A detailed morphological study of head stridulatory structure and related pronotal structures in ischyrosonychine tortoise beetles (Coleoptera: Chrysomelidae: Cassidinae)

The tribe Ischyrosonychini is comprised of 69 species in seven genera.  The members of Ischyrosonychini are generally divided into three groups:  species of Asteriza, ischyrosonychines (Cistudinella and Eurypedus) and physonotines (Enagria, Eurypepla, Physonota and Platycycla).  However, because of their diverse external morphology, its monophyly has been in doubt and no evidence has been suggested to support them as a natural group.  The members of Ischyrosonychini have been regarded as one of the most derived groups within Cassidinae based on their pronotal morphology, which completely covers the head in dorsal view.  Related to this pronotal morphology, head stridulatory files (par stridens) are found in all member of Ischyrosonychini and several other groups.  These stridulatory files are scraped against by projected plectra on head cavity of pronotum.  In this study, these stridulatory files are illustrated using scanning electron microscopy and detailed morphological features are documented, including location of file, shape, and number of file ridges.  The plectrum on the pronotum is also illustrated and compared among the tortoise beetles.  As a result, physonotines and species of Asteriza have a plectrum comprised of a single projected line, and the number of file ridges is over 120, with a microtrichial patch in front of the stridulatory file. In contrast, ischyrosonychines have a plectrum with double lines (a band-like structure) and the number of file ridges is less than 100 and without a michrotrial patch.  These different plectral structures allude to independent origins of stridulation in target taxa.  Characters and structures related to head stridulation also are discussed further for phylogenetic analysis.