Biological
control
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.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 programmes 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
programmes 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.
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