Host Range ofBrachycaudus rumexicolens(Patch), an Aphid Associated with the Polygonaceae

The aphidBrachycaudus rumexicolensis a recent arrival in Australia where the weedsEmex australis, E. spinosa,andRumexspecies are its recorded hosts. Host range on 114 species representing 42 plant families was assessed in the laboratory to determine the aphid speciesʹ potential as a biological control agent againstE. australis.Survival and reproductive success were measured in clip and/or dialysis-tube cages.B. rumexicolensdeveloped most successfully onEmexspp. andRumexspp. and to a lesser extent on other Polygonaceae.Lupinus albus(white lupin) andTriticum aestivum(wheat) were the only non-Polygonaceae plants on whichB. rumexicolensdeveloped to a degree similar to its usual hosts. At a field site in Western Australia,E. australisandPolygonum avicularewere the only Polygonaceae present and the primary host species ofB. rumexicolens.At peak abundance, it was found on other pasture and crop species, but at considerably lower numbers than on its Polygonaceae hosts. It was concluded that this was due to local migration and that populations would not be sustained on non-Polygonaceae plants. It was also concluded that the risk of virus transmission would not be increased by the presence ofB. rumexicolenson nonhosts.B. rumexicolensis considered sufficiently safe to use in programs aimed at augmenting the impact of biological control agents on the weedE. australis.