The Collaborative International Dictionary of English v.0.48:

Heteroecious \Het`er*[oe]"cious\, a. [Hetero- + Gr. ? house.]
   (Bot.)
   Passing through the different stages in its life history on
   an alternation of hosts, as the common wheat-rust fungus
   (Puccinia graminis), and certain other parasitic fungi; --
   contrasted with aut[oe]cious. -- Het`er*[oe]"cism, n.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

heteroecious
    adj 1: of parasites; passing through different stages of the
           life cycle on different host species; "heteroecious
           fungi"; "heteroecious insects" [ant: autoecious,
           homoecious]