UNEXPECTED SPATIAL PATTERNS IN AN INSECT OUTBREAK MATCH A PREDATOR DIFFUSION-MODEL

An outbreak of the western tussock moth (Orgyia vetusta) with a sharp spatial boundary has been hypothesized to be the result of an interact ion with mobile parasitoids. We report here a striking correspondence between the qualitative prediction of a general model for a mobile pre dator and a sessile prey and initial observations of the outbreak of w estern tussock moth. The model makes the counter-intuitive prediction that the prey species will have its highest population density at the edge of an outbreak, which corresponds to observations made of the wes tern tussock moth. This is a striking pattern that should be looked fo r in other population systems.