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A Ptenidium from Sandwich Bay

I am no great fan of the featherwing beetles (Ptiliidae) but they are growing on me and I’ve been trying hard to get to grips with the genus Ptenidium and others, though still largely ignoring the dreaded Acrotrichis. This blog is just to put on record an interesting specimen of Ptenidium which might be a species new to Britain:

A male Ptenidium from Sandwich Bay, East Kent from an Autokatcher sample on 31st August 2012. It is an unusual specimen of P. pusillum (or maybe an additional species of the pusillum-complex?). Click for large photo.

It is closest to P. pusillum (probably the commonest British species of the genus) but differs most strikingly in having much deeper and more extensive puncturation on the elytra. In addition, it has slightly more elongate elytra with less strongly rounded sides, elytral hairs a little shorter, pronotum sides a little more strongly rounded and with slightly broader side-margins, and the antennal clubs a little darker than the average pusillum. Michael Darby kindly examined it and agreed that it could be a species new to Britain, but what?

I sent my photo to Mikael Sörensson in Lund, Sweden who is an expert on European ptiliids and got an excellent response. In fact, Mikael’s reaction was that this looks the same as specimens of P. pusillum which he sees from Sweden and continental Europe. P. pusillum is apparently highly variable in body shape, colour of body and appendages, and also length of the pubescence. Mikael was struck by the somewhat darkened last two antennal segments of my specimen but has seen such colouration before in occasional specimens. So the conclusion is that “your specimen is a mere variant of P. pusillum“.

However, Mikael stressed that “because of the external variation, the taxon ‘P. pusillum‘ seems complex and might include ‘hidden’ taxa within. Viewed on a western Palaearctic level it is extremely difficult to tell if we have one single, much variable species, or two (or more?) ‘hidden’ within. Until we have applied other methods (molecular) for separating populations and variants on a pan-European basis I hesitate to split P. pusillum and therefore regard it as one single variable species”.

So what next? Mikhael writes: “It would be nice to uncover more specimens from that part of Britain, and also from France, in order to get an idea of the local variation. The problem of P. pusillum sensu lato is indeed intriguing and calls for more work”. I plan to pay much closer attention to Ptenidium, especially if I’m on the Kent coast, and I’d be interested to hear from anyone who has found similar specimens in Britain or abroad.

It would also be good to start applying molecular techniques to these kinds of taxonomic problems but I still don’t know of anyone who I can send a beetle to, with a cheque enclosed, and get it sequenced. Any suggestions?

I thank Michael Darby, Peter Hammond and Mikael Sörensson for helpful discussions and for sharing their expertise. As always, I have Darren Mann and James Hogan (of the Hope Department of Entomology, Oxford University Museum of Natural History) to thank for allowing me to use their auto-montage kit.

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