The Dynamics of Multiparasitoid-Host Interactions

In this paper, we have explored the dynamics of some simple multiparasitoid models, concentrating on the factors affecting coexistence and equilibrium levels. As a prelude, a one parasitoid-one host system is examined since this provides the basic submodel for parasitism that is used throughout. This is followed by a system with two parasitoid species attacking the same host species, a system with facultative hyperparasitoids, and finally one with hosts, parasitoids, and hyperparasitoids. In each case, the conditions permitting the three species to coexist are examined and, by introducing a host rate of increase that is density dependent, we also show the extent to which parasitism can depress the host equilibrium below its carrying capacity. The results are discussed within the context of biological control. We conclude that the practice of multiple parasitoid introductions, and the use of parasitoids with high searching efficiency and a marked ability to seek out patches of high host density, are sound strategies for maximizing the depression in the host equilibrium populations and for ensuring that they remain locally stable. While obligate hyperparasitoids will always lead to an increase in host equilibria, truly facultative hyperparasitoids can be classed with other primary parasitoids as candidates for use in multiple introduction programs.