Tiny mite could prove a ‘mighty’ weapon in the fight against one of the UK’s most invasive weeds

CABI scientists are stepping up the fight against one of the UK’s most invasive non-native aquatic weeds.

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Crassula is an aquatic plant that can take on various growth forms; able to act as a submerged, emergent, or semi-terrestrial species.

Approval has been given for the release of a novel biological control agent – the mite, Aculuscrassulae – to assess its ability in the real-world environment to suppress Australian swamp stonecrop (Crassula helmsii), also known as New Zealand pigmyweed. This follows carefully controlled laboratory testing to ensure the safe, controlled release of the mite in the UK.

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Enlisting microbes to enhance Himalayan balsam biocontrol

Bee on Himalayan balsam
Himalayan balsam flower drawing bee pollinators away from native flowers

Building on CABI research into the biological control of Himalayan balsam (Impatiens glandulifera) using a rust fungus (Puccinia komarovii var. glanduliferae), a Natural Environment Research Council (NERC) funded collaboration between Royal Holloway, CABI and the University of Reading is investigating the role of the microbial community associated with the plant and how these microbes may be exploited to enhance biocontrol efficacy and aid in the recovery of invaded sites. It is hoped that the findings of the study may be applicable to biocontrol programmes more widely.

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CABI releases rust fungus to control invasive weed, Himalayan balsam

26 August 2014 – From today, not-for-profit research organization, CABI, will be releasing a rust fungus at locations in Berkshire, Cornwall and Middlesex as part of field trials to control the non-native, invasive weed Himalayan balsam (Impatiens glandulifera) using natural means.

Himalayan balsam has rapidly become one of the UK’s most widespread invasive weeds, colonizing river banks, waste land, damp woodlands, roadways and railways. The Environment Agency estimates that the weed occupies over 13% of river banks in England and Wales. It can reach over three metres in height and competes with native plants, reducing biodiversity. Large scale chemical and manual control is often not feasible and not economically viable.

Himalayan balsam infestation on the river Torridge, Devon, UK
Himalayan balsam infestation on the river Torridge, Devon, UK (Rob Tanner, CABI)

Using existing measures, the Environment Agency estimates it would cost up to £300 million to eradicate Himalayan balsam from the UK.

The release of the rust fungus comes after an eight-year research programme funded primarily by Defra and the Environment Agency, with contributions from Network Rail, the Scottish Government and Westcountry Rivers Trust. During the course of the research, testing in quarantine laboratories has established that the rust fungus causes significant damage to Himalayan balsam and does not impact on native species.

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The advance of the Asian hornet creates a buzz in the UK media

Some of the species that are included in our open-access Invasive Species Compendium are well known to the general public, for example Japanese Knotweed. Others are more obscure, and I had never heard of the Asian Hornet, Vespa velutina, until I edited the datasheet about it earlier this year. I was therefore interested to hear an item about it a few days ago on the Today programme, one of the best-known programmes on BBC radio (you can listen to the item here).

Picture: ©Muséum de Toulouse/Didier Descouens-2013. CC BY-SA 3.0

The species originates from eastern Asia and was accidentally introduced to southern France about 10 years ago in a consignment of terracotta pots from China. It spread rapidly through France, soon reaching the stage where eradication was impossible, and into neighbouring countries. As it is a predator of honey bees, it is of serious concern to the beekeeping industry (where it is native, bees have some ability to kill hornets by surrounding them with a ball of bees and heating them to death, but European bees are much less effective at this). It can sting people badly too, although European populations are generally not very aggressive.

It is considered very likely that V. velutina will spread to the UK, either through accidental transport by humans or by flying across the English Channel (see here for a risk assessment). Eradication will only be possible if it is spotted promptly, and long-term management will also require knowledge of where it is present, so the public (especially beekeepers) are being asked by the Department for Environment, Food and Rural Affairs to look out for it and report any sightings to alert_nonnative@ceh.ac.uk. This request has been picked up by several parts of the UK media, including the Independent, the Daily Mail and even the local newspaper here in south Oxfordshire.

An information sheet describing how to recognise the species is available here; August and September are the peak months for V. velutina activity, so if you live in the southern part of the UK, or indeed anywhere else in western Europe, please look out for it!

Mark Palmer
Content Editor
CABI