A functional overview of conservation biological control

Conservation biological control (CBC) is a sustainable approach to pest management that can contribute to a reduction in pesticide use as part of an Integrated Pest Management (IPM) strategy. CBC is based on the premise that countering habitat loss and environmental disturbance associated with intensive crop production will conserve natural enemies, thus contributing to pest suppression. The abundance and diversity of natural enemies increases in response to a variety of conservation measures, including plant and habitat diversification, a reduction in cropping intensity, and increased landscape complexity. However, the response of natural enemy populations to conservation measures is not consistent; often it fails to translate into pest suppression or improved crop yield, and is seldom utilised in commercial crop production settings. CBC is a complex strategy drawing on a number of ecological and behavioural processes, operating at multiple scales, and mediated by management actions that are, potentially, targeted at a wide range of pest organisms. Given this inherent complexity, it is not surprising that the scientific understanding of CBC is incomplete, or that the design and adoption of reliable CBC prescriptions have proved elusive. To tackle this, we consolidate existing knowledge of CBC using a simple conceptual model that organises the functional elements of CBC into a common, unifying framework. We identify and integrate the key biological processes affecting natural enemies and their biological control function across local and regional scales, and consider the interactions, interdependencies and constraints that determine the outcome of CBC strategies. Conservation measures are often effective in supporting natural enemy populations but their success cannot be guaranteed; the greatest limitation to the development of effective CBC is due to a failure to adequately direct biological control services to achieve suppression of the target pests. By considering the performance of these and other components of CBC within the context of an integrated system, we believe that the limiting factors can be identified, and removed, allowing effective CBC strategies to be implemented.