HOST HETEROGENEITY IN SUSCEPTIBILITY AND DISEASE DYNAMICS - TESTS OF A MATHEMATICAL-MODEL

Most mathematical models of disease assume that transmission is linear ly dependent on the densities of host and pathogen. Recent data for an imal diseases, however, have cast doubt on this assumption, without as sessing the usefulness of alternative models. In this article, we use a combination of laboratory dose-response experiments, field transmiss ion experiments, and observations of naturally occurring populations t o show that virus transmission in gypsy moths is a nonlinear function of virus density, apparently because of heterogeneity among individual gypsy moth larvae in their susceptibility to the virus. Dose-response experiments showed that larvae from a laboratory colony of gypsy moth s are substantially less heterogeneous in their susceptibility to the virus than are larvae from feral populations, and field experiments sh owed that there is a more strongly nonlinear relationship between tran smission and virus density for feral larvae than for lab larvae. This nonlinearity in transmission changes the dynamics of the virus in natu ral populations so that a model incorporating host heterogeneity in su sceptibility to the virus gives a much better fit to data on virus dyn amics from large-scale field plots than does a classical model that ig nores host heterogeneity. Our results suggest that heterogeneity among individuals has important effects on the dynamics of disease in insec ts at several spatial and temporal scales and that heterogeneity in su sceptibility may be of general importance in the ecology of disease.