On the taxonomy of Rhynchophora larvae: Adelognatha and Alophinae (Insecta: Coleoptera)

Authors


Summary.

Problems of phylogeny and adult classification as well as the need for identifying the numerous noxious species of short-nosed weevils in the larval stage, which is usually polyphagous and feeds externally on roots, and therefore identifiable only by taxonomic methods, have prompted this piece of research. Some of the subfamilies used in classifying adult short-nosed weevils are not reflected in larval taxonomy, but the current system for adults is probably not entirely natural.

A general discussion of morphology shows that pigmented ocellar spots are often present, but that ocelli with a cornea are exceptional. The antenna1 segments have disappeared, only some sensorial cones and the main sensorial appendage, which in Adelognatha is wider than long and dorso-ventrally compressed, being preserved. The mandibular cutting edge is toothed only in three systematically isolated groups. The terminology of the labial parts is discussed and “mentum” is accepted for the cardines region of the second maxillae. The chaetotaxy is amazingly similar in all forms but supplies important taxonomic characters, if not only the number of setae on a segment but their size and exact arrangement are used. On the eighth and ninth abdominal segments the number of setae is successively reduced, the second seta of the posttergnm being the first to disappear, and the first (i.e. the one nearest median line), or fourth the second. In very few genera increased numbers of setae or fissile ventral setae are found. The main seta of the spiracular area tends to be shifted caudad on the posterior segments. In many genera the apical abdominal segments show distinctive sclerotizations, three types of which are distinguished. In Maleuterpes a dorsal disc surrounded by a crown of setae is present, and a few other genera have bare flattened discs with a central pit onsome of theepipleurites.

Biology and breeding methods are treated together. Parthenogenesis is frequent, and males are often unknown. Apart from a few oligophagous genera the adults show feeding preferences for young leaves more than for definite species or systematic groups of plants, and are thus polyphagous. This combination of parthenogenesis, polyphagy, and, probably frequent reproduction in several successive years renders i t easy for some species to establish themselves wherever they may be introduced. Eggs are deposited between, and glued to, two adjacent surfaces in the majority of species (Rrachyderes-type), but Sitona, Alophus and some others drop eggs singly and a t random (Sitona-type). The latter become black after one to two days, both types and transitions occurring within Otiorrhynchus. For oviposition of the Brachyderes-type “pleated” strips of blotting paper can be used conveniently to receive the eggs, and this may indicate a possibility for control. The size of the eggs in proportion to the adult is discussed. At room temperature larvae hatch after ten to thirty-two days, Sitona and some Otiorrhynchus requiring only a short incubation period, Barynotus and Alophus a long one. The young larvae of all but a few genera drop to the ground and burrow into the soil in search of roots. The first instar is almost always characterized by a clavate tip to seta w; egg-bursters are not present, except perhaps in Calomycterus. Five to ten larval instars have been ascribed to Adelognatha.

The main part of the paper is systematic and contains keys to the principal groups of weevil larvae, to three genera and species of Alophinae and to fifty genera of Adelognatha. Where several species are available or have been suitably described, the distinguishing characters are set out, mostly in keys, 102 species (among them twelve species of Otiorrhynchus and eight of Sitona) being characterized. Detailed descriptions of the fifty-three genera and short descriptive notes on the species are appended.

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