Parasitoide

Parasitoide, also known as parasitoids in many languages, refers to organisms whose developmental strategy hinges on a single host, often leading to the host’s death. Unlike free-living parasites, parasitoids typically kill their host as part of their life cycle, and a host generally supports only one parasitoid lineage.

Most parasitoids lay eggs on or inside a host. The hatching larva then feeds on the host tissues, often through several instars, and the host remains alive for some time before dying. The developing parasitoid may emerge from the host as an adult after pupation. Parasitoids can be internal (endoparasitoids) or external (ectoparasitoids) to the host. Some attack eggs or larvae of other insects, while others target caterpillars, aphids, or beetles. Within the life history, hosts may be immobilized (idiobiont) or allowed to continue development (koinobiont) during parasitism.

Diversity is high, with major groups including ichneumonid and braconid wasps, tachinid flies, and various beetles and bugs. Examples include Trichogramma species, which are tiny egg parasitoids of Lepidoptera, and Cotesia species, which parasitize caterpillars. Tachinid flies often develop inside larval hosts such as caterpillars or beetle grubs.

Ecological and practical significance is substantial. Parasitoids help regulate insect populations and are employed in biological control programs to reduce pest damage. Their effectiveness depends on host specificity and ecological interactions, including the presence of hyperparasitoids, which can influence control outcomes.