Unique rostrate larvae and basidiomycophagy in the beetle family Corylophidae

•Rostrate larvae of Corylophidae (Coleoptera) were examined.•The snout-like elongation of the head is a unique feature in larval beetles.•Associations with basidiomycete fungi are discussed.•The larval rostrum probably has a feeding performance advantage.

The head morphology of larvae of two undescribed species of the corylophid genus Holopsis were examined. Both are associated with the same basidiomycete host Ganoderma cf applanatum. Whereas the round and convex adults are very similar, one of the disc-shaped larvae is characterized by an elongate weevil-like snout, which is a unique feature in larval beetles. The posterior head region, the mouthparts and the general configuration of the musculature are similar in the larvae of both species. However, in the rostrate Holopsis sp. 1 most muscles are either widened along the longitudinal axis or elongated. Moreover, an additional bundle of M. frontobuccalis posterior is present, which strengthens the pharyngeal pumping apparatus. Both species share an unusual connection between the prepharynx and pharynx. This is a potential autapomorphy of the genus. The larval cephalic morphology of Holopsis sp. 2 and the corylophine genus Sericoderus is quite similar. However, they differ in some muscular features and in the configuration of the foregut. Holopsis species are associated with Basidiomycetes. Whether this is an ancestral condition in Corylophidae remains ambiguous due to conflicting phylogenetic hypotheses and the largely unknown biology of the Australian subfamily Periptyctinae. Several features of Holopsis are likely plesiomorphic and possibly related with the association with basidiomycetes. However, the larval rostrum of sp. 1 is doubtlessly derived, and could have a performance advantage over other species feeding on the spores of Ganoderma cf applanatum including Holopsis sp. 2.