In evolutionary ecology, a parasitoid is an organism that lives in close association with its host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionary strategies within parasitism, distinguished by the fatal prognosis for the host, which makes the strategy close to predation.
A parasitoid wasp (Trioxys complanatus, Aphidiinae) ovipositing into the body of a spotted alfalfa aphid (Therioaphis maculata, Calaphidinae), a behaviour that is used in biological pest control
A hyperparasitoid chalcidoid wasp on the cocoons of its host, a braconid wasp, itself a koinobiont parasitoid of Lepidoptera
Potter wasp, an idiobiont, building a mud nest; she will provision it with paralysed insects, on which she will lay her eggs; she will then seal the nest and provide no further care for her young
The head of a sessile female strepsipteran protruding (lower right) from the abdomen of its wasp host; the male (not shown) has wings
In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist guest (symbiont). The guest is typically provided with nourishment and shelter. Examples include animals playing host to parasitic worms, cells harbouring pathogenic (disease-causing) viruses, or a bean plant hosting mutualistic (helpful) nitrogen-fixing bacteria. More specifically in botany, a host plant supplies food resources to micropredators, which have an evolutionarily stable relationship with their hosts similar to ectoparasitism. The host range is the collection of hosts that an organism can use as a partner.
The black rat is a reservoir host for bubonic plague. The rat fleas that infest the rats are vectors for the disease.
Buff ermine moth caterpillar, a polyphagous micropredator
Mycorrhiza, a mutualistic interaction between a plant's roots and a fungus
Cleaning symbiosis: a Hawaiian cleaner wrasse with its client, a yellowtail wrasse
