Host plant alternation

Definition

A cyclical life-history strategy in which successive generations of a herbivorous insect species, or different seasonal morphs within a single year, feed on taxonomically unrelated host plant species, typically involving a shift between a primary (usually woody) overwintering host and one or more secondary (usually herbaceous) summer hosts. The phenomenon is obligate in many aphids (Aphididae) and occurs in some gall midges, adelgids, and rust fungi (though the term is most firmly established in entomology).

Etymology

Example

The green peach aphid (Myzus persicae) exhibits facultative host alternation, overwintering as eggs on Prunus spp. (stone fruits) and migrating to herbaceous crops such as Brassica and Solanum for summer generations; by contrast, the black bean aphid (Aphis fabae) is an obligate host-alternator, unable to complete its full life cycle without returning to its woody primary host (usually Euonymus or Viburnum) for sexual reproduction and egg-laying.

Synonyms

• heteroecy
• host switching (seasonal)
• dioecy (historical, now discouraged)

Related Terms

• monoecy
• autoecy
• primary host
• secondary host
• fundatrix
• Alate
• Parthenogenesis
• holocyclic
• anholocyclic
• gall induction
• specialist herbivore
• generalist herbivore

Usage Notes

Distinguished from occasional host switching or polyphagy: host plant alternation is predictable, generation-linked, and often obligate. 'Heteroecy' is the precise synonym but is falling from use; 'dioecy' once appeared in older literature but now refers exclusively to separate-sexed organisms and should be avoided. Not all aphids alternate—many species are monoecious (single-host) year-round, and some populations have secondarily lost the sexual/primary-host phase (anholocyclic). The term applies primarily to insects with complex, often apomictic life cycles; it is less commonly used for vertebrate herbivores or non-cyclical host shifts.