Weeds – the real alien invaders
Box 3 | Prickly pear – a biocontrol success story
A classic example of successful biological control in Australia is the control of the noxious prickly pear cactus through the use of the Cactoblastis caterpillar.
One species of prickly pear was first brought to Australia with the First Fleet to help establish an industry in cochineal – the red dye used to colour the coats of the British soldiers. The dye was extracted from the cochineal beetle, which lives and feeds on prickly pear. By the late 19th century a different species of prickly pear had spread out of control in New South Wales and Queensland, and by the 1920s covered more than 25 million hectares. The spiky cactus formed dense stands that made the areas it infested nearly impossible to raise animals on, driving many farmers from their land. Various methods of chemical and physical control of the cactus were tried without much success.
In 1926, the caterpillars of the Argentinian Cactoblastis moth were first released into affected areas. The moth larvae burrow into and eat the cactus, eventually killing it. Cactoblastis was a great success, and in less than 10 years after its introduction the prickly pear population had been brought largely under control.
Biocontrol agents do not completely eradicate the organism they target. Instead, they reduce and control its population enough that it no longer causes serious harm, bringing it into a sustainable balance with its new environment.
Boxes
Box 1. Cash for weeds
Box 2. How to be a good weed
Related sites
Biological control – common questions and answers (Weeds Cooperative Research Centre, Australia) Prickly pear (Queensland Department of Primary Industries and Fisheries, Australia)
Prickly pear history (North West Weeds, Australia)
Posted February 2006.