Plants that have become weeds in Australia are rarely invasive and troublesome in their natural range. This is often because natural populations are regulated by a variety of natural enemies such as insects and pathogens (disease-causing organisms like fungi and bacteria) that attack the seeds, leaves, stems and roots of a plant. If plants are introduced to a new region that does not have these natural enemies, their populations may grow unchecked to the point where they become so prevalent that they are regarded as weeds.
What is biological control?
The biological control approach makes use of the invasive plant's naturally occurring enemies, to help reduce its impact. It aims to reunite weeds with their natural enemies and achieve sustainable weed control. These natural enemies of weeds are often referred to as biological control agents.
It is critical that the biological control agents introduced into Australia do not become pests themselves. Considerable testing is done prior to the release of biological control agents to ensure they will not pose a threat to non-target species such as native and agricultural plants.
Although in the long term, biological control can be cost effective and can reduce the need for less desirable management practices, not all weeds are suitable for biological control. Developing a biological control project requires a substantial investment, sometimes costing millions of dollars over many years.
An early success in biological control of weeds in Australia was the use in the 1920s of the Cactoblastis Moth (Cactoblastis cactorum) to control Prickly Pear (Opuntia stricta), which at the time was smothering large tracts of north-east Australia, and spreading rapidly each year. The larvae of the Cactoblastis Moth eat the leaves and seed pods of the Prickly Pear. The release and spread of Cactoblastis Moth in Australia virtually destroyed Prickly Pear populations.
There have been several other successful biological control programs in Australia. Insects that attack leaves, fruits or stems have been released, following stringent screening, to control weeds such as Skeleton Weed, Bridal Creeper, and Salvinia. There is also major research being undertaken on biological control for a number of other weed species.
Procedure to import and release a biological control agent
There are some well known examples of biological control programs that have been unsuccessful (such as the introduction of Cane Toads to control Cane Beetles). To avoid such problems in future, the process for approving biological control agents is much more rigorous now than it has been in the past.
Before commencing the search for biological control agents, agreement needs to be sought with initial application through the Invasive Plants and Animals Committee to target the weed species for biological control.
The next step is to undertake host specificity testing. This is a requirement under the Australian Government Department of Agriculture - Biosecurity to ensure that the agent will not damage native flora or agricultural stock or crops. Once host specificity testing is completed, biological control agents must be assessed to meet the requirements of the Quarantine Act 1908 and the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act) before approval can be given for their introduction and release in Australia.
To meet the requirements of the Quarantine Act 1908, the Department of Agriculture assesses the risk regarding the proposed importation and release of biological control agents via a risk analysis, based on the results of host specificity testing.
The Australian Government Department of the Environment has a parallel approval process under the EPBC Act, whereby a report produced by the Australian Government Department of Agriculture - Biosecurity may be used by the responsible minister in making a determination to include the item on the list of specimens suitable for live import (the live import list).