Evolution of the weevil rostrum (Coleoptera: Curculionoidea): internal structure and evolutionary trends

Weevils (Coleoptera: Curculionoidea) are one of the most diverse groups of extant organisms, with approximately 60,000 described species. They are extremely important economically, being of great agricultural significance because they are associated with all major groups of plants and plant parts. The current classification of weevils, despite having witnessed numerous hypotheses, is still quite unstable at the higher levels and even more so at the lower levels. In order to develop a more robust morphological character system for cladistic analysis of the higher lineages and to gain a comprehensive understanding of rostrum structure prior to developmental studies examining its formation, a comparative study was conducted of rostrum structure throughout Curculionoidea. Thin sections were made of the rostra of exemplar taxa representing most of the weevil families, as well as several subfamilies within the largest family, Curculionidae, and internal structures were examined for useful characters. While the morphological diversity of rostral forms is rather astounding, general trends are apparent with respect to life history traits and modes of feeding. Internal rostral morphology also represents a valuable set of largely unexplored characters; serving as informative complements to traditional external morphology, these features provide new insight into rostral morphology and have implications for settling current incongruence in the higher classification.