Every Monday, scientists at the University of Pretoria’s biological control facility send small plastic sandwich bags containing a cloudy liquid and more than 6-million microscopic worms, called nematodes to pine plantations all over the country.
Since 2007, the South African Sirex Control Programme, a collaboration between academia, government and Forestry South Africa, has reduced Sirex-related pine losses by R404-million, Forestry South Africa says.
These tiny creatures are one of the country’s major weapons in the fight against the pine-tree-killing invasive Sirex wasp. South Africa’s forestry industry is worth more than R16 billion, of which pine accounts for about half of the total area under plantation.
First detected in 1994, this wasp has spread throughout the country. In KwaZulu-Natal and the Eastern Cape, the wasp and its symbiotic fungus killed up to 35% of the pine trees in some stands.
The wasp drills a hole into the tree trunk with its sting, and deposits its eggs and a fungus called Amylostereum areolatum into the tree. This fungus spreads throughout the tree, and when the young wasps leave, they take the fungus with them. It has no local predator in South Africa.
“This nematode co-evolved with the wasp-fungus system,” says Bernard Slippers, director of the Forestry and Agricultural Biotechnology Institute at the University of Pretoria. It has two parts to its life cycle, he says. One form eats the fungus and another penetrates the wasp larvae and renders them infertile.
Called biological control, this form of invasive species management involves finding a species natural predator. The programme inoculates about 8,000 trees a year.
However, invasive species – including plants, animals, insects, and other organisms – remain a problem in South Africa, costing billions of rands annually.
“There’s been an incredible explosion [in invasive species],” says Slippers.
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