Author
Djamila H Djeddour
d.djeddour@cabi.org
CABI
Ascot
Coauthors
Suzy V Wood, CABI , Ascot, United Kingdom
Corin F Pratt, CABI , Ascot, United Kingdom
Guillermo Cabrera Walsh, FuEDEI, Buenos Aires, Argentina
Abstract
Introduced through the ornamental aquatic trade in the 1980s, floating pennywort (Hydrocotyle ranunculoides, Araliaceae) quickly naturalised and has become one of the most rapidly spreading and costly aquatic weeds in the UK and Northwest Europe. After a decade of safety testing, the Argentine weevil Listronotus elongatus (Curculionidae) was granted ministerial approval for release in England in late 2021. Field trials have since been undertaken at more than 25 sites across varying aquatic habitats in England. In 2025, following further research, the Dutch regulatory authorities also approved release in the Netherlands and parallel field trials are being conducted at two sites, in collaboration with Dutch waterboards. Seasonal monitoring at each site for weevil persistence, spread and impact, together with temperature analysis, is helping to build our knowledge of the weevil’s establishment potential and climatic tolerance. Successful overwintering and establishment have been achieved across most sites in the south of England and up to the Midlands, alongside significant damage to the target host. Establishment in the north of England is possible but climatically challenging. An all-sector approach to the strategic management of floating pennywort across affected catchments, including the use of biocontrol, is helping to coordinate efforts and share best practices. The results of the field trials, establishment criteria and challenges faced are presented here.
keywords
Invasive aquatic weed
Listronotus elongatus
national management strategy
Highlights
Classical biological control as a viable management strategy for invasive Hydrocotyle ranunculoides
Establishment potential of the weevil Listronotus elongatus across different aquatic habitats
Challenges and opportunities for coordinated and integrated management based on field trial results