Prickly Pear

Australia had no cacti.  But there are large areas where Prickly Pear and other cacti can grow well.

Introduction

In the eighteenth century the British soldiers of many regiments were known as Red Coats because their uniforms were red.  The dye for the uniforms was called Carmine and was made from an insect.  This insect was the Cochineal Insect; it grows on the Prickly Pear plant.

One species is called Dactylopius coccus.   The British import this dye from South America.  Nowadays much of it comes from Peru.

The first fleet of European settlers brought some Prickly Pear plants infected with Cochineal Insects in the hope of providing the British with an alternative source of Carmine.

The type of Prickly Pear brought was the Smooth one, Opuntia vulgaris.  Although the smooth Prickly Pear is a problem in some areas, it was the Common Prickly Pear, Opuntia stricta, which became the most invasive weed in history.

Spread

In the late nineteenth and early twentieth centuries, this weed was taking over millions of acres of the state of Queensland.  Attempts were made to control it using extremely dangerous chemicals like Arsenic pentoxide and Sulphuric acid.  It was certainly possible to kill the plants. But the task was well beyond the resources available.

Cactoblastis

Various pests of the Prickly Pear were tested until scientists found a moth, Cactoblastis cactorum.  After very extensive testing the moth was released and within six years had totally devastated the worst infestations of Prickly Pear.

Monument

The Town of Dalby in Queensland built a monument to Cactoblastis.  This was probably the first monument in the world to an insect.

The Battle Continues

Although Cactoblastis devastated much of the weed, it was not effective in all areas, and control of the Prickly Pear still continues.

Sources

http://www.northwestweeds.nsw.gov.au/prickly_pear_history.htm