Parasitoid

Definition

An organism that lives in or on a host organism, deriving nutrients at the host's expense and invariably killing the host, typically after completing its own development. Parasitoidism represents an evolutionary intermediate between parasitism and predation: like a parasite, the parasitoid exploits a single living host, but like a predator, it ultimately destroys that host. In entomology, the majority of parasitoids are Hymenoptera—especially Ichneumonidae, Braconidae, and Chalcidoidea—though Diptera (Tachinidae) and some Coleoptera and Lepidoptera also include parasitoid species.

Etymology

From Greek parasitos (one who eats at another's table) + -oeidēs (resembling), reflecting the intermediate nature between parasite and predator

Example

The braconid wasp Cotesia glomerata lays eggs in caterpillars of Pieris brassicae (large white butterfly); larvae feed internally on non-essential tissues before emerging through the host's cuticle to pupate, killing the caterpillar.

Related Terms

• Parasite
• Predator
• ectoparasitoid
• endoparasitoid
• koinobiont
• idiobiont
• Host
• Biological control
• brood parasitism

Usage Notes

Distinguished from true parasites by the fatal outcome for the host; distinguished from predators by the extended intimate association with a single host individual. The term is primarily ecological, not taxonomic—parasitoids occur across multiple insect orders. Specialists further classify by development mode: koinobionts allow the host to continue feeding and growing, while idiobionts arrest host development immediately. Ectoparasitoids feed externally; endoparasitoids feed internally.