Enochrus quadripunctatus

I iniitally misidentified the first two shown below, though flagged the records as tentative and needing review as one key character was wrong on both. My problem was with eliminating ochropterus. One had a dark final segment of the maxillary palps and on the other the apical half of this segment was dark - on ochropterus this segment is supposed to be pale. However, I could not make out the rows of coarser setiferous punctures that are supposed to be present on the alternatives (including quadripunctatus) and I couldn't make out the ellipse of punctures on the sides of the pronotum which is supposed to be less clear on ochrotperus, and on that basis I plumped for ochropterus, albeit without much degree of certainty. The tarsal claws seemed to match ochropterus but the references that showed this failed to say what they were like on quadripunctatus, so this was of limited help.

The following characters ruled out all the Enochrus species apart from ochropterus, halophilus, quadripunctatus and fuscipennis:

• Last segment of maxillary palps shorter than penultimate segment - rules out melanocephalus (elytral striae also wrong for this)
• Absolutely no notch or incision in the tip of the last abdominal segment - rules out several (those species also all too small)
• Second segment of maxillary palps clearly pale yellow with no darkening on either side - rules out testaceus (which also too big)
• Head entirely black except for very small paler patches at sides in front of eyes - rules out the paler-headed bicolor.

Of the two, one was a male and the other was a female. I've since caught another male and am now satisfied that the genitalia rules out ochropterus, though I had initially been unclear about that. The differences in male genitalia are rather slight, and I'm still unclear what, if any, the difference is between quadripunctatus and fuscipennis genitalia. Duff doesn't show the genitalia for any of these species but Hackston includes a diagram for ochropterus and quadripunctatus, the main difference being in the length of the median lobe. The tip of the median lobe is, assuming I now understand it correctly, quite membranous and hard to see, but just beneath the tip is a dark crescentic bar. At the Käfer Europas website the photos of ochropterus genitalia show the parameres (?) more divergent, but this not shown in the accompanying diagram. Anyway, after examining another male I now think that the length of the median lobe on both of my males indicates that they are either quadripunctatus or fuscipennis and not ochropterus.

The Käfer Europas website credits Litovkin et al. with differences in the shape of the mesosternal tooth between quadripunctatus, fuscipennis and halophilus. Although this doesn't help with ochropterus (it might, but we aren't told what the shape of the tooth is for ochropterus) it does help give me confidence that this one is quadripunctatus and not fuscipennis.

male Enochrus quadripunctatus showing head, maxillary palp, pronotum puncturing, apical sternite, elytal puncturing (3 views), corner of elytra, mesosternal tooth (2 views), genital capsule (2 views) and fore tarsus with claw, Wendling Beck Environment Project (Norfolk, UK), 23rd August 2023

Based on my reidentification of the male above I think it's safe to say this one isn't ochropterus either. I hadn't picked up on the mesosternal tooth character at this point so it's a bit harder to decide retrospectively between quadripunctatus and fuscipennis. On balance I think it's probably safe to call this one another quadripunctatus. It was taken from exactly the same location as the male above.

female Enochrus quadripunctatus showing scutellum, maxillary palp, tip of abdomen (ventral), elytra and head/pronotum, Wendling Beck Environment Project (Norfolk, UK), 12th June 2023

This next one was the one that helped me resolve the two above. I still cannot make out the ellipse of punctures on the pronotum no matter how hard I look, and I'm far from convinced that I can see what is meant by the rows of coarser setiferous punctures on the elytra (it might help if I knew exactly where they were meant to be). But the maxillary palps and the aedeagus eliminate ochropterus and the mesosternal tooth points to quadripunctatus. This was at a different site to the two above, though all were within the same project area.

male Enochrus quadripunctatus showing head, maxillary palps (3 views), pronotum, elytra (2 views), apical sternite, mesosternal tooth (2 views), hind tarsus and genital capsule (2 views), Wendling Beck Environment Project (Norfolk, UK), 8th September 2023

I keyed this one before the any of the ones above and for some reason didn't have the same difficulty eliminating ochropterus. I suspect that's because I paid more importance on the colour of the palps relative to the elytral and pronotal punctures, but perhaps I did manage to see the relevant details on this occasion. Anyway, I keyed it to quadripunctatus or fuscipennis but had more difficulty separating between those two species and was not aware of the differences in the prosternal keel at this point. On the photo of the live insect the dark on the pronotum seems much more extensive than on either species, but looking at the specimen under the microscope it's not so extensive. I think what's happening is there is dark beneath the pronotum which shows through to a degree in the photo making it hard to see where the dark pigment of the top of the pronotum starts and finishes. In theory quadripunctatus should show four 'satellite' spots surrounding the dark centre - I can see two at the basal sides clearly but not really the front pair. On fuscipennis the 'satellite' spots are, to a degree, obscured by the central spot - and on images of fuscipennis that I've seen where two of the spots are still evident, these are the front pair (as in the diagram in Duff). So on this character I'm not entirely clear, but am leaning towards quadripunctatus (which happens to be the commoner species).

Using Hackston's key it also came down to a choice between these two species. Hackston gives a number of supporting characters for quadripunctatus but doesn't state that these are absent in fuscipennis. There's at least one quadripunctatus on the Bold Systems database that doesn't show four distinct 'satellite' spots (assuming it's been correctly labelled), so I figured this was within range for quadripunctatus but at the time I was reluctant to name it positively as such. Looking back at it now I think the limited extent of the dark at the centre of the pronotum is probably enough to rule out fuscipennis.

female Enochrus quadripunctatus showing close-up of pronotum, maxillary palps and terminal sternites, North Elmham (Norfolk, UK), 28th August 2018

I think I could see the rows of coarser punctures on the elytra ok on this one but I couldn't see that they were setiferous. I measured it as 4.6mm long which is 0.1mm below the size range given in Duff - I'm not too bothered about that as it was dead and so it may have contracted in slightly.

Enochrus quadripunctatus shwowing maxillary palp, apical sternite, head, mesosternal tooth and aedeagus (2 views), Wendling Beck Environment Project (Norfolk, UK), 14th July 2024

2017 was the first year I started keying out beetles and looking back I know I made a few mistakes and I'm going to have to withdraw two of my Enochrus records from 2018. This one from 2017 was my first Enochrus and I keyed it (would have been using Hackston only) to quadripunctatus and made no note of having had difficulties reaching that conclusion. I can't see the critical pronotum pattern in the photos, but like the one above this probably looked different under the microscope than it does in the photo of the live insect. At this point I have no reason to think I went wrong...

Enochrus quadripunctatus, North Elmham (Norfolk, UK), 4th July 2017

This one came to light and was as baffling as the others at first, with me still being unable to figure out what's meant by (or see) the coarser rows of setiferous punctures on the elytra. However this one did show the four neat black spots around the larger central black spot on the pronotum, thnough it's worth noting that these were not immediately visible and I had to angle to pronotum right to see all of them. Other characters matched the previous individuals including the genitalia (but not that during my attempts to clean the aedeagus I accidentally pulled the central membrane down and with it the dark bar). With its head down after death it measured 4.0mm which is below the stated range for quadripunctatus but I think that it would have been longer when it was alive and its head was in natural position. In any case given its un-notched apical sternite and short palpomere 4 it can't have been any of the species that are meant to be smaller.

Enochrus quadripunctatus showing pronotum, mid tarsus, maxillary palp (including close-up of segments 3 & 4), apical sternite, mesosternal tooth and aedeagus, North Elmham (Norfolk, UK), 12th August 2024