Australian Plants online
Index   Back Issues   ANPSA Home

Cactoblastis Moth and Prickly Pear

Caboolture Daytime Branch of SGAP

   Prickly Pear
   Plants of Prickly Pear can still be seen along roadsides but they are no longer a serious environmental threat

It is hard to imagine today, but by the 1920s there were 24,250,000 hectares of Australia covered with Prickly Pear (Optunia inermis). The cactus had been introduced into Australia in 1839 and by 1862 it had reached the Chinchilla area in central Queensland. By the turn of the century it was increasing at a rate of 400,000 hectares a year. Farmers tried to fight it by cutting and burning but their labours met with little success. In 1925 the Commonwealth Prickly Pear Board, realising the scale of the problem, introduced the Cactoblastis moth and larva from South America (Cactoblastis cactorum).

Initially 3,000 eggs arrived from Argentina and, from a population of 527 females, a total of 100,605 eggs were hatched. Half these eggs were sent to the Chinchilla Prickly Pear Experimental Station and half were kept in Brisbane.

The moth was spectacularly productive. The second generation yielded 2,539,506 eggs. At the height of the operation Chinchilla was sending out as many as 14 million cactoblastis eggs a day.

In 1910 Prickly Pear was declared a pest and the Queensland Government offered 100,000 acres (40,469 ha) reward to the first person to eradicate prickly pear. In 1926 the Cactoblastis moth was released to attack prickly pear and by 1933 most of the land was cleared of the pest.

No wonder the locals decided to dedicate a hall to this small insect. Located 10 km east of Chinchilla on the Warrego Highway is the Boonargo Cactoblastis Hall which was built by the local farmers in 1936 and dedicated to the redoubtable insect which had managed to eat its way through the jungles of Prickly Pear. It was seen as the true saviour of rural Australia and thus it is entirely reasonable that a hall should have been dedicated to its memory.

The caterpillars live and feed communally inside the tough leathery (and prickly) skin of the host plant, reducing the plant material inside to a gooey green mess. The caterpillars are initially pinkish-cream coloured, with dark red dots on the back of each segment. Later they become orange, and the dots expand and then fuse to become a dark band across each segment. The caterpillars grow to lengths of about 1.5 cm. The adult is fawn with faint dark dots and lines on the wings, and has a long nose. It normally rests with its wings wrapped around its body. The moth has a wingspan of about 2 cm.

Photographs of the Cactoblastis moth and larvae can be seen on the Lepidoptera Larvae of Australia website

From the newsletter of the Caboolture Daytime District Group of the Society for Growing Australian Plants (Qld), September 2005 (via the SGAP Regional Newsletter of December 2006).

Index   Back Issues   ANPSA Home

Australian Plants online - 2008
Association of Societies for Growing Australian Plants