What's in the box? No.9 - groovy beetles

If you've been here before, you'll be used to my ongoing series about the identification of beetles that are sent to me my post. If, not here's a recent (and rather pretty) example to get you started. So, working through the recent numerous selection I received in an old Kodak slide box, I found a pair that summed up how the flea beetles (within the Chrysomelidae) are often perceived - small and sort of brownish...

A pair of flea beetles - even if you are new to this group, it's easy to see that the one on the left is male...

The presence of an exposed aedeagus (not usually seen without dissection) helpfully shows the difference in size between the male on the left (4mm long without appendages) and the female (5mm). The enlarged hind femurs are visible in dorsal view and show these to be 'flea beetles'. I won't go through the full identification process, but the combination of (1) hairless elytra (wing cases), (2) a strong unbroken groove at the rear of the pronotum (with foward-pointing ends), (3) bulges above the antennal bases being separated from the top of the head by a weak groove, (4) overall colour and (5) the top of the head without coarse/dense punctures show that it is in the genus Neocrepidodera.

Pronotum with a clear, broad groove along the rear edge with thin forward-pointing ends. The shallow, fairly sparse punctures and splayed edge can also be seen.

There are only three species within this genus in Britain. One, N. ferruginea, does not have the forward-pointing ends to the pronotal groove, which leaves us with N. impressa and N. transversa. Although very similar, N. impressa is found in coastal habitats such as saltmarshes and dunes unlike these specimens which were found inland. So, N. transversa is likely, but needs to be checked using the aedeagus - in this case easily visible.

Dorsal view of the aedeagus

Ventral view of the aedeagus

In this case, the identification is straightfoward - the tip of the aedeagus is spear-shaped, a characteristic of N. transversa, while in N. impressa it would be broadened and leaf-shaped (an example can be seen here, though note that the genus is given as Asiorestia as there is some taxonomic disagreement between British and continental authors). So, we have N. transversa, a widespread species found on a range of plants in various habitats (so, location may not help that much), but it is a nice easy example of the use of the aedeagus to separate closely related species. More small beetles coming soon...