HOST-RANGE OF BRACHYCAUDUS RUMEXICOLENS (PATCH), AN APHID ASSOCIATED WITH THE POLYGONACEAE

The aphid Brachycaudus rumexicolens is a recent arrival in Australia w here the weeds Emex australis, E. spinosa, and Rumex species are its r ecorded hosts. Host range on 114 species representing 42 plant familie s was assessed in the laboratory to determine the aphid species' poten tial as a biological control agent against E. australia. Survival and reproductive success were measured in clip and/or dialysis-tube cages. B. rumexicolens developed most successfully on Emex spp. and Rumex sp p. and to a lesser extent on other Polygonaceae. Lupinus albus (white lupin) and Triticum aestivum (wheat) were the only non-Polygonaceae pl ants on which B. rumexicolens developed to a degree similar to its usu al hosts. At a field site in Western Australia, E. australis and Polyg onum aviculare were the only Polygonaceae present and the primary host species of B. rumexicolens. At peak abundance, it was found on other pasture and crop species, but at considerably lower numbers than on it s Polygonaceae hosts. It was concluded that this was due to local migr ation and that populations would not be sustained on non-Polygonaceae plants. It was also concluded that the risk of virus transmission woul d not be increased by the presence of B. rumexicolens on nonhosts. B. rumexicolens is considered sufficiently safe to use in programs aimed at augmenting the impact of biological control agents on the weed E. a ustralis. (C) 1998 Academic Press.