Impunctate Mini-miner Andrena subopaca

Once I'd worked out that this was genus Andrena I first assumed it was one of the mini-miners given the size. But keying it as such wasn't straightforward as Falk's key allows for some non-mini-miners being small and says for the mini-miner group, "Tergites 1-4 hairless except for lateral fringes of white hairs along the hind margins of most species." Tergites 1-4 had extensive reasonably long sparse hairs along the sides, not restricted to the hind margins. Hairs were harder to see at the centres of tergites 1-3 (not 4 where they were just as obvious as at the sides) but even here there were short hairs on (very short on tergite 1). The mandible tips crossed well past the centre-line, but not as far as I'm used to seeing on larger Andrena, so that didn't clear things up, and I wasn't sure about the other character given either. Well, in the end I figured it had to be one of the mini-miners despite this contrary character - and indeed I then discovered that several of Steven Falk's own photos of mini-miners on Flickr show similarly hairy tergite sides. Just in case though, I tried keying it as a non-mini group and reached a dead end.

So, once I was happy it was indeed a mini-miner (group B in Falk's key) and established that there were no black hairs on the head, it didn't get a lot easier! It isn't always clear (to me at least) how to interpret surface sculpture descriptions and although my gut feeling, based on experience so far, was that I was looking at microsculpture not punctures, the form of the microsculpture was such that you could, I think, interpret it as a dense covering of tiny punctures. But as the first choice was between obvious punctures with little microsculpture between them and obvious microsculpture with few or no punctures, it had to be microsculpture - if they had been tiny punctures there was no space between them to be able to look for microsculpture. Next problem was establishing if dip differentiating the base of the tergites from the apical depression constituted a "deep transverse rim" as in semilaevis. Comparing with the figures I decided the apical depressions weren't polished enough for semilaevis - the microsculpture was clear, albeit more micro than on the base of the tergites - which was important at the next couplet eliminating niveata. Eliminating falsifica relied on relative lengths and widths of antennal segments 3-5. It was clearly wrong for falsifica, but not quite perfect for the alternatives either with segment 5 being distinctly, if only slightly, shorter than segment 3. Near enough though, and the other character (shape of tergite 1) supported this. Finally it was back to surface sculpture, this time on the scutum and scutellum, and aided by the useful photos in Falk's figures, this was pretty straightforwardly pointing to subopaca.

male Impunctate Mini-miner Andrena subopaca showing forwing, tergites 1-3, scutum and antennal bases, Dillington Carr (Norfolk, UK), 26th April 2022