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]