Mealybugs that suck plant juices and cover themselves in wax, a beetle the size of a sesame seed that can tunnel into and kill a giant tree and armyworms that fly up to 100km a night.
No, not the zombie apocalypse. These are some of the latest alien invaders to infest SA.
Collectively, they are responsible for wiping out millions of rands worth of crops every year and, according to an international study published earlier this year, cost the African continent about R50-trillion annually. This is more than the combined GDP of the continent.
Alien plants and animals, so called because they evolved outside SA’s borders, are increasingly on the march, sometimes hitching rides with humans as they colonise fresh terrain, according to new scientific research.
A report released last month by the department of forestry, fishing and environmental affairs suggests SA faces a grim battle against hungry critters intent on devouring local plants, water and weaker animals.
It is the second national status update on invasive aliens and, worryingly, shows the number of such species has increased from 1,637 to 1,880 since the first report three years ago, and none has been officially eradicated. Of those studied so far, several have already caused “major or massive environmental impacts”, concluded the report, which has proposed a national registry of invasive aliens to help government better control their spread and impact.
However, it’s not all bad news. The “invasives” are up against a new generation of “bio-controls” — other critters mobilised to battle them in the interests of restoring a natural balance, or as close to that as possible.
More than 150 biocontrol aliens have been released to contain invasives, of which more than 800 “escaped” into SA from foreign climes.
Since the first status report in 2017, 10 new species-specific control interventions have targeted four freshwater fish, two bird, two plant, one marine and one freshwater invertebrate species. Interventions are effective if properly monitored, the report noted.
The fightback is costing the government about R1bn a year, much of that targeting notorious culprits — thirsty pine and gum trees that are a fire risk and reduce available fresh water.
However, some of the latest invasives are relatively unknown and no less concerning. These include the polyphagous shot hole borer beetle, first detected in the KwaZulu-Natal National Botanical Gardens in Pietermaritzburg in 2017. It has already killed thousands of tree, including agriculturally important species.
Other worrying immigrants include water weeds, spiny cacti and fish that feast on local species.
A large proportion of new invaders entered via a few known accidental “pathways’”, among them shipping and timber, and as contaminants on imported animals.
“SA’s ability to know where, when and how alien taxa are being introduced, or are likely to be introduced, has been improved by recent research on the pet trade, medicinal plant trade, biofouling and contaminants of animal imports,” the report noted.
“The movement of alien taxa between countries in Africa, in particular damaging agricultural pests, is a growing concern. For example, the tomato leaf miner (Tuta absoluta) was detected in 2016 and the fall armyworm (Spodoptera frugiperda) in 2017.”
Scientists said the latest research highlights the need for targeted strategies to deal with the worst invasives, particularly in the context of dwindling budgets.
“The bottom line is that these things are spreading faster than we can clear them and we have to make decisions on how best to address the problem,” said Brian van Wilgen, one of the status report lead authors and a professor at Stellenbosch University’s Centre for Invasion Biology.
“It doesn’t work if you start many projects all over the place. We have to decide on priority areas and put all effort on those areas. We do not have the resources to effectively clear everything everywhere and we have to practise conservation triage, deciding what to save and what to sacrifice, if we are going to at least make some progress,” he said.
A case in point was the current effort to clear alien trees from valuable water catchment areas. The status report noted that government-supported teams treated about 160,000 hectares of invaded land annually. However, “at the few sites where the effectiveness of such control has been assessed, the control efforts appear to be largely ineffective”, the report said.
Invasive species are not the only biological headache for farmers, as evidenced by the brown locust infestation in Free State maize fields.
Free State Agriculture commercial manager Jack Armour said the organisation had imported a beetle for the biological control of a reviled alien weed called Satan’s bush. Another weed, Seriphium plumosum, commonly known as Bankrupt bush, has been formally gazetted as an indicator of bush encroachment, Armour said, adding that untended road reserves provided pathways for invasives.
The Sanbi Invasives Status Update Report was formally launched last month by forestry, fisheries and environment minister Barbara Creecy, who also announced a 10-year National Invasive Species Strategy and Action Plan.
Speaking at the launch, Creecy said the aim of the strategy was to improve rural food security and livelihoods.
“It is envisaged the project will [make] a significant contribution towards the efforts to mitigate the impact of biological invasions on SA’s biodiversity,” she said.
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