The distribution and habitat requirements of the large speargrass weevil (Lyperobius huttoni) and characteristics of host speargrass plants (Aciphylla squarrosa) and their vegetation associations

Abstract

The abundance and distribution of the endangered Speargrass Weevil (Lyperobius huttoni) on the South Coast of Wellington is determined and the key features of the habitats in which the weevil occurs are established, particularly the specific characteristics of host Aciphylla squarrosa plants and their vegetation associations. Comparison is made between the characteristics of Lyperobius host plants at the Seaward Kaikoura Ranges, South Island and the Wellington South Coast. Comparison of Aciphylla plants with and without weevils shows that weevils are more likely to be found on large Aciphylla plants, and on plants which are in flower or which have more than one crown. On the Wellington South Coast, weevils are more commonly found on Aciphylla plants in unstable environments, and where the host plant is not overgrown by other plant species. The current North Island distribution of Lyperobius huttoni is established through identification and mapping of weevil feeding sign. Population estimates derived from sign distribution and from a weevil tag-recapture survey both give a minimum population of approximately 135 individuals on the Wellington South Coast, though in over 12 months the total number of weevil sightings was only 39. Lyperobius huttoni is now limited to a single south coast site and the disjunct distribution at that site means it must be considered highly endangered. previous studies of Lyperobius huttoni are reviewed, and previous conservation efforts and the change over time in weevil status and vegetation characteristics at known weevil sites summarised. Observations of weevil activity, behaviour and sexual dimorphism are recorded and, together with the host plant and habitat preferences, are used in forming a management proposal for the conservation of L. huttoni on the Wellington South Coast, or for its translocation to a more secure island location.