Morphology of the larvae and biology of the adults of Psilorrhynchus bifasciatus do not confirm previous hypotheses about systematics and feeding habits (Coleoptera: Cantharidae)

Abstract

Psilorrhynchus bifasciatus (Blanchard, 1844) is broadly distributed through South America, but its biology, behaviour and life cycle are unknown. The most characteristic feature of the adults is slender rostrum, presumably associated to a specialised feeding habit. However, new observations of P. bifasciatus feeding on nectar in inflorescences of Matayba guianensis Aubl. (Sapindaceae) do not support such a hypothesis. Here, we describe and illustrate their early larval instars in details and compare them with the other Chauliognathini. The larvae are remarkably characterised especially by a long and thick pubescence, conspicuous roughness on the head and thoracic terga, and head with sharp lateral projections. These features are unique amongst the known Cantharidae larvae and do not confirm a previous hypothesis of close affinity between Psilorrhynchus Gemminger & Harold, 1869 and bromeliad-inhabiting Chauliognathini species.

The systematics of Dysmorphocerinae (Cantharidae) based on larvae

“…Cantharidae larvae are usually easily recognised by their soft body densely covered with short pubescence, giving them a velvety appearance; other characters, like the prognathous and slightly flattened head, and body with lateral and transversal ampullae with pairs of glandular pores are also diagnostic (Crowson 1972;Ramsdale 2010). They have a rich diversity of structures useful for characterising lineages of Cantharidae and have enabled the production of identification keys, the recognition of genera and groups of species, and the definition of subfamilies (cf., Bøving & Craighead 1931;Striganova 1962;Fitton 1976;Klausnitzer 1997;Biffi & Casari 2017;Biffi & Rosa 2019;Biffi et al 2022). As highlighted by Crowson (1972), the known Cantharidae larvae seem to fall readily into groups corresponding to the four commonly accepted subfamilies of the adults at that time (Cantharinae Imhoff, Malthininae Kiesenwetter, Chauliognathinae LeConte, and Silinae Mulsant) apart from one, an 'aberrant' cantharid larva.…”