Fleadom! Holland releases 5,000 fleas to solve knotweed problem

Dutch researchers have released thousands of Japanese leaf fleas in hopes of getting a harmful and invasive plant species under control.

Japanese knotweed, also known as Asian knotweed, was first introduced to the Netherlands in the 19th century as an ornamental plant, but the species is now notoriously invasive. Its roots can damage concrete pavements and foundations and it is so proliferous that it chokes out local flora.

For the first time, the Dutch government issued an exemption on a nationwide ban on introducing an alien species to the Netherlands in order to combat the plant. Five thousand of the insects will be released on three field locations initially, to determine if they will survive the winter and establish themselves through the new year.

The leaf flea, also known as the Japanese knotweed psyllid (Aphalara itadori), is a natural predator of knotweed. It feeds on young shoots of knotweed plants and can slow down or even stop its growth by sucking on the nutritious sap of the plant.

Researchers from the Institute of Biology in Leiden, where Japanese knotweed was first brought into the Netherlands, started field experiments this week to use the psyllid as a “weapon” against the incendiary plant.

Entomologist Suzanne Lommen, 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.

As to whether the psyllid could turn the tables and cause widespread damage to other plants, Ms Lommen said: “There are very reliable methods to determine this. For example, extensive risk analyses have been performed for plant species in North America, England and northwestern Europe.

“This shows that the Japanese knotweed psyllid does not pose a risk to native plants or plants of economic value. All native Dutch species of the knotweed family have also been tested, and none proved to be a suitable food source for the Japanese knotweed psyllid.”

The Netherlands Food and Consumer Product Safety Authority, which monitors animal and plant health, animal welfare and consumer food and product safety in the country, determined that the fleas do not pose a threat to native biodiversity.

But whether or not the psyllid will thrive in the Netherlands is not yet known, said Ms Lommen.

“He comes from an area in Japan where the climate most resembles that of the Netherlands,” she said. “In the laboratory, he thrives on the interbreed knotweed that grows here. But reality will show whether he can survive in our country.”

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

More fleas will be released next spring in hopes of getting them to reproduce. Once their population grows larger, scientists will be able to determine if the psyllid are “doing enough damage to the Asian knotweed to push it back”, said Ms Lommen.

“It will take a few years before we see any results,” she cautioned. “I do not expect any side effects and hope for a quick establishment. If we can confirm that, we hope to release the knotweed psyllid in more places in the future to help its spread.”