<P> Prickly pears (Genus Opuntia) are an invasive plant species in Australia . </P> <P> Prickly pears (mostly Opuntia stricta) were imported into Australia in the 19th century for use as a natural agricultural fence and in an attempt to establish a cochineal dye industry . Many of these, especially the Tiger Pear, quickly became widespread invasive species, rendering 40,000 km (15,000 sq mi) of farming land unproductive . The moth Cactoblastis cactorum from South America, whose larvae eat prickly pear, was introduced in 1925 and almost wiped out the population . This case is often cited as an example of successful biological pest control . In the early days it was used as a clothing dye . </P> <P> There is a monument to the Cactoblastis cactorum in Dalby, Queensland commemorating the eradication of the prickly pear in the region . The Cactoblastis Memorial Hall in Boonarga, Queensland, also commemorating the eradication . </P>

What problems did the prickly pear cause in australia
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