seemed 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 they both proved to be females so according to Duff they cannot be determined to species. But when I looked at Hackston's key (which is based on the German key by Lompe) I thought it said you can identify females, and using the criteria there I identified both as jacobaeae. However, looking at it again, I don't think it's saying what I thought it was saying - I'm not sure if that's because Mike has updated it or if it never said that and I had just misunderstood. What may have confused me is that Hackston only includes flavicornis in his key as a note in the text under jacobaeae: "Longitarsus flavicornis is also very similar and is distinguished by details of the male genitalia (see below)". As flavicornis doesn't key out in Hackston other than via this note under the entry for jacobaeae, the characters given in the couplet for jacobaeae presumably also apply to flavicornis. I suspect that was always thus, but I didn't realise it previously and therefore took the characters listed as relating to jacobaeae (namely that hind tarsomere 1 is less than half the length of hind tibia and that the first two hind tarsomeres broadened towards the apex) applied to jacobaeae and not to flavicornis.

Hackston (based on the diagrams at coleonet.de) illustrates the spermatheca for both jacobaeae and flavicornis, and there's an arrow pointing to the gap between the cornu and nodulus which is larger in jacobaeae, and this difference is also evident in Duff's diagrams. On both of these I judged the spermatheca to be a better match for jacobaeae.

So my original identification of these two as jacobaeae was based on a minor difference in the spermatheca supported by two further characters which I now realise were never actually intended to be provided as a means of separating jacobaeae from flavicornis. Therefore it now seems that it is not safe to identify these as jacobaeae but to wait for a male before I formally record this species. 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 or Longitarsus flavicornis showing hind leg, frons, elytral puncturing and microsculpture, humeri and spermatheca, North Elmham (Norfolk, UK), 6th July 2022

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

This one may also be jacobaeae based on the size of the gap between the cornu and nodulus, but I don't think it can be safely named as such as it's another female.

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