This chapter reviews the mechanisms contributing to the reduction of pest population levels and to population regulation. The dynamics of single-species systems spans the range of behavior from geometric (or unconstrained) growth, monotonic approach to a stable equilibrium, damped oscillations approaching a stable equilibrium, stable cyclic behavior, and, finally, systems characterized by aperiodic oscillations or “chaos.” The type of behavior that occurs in a particular case depends both on the reproductive rate and the strength (nonlinearity) of density-dependent competition. Most populations are separable into distinct age or stage classes that can affect the outcome of competition. In most insects, the preimaginal stages compete for resources for growth and survival, while adults may compete additionally for resources for egg maturation and oviposition sites. In such cases, competition within populations naturally divides into sequential stages. Many insect populations are dependent on resources that occur in patches. Dividing the resource into discrete patches can have important effects on the conditions for coexistence of the competing species.
