Amsterdam releases five thousand leaf fleas to take on Japanese knotweed

Psyllids have been release to fight knotweed

Credit: DEFRA/PA Wire

Dutch researchers have released thousands of leaf fleas in the desperate hope of getting Japanese knotweed — a harmful and invasive plant species that is causing millions of euros in damage — under control.

The knotweed was first introduced to the Netherlands in the 19th century as an ornamental plant, but its roots can damage concrete pavements and foundations and can choke out flora.

The species has become so invasive there that unprecedented measures are being taken. For the first time, the Dutch government issued an exemption on a nationwide ban on introducing an alien insect species to the Netherlands in order to help bring the spread under control.

It has released an initial 5,000 Japanese knotweed psyllids, or Aphalara itadori, to determine if they will survive the winter and establish themselves through the new year.

The psyllids, a natural predator to the knotweed, can slow down or even stop its growth by sucking on the nutritious sap of the plant. 

The knotweed’s aggressive roots, which can grow up to 20cm a day and break through concrete or tarmac, are a major issue across the UK and Europe. 

Amsterdam has previously looked at using fire, hot water and even lasers in controlling the plant’s growth without success.

Suzanne Lommen, an entomologist who is coordinating research on the Japanese knotweed psyllid, said the plant costs millions of euros per year to control, but hopes the tiny fleas can provide a “very cheap and environmentally-friendly solution”.

“If the psyllid can establish, reproduce and spread, and to the damage we see in the breeding trials, it can hopefully inhibit the growth and spread of Asian knotweed,” she said.

In 2010, the insects were licensed as a means of biological control of Japanese knotweed in the UK. Before the insects were introduced, it cost the Government over £150m a year to control and clear.