1. Time-series data from a twice-replicated population experiment (consisting of a seed beetle (host), Callosobruchus chinensis, and two parasitoids, Anisopteromalus calandrae and Heterospilus prosopidis) were studied in order to identify and to estimate the density-dependent structure. 2. A non-parametric host-parasitoid model based on the Nicholson-Bailey model, was studied through non-parametric autoregressive modelling. An additive non-linear structure was found in the population growth/parasitism rates for all three species. 3. The analysis suggests that the abundance of A. calandrae only weakly affects its own parasitism rate as well as H. prosopidis parasitism rate. 4. The analysis also suggests that the net population growth rate of C. chinensis is highly non-linear, which may be due to disproportionately higher egg mortality at high adult densities. 5. Non-linearity was also demonstrated in the parasitism rate of H. prosopidis, which is consistent with assuming that the density-dependent mutual interference becomes disproportionately higher at high H. prosopidis adult densities. none