Simple models of host-parasitoid interactions often predict that local populations will exhibit unstable cycles, leading to the extinction of one or both species.  Several mechanisms have been posited to stabilize host-parasitoid interactions, so that persistent cycles or stable equilibria become possible.  Heterogeneity of parasitoid attacks is one such mechanism, but most work on the effects of heterogeneity is theoretical and incorporates it in a phenomenological way, without a clear biological mechanism.  I have found that the rate at which larvae of the bean beetle Callosobruchus maculatus are attacked by a pteromalid parasitoid depends on the type of bean in which the larvae are feeding.  Some species of beans provide partial structural refuges for beetle larvae, where the parasitoids are less successful.  By manipulating the diversity of bean resources for the beetle population, I manipulated the heterogeneity in parasitoid attack rates, and then followed host and parasitoid population dynamics over time. 

Results/Conclusions

When reared in the lab on a single type of bean, the beetle and parasitoid population dynamics are unstable, and no populations persist more than a few generations.  In contrast, host and parasitoid populations that are provided with a mixture of resource types may coexist for at least tens of generations (currently approaching thirty generations in the lab, over three years).  Simple models of this host-parasitoid interaction, parameterized with data from independent experiments on beetle and wasp recruitment, suggest that the heterogeneity provided by a diversity of beans is sufficient to explain the stability (or lack thereof) of these laboratory populations.  I also use data from these time series of host-parasitoid population dynamics to motivate models of host-parasitoid population dynamics that incorporate population-level effects of beetle behaviors.  These models, together with data from a literature review, suggest that resource diversity is a common stabilizing influence on population dynamics in tri-trophic systems.