Heteroecious

A heteroecious parasite is one that requires at least two hosts. The primary host is the host in which the parasite spends its adult life; the other is the secondary host.

Heteroecious parasites include:
 * Gymnosporangium (Cedar-apple rust); the juniper is the primary (telial) host and the apple, pear or hawthorn is the secondary (aecial) host
 * Cronartium ribicola (White pine blister rust); the primary host are white pines, and currants the secondary.