Elytro-tergal stridulation in weevils (Insecta: Coleoptera: Curculionoidea)

Many Curculionidae, Scolytidae and Platypodidae stridulate by rubbing a plectrum on tergite VII against a subapical file on the elytral underside. The file on the right elytron may be smaller than that on the left, or absent; on either elytron it usually comprises a series of parallel ridges. The plectrum generally consists of one or more pair of setiferous tubercles, although other structures are sometimes employed. This stridulatory system (‘type 1’) is found in members of 14 curculionid subfamilies and in Scolytidae. Platypodidae have a similar and probably homologous organ, although the morphology of the file differs somewhat from that found elsewhere and the plectrum is a simple flange. Within Curculionidae three other elytro-tergal stridulatory systems have been found. Firstly, in some Cossoninae and Molytinae, the file is a row of tubercles on tergite VII and the plectrum is a ridge on the elytron (‘type 2’); this is newly reported here. Secondly, females of Ithyporini, some Camptorhinini and some Cryptorhynchini have part of the wing binding patch on tergite VII modified to act as a file, with a plectrum on the elytra (‘type 3’). Thirdly, some Amycterinae have a file of ridges on tergite VII and a plectrum on the elytra (‘type 4’), apparently an autapomorphy of a restricted group of species. In addition, some Curculionidae have a plectrum on the hind femur and a file on the abdominal sternum (some Cryptorhynchinae) or elytron (some Otidocephalinae). Scolytidae have at least three other stridulatory organs: two on the head and one involving the elytra and sternum VIII. Some systematic conclusions are drawn: the clear homology of the type 1 structures in Scolytidae and the majority of the stridulating Curculionidae indicates that the Curculionidae is paraphyletic with respect to the Scolytidae; Scolytidae should therefore be treated as a subfamily of Curculionidae. The structure of the platypodid file and plectrum provide equivocal information and do not aid resolution of the phylogenetic placement of this family. Monophyly of some Ithyporini and Camptorhinini is suggested by the distribution of type 3, but there is insufficient evidence to demonstrate paraphyly of the Cryptorhynchini. The distribution of type 2 does not indicate monophyly of the Cossoninae and Molytinae since the structures in the two are almost certainly homoplastic. All known records of elytro-tergal stridulatory organs in the Scolytidae, Platypodidae and Curculionidae are listed.