Environmental risk assessment of exotic natural enemies used in inundative biological control

In the past 100 years many exotic natural enemies have been imported, mass reared and released as biological control agents. Negative environmental effects of these releases have rarely been reported. The current popularity of inundative biological control may, however, result in problems, as an increasing number of activities will be executed by persons not trained in identification, evaluation and release of biological control agents. Therefore, a methodology for risk assessment has been developed within the EU-financed project 'Evaluating Environmental Risks of Biological Control Introductions into Europe [ERBIC]' as a basis for regulation of import and release of exotic natural enemies used in inundative forms of biological control (i.e. not in 'classical biological control' though some of the same principles and approaches apply). This paper proposes a general framework of a risk assessment methodology for biological control agents, integrating information on the potential of an agent to establish, its abilities to disperse, its host range, and its direct and indirect effects on non-targets. Of these parameters, estimating indirect effects on non-targets will be most difficult, as myriads of indirect effects may occur when generalist natural enemies are introduced. The parameter 'host range' forms a central element in the whole risk evaluation process, because lack of host specificity might lead to unacceptable risk if the agent establishes and disperses widely, whereas, in contrast, a monophagous biological control agent is not expected to create serious risk even when it establishes and disperses well. Drawing on published information and expert opinion, the proposed risk assessment methodology is applied to a number of biological control agents currently in use. These illustrative case histories indicate that the risk assessment methodology can discriminate between agents, with some species attaining low 'risk indices' and others scoring moderate or high. Risk indices should, however, not be seen as absolute values, but as indicators to which a judgement can be connected by biological control experts for granting permission to release or not.