Optimal release strategies for biological control agents: an application of stochastic dynamic programming to population management

1. Establishing biological control agents in the field is a major step in a ny classical biocontrol programme, yet there are few general guidelines to help the practitioner decide what factors might enhance the establishment o f such agents. 2. A stochastic dynamic programming (SDP) approach, linked to a metapopulat ion model, was used to find optimal release strategies (number and size of releases), given constraints on time and the number of biocontrol agents av ailable. By modelling within a decision-making framework we derived rules o f thumb that will enable biocontrol workers to choose between management op tions, depending on the current state of the system. 3. When there are few well-established sites, making a few large releases i s the optimal strategy. For other states of the system, the optimal strateg y ranges from a few large releases, through a mixed strategy (a variety of release sizes), to many small releases, as the probability of establishment of smaller inocula increases. 4. Given that the probability of establishment is rarely a known entity, we also strongly recommend a mixed strategy in the early stages of a release programme, to accelerate learning and improve the chances of finding the op timal approach.