Springtime beetles, legs go spring

Having a garden pond means occasionally finding dead things floating. No, not hedgehogs or other larger fauna - the sides are profiled so that mammals can get out - but sometimes incautious invertebrates drown. Naturally, if they look interesting (and haven't been eaten by pond skaters and other small predators), I fish them out for a closer look. When I saw a flea beetle (in the Chrysomelidae, my specialist group - they are in the tribe Alticini within the subfamily Galerucinae) I identified it easily enough as Longitarsus pellucidus, a common species, though it's always worth checking. It lives on bindweeds (Convolvulaceae) which are growing near the pond so presumably jumped into the water by accident when disturbed by a spider, bird, cat, human or other potential threat. However, it did give me an opportunity to look at why flea beetles are so named.

Longitarsus pellucidus - the swollen himd femora can be seen, as well as the elongate tarsus that gives it its generic name.

The hind femur in flea beetles is swollen to accomodate jumping muscles and the 'metafemoral spring' which is visible through the cuticle as a slightly paler comma-shaped structure taking up much of the inside of the femur.

Hind femur and metafemoral spring of L. pellucidus.

The spring is a long-oval chitinous structure coiled much like a loose fist. Muscles squeeze the spring closed and then a 'catch' is released and the stored energy is released, extending the leg so the beetle can jump.Here you can see a ligament extending from the spring to the tibia so the leg is folded when the spring is compressed. This mechanism differs from that in fleas which have a blob of resilin (a natural rubber) which is compressed instead of a spring. Although fleas may be more familiar for their leaping ability, some alticine beetles are actually able to jump comparatively further, and of course some of these beetles are no bigger than a large flea - smaller beetles jump further relative to their size (Schmitt 2004). Also, the spring may be useful for identification and for grouping species taxonomically by looking at similarities and differences in the form of their springs. However, this is not a mainstream technique, largely because of the difficulty of dissecting out the spring and the lack of readily available published material forming a guide to identification this way, although there is useful information in Furth (1988) along with images and drawings from various species.

References

Furth, D.G. (1988). The jumping apparatus of flea beetles (Alticinae): the metafemoral spring. In: Biology of Chrysomelidae, eds. P. Jolivet, E. Petitpierre & T.H. Hsiao, pp. 285-297. Kluwer, Dordrecht.
Schmitt, M. (2004). Jumping flea beetles: structure and performance (Insecta, Chrysomelidae, Alticinae). In: New developments in the Biology of Chrysomelidae, eds. P. Jolivet, J. Santiago-Blay & M. Schmitt, pp. 161-169. SPB, The Hague.

What's in the box? Beetle-related joy (part 2)

Following on from identifying a couple of specimens of Aphthona pallida, I was left with one small dark beetle, another Aphthona. This was a female but also very well dissected, and keyed out quite easily as A. melancholica - a gloomy name for a dark-coloured insect.

Aphthona melancholica - female with genitalia dissected out.

As you can imagine, as the beetle is only about 2.5mm long, the genitalia you can see in the above photo are not large. They tend not to be as useful for identification as those of males (as the differences between species are so slight), but can be helpful and are included in some keys such as Doguet (1994). The structure visible here is the spermatheca - the structure that receives and stores sperm.

Spermatheca of A. melancholica

Reference

Doguet, S. (1994). Faune de France 80 – Coléoptères Chrysomelidae, Volume 2: Alticinae. Federation Francaise des Sociétes de Science Naturelles, Paris. [in French]

What's in the box? Beetle-related joy (part 1)

Sometimes I get sent emails with photos of beetles, sometimes I get little packets of unsorted beetles with a letter asking for identification, but sometimes I get beautifully, neatly mounted and pinned specimens and that makes my entomological heart happy. In this case some specimens of Aphthona flea-beetles (Chrysomelidae: Alticini) needing to be checked at species level.

Neat arrangement of Aphthona specimens

The two on the left are similar (yellowish with a dark stripe) and are what I'm looking at here (the other darker one will appear in a separate post). They are both possible A. pallida which needs checking as the species was only recognised as being British (Sinclair & Hutchins, 2009) a few years ago, so its abundance and distribution is not well understood. This doesn't mean it's only just arrived, but that it hadn't been noticed before and was probably confused with the similar A. nigriceps (Jobe & Marsh, 2012).

Probably Aphthona pallida - a male with the aedeagus dissected out. Beetle approx 2.5mm long, excluding appendages.

The yellow-brown colour with a darker head and partial dark stripe along the suture (where the wing-cases or 'elytra' meet) is typical. Looking more closely at the aedeagus, the end has a small blunt point which is the final feature needed to confirm that this, and the other specimen, are A. pallida - in this case found in Cumbria.

Aedeagus of A. pallida - note the small blunt point top left.

References

Jobe, J.B. & Marsh, R.J. (2012). The status of Aphthona pallida (Bach) (Chrysomelidae) in Yorkshire. The Coleopterist 21(1): 19-20.
Sinclair, M. & Hutchins, D. (2009). Aphthona pallida (Bach, 1856) (Chrysomelidae) is a British species. The Coleopterist 18(3): 155-157.