Parasites vs. Parasitoids

In MBCN we try not to be too technical, but occasionally some terms need explaining. In Issue 1 we described the three main groups of beneficials as predators, parasites (or parasitoids), and insect pathogens. Both terms, parasite and parasitoid, have been used in articles in the newsletter; so what's the difference? A standard (but very general) definition of parasite is " organism that lives in or on another (the host), from which it derives food, shelter, or other requirements." Our biological control parasite fits this definition fine.

But there are significant differences between the life history of insects such as parasitic wasps and other types of parasites. For example, a "true" parasite is usually much smaller than its host, lives a shorter period of time, often reproduces within (or on) its host, and often does not kill its host. Examples are tapeworms and human body lice. Biological control parasites are quite different: they are close in size to their hosts, they live about the same length of time, most are incapable of reproducing in or on their hosts (they require a free-living period), and they usually kill their hosts. For this reason, the term parasitoid was coined in 1913 to describe those insects, such as ichneumonid wasps and tachinid flies, that parasitize, and kill, other insects.

Many biological control workers are comfortable with the broader definition of parasite. Others prefer the functional distinction between parasite and parasitoid. Contributors to MBCN fall into both schools of thought; therefore both terms will appear in articles in the newsletter. Just remember that, when seen in this newsletter, both terms refer to an insect, usually a wasp or fly, whose larval stage feeds in or on a host insect, eventually killing that host.

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