Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 39 - Molytini (Insecta: Coleoptera: Curculionidae: Molytinae) - Popular Summary

Craw, RC 1999. Molytini (Insecta: Coleoptera: Curculionidae: Molytinae). Fauna of New Zealand 39, 68 pages.
( ISSN 0111-5383 (print), ; no. 39. ISBN 0-478-09325-X (print), ). Published 4 Feb 1999

Popular Summary

These flightless weevils are some of the largest beetles in New Zealand, and they are some of the largest members in the world of their tribe Molytini. Adult speargrass weevils (genus Lyperobius) can range in colour from a red-brown to black, and many species have elegant white stripes on their backs, whereas adult karo and knobbled weevils (genus Hadramphus) are predominately dark brown with triangular or rounded tubercles on their sides and backs.

This study redescribes the twelve known species and provides descriptions of eight new speargrass weevils. How to identify these weevils is covered in detail, and there is a key to the known and new kinds. Habitus drawings of these weevils, as well as detailed illustrations of key external and internal features, are provided.

As the popular name speargrass weevil implies, adults of most species feed on the rigid spiky leaves and large flowering heads of speargrasses or spaniards (taramea), and they are sometimes also found on kopoti. Grubs of most species feed on roots and the growing leaf crown of these members of the carrot family (Apiaceae), whereas the karo weevil grubs bore in the trunks of karo trees on the Poor Knights Islands.

These weevils are known to occur in insular habitats from the subtropical Poor Knights Islands off the Northland coast, to the isolated Chatham Islands in the east, and the cold subantarctic Snares Islands in the south. They are most numerous and diverse in the South Island mountains, with maximum species diversity in West Otago and Fiordland.

An attempt to reconstruct the genealogy of these weevils is presented. Using this genealogy as a basis, the ecological and biogeographic history of their divergence in New Zealand is estimated. It is suggested that they are an old group, of at least 65 million years duration in Aotearoa, descended from a widespread ancestral complex of coastal, insular, lowland, and mountainous sites that have long been conspicuous features of our country.

These weevils are generally considered in New Zealand conservation biology as threatened species that are highly vulnerable to the combined impact of rodent predators and habitat modification. One species appears to have become extinct since European settlement. Insect ecologists who have made detailed studies of the knobbled weevil consider that they are good indicators of whether there are rats on an island.

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