Conservation Biocontrol in Fragmented Landscapes: Persistence and Parasitation in a Host-Parasitoid Model

In the context of agricultural landscapes, conservation biocontrol practitioners attempt to secure and enhance the presence and effectiveness of natural enemies of insect pest species, for example parasitoids. Conservation biocontrol aims at maximizing both parasitoid persistence and parasitation rate. It is, however, still poorly understood how the amount, fragmentation and isolation of non-crop habitat of the host and its parasitoid affect persistence and parasitation rate. We developed a spatially explicit simulation model of a host and its specialized parasitoid and simulated their spatiotemporal population dynamics in virtual landscapes. We found that the total habitat amount in the landscape modulates the impact of fragmentation on parasitoid persistence. If habitat is abundant, parasitoid persistence decreases with fragmentation, whereas if habitat is scarce, persistence is highest at intermediate levels of fragmentation. In any case, persistence is best for intermediate levels of isolation. Parasitation rate, on the other hand, is negatively influenced by fragmentation and isolation regardless of the habitat amount. Our results suggest that in landscapes with abundant habitat, both parasitation rates and parasitoid persistence can be increased by arranging habitat to be as clumped as possible. However, if habitat is scarce, landscape management can optimize either parasitation rates or parasitoid persistence but not both simultaneously.