DISCRETE GENERATIONS IN HOST-PARASITOID MODELS WITH CONTRASTING LIFE-CYCLES

(1) Previous theoretical studies have shown that parasitoids are capable of producing cycles in their host populations with periods of about one host generation. These studies have modelled host-parasitoid interactions where parasitoid development proceeds independently from that of its host. (2) We present experimental results of a particular host-parasitoid association, Cadra cautella-Venturia canescens, and show that the development of the parasitoid is synchronized with that of its host. (3) The empirical evidence is used to formulate an age-structured model of an idealized host-parasitoid system where the onset of parasitoid development is dependent on the state of the host. The properties of the model are described and contrasted with a model that assumes there is no developmental synchrony in host and parasitoid life cycles. (4) Our results are similar to the findings of previous studies, showing that the differences in the behaviour of population models with and without life cycle synchrony are quantitative rather than qualitative. We show that when developmental synchrony occurs, ratios of parasitoid/host development durations must be interpreted with care, when predicting whether single generation cycles are to be expected in a particular host-parasitoid system.