South American weevils released in UK waterways to tackle invasive weed

Non-native bugs will be first attempt at using biocontrol on floating pennywort, after years of research

South American weevils have been released into Britain’s waterways by the government in order to tackle the invasive species floating pennywort.

The industrious bugs are being heralded as a hope to cut back the weed, which grows rapidly and blankets rivers and canals, drowning out the light and choking the life within.

Floating pennywort was brought over from North America as an ornamental plant. It can grow up to 20cm a day, forming dense rafts over rivers that are not only detrimental to biodiversity but disrupt recreational activities such as fishing and canoeing, and exacerbate flood risk.

It is highly unusual to release non-native species into the wild to tackle invasive species, and this is the first time biocontrol has been used to tackle pennywort.

When asked whether the release couldturn into an old-woman-who-swallowed-a-fly situation, with the weevils later needing to be controlled, officials assured the Guardian that there had been a decade of tests into the safety of the release. The government has also stressed that releases of weevils are strictly controlled, and require a licence from the Environment Agency.

Richard Benyon, the minister for biosecurity, said: “It is important that we tackle invasive non-native species to protect our native plants and animals and safeguard our environment, economy and health.

“We all have a role to play in stopping the destruction caused by floating pennywort – and the release of the South American weevil will boost our efforts to eradicate this pest from our waterways once and for all.”

The releases were carried out during the winter, with more planned for this summer. Since 2011, the Centre for Agriculture and Bioscience International (CABI), with Defra funding, has been investigating the potential use of a biocontrol agent for floating pennywort. They found that Listronotus elongatus were effective at removing it as they laid eggs on and ate the plant. The larvae also eat into the stems, reducing its ability to grow.

Djamila Djeddour, a senior scientific officer at CABI, said: “Following years of extensive research into the potential biocontrol of floating pennywort, we are pleased and excited to have released the weevil into the wild. Field studies by CABI scientists and collaborators in South America found this weevil to be the most promising agent and after comprehensive screening in CABI’s quarantine facility in the UK, it was confirmed to be highly specialised, only feeding and developing on this damaging weed.

“Further releases will begin later this year, supported by a range of sponsors, and the weevil’s impact, establishment and spread will be closely monitored.”