Trophic egg provisioning in a passalid beetle (Coleoptera)

Abstract

Trophic eggs, which are not viable and eaten by larvae, are produced by the passalid beetle Cylindrocaulus patalis. This is the first record of trophic eggs in subsocial Coleoptera. There are differences in the morphology of trophic and fertile eggs; the former are a paler colour and softer than the latter. The surface of the chorion of trophic eggs is also smoother than that of fertile eggs. The trophic eggs are fed directly by the female parent to 3rd instar larvae following a series of specific behavioural interactions between them, including repeated stridulation by the larva. It is likely that trophic eggs supplement the protein-poor diet of the larvae and contribute to their growth and survival. The production of trophic eggs may be associated with the evolution of an extremely small clutch size in C. patalis.