Simple Models of Natural Enemy Action and Economic Thresholds

Abstract

Simple population models are linked to a widely used economic injury level model to produce equations for economic thresholds that include the effect of natural enemies. Two classes of models are recognized; those in which natural enemy dynamics are not coupled to that of the pest, such as generalist predators, and those where coupling is integral to natural enemy dynamics such as pathogens, parasitoids, and specialist predators. Both of these models are extended to multiple species or complexes of natural enemies. Implications of these models are then discussed. The concept of biocontrol gain threshold is introduced as a method to balance the relative impact of a given natural enemy against the additional monitoring costs incurred as a result of adding the species to an integrated pest management program. The use of these models to reduce the risk of incorrect management decisions is also discussed.