Abstract
The mature larva of Cionus olivieri 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, Verbascum songaricum (Scrophulariaceae), in central Asia are also reported.
Highlights
The tribe Cionini Schoenherr, 1825 in the subfamily Curculioninae Latreille, 1802 (Curculionidae) currently comprises seven genera occurring predominantly in the Palearctic region (Alonso-Zarazaga et al 1999)
The aim of the present study is to describe the larva of C. olivieri in detail for the first time, in order to provide further characters for the identification of this taxon, and to compare this larva with the larvae of other species of Cionus, Cionini, and the apparent sister tribe Mecinini Gistel, 1848
The descriptions of four species were partly useful for comparison ‒ Cionus helleri Reitter, 1904 (Lee and Morimoto 1988b), C. hortulanus (Geoffroy, 1785) (Grandi 1929), C. olens (Fabricius, 1792), and C. scrophulariae (Linnaeus, 1758) (Grandi 1938) ‒ whereas the descriptions of another four ‒ C. alauda (Herbst, 1784), C. tuberculosus (Scopoli, 1763), C. olivieri, and C. thapsus (Fabricius, 1792) (Scherf 1964) – were almost completely useless because they were very lacking in details
Summary
The tribe Cionini Schoenherr, 1825 in the subfamily Curculioninae Latreille, 1802 (Curculionidae) currently comprises seven genera occurring predominantly in the Palearctic region (Alonso-Zarazaga et al 1999). Based on the Palearctic species, Caldara and Korotyaev (2002) delimited the tribe as a monophyletic group identified by several synapomorphies in character states of the head, antennae, abdomen, and genitalia. They analyzed the phylogenetic relationships of the genera, based mainly on the presence of a rostral prosternal canal and tibial unci. After the revision of the Palearctic species of Cionus based on a preliminary study of species of other regions, Košťál and Caldara (2019) realized that some genera seem to be paraphyletic and that most of the characters currently used to distinguish them are conflictive and need to be reassessed. The study of immature stages appears very important to provide additional morphological evidence
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