Parasitoid

A parasitoid is an organism, typically an insect, whose immature development is intimately tied to a single host, on or in which it feeds, and whose life cycle ends with the death of the host. Unlike most parasites, which generally do not kill their hosts, a parasitoid usually consumes the host from within or while attached, ultimately causing the host’s death. Parasitoids are diverse and occur across several groups, most prominently among parasitoid wasps and tachinid flies, but also in some beetles and nematodes.

Life cycles of parasitoids typically involve locating a suitable host, laying eggs on or in it, and allowing one or more larvae to develop at the host’s expense. The host may be consumed inside its body (endoparasitoid) or fed upon from outside (ectoparasitoid). Many parasitoids are solitary, with a single offspring per host, while others are gregarious and multiple offspring develop within a single host. They can be idiobionts, which arrest host development at parasitism, or koinobionts, which allow continued host growth and development after parasitism. Hyperparasitoids, which parasitize other parasitoids, add another layer of ecological complexity.

Ecologically, parasitoids play a major role in regulating insect populations and shaping community interactions. They are important in natural ecosystems and are widely used in biological control programs to suppress pest species. Notable examples include Trichogramma wasps that parasitize moth eggs, Aphidius parasitoids of aphids, and Encarsia formosa that attack whiteflies. While effective, biocontrol programs require careful consideration of host specificity and potential non-target effects.