Weevils to eat invasive plant on Yorkshire waterways

The weevils have evolved to only feed on the invasive floating pennywort

South American weevils have been introduced to waterways in West Yorkshire in an effort to control the invasive floating pennywort plant.

The weevils have been released into the Aire and Calder Navigation and one of the tributaries of the River Holme.

The pennywort, native to Central and South America, was brought to the UK in the 1980s as an ornamental pond plant.

It forms dense mats which choke waterways, reducing oxygen supplies to fish, insects and water plants.

The weevils - which have evolved to only eat the floating pennywort - are being introduced in a collaboration by Yorkshire Water, the Centre for Agriculture and Bioscience International (CABI), Leeds City Council, River Holme Connections and a private landowner.

The plant chokes the waterways, restricting the oxygen for fish and other wildlife

They have been approved for release as a natural pest control for the plant, which CABI said could grow up to 20cm (8in) a day.

The adult weevils feed on the leaves of floating pennywort and females lay eggs into their stalks, where larvae then eat into the stems of the plant, reducing its ability to grow and spread further.

Dr Steph Bradbeer, invasive species and biosecurity adviser at Yorkshire Water, said: "Invasive non-native species pose a very real risk to Yorkshire's environment and wildlife.

"They can also impact on our ability to treat and distribute water to homes and return wastewater safely to the environment.

"Floating pennywort, if unchecked, can cause significant problems in slow-flowing watercourses and impact drainage systems.

"We hope the release of these specialist weevils will provide a way of tackling it without the need for mechanical or chemical intervention."

Djami Djeddour, senior project scientist at CABI, said: "These weevil releases are the culmination of over a decade of collaboration with South American scientists and comprehensive safety and efficacy testing in our quarantine facilities, so it is thrilling to finally get them out into the wild."

Djami Djeddour (l) has also helped to clear some of the plant from the waterways