Risks of biological control for conservation purposes

Striking successes in classical biological control in agriculture and rangelands engender great interest in using this technology for wildlands conservation and environmental purposes. However, well known unintended consequences of several biological control projects have led to concern that possible environmental benefits do not warrant inherent risks. Four risks demand attention: (1) direct attack on non-targets; (2) indirect effects on non-targets; (3) dispersal of a biocontrol agent to a new area, either autonomously or with deliberate or inadvertent human assistance; (4) changed relationships between a control agent and a native species, particularly as generated by global climate change. Procedures for assessing risk of direct attack on non-targets by phytophagous biological control agents have steadily improved and an expanded centrifugal phylogenetic approach appears to provide adequate insight. Direct non-target impacts by entomophages are more difficult to predict. Myriad possible indirect effects, some subtle but nonetheless important, present a far greater challenge, and techniques of assessing such risks are in their earliest infancy and not as closely regulated. Despite prominent examples in both the general invasion literature and that for biological control, the risk that a species, once introduced, will spread beyond its intended range, and the consequences of such spread, are not routinely treated by risk assessors. This phenomenon deserves far more attention. Global changes—especially climate change—can lead to modified ranges and efficacies of introduced biological control agents and their targets. Although many examples show that climatic niches are often not conserved, an important first routine step would be to combine climatic envelopes with general circulation models for predicted future climates. Finally, actions based on a risk assessment are always implemented in a framework of predicted costs and benefits, which are inevitably asymmetric, so it is critically important that all stakeholders, including conservationists, participate in the decision-making process.