Rhyzobius chrysomeloides/litura

The most immediately obvious character separating these species is the dark elytral pattern, at least when this is more or less typical, this is what alerted us to the presence of chrysomeloides in Watford, and in the field well-defined horseshoe marks are almost always going to be litura while more extensively darkened specimens need to be examined closer. These marks vary widely (Fursch, 1967) and so one may be inclined to examine all specimens. Ground colour and shape may also be distinctive but this is very subtle and, without experience, is probably academic; litura is generally a paler testaceous compared with chrysomeloides and is more convex and proportionally broader. The pronotum in litura is broadest across the hind angles and narrows smoothly to the front angles while the basal half in chrysomeloides is subparallel, in our experience this varies and we have yet to see a specimen such as that figured by Fursch (fig.6.2 p.240) where the pronotum is broadest in the middle and tapers both anteriorly and posteriorly. The prosternal carinae provide a good character; in litura they are triangular, straight sided and diverging widest near the hind edge of the coxae. In chrysomeloides they converge from the base of the prosternal process and then become parallel before a rounded apex.

The male genitalia are very different; in litura the median lobe is bifid with a short dorsal extension, the tip of the long lobe is about level with the parameres. In chrysomeloides the lobe is longer, more slender and characteristically pointed, there is no dorsal extension and it extends beyond the tip of the parameres. In the female the genital coxites are more elongate and slender in chrysomeloides but, having dissected several female litura, we think this must be a pretty comparative feature.

Dissection (for the experienced) is straightforward and we have kept the entire genital structure intact (below) to show what to look for. It is easiest to remove the whole abdomen (which is easy with carded specimens by probing between the elytra), after soaking this for ten minutes or so in warm KOH the tergites and sternites may be peeled apart and the genitalia teased out intact from among the fatty tissue.