The life cycle and reproductive habits of beneficial parasitoids can be complex. In some species, only one parasitoid will develop in or on each pest while, in others, hundreds of young larvae may develop within the pest host. Overwintering habits may also vary. Female parasitoids may also kill many pests by direct feeding on the pest eggs and immatures.
Major characteristics of insect parasitoids:
Whereas insect predators immediately kill or disable their prey, pests attacked by parasitoids die more slowly. Some hosts are paralyzed, while others may continue to feed or even lay eggs before succumbing to the attack. Parasitoids, however, often complete their life cycle much more quickly and increase their numbers much faster than many predators. Parasitoids can be the dominant and most effective natural enemies of some pest insects, but their presence may not be obvious. It is often necessary, to determine the extent of parasitism, to dissect or rear samples of pest insects to see if any adult parasitoids emerge.
Parasitoids can be parasitized by other parasitoids. This phenomenon, known as hyperparasitism, is a natural occurrence, can be common, and may reduce the effectiveness of some beneficial species. Little can be done to manage hyperparasitism.
Parasitoids are often more susceptible to chemical insecticides than predators. Adult parasitoids are usually more susceptible than their hosts. Immature parasitoids, especially if protected within the egg of their host or in their own cocoon, may tolerate pesticides better than adults, but immature parasitoids will usually die if their host is killed.
Hoffmann, M.P. and Frodsham, A.C. (1993) Natural Enemies of Vegetable Insect Pests. Cooperative Extension, Cornell University, Ithaca, NY. 63 pp.