Floating pennywort is a non-native invasive species, which spreads rapidly and causes major destruction to our waterways. Its large mass depletes oxygen levels in the water, in turn affecting other native plants and animals.
Its presence is also felt by boaters and other waterway users, who are unable to paddle or propel their way along the navigation as a result.
South American weevils had never been used to aid in floating pennywort removal before.
What are South American weevils?
Imported from Argentina and measuring approximately 5cm in length as adults, South American weevils are a type of beetle which offer a natural and environmentally-friendly alternative to chemical sprays.
How do weevils combat floating pennywort?
These plant-munchers feed and breed amongst the foliage, slowly but effectively reducing its vast quantities which span across our canals and rivers.
If weevils are a non-native species, how is releasing them on our waterways safe?
Along with other collaborators, CABI spent time in Argentina monitoring and observing various insects and pathogens, including the South American weevil.
After ten years of comprehensive testing and research, there was no evidence to suggest that the weevil would attack any other living organisms beyond floating pennywort.
As a result, in 2021 the South American weevil was cleared for combat under a carefully coordinated release strategy along our canals and rivers.
How long do South American weevils live for?
Given that they don't attack other plant species, we expect the weevils to remain in the waterways and feed until the plant has gone.
However, it was evident that climatic factors such as air and water temperature have a significant impact on the successful overwintering and feeding activity of the weevils, and this must be a key consideration on both invasive plant growth and the biocontrol methods that are used to eradicate them.
Was the trial a success?
The weevils got a big thumbs up from our team. By the end of the project, we had successfully deployed thousands of weevils across 22 sites, many with multiple release locations - and the visible reduction of floating pennywort was as we had hoped.
We were also thrilled to note evidence that weevils had persisted for consecutive years in some areas, prompting a return of native water cress.
How you can join the fight against invasive non-native species (INNS)
If you spend time on our canals and rivers, one of the most important things you can do is to remember to Check, Clean, Dry. These steps help stop the spread of harmful plants and animals to a new area, and should always be done before exiting a waterway, even if you are moving to another spot just a few miles away.
