Is river weed-eating insect the lesser of two weevils?
South American bug to control pennywort, which threatens fish and makes waterways inaccessible
A “WONDER WEEVIL” has been introduced to fight the pennywort weed that grows 20cm a day in English rivers.
The non-native South American weevil has been released into waterways in a world-first effort to tackle the highly invasive plant, which is making rivers inaccessible to canoes and anglers.
It marks the first time floating pennywort has been tackled through ta “biocontrol” measure, where an animal, rather than pesticide or mechanical method, is used to reduce the spread of the plant.
The move marks the culmination of a decade-long research project funded by the environment department to explore using this method to control the plant, which is invasive in England, in European countries and Australia.
Originally from North America, floating pennywort (Hydrocotyle ranunculoides) was imported into the UK as part of the aquatic horticultural industry.
It was first found in the wild at a site in Essex in 1990 and has since spread widely, mostly in the south-east of England but increasingly in Wales and the Midlands and west of England. It was banned from sale in 2014 after campaigning from conservation charities.
It chokes native wetland plants and threatens fish and invertebrates by reducing oxygen levels, and is difficult to control.
Among efforts to tackle the plant are an annual event run by British Canoeing and the Angling Trust.
Scientists at the Centre for Agriculture and Bioscience International (CABI) have been researching the use of the weevils and other methods to con- trol the plants.
The South American weevil (Listronotus elongatus) eats the leaves of the pennywort and also lays its eggs in its stalks. Larvae eat the stem of the plant and restrict its ability to spread.
Non-native insects have been released into the UK for decades in projects to control the spread of other species, targeting plants or other insects.
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.”
Trevor Renals, senior technical adviser on invasive species at the Environment Agency, said: “Releasing South American weevils offer us a safe and self-sustaining management option for floating pennywort without the cost and damage associated with herbicide treatment and mechanical removal.
“It’s a natural solution to a problem that we anticipate could get much worse as our winters get milder due to climate change. We need to act now.”
Djami Djeddour, senior scientific officer at the 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. 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.”