Ingeniro Ambiental

PERSPECTIVES
or how this interaction might influence the dynamics of nontarget species. Thus, although essentially a preliminary test, screening against nontargets provides little indication of potential impacts beyond a basic categorization of host range. Another major defence of the biocontrol lobby regards the way in which biocontrol programmes are frequently initiated – biocontrol is oftenconsidered as a last resort after other control options have proven unsatisfactory14. Under such a ‘firefighting’ attitude, opportunities for exhaustive evaluation studies are significantly reduced. This is partly because the costs of maintaining the status quo and delaying control activities are themselves often great. For example, data from a recent programme to control the ensign scale (Ortheziainsignis) attacking gumwood (Commidendrum robustum) on the island of St Helena indicate that all relict field populations of this endemic tree species would have been lost within two to three years had biocontrol workers not intervened15. Under these conditions, even the critics concede that biocontrol should be considered. Unfortunately, this creates a paradox because these extreme conditionsare far from desirable in the first place. Surely we can do better than this in evaluating risks and benefits?

Biocontrol – risky but necessary?
M.B Thomas A.J. Willis
There is currently much debate concerning the risks of biological control and the potential harmful effects of nonindigenous species introduced for controlling exotic pests. Biocontrol advocates generally appear reluctant toaccept the possibility that there could be side-effects associated with biocontrol, often refuting evidence of harmful effects and suggesting that current practices are sufficient to minimize any risks. The biocontrol critics, on the other hand, although eager to provide evidence to the contrary, appear reluctant to propose any detailed, constructive criticisms or workable solutions. Here, we attemptto put these arguments into context, and suggest some directions for future research that might help to resolve some of the problems.
M.B. Thomas and A.J. Willis are from the Leverhulme Unit for Population Biology and Biological Control, International Institute of Biological Control and NERC Centre for Population Biology, Imperial College, Silwood Park, Ascot, Berks, UK SL5 7PY(m.thomas@cabi.org); A.J. Willis is currently at the CRC for Weed Management Systems, CSIRO Division of Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia (tony.willis@pi.csiro.au).

B

iocontrol, the use of living organisms as pest control agents, is now an important alternative to the use of chemical pesticides and, therefore, a potential means of reducing pesticide use and its undesirable effects onhuman health and the environment. As a scientific discipline, biocontrol against agricultural and environmental pests dates back over 100 years. Although a powerful tool, concerns are increasing over the risks of biocontrol to natural biodiversity1–6, in particular that of classical biocontrol (the introduction of exotic natural enemies to control exotic pests). Simberloff and Stiling7,8 haveproduced two comprehensive reviews cataloguing potential adverse environmental effects from species introduced for biological control, and two recent articles in Science9,10 have further highlighted the issue. The basic theme arising from this literature is that numerous biocontrol introductions have adversely affected nontarget native species and that insufficient consideration is paid to thesepotential risks in biocontrol programmes. One of the major rebuttals from the biocontrol lobby is that many of the purported problems with biocontrol derive from early programmes, where procedures were less regulated and the risks less appreciated. Certainly, current biocontrol practices and legislation make it extremely unlikely that early errors of introducing generalist vertebrate predators, such...