Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 29 - Cryptorhynchinae (Insecta: Coleoptera: Curculionidae) - Popular summary

Lyal, CHC 1993. Cryptorhynchinae (Insecta: Coleoptera: Curculionidae). Fauna of New Zealand 29, 308 pages.
( ISSN 0111-5383 (print), ; no. 29. ISBN 0-478-04518-2 (print) ). Published 02 Dec 1993


In isolation and in the absence of many of their natural enemies members of this beetle family have multiplied and diversified. The weevils are a group of beetles that have more known species worldwide - some 50 000 so far in the family Curculionidae - than any other family of organisms. In terms of weevil abundance and diversity, New Zealand is one of the richest countries in the world. In the absence of many of their natural enemies and competitors, members of the family have multiplied and diversified to an extraordinary degree. One of the largest subfamilies of weevils are the Cryptorhynchinae, of which in New Zealand some 250 species are known and many more await discovery.

Although there are so many cryptorhynchine weevils in New Zealand, they are mostly inconspicuous insects, and one rnight be forgiven for not being aware of them at all. However, even brief examination of native plants, or of the leaf-litter layer in native bush, will reveal large numbers of them.

Almost all weevils feed on living or dead plants as both adults and larvae. However, within a single species these two life stages do not necessarily feed on the same part of the plant, or even the same plants. Most of the New Zealand cryptorhynchine larvae feed on (or at least in) dead wood; whether they are digesting the wood itself, or fungi growing on it, is not known. While larger species will tunnel in quite thick branches and tree trunks, some of the smaller species will develop happily in leaf stalks. A few species are leaf-miners of growing plants as larvae.

Remarkably, while the larval food has been determined for many species, the food used by the adults has yet to be ascertained, although it is probably living leaves for a majority of species. Sadly, from the point of view of biological understanding, although an adult beetle may be found on a given plant species, this does not necessarily signify that the insect is feeding on that plant.

Perhaps best known of the New Zealand cryptorhynchines is the so-called 'elephant weevil', Rhynchodes ursus. This large insect is found all over the country, the larvae making tunnels in dead branches and trunks of such trees as kauri and southern beech. Many other Cryptorhynchinae tunnel in wood as larvae, and sometimes as adults. Perhaps the most significant of them economically are members of the tribe Psepholacini, 'pit weevils', particularly those in the genus Psepholax. Both adults and larvae of these insects make tunnels in the dead and dying wood of both native trees and exotics, including species of pine. Among the easiest to observe of the Psepholacini are members of the genus Strongylopterus, beetles up to 13 mm long which make round holes in pohutukawa branches and trunks. During the night the adult beetles will emerge from their burrows and move around over the bark.

Whilst these relatively large-bodied species can be collected from their host trees at any time, most New Zealand cryptorhynchines are small and inconspicuous insects, spending the daylight hours hidden in leaf litter or similar cryptic habitats, and becoming active at night.

Despite knowing more about the feeding habits of larvae than of adults, we know more about adult structure than that of the larvae, and our classification of cryptorhynchines is based on the adult form. Indeed, for many species the larvae and pupae have not been found or described. Thus identification guides may treat only the adults, as here. Some cryptorhynchine larvae are described in Fauna of New Zealand no. 28, 'Larvae of Curculionoidea', by Brenda May.