Introduction of the gall fly Rhopalomyia californica from the U.S.A. into Australia for the control of the weed Baccharis halimifolia.
B. halimifolia is a woody shrub native to the E. coast of North America and is a serious weed in cattle pastures in E. Australia. In an attempt to control B. halimifolia, the gall fly Rhopalomyia californica was introduced from California where it was collected from B. pilularis. In 1982, releases were commenced and the gall fly has established at most sites. It has spread >10 km in 18 months and has stopped about 90% of seed production at a heavily infested release site. This is highly significant as the massive annual production of wind-borne seed is one of the principal reasons why this plant is a serious weed. At this stage, it appears that the gall fly will give significant control of the weed.