Most species of cacti were introduced to this country in the 1900s – or even before. They have become so prolific, however, that cochineal insects (Dactylopius austrinus) that feed on the sap of cactus species were introduced to South Africa, firstly in 1935 and again during the 1970s, as a biological control for these invasive cacti species, including the jointed cactus and prickly pear. These insects usually live together in colonies seen on the surface of cactus plants.
The jointed cactus, (Opuntia aurantiaca), originally from Argentina and Paraguay, has invaded pastoral lands, threatening indigenous plants as well as the health of livestock – and is a particular pest in the Eastern Cape. I pointed out in a post on jointed cactus (February 2018) that they not only compete for resources such as water, sunlight, and nutrients but their viciously sharp spines prevent animals from grazing and can cause considerable harm to livestock.
By all accounts, the introduction of a variety of the various varieties of cochineal insects has not been as successful as might have been hoped. Nonetheless, should you spot white masses on prickly pears, know that one import is doing its bit to get rid of another import!