Effectiveness of classical weed biological control agents released in Australia

The historical record of releases of 288 species of weed biological control agents in Australia was analysed to examine if considering the damage/host type relationship of agents can offer insights into why some agents and not others have proved to be effective in producing partial or complete control of the target weed. Specifically, the effectiveness of agents released in Australia was examined in relation to their feeding guild and the functional group (growth form) of the target weed. Biotrophic pathogens (rusts/smuts), sap feeders and root/crown feeders were effective in producing control more often than other guilds. Effectiveness of biological control across weed functional groups was somewhat similar, although herbaceous biennials/perennials tended to be more effectively controlled than other functional groups. Significant biological control was recorded for at least one case in each of the 31 of the 37 feeding-guild/weed functional group combinations for which there were data. Possible explanations for the greater success of some guilds are explored, as are caveats with using such inductive approaches to predict effectiveness in classical weed biological control.