Complexity, Evolution, and Persistence in Host-Parasitoid Experimental Systems With Callosobruchus Beetles as the Host

Experimental laboratory systems of bruchid beetles, Callosobruchus in particular, and their parasitoids have been used as models to study population dynamics of single species and host-parasitoid interactions since the early 1940s. First, this paper reviews the recent advances in ecological studies on laboratory systems of bruchid hosts and their parasitoids as represented by bottom-up and top-down controls. Factors controlling the persistence of simple host-parasitoid systems that can be modified by an evolutionary change in a host beetle are demonstrated with reference to local carrying capacity, vulnerable time window of hosts to parasitism, and functional response of parasitoids. Second, we present experimental results on persistence of larger species assemblies analyzed in the light of the simple two-species host-parasitoid control factors. The most persistent association of species showed that both host and parasitoid control factors in the simple host-parasitoid system were consistently effective in the larger species complexes. There was also a general loss of persistence of host-parasitoid associations as species richness increased. Finally, at the interface between simple and complex assemblies, we asked how an addition of a third species to a simple host-parasitoid system affects resilience and duration of transients, with the Callosobruchus beetles as the host and two parasitoids (the pteromalid Anisopteromalus calandrae and braconid Heterospilus prosopidis). Semi-mechanistic models parameterized by fitting to the population data were constructed to help understand the driving forces that govern the behavior of interacting populations. The population dynamics of the three-species system was ascribed to cyclic/chaotic transient dynamics towards an attractor that has potential of not only a stable equilibrium but also a chaotic one. By comparing the three-species dynamics to the stable two-species (one host-one parasitoid) dynamics before H. prosopidis was introduced, the instability that leads to chaos was revealed to be induced by density-dependent host-feeding by A. calandrae. Although the destabilizing host-feeding was under the control of a stabilizing effect of mutual interference, the effect was estimated to be weakened by the introduction of the second parasitoid, H. prosopidis.