For many years, the larvae of the New Zealand grass grub Costelytra zealandica and that of its congener C. brunneum have been considered cryptic. To progress the research in my PhD project using these two scarabs as pest and non-pest species model, I developped novel molecular methods, based on the use of frass and larval exuviae as non-invasive sources of DNA, to differentiate them (Lefort et al. 2012).
Later on, and based on the use of these molecular tools, a detailed comparative taxonomic assessment between C. zealandica and C. brunneum revealed that three morphological characters allowed accurate identification of third instar larva. For live larvae, especially in field conditions, the morphology of the septula of the raster is usually sufficient to differentiate the two species (Lefort et al. 2013).