White butterfly (Pieris rapae) and the white rust Albugo candida on Cook’s scurvy grass (Lepidium oleraceum)

Once widespread, Cook’s scurvy grass (or nau, Lepidium oleraceum) is now confined to a few offshore populations. Classed as nationally endangered by the New Zealand Department of Conservation, populations of Cook’s scurvy grass are threatened by a number of factors, including introduced herbivorous insect species such as the white butterfly (Pieris rapae) and white rust infection caused by the oomycete Albugo candida.

Impacts of exotic invertebrates on New Zealand’s indigenous species and ecosystems

Biological invasions have significantly affected New Zealand’s native species and ecosystems. Most prominent are the effects of exotic mammals and plants, whereas few invertebrate invasions are known to have major effects on native ecosystems. Exceptions are the well-known cases of Vespula wasps in Nothofagus forest ecosystems and Eriococcus scale insects in Leptospermum shrublands. This limited impact is surprising because over 2000 exotic invertebrates have become established in New Zealand, among them many pests of exotic crop plants.