Why have some introduced Opuntia species become pests in Australia and South Africa?

Species of the genus Opuntia, commonly known as prickly pear, are native to the Western Hemisphere. When these plants were introduced to Australia and parts of South Africa, they became invasive pests primarily because they were removed from their natural ecological context.

In their native range, these cacti are kept in check by specific parasites and competitors. Upon their introduction to new regions, they escaped these natural controls, allowing them to prosper and spread rapidly. Furthermore, Opuntia species are highly resilient and capable of reproducing easily through asexual propagation, as their paddle-like stem segments can readily take root.

To manage these infestations, authorities have introduced biological control agents, such as moths of the genus Cactoblastis, which are native to the cactus's original habitat and help regulate their population growth in the invaded territories.123