Endemic biodiversity, natural enemies, and the future of biological control

Abstract

In recent public comment on proposed introductions for biological control of weeds in New Zealand, the issues of dilution of endemic biodiversity and homogenization of the fauna, have been raised as a reason for not introducing biological control agents. Although the impact of biological contol agents can be shown to be minimal in this process, the issue of homogenization appears to be gaining currency with government agencies and regulators. The main current causes of homogenization of the fauna and flora in New Zealand, and probably in most other countries, come from the purposeful introduction of plants for horticultural and other purposes, often with minimal assessment of their weediness, followed by their subsequent naturalization, and the accidental introductions of insects and other invertebrates. In New Zealand, naturalized alien plant species already outnumber native species and adventive insects are estimated to comprise 13% of the insect fauna. Only about 2.5% of all exotic insects have been introduced for biological control purposes. Up to the present, 20 carefully screened, host specific, species of insects have been established for biological control of weeds. These represent less than 1% of the exotic insect fauna. Recent developments in the regulatory environment outside New Zealand, suggest that the issue of global homogenization of the fauna and flora is also being considered in other jurisdictions, and has the potential to place severe limitations on the practice of classical biological control, even though the contribution of biological control agents to the process is almost negligible in most places.