A DYNAMIC REFUGE MODEL AND POPULATION REGULATION BY INSECT PARASITOIDS

1. The population dynamic effects of refuges, which hosts enter and le ave by diffusive movement, in host-parasitoid interactions are explore d using simple models in continuous time. 2. This type of refuge has a stabilizing effect on a host-parasitoid interaction, which is contrar y to the implications of some previous models. 3. Stability can be exp lained by considering how depletion processes lead to a refuge proport ion (proportion of hosts protected at a given instant) that increases as parasitoid density increases. This effect is synonymous with pseudo interference in the context of the model. 4. Very high rates of moveme nt of host larvae largely destroy this stability process. Stability is greatest at intermediate levels of movement. 5. Density-dependent hos t movement can alter the effect of these refuges such that they are ei ther mon stabilizing, or tend to destabilize, the dynamics of host-par asitoid systems, depending on the type of density dependence assumed. The conclusion that intermediate movement rates are likely to generate stability with this general type of refuge is not altered in the pres ence of any type of density dependence, unless the density dependence is at levels which we consider unrealistically high and unlikely to be encountered in nature. 6. It is the assumption that larvae do not mov e into the refuge prior to becoming vulnerable to parasitism that ensu res top-down population control in the model, Thus, parasitoids attack ing very early instars make good candidates for biological control whe n faced with a structural refuge.