ABSTRACT
In this chapter, the authors discuss host-range changes, in particular those associated with the genera Cales, Encarsia, and Eretmocerus. The topics of their discussion include adaptations by indigenous parasitoids to newly introduced hosts, by exotic parasitoids to the hosts available in a new area, and to new hosts by heteronomous parasitoids. While the danger of whitely parasitoids becoming injurious due to their oligophagy and host-range increases could exist in theory, this possibility should be examined under the practical circumstances which occur in nature. Biological control theory assumes a certain level of stability in host/parasitoid relationships, at least to a degree in which the introduced parasitoid will attack the pest against which it is intended without becoming itself a pest insect. A flexible host range was also observed in the selection of hosts for male development of heteronomous parasitoids, i.e., parasitoids with sex-deviate ontogeny. The authors present the cases of host resistance to range increases by the parasitoids.
