Beetle handed starring role in river restoration project

A plant-eating beetle has been playing a key role in a river restoration project in west Wales.

Azolla weevils (Stenopelmus rufinasus) were released in June at Natural Resources Wales’s (NRW) Llangloffan Fen National Nature Reserve near Fishguard to help control an invasive plant.

The weevil will help to eradicate the Azolla plant (Azolla filiculoides) that is dominating some parts of the reserve and the nearby Cleddau River.

Azolla is classed as an invasive non-native species and is one of the most invasive plants in the UK today, however it is highly susceptible to the weevil, which feeds and lives on the plant.

Aquatic fern

Azolla is a floating aquatic fern that grows rapidly and spreads across the surface of standing water and slow running water to form mats which can be up to 30cm thick.

During hot weather the mats can double in size in just four or five days. These block out light, killing other aquatic plants and reducing oxygen, which can lead to the death of fish and invertebrates.

Duncan Dumbreck from the Four Rivers for LIFE Project said: “Last summer we found several areas on the reserve where Azolla was taking over from native plants.

He adds: “With the Centre for Agriculture and Biosciences International’s (CABI) advice and support we released Azolla weevils at the reserve and the impact has been significant and we are delighted with the changes so far.”

The project contacted CABI as the organisation has successfully controlled Azolla in a number of areas using the Azolla weevil. More on this work can be found here.

Duckweed

After only eight weeks the impact has been substantial with most of the Azolla eaten and replaced by native duckweed.

The project will continue to monitor the progress of the weevils over the winter and early in the growing season next spring to assess whether they have managed to bring the Azolla under complete control.

The Azolla weevil is totally reliant on the Azolla plant and does not spread to other plants, therefore there is no risk to important fen plants and farming crops in the area.

The beetles are hardy but could be killed off by a very harsh winter.

The Four Rivers for LIFE Project is funded by the EU LIFE Programme with support from Welsh Government and Welsh Water.