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The discovery of a stink bug in a Surrey garden has caused worries the insects may be becoming established in the UK.
The brown marmorated stink bug is a pest of fruit crops, previously causing millions of dollars' worth of damage in the US.
While scientists think the bugs will begin to breed in the UK, they also believe that the insects are more likely to become a home nuisance rather than a major crop pest.
Concerns have been raised after an invasive insect pest was found at one of the UK's 'flagship' gardens.
An adult brown marmorated stink bug was caught in a trap at the Royal Horticultural Society's (RHS) garden at Wisley, Surrey, following on from others being found in Essex and in the Museum's Wildlife Garden.
The insect is a crop pest from Asia, and has caused millions of dollars' worth of damage since arriving in the US 30 years ago. While it is not yet believed to be a permanent resident of the UK, there are worries it could become a threat to crops if it becomes established.
Dr Glen Powell, the head of plant health at RHS Wisley, says, 'While there is currently no evidence of breeding, we would expect the stink bug to grow in prevalence and it may become problematic in gardens during summer and homes in the winter months within five-ten years.'
Scientists recommend that anyone finding what could be one of the insects should get in touch to help them understand where the stink bugs are in the UK.
Brown marmorated stink bugs are natives of southeast Asia, where they live in China, Japan and Korea. They feed on a range of plants by inserting a straw-like appendage known as a stylet into fruits to suck out the sap.
This causes fruit to become scarred and blemished, which reduces their value for sale. In some instances the stink bugs, which produce a noxious liquid when threatened, can be blended into products such as juices and contaminate them.
There is also some evidence that the insects may be able to transmit bacteria between different plants as they feed on them.
The combination of these effects mean that the insect causes severe financial damage to farms, with losses of over 50% possible in some cases. The worst of these are caused by swarms of the insects, which gather together when they release certain pheromones.
While they are adapted to life as a pest in their native countries, their global spread is down to humans, rather than the stink bugs themselves.
Dr Max Barclay, the Senior Curator in Charge of Coleoptera (beetles) at the Museum, says, 'They get to the UK as they often try to overwinter in objects like packing cases and end up being brought to different countries.
'We had a few importations last year around Christmastime when they showed up in people's houses but we didn't treat these as seriously as they probably came in a parcel from China or any of the other countries where it lives.'
In addition to occasionally turning up in people's luggage, the odd adult stink bug has also been discovered in the wild in the UK. This is of more concern to scientists as concern grows they may be establishing populations.
Two adult beetles were discovered in Hampshire in 2018 and 2019, while three more were found in Essex, Leicester and the Museum itself in 2020. While useful for scientists, these finds aren't yet enough to work out if the stink bug is here to stay.
'It's too early to say whether they're going to establish,' Max says, 'but they could establish across the south of England more or less south of the Wash, because the climate is warm enough.
'The southeast is the mildest area so it's also where the fruit and wine industry are concentrated so the places where the stink bug is most likely to occur are the places we least want them to be.
'It's not here yet, but it can be expected that it will become more commonplace over the next few years.'
While the bugs are likely to get a permanent foothold in the UK in the coming years, Max believes that they aren't likely to become as big a threat to crops as they have been in the US.
'While we can probably expect it to establish in city areas, I think they are likely to restrict themselves to the managed environment,' says Max. 'When the stink bug showed up in Prague in about 2018 it became common in the metropolitan areas, but not yet in the countryside. They’ve done a similar thing in Switzerland and Germany.'
This means that the stink bug is also less likely to pose a threat to native species it might compete with, such as shield bugs.
'I don't think it's likely that they will compete with native species,' Max says. 'We had competition with the harlequin ladybird, which initially did have an impact on native ladybirds, but the situation is stabilising now.
'The ladybirds became almost universal at one point, though they’re now beginning to die back again. That sometimes happens with an invasive species, it can be a bit of a pest at first but then become less of a problem when its diseases and parasites catch up with it.'
If the stink bug does become established, it is mostly likely it will become a smelly nuisance in homes, rather than of crops. While it may be tempting to try and get rid of them, most of the insects in the UK's houses and gardens will not be the brown marmorated stink bug.
'There are a lot of similar native stinkbugs and shieldbugs,' Max says. 'If you find one in the garden, 99% of the time it will not be the brown marmorated stink bug. If you find one inside, it's more likely to be one, but still very uncommon.'
Alternatively, members of the public can send images of suspected stink bugs to the Museum's Angela Marmont Centre for UK Biodiversity or the horticultural research organisation NIAB EMR for an expert to identify it. This information can then be used to assess the reach of these insects in the UK, and whether or not they are becoming more common.