Tuesday, September 6, 2011

Prickly pear: the caterpillar that saved Outback Australia

Bottle trees and prickly pear mark the Australian outback with a distinctive stamp. Add to that red dirt, huge skies and seemingly endless plains and you begin to have a picture.

In the days of early settlement, prickly pear covered huge areas of inland New South Wales and Queensland. The cactus plant was introduced from South America to establish a cochineal dye industry, using the scale insect that lives on the pear. By the 1920s, 26,000,000 ha were severely infested, with station homesteads and farmhouses literally walled in by the plant. Many properties became an impenetrable jungle. Families were forced to abandon their properties and homes. The situation seemed hopeless.

In 1925, an enterprising entomologist went to Argentina and collected 3000 eggs from the tiny cactoblastis moth. After breeding up the numbers, he distributed eggs to landholders throughout the areas infested with this noxious cactus weed. In the space of only a few years, the orange-striped caterpillars ate their way through most of the fleshy cactus. By 1933, eighty per cent of the pear in Queensland had been destroyed by the caterpillars. To the present day, this miracle insect continues its good work on any rogue cactus, never touching any other plant.

What an incredible story. Huge areas of New South Wales and Queensland were saved by an introduced insect. This is biological control at its very best.

The photos show prickly pear trees which are larger than the prickly pear plant that caused so much trouble.

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