Pre-emptive Selection of Natural Enemies of Invasive Pests

Pre-emptive biological control involves the evaluation of the benefits and risks of the natural enemies of an invasive pest in advance of its arrival, allowing the swift approval and deployment of the natural enemies in an emergency.

Invasive species cause enormous damage in both agriculture and the environment. The release of natural enemies or biological control agents (BCAs) from the area of origin of a pest can be a sustainable control solution.

As a rule, studying the biological basis of BCAs, clarifying their potential risks and obtaining final regulatory approval before their use can take several years. If such programmes are not initiated until the arrival of the pests, valuable time is lost during which damage accumulates. It is therefore important to be able to predict which invasive species could pose a problem in future, and how these can be controlled.

Guidelines for evaluating potential BCAs

An international consortium including Agroscope has developed guidelines for evaluating whether the natural enemies of a pest are suitable for its pre-emptive biological control. The process involves investigating the gravity of the threat posed by the pest and the likelihood of an invasion, and determining the existence or otherwise of sufficiently effective natural enemies. Key considerations here are:

• the climatic suitability of the organisms for the target area;
• their reproductive and dispersal potential;
• their synchrony with the target pest.

Climate modelling can be particularly helpful in this regard.

Clarifying the risks to native species

To ensure biosecurity, there must also be sufficient information available on the specificity of the natural enemy, as well as the risk posed to native species as potential prey, competitors or hybridisation partners of the BCA. Unresolved safety issues can be resolved in bioassays in the country of origin or in the target country under quarantine conditions.

Practicality criterion

Finally, practical hurdles must be identified. These may consist in limited opportunities for obtaining and breeding both the BCA and the potential non-target organisms for biosecurity experiments. Suitable premises for handling exotic organisms and the regulatory environments for the importation, keeping and release of exotic BCAs are also important.

Case studies

Various case histories in the European context were then evaluated using the guidelines that had been developed. Natural enemies of the potato psyllid and the emerald ash borer [photo] were deemed suitable in principle. In both cases, however, biosafety and establishment ability issues have yet to be clarified conclusively.

By contrast, a natural enemy of the two-lined chestnut borer was rated as unsuitable because it is very difficult to breed, and there is currently no chance of obtaining sufficient individuals to investigate biosafety or conduct releases.