Cacopsylla peregrina

Previously known as Psylla peregrina but now placed in the genus Cacopsylla.

My identification of this first individual wasn't straightforward. I thought it looked a lot like Psyllopsis fraxinicola but I checked both hindlegs carefully and they definitely only had 6 spurs (9 on Psyllopsis) so that was swiftly eliminated. Except in the most obvious cases I tend to struggle assessing the shape of genal cones, so my first point of uncertainty was at couplet 21 in the RES key. I went the way I favoured first, but returned here to check the other option. I could eliminate ulmi on the shape of cell cu₁ although my interpretation of the proctiger to head with ratio seemed to favour ulmi here, which cast some doubt. Carrying on, the next and final couplet if I got the genal cones right was a clear result, peregrina. The forewing length was 2.8mm and the surface spinules were absent from cell c+sc. Checking the other option for the genal cones it was again the proctiger to head with ratio that prevented a conclusion, with sorbi being closest in other respects. Comparing the genal cones to the diagrams for peregrina and sorbi I think peregrina is about right and sorbi too pointed. The proctiger to head width ratio was even worse for sorbi than it was for peregrina.

My notes say that I potted this from rest, but I neglected to record what it was on. However my notes do say that it was along the track that is lined on both sides by Hawthorns. Given peregrina's association with Hawthorn I think this ID is safe (though always welcome feedback if anyone disagrees). I wonder if I'm interpreting the ratios correctly? I'm assuming head-width includes the eyes (it's wrong if it doesn't as well!). See the measurements in the photos below - I took it to be 0.54 / 0.76 = 0.71 - should be greater than 0.84.

Ok, an update to this. It occurred to me that the problem with the ratios might be down to the specimen being dried and the proctiger withdrawn into the last abdominal segment, so perhaps I wasn't getting its true length by measuring it dry. I still had the specimen so macerated in potassium hydroxide solution and hey presto, I now have measurements of 0.69mm for the proctiger and 0.78mm for the head width - making a ratio of 0.88 and within range for peregrina (and, for what it's still worth, still short for sorbi). Phew!

female Cacopsylla peregrina showing forewing (including close-ups of cell cu₁ and c+sc), genal cones, terminalia and measurements used to calculate proctiger to head width ratio (before and after clearing), North Elmham Cathedral Meadows (Norfolk, UK), 27th May 2020

I went round the houses with the next one too, though I eventually settled on peregrina. Initially examining the dry specimen I struggled to interpret the shape of the genal cones and homed in on ulmi based on the proportions of cell cu₁. The tip of the paramere was hidden but with a bit of imagination I could imagine it was possibly ok for ulmi. I find assessing the antenna length to head width ratio troublesome as it's hard to get the antennae to lie straight, but my best efforts suggested a ratio of 1.4, far too small for ulmi. So I needed to clear it for a better view of the paramere and genal cones to resolve this, and in doing so quickly found other reasons to discount ulmi - the parameres and the genal cones were both wrong.

Still unsure which way to interpet the genal cones so far as couplet 21 was concerned I tried the other route. The paramere seemed to me to be a dead-ringer for hippophaes but that seemed unlikely for an insect caught in my garden - there's no Sea Buckthorn here or, to the best of my knowledge, anywhere close. Of the remaining options mali has a twisted tip to the paramere too, so this seemed the next best option - except that it didn't have spinules throughout cell c+sc. Upon closer inspection there was a small patch of spinules towards the rear of the cell and a tiny number of spinules across the centre of the cell. Not exactly "throughout" but also not "absent" as the alternative required, so maybe this is ok for mali, I mused. Another look at the diagrams of genal cones and parameres in the key and no, surely this cannot be mali. At this point I noticed that peregrina had very similar genal cones and twisted parameres. I had to ignore the proportions of cu₁ to key it to ambigua (I actually compared the wing side by side with the peregrina above - the proportions of cu₁ were clearly different), and this time I had to interpret the very restricted patch of spinules on c+sc to be "absent" rather than "throughout" although in reality it was clearly somewhere in between. So a couple of reasons to doubt the ID but on balance I think it's got to be peregrina. Again, happy to hear if others agree or disagree. The forewing length was 2.5mm, within range for peregrina.

male Cacopsylla peregrina showing head and antenna, genitalia (before and after clearing), wings (including close-up of forewing cell c+sc and genal cones, North Elmham (Norfolk, UK), 7th June 2022

I had identified the next one previously but re-examined the evidence in the light of my new experience. The photo of the isolated paramere looks a bit straight, but I think it's probably ok. It had been beaten from Hawthorn which is reassuring!

male Cacopsylla peregrina showing genitalia and paramere, St Mary's churchyard, North Elmham (Norfolk, UK), 7th June 2021

The next two were both beaten from Hawthorn. I was with Graham Moates who also found 3 green female Psyllids and if I remember rightly had suggested they might be Cacopsylla peregrina (at least they were subsequently confirmed as such). I was therefore expecting my green female to be this, though other species are possible on Hawthorn so this needed checking. The brown male was so completely different that I imagined it would prove to be something else, but it turned out to be the same. They turn brown in autumn, but whether males turn earlier or it was just coincidence that the only brown one was the only male, I don't know.

male Cacopsylla peregrina showing forewing (with 2 close-ups), genal cones, abdomen from side (before and after partial clearing) and abdomen from rear, Wendling Beck Environment Project (Norfolk, UK), 12th September 2024

female Cacopsylla peregrina showing forewing (with close-up), genal cones and abdomen from side (before and after partial clearing), Wendling Beck Environment Project (Norfolk, UK), 12th September 2024

I have sometimes mistaken the depressions in leaves housing psyllid nymphs as galls, but this very mis-shapen (and discoloured) Hawthorn leaf was very extreme for something that isn't a gall - but it was full of psyllid nymphs. Was it an aphid (Dysaphis crataegi agg.) gall, taken over by psyllids, or do the psyllids cause this? Anyway, the final instar nymph checks out for Cacopsylla peregina.

Hawthorn leaf discolouration possibly caused by Cacopsylla peregrina and final instar nymph of Cacopsylla peregrina, North Elmham Cathedral Meadows (Norfolk, UK), 31st May 2021

These were on the same leaf and I presume are their eggs.

presumed eggs of Cacopsylla peregrina, North Elmham Cathedral Meadows (Norfolk, UK), 31st May 2021

I initially assumed that this was a gall - after all the leaf is mis-shapen as well as discoloured. The aphid Dysaphis crataegi agg. produces a gall that can look extremely similar to this and so that's what I initially identified it as. However, the Hawthorn leaves above, photographed just a few days earlier, look very similar and contained the nymphs of Cacopsylla peregrina. What's more the adult shown above was taken from the same Hawthorn as this. So my working assumption is that this is in fact not a Dysaphis crataegi agg. gall, but rather the vacated home of Cacopsylla peregrina nymphs. Or is it that the psyllids occupy vacated galls of the aphid and I was right in the first place? Please let me know if you know!

Hawthorn leaf discolouration possibly caused by Cacopsylla peregrina, St Mary's churchyard, North Elmham (Norfolk, UK), 27th May 2021