PROSPECTIVE MODELING IN BIOLOGICAL-CONTROL - AN ANALYSIS OF THE DYNAMICS OF HETERONOMOUS HYPERPARASITISM IN A COTTON-WHITEFLY-PARASITOID SYSTEM

1. 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 us ed for the classical biological control of whiteflies, scale insects a nd mealybugs. An unresolved question in biological control is whether heteronomous hyperparasitism is compatible with the goals of biologica l control. 2. In this study we use a tritrophic model to examine the i nfluence of parasitoid developmental biology on the ability of aphelin ids 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), a n obligate autoparasitoid (where males develop only on conspecific fem ales) and a facultative autoparasitoid (where males develop on all oth er parasitoids including conspecific females). 3. The parasitoids are assumed to attack the set of available hosts in relation to their rela tive abundance, with no preference for particular host types, and thei r impacts on the cumulative abundance of immature whitefly and competi ng parasitoids are compared through graphical and stepdown multiple re gression analysis. 4. The results indicate that a primary parasitoid c an 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 parasi toid and an obligate autoparasitoid provides the greatest suppression of cumulative whitefly abundance, and the addition of a facultative au toparasitoid disrupts the control potential of the other parasitoids. 5. These results caution against the indiscriminate introduction of ap helinid parasitoids in biological control programmes, and highlight th e need for detailed experimental observations on sex allocation and ho st discrimination in facultative autoparasitoids.