Scientists invent unique solution to combat invasive plants without chemicals: 'They have natural enemies'

A team in South Africa is fighting invasive plants with their natural enemies: bugs, the Daily Maverick reported.

For example, sustenance farmers in northern KwaZulu-Natal are losing thousands of goats — and children are getting rashes — because of an invasive weed, parthenium. Parthenium spreads easily through grazing land because it outcompetes native grasses, and none of the local insects eat it.

That's the problem with invasive plants — species that are transported from their native areas to new regions and turn out to do unreasonably well there. They don't have natural predators or diseases to check their spread, so they multiply and overwhelm other species that have normal relationships with their ecosystems. If they happen to be poisonous like parthenium, they can cause real damage.

The researchers set out to find a bug they can safely release that will eat the plant and control its spread.

"Parthenium is indigenous to the lands around the Gulf of Mexico in North America," researcher Lorraine Strathie said. "... In their native range, plants have evolved for millions of years, and they have natural enemies in the form of insects which feed on them, fungi and other pathogens. So it's what we call top-down control.

"So, they reduce their reproductive output, the number of seeds they produce, and their growth rates. And these insects, many of these natural enemies … that feed on them have become highly specialised to get around those chemicals and other defences. So they become highly, what we call host-specific — they only feed on one species of plant."

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The last thing researchers want is to introduce another invasive species — a bug that would start chowing down on native plants. So, they are highly selective about choosing species to eat, for instance, only a single color of a single strain of parthenium — and even then, researchers rigorously test whether the bugs will eat native plants before releasing them.

Getting to a point where the bugs are controlling the invasive species could take 20 years.

However, efforts to control weeds without toxic pesticides are worthwhile to reduce unintended consequences, and the work in this case is moving forward. Similarly, another South African team is using weevils to control invasive water plants.