Aphalara polygoni

Using the RES key this would key to either Aphalara polygoni or Aphalara borealis (which is considered unlikely to be present in Norfolk), however thanks to James Emerson I now know there is a third species that needs ruling out, Aphalara freji. Before I examined mine, James advised me that In Norfolk there are three old records of the species pair that are not confirmed either way and a single more recent record of freji, but none confirmed as polygoni.

Thanks also to James for supplying scans of the relevant bits of Fauna Entomologica Scandinavia psylloidea by Ossianilsson (1992) which show the differences in terminalia and wing spinules. Anyone using this should note that the taxonomy has undergone a few changes - freji is referred to in Ossianilsson as polygoni and the real polygoni is referred to as rumicicola.

After comparing my specimen with the diagrams in Ossianilsson I am satisfied that my specimen is polygoni and not freji. The spinules in the wing are denser and appear in lines as illustrated in Ossianilsson. Also the proctiger has an indentation in the upper surface which corresponds to the diagram in Ossianilsson. The diagrams also show a difference in the shape of the lower edge of the proctiger, sinous on polygoni, curving down at first and then curving back to run more-or-less parallel with the midline of the abdomen, but more evenly curved downwards on freji. This was hard to see even after clearing the abdomen but mine was sinous as shown by Ossianilsson for polygoni. The details of the terminalia were impossible to see before clearing it in potassium hydroxide solution.

The only discrepancy in the ID process is the peri-anal ring (aka anal ring or peri-anal wax glands) which is illustrated and described in the RES key for both "f. typica" and "f. rumicicola", rumicicola being the form which was subsequently split and, after a spell being known as Aphalara rumicicola, was discovered to be the identity of the type specimen of Aphalara polygoni (leading to f. typica becoming Aphalara freji). Anyway, mine has eight rows of pores in the posterior portion which the RES key links to f. typica, i.e. what we now know as Aphalara freji, whereas f. rumicicola (which we now know to be the true Aphalara polygoni) is supposed to have just two rows of pores. Whether this discrepancy is down to variation I'm not sure, but it's shown more like mine in Ossianilsson and the spinule and terminalia characteristics are clearly as described for the true polygoni.

In the set of wing photos below the first four are taken with one microscope and show the colour of the wings best (lit from above and below, just enough from below to counter the reflections appearing when only using the top light). The other four are taken using a different microscope lit only from beneath - the dark patches on the wings don't show up well this way but the detail of the spinules is easy to see. The close-ups show the part of the wing illustrated in Ossianilsson.

This was a small psyllid - the forewing was 2.3mm long and as shown below the width of the head across the eyes was just under 0.6mm.

female Aphalara polygoni showing genal cones (or lack thereof), forwings (eight views covering both wings, hindwing also shown in the first photo) and terminalia (side views before and after clearning and dorsal view after clearing showing peri-anal ring), North Elmham (Norfolk, UK), 17th September 2023

When I caught the individual above I didn't notice, or at least register, the fairly obvious dark spot on the forewing, and after taking the photos I potted it up for subsequent examination. Before I had looked at it I caught the individual shown below. This time I noticed the spot and realised it was a species I had not identified before. Rather too excitedly I decided to try and examine it before it had died. It had seemed pretty moribund, lying on its back for a bit, so having it at the bottom of an open pot while I viewed it under the microscope didn't seem too risky. But I glanced up at my laptop screen to view the key for a second, looked back and it had gone! Clearly it wasn't as moribund as I thought as it had jumped out of a tall narrow pot and I hadn't seen which way it had gone. Unlike many escapees, it hadn't gone to the windows or the light, so it was now missing. It was after this that I communicated with James and learned of the need to eliminate freji, but alas it was now too late to do so. This was enormously frustrating for me, so it was an equally great relief when I later discovered that I had another one in a pot from about three weeks earlier. But for this one, unless I find the corpse when I next get round to tidying my desk, I won't ever know for sure if it was polygoni or freji, but in view of the earlier record I guess it's most likely to have been another polygoni.

female Aphalara polygoni or Aphalara freji, North Elmham (Norfolk, UK), 8th October 2023

My next encounter with an Aphalara (beaten from pine in the Brecks) has left me scratching my head a bit. There were some clear differences from the first one above - enough for me to suspect it was a different species. Firstly the peri-anal ring seemed to be a consistent width of about two pores all the way round, not noticeably wider in the posterior portion (in fact, once fully cleared it proved to be slightly wider at the posterior tip, but not much). Secondly the wings were much more cloudy, with a strong brown wash covering most of the wing (especially the outer section). Thirdly, the forewing spinules were much more conspicuous, being darker and larger (I had retained the first specimen so was able to compare them side-by-side - the difference isn't so obvious in the photos as it was looking at them together under the microscope).

However, although the spinules were much more obvious, there wasn't any obvious difference in their density. Indeed, I went to the effort of drawing a 100μm x 100μm square over the same place at the middle of both insects' wings and counting the spinules within the square - there were 47 in the original one and 48 in the new one (give or take two or three - some were indistinct so hard to call). Both had some spinules arranged in lines as much as each other. So despite the difference in spinule prominence, there was no appreciable difference in spinule density or arrangement, and that - apparently - suggests they are both polygoni.

I couldn't detect any differences in the shape of the proctiger - thus this one also resembled the diagram in Ossianilsson for polygoni more than freji - but I'm not clear if the differences in the diagrams are significant for this to matter.

I've got to say, I'm surprised that the pattern and density of spinules is a more important diagnostic character than the width of the peri-anal ring and the size/prominence of the spinules, but on this individual the peri-anal ring matches how it's shown in the RES key whereas the first one matched how it's shown in Ossianilsson. I'm grateful to James Emerson (county recorder) for a second opinion supporting my identification.

female Aphalara polygoni showing forewing (with close-ups of centre of wing), uncleared abdomen from below, abdomen from side (3 views, uncleared to cleared) and peri-anal ring, Ringmere (Norfolk, UK), 7th February 2024

In the following photos the whole wings are the Ringmere one above the September Elmham one, and the close-ups showing the spinule density in the 100μm x 100μm squares are the Ringnere one first and the September Elmham one second.

2x female Aphalara polygoni, Ringmere (Norfolk, UK), 7th February 2024 and North Elmham (Norfolk, UK), 17th September 2023