Biological control is the practice of managing a weed by the deliberate use of one or more natural enemies (biocontrol agents) that suppress it. Following their introduction and establishment, populations of biocontrol agents build up to very high levels due to the abundance of the weed. Eventually their attack on the plant causes a decline in the weed biomass, reproduction and/or population density. Biocontrol agents of weeds, once established, are self-sustaining and don’t have to be reapplied. A series of cost-benefit analyses in 2006 revealed that for every dollar spent on biocontrol of weeds, agricultural industries and society benefited by A$23. This was due to increases in production, multi-billion dollar savings in control costs and benefits to human health.