Local and spatial dynamics of a host-parasitoid system in a field experiment

Local extinction and colonisation rates are key factors in host-parasitoid metapopulation theory, but experimental evidence from the field is scarce. We studied the host-parasitoid system consisting of the aphid Metopeurum fuscoviride and its specialist parasitoid Lysiphlebus hirticornis. This system is characterised by a patchy distribution of the host plants (Tanacetum vulgare) and by frequent extinctions of local aphid populations. In a first field experiment, we found that the presence of the parasitoid increases the likelihood of extinction of local host populations (= all aphids living on one plant). In a second field experiment, we manipulated the distance between local host populations. Parasitoid colonisation rate strongly decreased with increasing distance between local. host populations. Thus, our results show the importance of parasitoids for local host populations extinction and of distance between local host populations for parasitoid colonisation rate, suggesting the importance of spatial processes for host-parasitoid systems in the field