Life cycle, behaviour and conservation of the large endemic weevil, Hadramphus spinipennis on the Chatham Islands, New Zealand

Abstract

Populations of the endangered weevil Hadramphus spinipennis (Coleoptera: Curculionidae), endemic to the New Zealand Chatham Is, were sampled five times from December 1993 to January 1997. All stages of its life cycle were closely associated with its host plant, the Chatham Is. endemic Aciphylla dieffenbachii (Apiaceae). Adult weevils were found throughout the year, predominantly on male A. dieffenbachii plants where they fed on foliage and flowers. Copulation took place from September to March, mostly on male flowers. Eggs were laid in the soil under host plants from September to April/May. The five larval instars fed on the roots, and pupation took place in the soil. In shadehouse studies, the shortest period from neonate to pupa was 147 days and pupation took less than 30 days. Field and laboratory data suggested that eggs laid early in spring developed into adults by early autumn, but that those laid in late summer overwintered as larvae and pupated the following spring. There is one extended generation a year. Occasionally, adult weevils could also be found on Pseudopanax chathamicum, but clearly preferred A. dieffenbachia in ‘choice feeding tests’. No larvae were found on the roots of P. chathamicum. To secure the long‐term survival of H. spinipennis, a third viable population is considered necessary. We suggest a survey of other islands for Hadramphus and/or the establishment of a third population.

Keywords:

• Hadramphus spinipennis
• Aciphylla dieffenbachii
• Chatham Islands.
• life history
• phenology
• behaviour
• conservation