Predicting risk from adventive herbivores to New Zealand indigenous plants

Biosecurity organisations need to assess the risk to their country's indigenous flora from invertebrate herbivores that may invade and establish. Some of the more than 600 known adventive herbivores in New Zealand attack indigenous plants. From an extensive review of the literature the numbers and proportion of each major taxonomic group of adventive Acari and Insecta herbivores in New Zealand and those attacking indigenous plants were tabulated along with their host range, which was categorised as: polyphagous; oligophagous (to a plant family); oligophagous (to a genus); monophagous or unknown. Results showed that different taxa of adventive herbivores pose different levels of risk to indigenous plants. For example, Hemiptera were the most numerous group feeding on indigenous plants, while no herbivorous Hymenoptera, Cecidomyiidae (Diptera) or Eriophyoidea (Acari) feed on indigenous plants. The breadth of host range is also important, with a higher proportion of polyphagous species attacking indigenous plants, though for Lepidoptera, oligophagous (family) species posed the highest risk. The predictive value of additional risk criteria could be tested on the adventive herbivores already in New Zealand.