On the Affinities and Systematic Position of Lachnaeus Schoenherr and Rhinocyllus Germar in the Tribe Lixini (Coleoptera: Curculionidae: Lixinae) Based on the Morphological Characters of the Immature Stages

Simple Summary The detailed descriptions of immature stages of Lachnaeus crinitus Schoenherr, 1826, Rhinocyllus alpinus Gultekin, Diotti and Caldara, 2019 and R. conicus (Frolich, 1792), belonging to the Lixini (Curculionidae: Lixinae), are very important for an increased understanding of the relationship between the species and of the taxonomic and phylogenetic value of the tribes and genera in the Lixinae. The complex of these new data has allowed us to support that (1) Lachnaeus and Rhinocyllus are two valid genera that are different from Larinus, (2) Rhinocyllini is not a tribe different from Lixini, and (3) the separation of Rhinocyllus into two subgenera is rational. In the tribe Lixini, these new data may have an important role, because Rhinocyllus conicus and several other species of the genera Lixus and Larinus have a practical or at least potential use as biological control agents against invasive and noxious weeds. Mature larvae and pupae of Lachnaeus crinitus Schoenherr, 1826 and Rhinocyllus alpinus Gultekin, Diotti and Caldara, 2019 and pupae of R. conicus (Frolich, 1792), belonging to the Lixini (Curculionidae: Lixinae), are morphologically described for the first time. They possess all the characters considered distinctive in the immature stages of this tribe and are distinguishable from all the related genera by a combination of some characters (e.g., presence of endocarina, shape of premental sclerite; the number of pds on the abdominal segments; size and presence of urogomphi). It is emphasized that the controversial tribe Rhinocyllini is not supported by the characters of the larvae and pupae of Rhinocyllus and that the two subgenera of this genus, Rhinocyllus s. str. and Rhinolarinus, are separable from each other not only by characters of the adult but also distinctive characters of the larvae and pupae. These results confirm that the morphology of the immature stages, which is usually overlooked, can be very important for the purpose of identifying new characters that are useful for clarifying taxonomical and phylogenetic complex situations based only on the study of the imagoes.

Automated summary

The detailed descriptions of immature stages of Lachnaeus crinitus, Rhinocyllus alpinus, and R. conicus belonging to Lixini (Curculionidae: Lixinae) provide valuable insights into the relationship between species and the taxonomic and phylogenetic value of the tribes and genera in the Lixinae. It is highlighted that the morphology of immature stages, often overlooked, plays a crucial role in identifying new characters for clarifying taxonomical and phylogenetic complexities based on adult studies only.