Prickly pear (Opuntia stricta) was imported into Australia in the late 1800’s and quickly became a pest weed spreading to cover four million hectares by 1900.
The pear was introduced to establish a colony of mealy bugs where red dye would be extracted to colour fabric. The fruit yielded high vitamin C and the cactus pads were used for drought fodder due to their highwater content. Feeding the pear to livestock became widespread and so did the weed which established itself in prime grazing land. By 1925 in its peak, prickly pear covered 24 million hectares in Queensland and New South Wales.
Manual control by digging, burning or crushing the pear were used and although arsenic pentoxide was effective, it was highly toxic and six times the value of the land.
In 1924, Queensland introduced a bounty in certain birds like currawongs, crows and emus to stop the spread of seeds and in 1925 a moth (Cactoblastis cactorum) was introduced from South America as a biological control agent. The moth larvae tunnelled into the cactus and feed on the pear and in less than a decade, the larvae almost completely wiped out the pear population.
While there is still prickly pear in Australia, the moth larvae continue to feed on this invasive plant and remains one of Australia’s successful biological pest control.
So next time you see a moth just have a thought for our Cactoblastis and its amazing ability to keep Prickly pear under control.
Yvonne Hennell | Bio-Control Manager