Ectoparasitoids

Ectoparasitoids are parasitoids whose immature development occurs on the exterior of a single host, rather than inside it. In their life cycle, a female lays eggs on or onto the outside of a suitable host, which is typically an insect or other arthropod in an exposed or accessible stage. The first instar larva hatches and remains attached to the host’s surface, where it feeds on host tissues and fluids from the outside. The host is usually debilitated over time and may die as the larva grows, though the host may survive for a period during early feeding. The larva then Pupates, often forming a protective case either on the host’s body or in the surrounding environment, and emerges as an adult wasp or fly.

Hosts targeted by ectoparasitoids are diverse but predominantly arthropods such as scale insects, mealybugs, aphids, whiteflies, caterpillars, and beetle larvae. Their external mode of development makes them distinct from endoparasitoids, whose larvae develop inside the host’s body. Ectoparasitoids can be important natural enemies in ecosystems and are frequently employed in biological control programs to suppress pest populations, sometimes in combination with other natural enemies such as predators and endoparasitoids.

Taxonomic diversity includes many families of wasps and some other insects. Notable ectoparasitoid groups include Encyrtidae and Aphelinidae, which parasitize scale insects and whiteflies, among other hosts. The effectiveness and behavior of ectoparasitoids depend on host accessibility, host defenses, and ecological context, with adaptations commonly related to locating hosts, oviposition on the host’s exterior, and managing exposure during larval development.