Acalles (Tolpiacalles), Stüben & Astrin, 2010

Stüben, Peter E. & Astrin, Jonas J., 2010, Molecular phylogeny in endemic weevils: revision of the genera of Macaronesian Cryptorhynchinae (Coleoptera: Curculionidae), Zoological Journal of the Linnean Society 160 (1), pp. 40-87 : 62-63

TOLPIACALLES STÜBEN & ASTRIN SUBGEN. NOV.

( FIG. 7A–E )

The only species of this monotypic subgenus is S. tolpivorus , which has been described only recently ( Germann & Stüben, 2006). It is monophagous on Tolpis cf. proustii , a member of the daisy family ( Asteraceae ). It is probably a plant endemic to La Gomera ( Germann & Stüben, 2006). We place this taxon in the genus Silvacalles as well. On the one hand the species has a slightly different ‘goblet-like’ structure of the internal sac, a character that discriminates it from all other Macaronesian Cryptorhynchinae . On the other hand, the habitus and preference of habitat leave no doubt that it belongs in this genus (it is recovered as sister to Silvacalles s.s. with near-total support). Thus again the attention of the taxonomist is focussed on the biology and ecology of the higher taxa presented (cf. following section).

Differential diagnosis: See below (‘Key to the genera and subgenera of Macaronesian Cryptorhynchinae’). Biology and ecology: All species of Silvacalles live in the shady and moist laurel forest of the thermo-Canarian and thermo-Madeiran belt. Silvacalles species are not found associated with more or less succulent plants as are, for instance, the specialized taxa of Crassulaceae growing in crevices of rock faces or Kleinia neriifolia (Asteraceae) of the coastal succulent belt (belonging to the plant association of the Kleinio–Euphorbietea). Instead, Lauraceae (for Silvacalles s.s.) and dendriform Fabaceae (for the subgenus Tagasastacalles ) are the host plants of these Cryptorhynchinae that prefer very moist habitats stretching across the belts of the laurel forest and the pine forest. There is another species that belongs to the group of taxa inhabiting the moist trade wind zone (including the forest areas and the upper succulent belt): the contrastingly coloured S. nubilosus ( Fig. 36A ), which is monophagous on Ixanthus viscosus Griseb. ( Fig. 36C ), a plant of the gentian family ( Stüben & Germann, 2005: 70), and – conspicuous through a differing endophallus – S. (Tolpiacalles) tolpivorus ( Fig. 7A ), which lives on Tolpis cf. proustii Pit. on La Gomera ( Fig. 7C ).

This also applies to the species of the subgenus Tagasastacalles . The very variable small tree Chamaecytisus proliferus (‘tagasate’, Fabaceae ), which belongs to the natural vegetation of the laurel forest and the pine forest (‘bosque mixto’) has been a cultivated plant of the western Canary Islands for centuries ( Fig. 8C ). The green shoots of the regularly pollarded trees are used as fodder. Today its use provides the only kind of protection for the species of Tagasastacalles , which have become very rare in their natural habitat – the remains of the endangered laurel forest (cf. Stüben, 2008a). The current populations of these cryptorhynchine species in the ‘treeless’ plantations of Tagasaste, e.g. on El Hierro should not result in the false notion that Tagasastacalles is a subgenus alien to the Canarian laurel (and pine) forest. This type of forest is almost extinct on El Hierro.

It is difficult to distinguish the habitat preference of the large species of Dendroacalles s.s. and the very small species of Silvacalles s.s., which both inhabit the laurel forest. However, many species of Silvacalles (e.g. S. lepidus from La Palma, S. cedroensis from La Gomera and S. lunulatus from Madeira) inhabit the margin of the laurel forest or its substitute vegetative associations. Specimens can be collected through beating dead, thin twigs and branches of especially Laurus spp. ( Fig. 6C ) or of Myrica (see also Kulbe, 2000). In contrast to this, the species of Dendroacalles s.s. inhabit exclusively the (undisturbed) primary forest ( Stüben, 2007b; Fig. 3C ).

Etymology: The name Silvacalles refers to the shady and moist laurel forest inhabited by this cryptorhynchine genus.

Distribution: Endemic to the western Canary Islands and (with only one species) on Madeira.

Figures

Figure 36. A, Silvacalles nubilosus (in dorsal view). B, aedeagus in ventral view (left), endophallus (right). C, Ixanthus viscosus Griseb., the host plant of S. nubilosus.

Figures 2–22. Morphological, biological, and ecological comparison of the genera and subgenera of Macaronesian Cryptorhynchinae along with the respective sections of the tree; (TS) = type species. Figures 4E and 5E show a section of the tree that results when 16S sequences for Aeoniacalles aeonisimilis* and Dendroacalles euphorbiacus* are excluded.