Host-limited dynamics of autoparasitoids

Autoparasitoids, an important class of intraguild predators used in classic al biological control, have a unique biology. Females develop as primary en doparasitoids of scale insects and whiteflies. Males develop at the expense of conspecific or heterospecific parasitoid prepupae. To evaluate the effe ct of autoparasitism on host suppression, system stability, and parasitoid coexistence, stage-structured differential equation models are developed an d analysed. For a host-parasitoid system, autoparasitism stabilizes host-pa rasitoid oscillations generated by developmental delays of the parasitoid. In host-autoparasitoid-primary parasitoid systems, a distinction between ob ligate (i.e. parasitoid only attacks conspecifics for the production of mal es) and facultative (i.e. parasitoid attacks conspecifics and heterospecifi cs for the production of males) autoparasitism is drawn. Coexistence betwee n an obligate autoparasitoid and primary parasitoid occurs if and only if t he autoparasitoid can invade at lower host densities than the primary paras itoid, and the primary parasitoid can suppress the host to a lower equilibr ium density than the autoparasitoid. When coexistence occurs, the primary p arasitoid determines the host equilibrium abundance. Interactions between f acultative autoparasitoids and primary parasitoids can lead to a priority e ffect, and, less likely, to coexistence. When coexistence occurs, the invas ion of the facultative autoparasitoid into the host-primary parasitoid syst em raises the equilibrium density of the host. In either coexistence scenar io, the invasion of an autoparasitoid can stabilize an unstable host-primar y parasitoid system. The analysis concludes by showing that the introductio n of an autoparasitoid to a host-primary parasitoid system can improve host suppression in the short-term despite possible long-term disruption. (C) 2 001 Academic Press.