Morphology and systematic significance of sclerolepidia in the weevils (Coleoptera: Curculionoidea)

Abstract

Sclerolepidia are minute specialized structures found only alongthe metepisternal suture in the weevil subfamilies Scolytinae, Cossoninae, Baridinae and some tribes in the Cryptorhynchinae, Conoderinae, Molytinae, Curculioninae and Cyclominae of the Curculionidae. Their presence has been used to establish relationships at subfamily level in the Curculionidae, although some of these are questionable, because of misperceptions of the distribution of the structure across taxa. Within the Curculionidae sclerolepidia are probably homologous, but provide limited information aiding establishment of sister‐group relationships between subfamilies, and multiple loss is likely. Analogous structures occur in the Erirhinidae and the Eucnemidae, but not elsewhere in the Coleoptera. Structural evidence shows sclerolepidia to be derived from scales. Their morphology allows division into ‘squamiform’, ‘digitate’, ‘peg‐like’ and ‘plumose’ types. Squamiform sclerolepidia are only slightly modified from the ancestral scale and are probably the plesiomorphic type, with modification probably occurring independently a number of times. Taxonomic characters and phylogenetic information are provided by distribution of different types within the weevils at species, genus and higher levels. Numerous systematic changes were identified as necessary during this project from the study of the sclerolepidia; 27 genera are transferred at tribal level and these changes are listed in an appendix. The functions of sclerolepidia probably differ across the Curculionidae, and may include sensing the relative positions of the metepisternum and metasternum during flight, and diffusion of secreted wax or other chemicals.