What is biological control?
Biological control, often shortened to 'biocontrol', is the use of natural enemies to suppress a pest or weed. Most of our invasive plants are not native to Australia but came here from other countries, often brought in deliberately as garden plants or for pasture or forestry. Their natural enemies were left behind, and so biological control usually requires these natural enemies to be introduced into Australia first.

Why should we control invasive weeds?
Because they are severely invasive in our natural environments. For example, dense infestations of bridal creeper crowd out natives species and reduce regeneration of orchids and other small plants, trees and shrubs. Several native plant species are threatened with extinction because of this. Lantana displaces grasses and herbaceous plants, increases fire intensity and prevents regeneration of rainforest or eucalypt forests. Bitou bush, broom and gorse infestations all have a similar impact on the ecosystems invaded by them.

Will the biocontrol agents attack other plants?
No. All biocontrol agents are tested and will feed only on the foliage of their host weed, even to the extent that they don't attack even closely-related weeds. All agents are thoroughly tested on dozens of crops, garden plants, and native plants before being approved by 21 Federal and State government agencies for release.

Will the weeds be completely eradicated by the biocontrol agents?
No. The agents need the weeds as a food source, so where the weed is dense, the agents breed and build up in numbers. When the weed declines, agent numbers decrease. In this way the agents will eventually reach a natural balance with the weed, but will not eradicate it.

Will these biocontrol agents become another "cane toad"?
No. Australian government authorities have required strict and thorough testing of all biological control agents to ensure they are safe to release. Experts from 21 organisations from throughout the country examine the results of the testing and advise the Australian Quarantine and Inspection Service and the Federal Department of the Environment and Heritage that each agent is safe to release. The cane toad was not subject to these testing protocols - it was released in 1930, just as in the early days rabbits and foxes were released into Australia without any thought of the damage they would do.

How long will it take for biocontrol agents to have an effect on the weed population?
Biological control is a slow process, depending on increases in numbers of the biocontrol agents and persistence of standing plants and seeds already in the soil. A range of biological control agents, including both insects and plant diseases, may be needed before a weed becomes visibly less common. These processes may take many years. Sometimes however, as with harrisia cactus in Queensland in the 1970s or salivinia in the 1980s, success is achieved within only 3 or 4 years.

Why do we use biocontrol?
Australia has a long history of successful biocontrol programs, starting with the prickly pear successes in the 1920s and continuing till today. Typical biocontrol programs cost between $2 and $3 million over 5 to 10 years and save $15 to $50 million per year. Results are permanent, self-sustaining and do not harm the environment. Every dollar spent on biocontrol typically saves between $10 and $100, the best return you will ever get on your money!

How can I participate in biocontrol?
Many gardeners, landholders, schools and community groups have participated in weed biocontrol programs around Australia in recent years. The table below lists some of the biocontrol agents being used across Australia at present. If any of the weeds in your district are listed in the table below, and you would like to participate in the distribution of control agents, you should contact your local Weed Officer or the relevant authority in your state. See the contacts list below. They will be able to advise on agent availability, whether existing populations already exist close enough for you to collect from, and what time of the year is best for releases. There may be costs associated with this process, depending on availability of agents at the time and the level of technical support required.

People participating in biocontrol work should appreciate that while agents will work very well in some areas, local conditions will play a big part in determining whether an agent will be successful in your area. Although some agents are known to be vigorously attacking weeds in some areas, it may take a decade or longer after the initial release before there is sufficient evidence to show that the agents are effective.

Further information
Weeds CRC Factsheets

Chromolaena website

DPI Vic Information Notes

Technical Series 7: Improving the selection, testing and evaluation of weed biological control agents

Australian Weed Management Systems Chapter 9: Classical Biological Control. (David Briese)
This book is priced at $32.90 (inc. GST) and can be ordered through Richardson's on (03) 5286 1533 or click here.

Proceedings of the XI International Symposium on Biological Control of Weeds, ed. Cullen et al, CSIRO 2004. Available from CSIRO Entomology.