An overview of biological control of weeds in Tasmania.
Thirty-five agents have been deliberately released for the biological control of 16 weed species in Tasmania, Australia, with 31 of these released during the last twenty years. The agents include three fungal pathogens and 32 species of invertebrates of which 29 are insects and three are mites. Of these, 24 have established, seven have failed to establish and the establishment of four is still to be confirmed. Four of the seven agents that failed to establish were foliage feeders on boneseed (Chrysanthemoides monilifera ssp. monilifera (L.) T. Norl.). Only the ragwort (Jacobaea vulgaris Gaertn.) program has been completed, with the establishment of a root feeder and two stem and crown borers now providing substantial to complete control. The benefit:cost ratio of the ragwort program has been estimated at 32:1 through annual multimillion dollar savings in lost production to pastoral industries, with benefits expected to increase through the continuing dispersal of established agents. Work on continuing programs involves inputs into the host testing, rearing and release of additional agents, the redistribution of established agents from nursery sites and agent efficacy assessments. Completion will continue to rely heavily on long term funding from state and national governments if the potential public benefits that these and future programs offer are to be achieved.