Prospective Modelling in Biological Control: An Analysis of the Dynamics of Heteronomous Hyperparasitism in a Cotton-Whitefly-Parasitoid System

Abstract

Heteronomous hyperparasitism, in which male parasitoids develop at the expense of conspecific females or competing parasitoid species, is characteristic of a number of aphelinid parasitoids that have been used for the classical biological control of whiteflies, scale insects and mealybugs. An unresolved question in biological control is whether heteronomous hyperparasitism is compatible with the goals of biological control. In this study we use a tritrophic model to examine the influence of parasitoid developmental biology on the ability of aphelinids to suppress the abundance of whitefly through a growing season on cotton. Three aphelinid parasitoids are considered, a typical primary parasitoid (where both males and females develop on whitefly hosts), an obligate autoparasitoid (where males develop only on conspecific females) and a facultative autoparasitoid (where males develop on all other parasitoids including conspecific females). The parasitoids are assumed to attack the set of available hosts in relation to their relative abundance, with no preference for particular host types, and their impacts on the cumulative abundance of immature whitefly and competing parasitoids are compared through graphical and stepdown multiple regression analysis. The results indicate that a primary parasitoid can substantially suppress the cumulative abundance of whitefly through a growing season on cotton, but that the impact of an autoparasitoid is constrained by self-limitation. The combination of a primary parasitoid and an obligate autoparasitoid provides the greatest suppression of cumulative whitefly abundance, and the addition of a facultative autoparasitoid disrupts the control potential of the other parasitoids. These results caution against the indiscriminate introduction of aphelinid parasitoids in biological control programmes, and highlight the need for detailed experimental observations on sex allocation and host discrimination in facultative autoparasitoids.