Niki Moore
In a high-tech, sealed room in the Sugar Experimental Station at Mt Edgecombe, human figures move around in white lab coats and sterile coverings. No, they’re not developing a new killer virus to wipe out mankind as we know it they’re actually breeding thousands of caterpillars.
The caterpillar in question, however, has the potential to be lethal and that is why the strict quarantine is necessary. Hundreds of these caterpillars (called Paraeuchetes Insulata) are going to be taken out of their little boxes and placed on the leaves of an extremely dangerous plant the Chromoleana Odorata, commonly known as the paraffin bush because it is combustible.
The paraffin bush is like the star of a 1970 skin-chill flick an insidious green mass that creeps slowly and implacably across the countryside, devouring everything in its path. Well, actually, it’s not that bad, but it’s bad enough. This stinking green plant can look quite pretty when covered with its small, white flowers, but it is toxic and spreads explosively a grim invader that is starting to have a major effect on the eastern seaboard of Southern Africa. And just like an environmental Aids, nothing can stop it. Except, perhaps, the Paraeuchetes Insulata.
But bringing in a foreign insect to control a foreign plant is just as dangerous. Lengthy trials need to be conducted to make sure the insect is not going to find an indigenous plant more delicious than Chromoleana and thereby create a new menace. The Sugar Experimental Station has the necessary quarantine conditions to circumscribe a possible threat.
“We have just completed a field trial of the caterpillar that is supposed to prey on Chromoleana,” says Peter le Roux, an alien plant specialist with KwaZulu-Natal Wildlife, “but unfortunately this first trial has not been an unqualified success.”
The past winter was exceptionally dry, so the paraffin bush very cleverly dropped its leaves (it can photosynthesise through its stem). This left the insect with nothing to feed on, so the caterpillars did not multiply the way they were supposed to. “Also, we discovered that the Paraeuchetes is preyed on by indigenous insects, which impacted on its breeding,” says Le Roux.
Debbie Muir, officer in charge of bio-control for the Department of Water Affairs and Forestry in KwaZulu-Natal, regards the setback to last year’s release as minor. “We can only tell after at least two winters whether a programme has been successful or not. This first release survived one very dry and difficult winter. Now we must see if they survive another winter and start to multiply in great numbers.”
But the Chromoleana combatants have not put all their caterpillar eggs into one basket. It is estimated that about 100000ha of land in Zululand and Maputaland has been infested with the plant. And the only long-term solution, says Le Roux, is biological control.
“Even if this caterpillar is a success,” he says, “we still have to try a number of other insects. The Plant Protection Institute at Cedara, near Pietermaritzburg, has quite a few other types of insects that are currently in quarantine. We have to hit this green plague hard. It has spread as far as Mozambique and Maputaland. The impact it is having is quite severe.”
Even private landowners are worried. The St Lucia Maputaland Biosphere Initiative is a loose association of land-owners and lodge owners in Zululand and Maputaland who have agreed to cooperate in tourism and conservation issues.
Biosphere chairperson Clive Viviers said the growth of the bush has accelerated so much recently that it’s now regarded as a national environmental problem. Introduced accidentally in 1943 in a consignment of horse feed through Durban harbour, the weed has found a natural home in Zululand and Maputaland.
Viviers said the spread of the plant is now out of control. “Even with the current control measures, it is estimated that the Hluhluwe Game Reserve will be almost 50% covered in paraffin bush by 2010. In 1985 it was judged to be spreading northwards from Durban at a rate of 10km per annum. It is now spreading northwards at a rate of 45km per annum.”
The danger of the paraffin bush is that it smothers natural vegetation and destroys habitats. “Natural forests will be destroyed by Chromolaena because the plant burns with a hot flame and the natural vegetation cannot survive hot fires. It also gives off an enzyme that inhibits the growth of other plants,” says Viviers.
The paraffin bush is also beginning to alter habitats in bush areas. “I was speaking to the owner of a private game lodge,” says Le Roux, “and he said that the game viewing for tourists was being affected. Before, they could drive past an area and peer through the indigenous bush to see the animals, or see animals over a grass plain. Now the drives are walled by impenetrable thickets of Chromoleana.”
According to a paper by scientist Alison Leslie, the Chromoleana is a threat to the Nile Crocodile. “The weed grows on sandy riversides and creates a physical barrier that prevents the female crocodile from coming ashore to lay her eggs. The luxuriant growth in crocodile nesting sites also reduces the temperature of the sand. Crocodile eggs are temperature sensitive and a low breeding temperature means that only female crocodiles will hatch.”
The Working for Water Programme is an interdepartmental government programme that tackles alien growth on state land in various ways. Apart from the biological control through the caterpillar, it also has a programme to employ rural communities to eradicate alien plant growth in protected areas.
The National Roads Agency has undertaken to clear the paraffin bush from road verges between the Umfolozi and Pongola rivers. The Danish government has expressed an interest in funding a training programme for rural women that will enable them to become small contractors and obtain contracts to clear the weed.
“We need a total onslaught,” said Viviers. “The Department of Water Affairs and Forestry is eradicating the plant within protected areas, but it will never succeed as long as it is allowed to flourish elsewhere. In its lifetime, a single paraffin bush plant can release 1,3-million seeds.”
These seeds spread rapidly by landing in mud that then sticks to vehicle wheels, mudguards and undercarriages. Given the enthusiasm with which off-roaders go into pristine areas, the toxic plant is literally getting a free ride to new terrain.
So perhaps the image of the voracious green blob spreading slowly over the countryside is not so far off after all. Only this is one war we cannot afford to lose.
ENDS