What's in the box? No.4 - some very small bits of very small beetles...

In case you've not read any of my 'what's in the box?' posts before, it is an occasional series detailing the specimens (generally leaf beetles, family Chrysomelidae) that land on my doormat when other entomologists send me specimens as part of my role as coordinator of the UK Leaf & Seed Beetle Recording Scheme.

Sometimes these are quite mysterious and have included both an aberrant specimen of a common species and a species new to the country (most exciting to a bug-nerd!). Next mission - a species new to science... but until then here's a close look at the contents of a small tube of tiny beetles that arrived preserved in ethyl acetate. In this case, the identity was clear as a letter was included stating that these were voucher specimens of Aphthona pallida from North Yorkshire in northern England, a small (1.5-1.8mm) species of 'flea beetle' found on Geranium and Erodium, in this case Geranium pratense.

Dorsal view of A. pallida showing the brownish-yellowish elytra and pronotum, and black head. Note the relatively coarse punctures on the elytra and the microsculpturation that is just visible between them (clearest around the centre of the image). The area covered in this photo is about 1.2mm wide

Ventral view of A. pallida showing sculpturing and bristles on the legs and abdomen; note the large hind femurs.

This may be nothing special in itself, but until 2009 there was considerable confusion between this species and A. nigriceps in Britain, with various taxonomic authors treating them as separate species, the same species, or subspecies. Not easy for those trying to produce accurate species records. They have been treated as separate species in some key continental European texts such as Warchałowski (2003) which separates them using the presence of a dark sutural stripe in A. nigriceps. Then, in a 2009 paper, Sinclair & Hutchins discussed the status of A. pallida, concluding that it was definitely a British species and separating it from A. nigriceps most clearly by the shape of the tip of the aedeagus.

Further work (summarised in the accompanying letter mentioned above which was from Jim Jobe, Coleoptera recorder for the Harrogate and District Naturalists' Society) suggests that the darkened suture is an unreliable feature and that the aedeagus is the only certain way to separate these two species. I do not have a specimen of A. nigriceps to hand, but there is an excellent image here, including the aedeagus. Comparing this with the aedeagus of A. pallida below, it is clear that the aedeagal tip of A. nigriceps is flatter/broader, a feature noted by Sinclair & Hutchins (2009).

Aedeagus of A. pallida; note the tip which is less flattened/broadened than that of A. nigriceps.

So, what is the upshot of this? Well, firstly A. pallida is a clear addition to the British list and can be separated from A. nigriceps using the aedeagus - a somewhat fiddly dissection, but it provides a reliable feature. Secondly, it does appear that the relevant part of the generally excellent (though expensive) Warchałowski (2003) is incorrect i.e. couplet 25 on p.396 as this uses the sutural feature as a separator. Lastly, it is likely that many British specimens labelled 'A. nigriceps' are actually A. pallida and ongoing work on this is due to be published in the relevant literature; when this occurs I shall post an update here. It will also allow me to amend this part of my test key to the Chrysomelidae when I start producing the final version this winter.

References

Sinclair, M. & Hutchins, D. (2009). Aphthona pallida (Bach, 1856) (Chrysomelidae) is a British species. The Coleopterist 18(3): 155-157.

Warchałowski, A. (2003). The Leaf-beetles (Chrysomelidae) of Europe and the Mediterranean Area. Natura Optima Dux Foundation, Warsaw.