Thistle cholla, Cylindropuntia pallida, is an extremely spiny cactus that is indigenous to Mexico. It has become a major problem outside of its indigenous distribution, in both Australia and South Africa. Many of the problems associated with thistle cholla are related to how spiny the plant is. Dense infestations of this invasive alien plant reduce the quality of grazing pastures, reduce yields of wool and mohair, and are harmful to livestock and wildlife. Similarly to many other cactus species, biological control is likely to be the best solution.
About two years ago, scientists released a biological control agent to control thistle cholla in Australia. The agent is a type of cochineal insect called Dactylopius tomentosus ‘californica var parkeri’, and it is very damaging to thistle cholla, which it feeds on. It was collected in the indigenous distribution in Mexico, where it occurs naturally, and was then imported into quarantine in Australia, where tests were conducted to ensure that it was suitably host specific for release. These tests showed that it can only feed on cactus species in the same genus as thistle cactus (Cylindropuntia), none of which occur naturally outside of the Americas. This cochineal insect is therefore safe to be released in both Australia and South Africa as a biological control agent for thistle cholla. The results after the releases in Australia have been very promising. The agent has spread, and large infestations of thistle cholla are dying. It seems like biological control will result in the complete control of thistle cholla in Australia.
Dr Iain Paterson from the CBC has been collaborating with scientists from the Queensland Department of Agriculture and Fisheries and the New South Wales Department of Primary Industry to release the biological control agent in South Africa. Recently, the South African Department of Agriculture, Land Reform and Rural Development (DALRRD), granted permission for the release of Dactylopius tomentosus ‘californica var parkeri’ in South Africa. The CBC will release the agent next summer, when conditions will be good for the establishment and spread of the new agent. The release of this biological control agent in South Africa will dramatically reduce the problems associated with thistle cholla in an environmentally friendly and sustainable manner.