Rhadinocyba Faust, 1889

Wanat, Marek & Munzinger, Jérôme, 2012, Biology of the Apionidae (Coleoptera: Curculionoidea) in New Caledonia, a preliminary report, Zootaxa 3554, pp. 59-74: 63

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Rhadinocyba Faust, 1889


Genus Rhadinocyba Faust, 1889 

This genus is currently the second largest genus of Apionidae  in New Caledonia, approximating 30 species in the collected material. As suggested by Wanat (2001) and confirmed in further field studies, it encompasses two distinct species groups: the more speciose Rh. singularis  -group, with apparently all members living on Hibbertia  species ( Dilleniaceae  ), and the enigmatic Rh. sulcifrons  -group, with still unknown host associations and most of the members known from single, incidentally collected specimens.

Rhadinocyba singularis (Wencker, 1863)  is by far the commonest species, widespread throughout Grande Terre. It was found on many species of Hibbertia  , usually on H. lucens  , but occasionally also on H. pancheri  , H. trachyphylla  , H. altigena  , H. baudouinii  , H. comptonii  and other, unidentified species. Eggs are laid probably directly into ovaries in open flowers or through the base of opening bud ( Figs. 4, 5View FIGURES 1 – 8. 1). Infested buds are lost, probably soon after the larvae hatch (no larvae were ever found in buds remaining on the plant), so further development likely takes place in fallen buds laying on the ground and shaded by the plant ( Fig. 1View FIGURES 1 – 8. 1). Larvae of Rh. singularis  were found occupying ovaries ( Figs. 2, 3View FIGURES 1 – 8. 1) and feeding on developing seeds inside the aborted flower buds of H. lucens  [1, 2]. Older larvae may leave the ovary chamber through gnawed holes and make “excursions for feeding to the flower bud inside. Freshly emerged beetles were regularly observed through a long period between 27 th October and 15 th January, hence two generations per season are most likely. Beetles are frequently seen on flowers, piercing the ovaries and gnawing small round holes in petals.

The mode of development for Rh. singularis  and its several close allies is likely not common for all members of Rhadinocyba  , especially those living on Dilleniaceae  . A number of these species are tiny beetles, with body length much less than 2.0 mm, and they have never been observed on Hibbertia  flowers or buds, though sometimes are abundantly beaten from the foliage of flowering Hibbertia  plants. Some teneral specimens of these minute species were collected in May and August, so out of flowering season of the host plants, therefore, their larvae are expected to feed in leaf tissue, stalks or thin twigs, rather than flower buds.

Members of the Rh. sulcifrons  -group, usually much greater than 3 mm in body length, were collected in forested sites, but never from the Dilleniaceae  . Two females of an undescribed species were once beaten from a small Cryptocarya  sp. cf. guillaumini  tree ( Lauraceae  ) [3], while one female cf. Rh. sulcifrons Wanat, 2001  was collected from Spiraeanthemum meridionale (Hoogland) Pillon  ( Cunoniaceae  ) in the Koghi forest [4]. Both records have not been confirmed by further findings despite several attempts to sample the same plant species.