Although case-bearing leafmining larvae ofColeophora klimeschiellaToll were released on Russian thistles,Salsola australisR. Brown (Chenopodiaceae), at 13 locations in southern California during 1977–85, this biological control agent remained tenuously established at only one site by late 1986. Neither insectary-reared or field-collected stocks released in field cages or in the open in numbers of 100–600 per site appeared to foster colony establishment. Poor host-plant adaptation as well as predation and parasitism by indigenous natural enemies are identified as possible sources of biotic resistance to the establishment of this imported insect. The predator,Phylobacnus atriplexus(Foster) (Coleoptera: Cleridae), and the primary parasite,Macroneurasp. (Hymenoptera: Eupelmidae), found attackingC. klimeschiella, also are known from gall-midge hosts on native saltbushes (Atriplexspp., also Chenopodiaceae).