Host

Definition

An organism that harbors and sustains another organism—typically a parasite, parasitoid, or pathogen—providing it with nutrition, shelter, or developmental substrate. In entomology and arachnology, hosts range from plants fed upon by herbivorous insects to vertebrates parasitized by ticks or fleas, and insects serving as living nurseries for parasitoid wasp larvae. The host-parasite relationship is often asymmetrical: the host suffers reduced fitness while the dependent organism completes all or part of its life cycle.

Etymology

From Middle English host, from Latin hospes, hospitis ('guest, stranger, host'), from Proto-Italic *hosti-pot- ('master of guests'), from *hostis ('stranger') + *potis ('master').

Example

The ichneumon wasp Netelia vinulae deposits eggs on the integument of a Puss moth caterpillar (Cerura vinula); the caterpillar serves as an ectoparasitoid host, with larvae feeding externally on its tissues until pupation.

Synonyms

• host organism

Related Terms

• Parasite
• Parasitoid
• Ectoparasite
• Endoparasite
• Vector
• Reservoir
• host specificity
• host switching
• brood parasitism
• Biological control

Usage Notes

Distinguished from 'prey' (killed and consumed immediately) and 'food plant' (consumed but not necessarily harboring the consumer). 'Host' implies sustained association and usually some degree of harm to the host organism. In medical/veterinary contexts, 'definitive host' harbors the adult/reproductive stage of a parasite, while 'intermediate host' supports larval or asexual stages. 'Accidental host' or 'dead-end host' describes atypical infections where the parasite cannot complete development.