Immature stages of Palearctic Mecinus species (Coleoptera, Curculionidae, Curculioninae): morphological characters diagnostic at genus and species levels

Description of immature stages of Rhinusa species (Coleoptera, Curculionidae, Mecinini) with a focus on diagnostic morphological characters at the species and genus levels

The mature larvae of the following fourteen Rhinusa species are described and illustrated: Rhinusaantirrhini (Paykull, 1800), R.asellus (Gravenhorst, 1807), R.collina (Gyllenhal, 1813), R.eversmanni (Rosenschoeld, 1838), R.florum (Rubsaamen, 1895), R.herbarum (H. Brisout de Barneville, 1862), R.incana (Kirsch, 1881), R.linariae (Panzer, 1796), R.melas (Boheman, 1838), R.neta (Germar, 1821), R.pilosa (Gyllenhal, 1838), R.rara Toševski & Caldara, 2015, R.tetra (Fabricius, 1792), and R.vestita (Germar, 1821). The pupae of thirteen of them (except R.incana) were also described. The comparison of larval morphological characters and plant preferences provides evidence supporting the existence of different species groups previously established according to a phylogenetic analysis based on adult morphological characters. The following diagnostic attributes distinguishing the genus Rhinusa are highlighted. For the larvae: (1) pronotal shield indistinct; (2) thoracic prodorsal fold small or even vestigial; (3) abdominal postdorsal folds (especially of segments III-VII) high or even in the form of conical protuberances; (4) cuticle of abdominal segments densely covered with asperities; (5) cuticle without dark spots or dark pigmentation; (6) head suboval, rarely round; (7) labrum usually with 2 als; (8) des1 short or absent, rarely elongated; and (9) fs1-3 usually absent or minute. For the pupae: (1) body stout; (2) head protuberances always present; (3) pronotal protuberances (if present), separated at bases of the pronotum, always wider than higher; (4) abdominal protuberance usually present, wide or round; (5) femora usually with a single fes; and (6) urogomphi short or vestigial. Keys to the larvae and pupae described here are provided. All the characters used for identification are illustrated by photographs or drawings. Biological and distribution data, including new information, are provided for all the species studied.

Morphology of immature stages, biology, and systematic position of the Violet seed weevil, Orobitiscyanea (Linnaeus, 1758) (Curculionidae, Conoderinae, Orobitiditae, Orobitidini)

The mature larva of the weevil species Orobitiscyanea (Linnaeus, 1758), one of only two Palaearctic members of the supertribe Orobitiditae, is re-described, while the pupa is described for the first time. The biology of this species was studied at two sites in Germany. It was reared from seed capsules of Violacanina L. (Violaceae), and feeding holes were observed on V.riviniana Rchb. Adults of Orobitiscyanea and O.nigrina Reitter, 1885, specialists of Viola, show a well-developed escape mechanism, to which contribute a smooth surface, a rounded, nearly spherical body shape, and a seed-imitating thanatosis behaviour. The molytine weevil Leiosomacribrum (Gyllenhal, 1834), the only other known weevil specialist of Viola in Europe, has a smooth surface, also, and is the most spherical species of the genus. The unique characters of the larva and pupa of Orobitiscyanea are discussed in regard to the systematic position of this taxon.

Description of immature stages of Gymnetron species (Coleoptera, Curculionidae, Curculioninae), with particular emphasis on the diagnostic morphological characters at the generic and specific levels

The immature stages of the following five Palaearctic Gymnetron species are described for the first time: G. tibiellum Desbrochers des Loges, 1900, G. veronicae (Germar, 1821), G. rotundicolle Gyllenhal, 1838, G. melanarium (Germar, 1821), and G. villosulum Gyllenhal, 1838. These species belong to four different groups previously established according to a phylogenetic analysis: the first two belong to the G. veronicae group and the other three to groups respectively bearing their name (G. rotundicolle, G. melanarium, and G. villosulum groups). All these species exhibit several diagnostic characters distinguishing them from each other. Some characters that can be used to separate Gymnetron from other genera in the tribe are also suggested. Three highly significant characters for the larvae and three for the pupae were identified. For the larvae they are: (1) labial palpi with single palpomeres, (2) all spiracles unicameral, and (3) epipharynx with a single pair of mes or none at all. For the pupae they are: (1) the pronotum with prominent pronotal protuberances, (2) abdominal segment VIII with a conical abdominal protuberance dorsally, and (3) very short or even reduced urogomphi. The species studied here are compared with those Gymnetron species already known and with other genera in the tribe Mecinini. Keys to the larvae and pupae described here are provided. All the characters used for identification are illustrated by photographs or drawings.

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 Gültekin, Diotti and Caldara, 2019 and R. conicus (Frölich, 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.

Abstract

Mature larvae and pupae of Lachnaeus crinitus Schoenherr, 1826 and Rhinocyllus alpinus Gültekin, Diotti and Caldara, 2019 and pupae of R. conicus (Frölich, 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.

Description and biological notes of the larva of Cionus olivieri Rosenschoeld, 1838 (Coleoptera, Curculionidae), with a comparison with other species of the tribe Cionini

The mature larva of Cionusolivieri Rosenschoeld, 1838 is described and illustrated in detail for the first time. It is compared with those known from the same genus and other genera in the tribe Cionini and with those of the hypothesized sister tribe Mecinini in the Curculioninae. The larvae of Cionus have three distinctive diagnostic features: the reduced number of setae on the epicranium (only two or three des and one or two fs) and on the epipharyngeal lining (only two als, two ams, and no mes); i.e., distinctly fewer than the most frequent number of setae in weevils, and mandibles dentate or angulate internally near the base. If considered together with Stereonychus Suffrian, 1854, the other genus of Cionini with larvae studied in detail, it is preliminarily suggested that mature larvae of this tribe might be characterized by six main diagnostic features: (1) labial palpi one-segmented, (2) labral rods absent, (3) pedal areas swollen to form large lobes or prolegs, (4) mandible with sharp apical teeth, (5) reduced number of fs on frons, only one or two fs, and (6) reduced number of epipharyngeal setae (two or three als and two or three ams, but no mes). It was noticed that C.helleri Reitter, 1904 from Japan, a very distinct species in the genus for some characters of the adult, also possesses distinctive characters in the larva which are uncommon among known cionines. New biological data on C.olivieri with the discovery of its host plant, Verbascumsongaricum (Scrophulariaceae), in central Asia are also reported.