Little larvae that love leaves

As you may know, I specialise in leaf beetles (Chrysomelidae) and quite often get sent specimens to identify as I run the national recording scheme for this family. These are usually adults, but now and again juvenile stages which are more difficult, but also useful reference material, especially as I (eventually) intend to write a guide to their identification. Some months ago I was sent some larvae preserved in alcohol to see if I could confirm whether they were Chrysolina marginata. It took me a while to find the time for this (it's been a busy year), but here's the process.

Tube of preserved larvae.

Contents of the tube. The larvae are of different stages (instars) and the largest ones are around 7-8mm long. The anal proleg is visible (especially in the specimen top right) and this is a feature of Chrysolina.

Sensory structures on the head. There are no compound eyes, but in Chrysolina there are six ocelli (simple eyes) on each side of the head as indicated by green arrows, four in a rough square and two the other side of the antenna which is circled in blue. The segmentation of the small antenna is clearly visible, including the small segments/structures at its tip.

Side view of one of the larger larvae. The blue lines show the joints between segments. The green lines show sclerites (hardened patches) arranged in irregular rows.

The end of one of the legs, showing the tarsal claw. The inset shows that the outline (solid) has no protrusion at the base. This is a feature of C. marginata with some other species having a protrusion (dotted line).

Close-up of the body surface. Sclerites are shown in green circles. The pale blue arrows show intermediate secondary bristles with small dark patches at the base of each. Between these there are tiny dark dots of microsculpturation as shown within the dark blue outlines. This mixture of features is seen in C. marginata.

So, the combination of features, along with the keys in Marshall (1979) and Zaitsev & Medvedev (2009) confirms that these larvae are C. marginata - easier than larval identification often is, and provides information that is due to be used in a report later this year.

References

Marshall, J.E. (1979). The larvae of the British species of Chrysolina (Chrysomelidae). Systematic Entomology 4: 409-417.
Zaitsev, Y. M. & Medvedev, L.N. (2009). Larvae of Leaf-beetles of Russia. KMK Scientific Press, Moscow. [In Russian]

This is why I geek those beetles

If you are a regular here, you'll know I spend a lot of time peering closely at small invertebrates in order to identify them, like here. For those interested in taxonomy and morphology (like me), that can be an end in itself - I find small creatures fascinating and I like to know what they are. I geek them, and do so proudly - plus I'm a professional entomologist/ecologist so there's the academic-kudos and getting-paid aspects. However, there is more to it than that.

I have been asked more than once why we need to identify species - and it's a fair question; after all, the beetles don't care whether we can name them, and individual ones would probably prefer not to be fatally sampled for the greater good. However, without identification (which often requires a dead specimen), there can be no survey, monitoring or collection of distribution data; and without these, we don't know what needs conservation effort. In an ideal world, their habitats would be fine, biodiversity would not be threatened, and conservation (if needed given the previous points!) would have limitless funding. Sadly these things are very very much not the case. So, samples are taken, species are identified (along with date, location etc) and data sent to recording schemes/centres, or now added to online systems such as iRecord to be validated by hard-working volunteers such as myself...

Once the data has made its way to the recording scheme database, it can be downloaded, interrogated - in short, used. This could be for any number of purposes - planning, research, amatuer interest, and so on. However, during the winter of 2013/14 I was lucky enough to be contracted to use this data to write a status review of the Chrysomelidae (leaf beetles), the group I specialise in. This meant looking at the change in distribution of all the British species and allocating them to categories such as 'Least Concern', 'Endangered' and 'Vulnerable'. Thus, scarce and threatened species could be identified and highlighted with extra information focusing on these, such as summaries of habitats, distribution, threats and conservation measures. This is important as it will inform conservation efforts, survey work, policy decisions and other activities. It's also part of a wider project with different specialists covering their groups of choice such as Carabidae (ground beetles) and is a major update to status review work published in the 1990s (e.g. Hyman & Parsons, 1992) some of which is now considerably out of date.

I won't go into any more detail here, but if you want to look at the report, it's called A review of the scarce and threatened beetles of Great Britain: The leaf beetles and their allies and is free to download here along with data covering the key species.

Reference

Hyman, P.S. & Parsons, M.S. (1992). A review of the scarce and threatened Coleoptera of Great Britain 1. JNCC, Peterborough.