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See resources and questions at Eradicating the prickly pear

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What problems were associated with attempts at controlling prickly pear before the Cactoblastis cactorum biocontrol was made?
Then consider the following extract from xxx

An ongoing problem
Although not on the same scale as the 1920s crisis, prickly pear continues to be a problem in New South Wales and Queensland, where new varieties that do not act as hosts for Cactoblastis moths have become established.

In 1957 Cactoblastis moths were introduced to the Caribbean, where Opuntia species are indigenous. The moths originated in South America and so the Caribbean plants had previously had no exposure to them.

They attacked the local species and from there progressed to Mexico, where they have started destroying Mexico’s commercial Opuntia crop.

In the United States there are grave concerns that the moths could destroy ecologically and economically significant Opuntia species right across the south of the country.

Is any form of biocontrol likely to be completely unproblematic?

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