Comparative morphology and evolutionary implications of larval mouthparts in ten lineages of Scarabaeoidea (Coleoptera)

Abstract Larvae of the megadiverse Scarabaeoidea play important economic and ecological roles, and their mouthparts provide valuable morphological clues for species identification and dietary inference. However, the underlying relationships between morphological characters and feeding habits remain insufficiently elucidated. In this study, the larval mouthparts of 22 species representing ten major lineages of Scarabaeoidea were examined in detail. Seventeen characters of the larval mouthparts were analyzed within a phylogenetic framework. Three characters were identified as candidate synapomorphies for the major lineages represented here: maxillary stridulatory teeth for Scarabaeidae, mandibular stridulatory ridges for Cetoniinae + (Dynastinae + Rutelinae), and a circular arrangement of epipharyngeal phobae for Aphodiinae + Scarabaeinae. By contrast, several homoplastic mouthpart traits were recurrently associated with larval feeding habits in the sampled taxa, including a setose acroparia, heli on the epipharynx, and a blade-like incisor region in phytophagous lineages, and the circular phoba complex together with the absence of nesium in coprophagous lineages. These results suggest that larval mouthparts in Scarabaeoidea may retain both phylogenetic and trophic signals, providing a morphological basis for interpreting the evolution of feeding habits in scarab larvae.