A brown marmorated stink bug pierces the stem of a plant with it's piercer

A brown marmorated stink bug feeding on a plant. Stink bugs are sometimes called shield bugs due to their shield-shaped bodies. They emit an unpleasant odour via glands inside the body to ward off predators. © Tim Haye/CABI.

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Brown marmorated stink bugs arrive in the UK and pose threat to crops

The brown marmorated stink bug has arrived in the UK, threatening fruit and vegetable crops during summer and heading inside people's homes during winter.

One of the first stink bugs to be identified was caught in the Museum's wildlife garden at South Kensington by Museum scientists . 

Native to China, Japan and Korea, brown marmorated stink bugs are fast-breeding insects that come in various shades of brown and grow up to 1.7 centimetres. They get their name from the foul smell they exude when they feel threatened.

Brown marmorated stink bugs eat fruit and vegetable crops

During the summer, these pesky pests feast on fruits and vegetables such as apples, pears, peaches, tomatoes and sweetcorn by piercing the surface and sucking out the juice. They distort the produce and leave behind rotting spots and blemishes which can make the plant inedible or unsellable.

Museum entomologist Max Barclay says, 'If you eat a damaged fruit, there's no risk to your health. The fruit just doesn't look beautiful, so the sale value is reduced. These fruits usually end up as juice.'

Sometimes stink bugs can end up in products made from fruits, such as wine, and contaminate the flavour. This often results in the entire crop being thrown away - a huge waste and loss of profit.

Max says, 'If you have a bunch of grapes that contain stink bugs and you grind them up into wine, you get the smell of stink bugs in the drink and people don't like that. You have the same problem with some ladybirds which get into wine and spoil the taste of it.'

Newly hatched stink bugs surround white egg shells on the back of a leaf

Newly hatched brown marmorated stink bugs. Eggs are normally laid on the underside of leaves in masses of up to 28, and nymphs grow into adults within 35-45 days. Image by Gary Bernon/wiki (CC BY 3.0).

Unwelcome visitors in British homes

Ancestrally, brown marmorated stink bugs would hibernate in abandoned caves throughout winter. In inhabited areas, they are drawn to people's homes for warmth and shelter.

These stink bugs were accidently introduced to the USA in the mid-90s and have since spread to 44 states. In North America, the stink bug population has grown exponentially and there are records of thousands gathering in houses.

'One of the reasons stink bugs are considered pests is because they cluster around window frames in large numbers and leave droppings,' says Max. 'If you try and sweep them away, they will produce these unpleasant-smelling oils which will stain the furniture. If the oils get on your fingers, it's really hard to remove.'

After visiting the US in 2014 and noticing a lot of brown marmorated stink bugs, Max predicted these pests would eventually arrive in the UK too, especially as they had already formed populations in some parts of Europe including Switzerland, France and Italy. That year, two brown marmorated stink bugs were found on imported timber at British borders.

'Once these things make a foothold, they establish pretty quickly,' says Max. 'We've seen this with a lot of invasive species before, like the harlequin ladybird. You find one or two, then five or six and then they're everywhere.'

A sliced apple reveals brown rot caused by stink bugs feeding

Common signs of stink bug feeding include spots or blotches, grooves and discolouration. Image by Rob Morisson/USDA-ARS.

Monitoring stink bugs to anticipate the future

Brown marmorated stink bugs are considered an invasive species.

The horticultural research organisation NIAB EMR, based in Kent, has coordinated a trapping programme, funded by the Department for Environment, Food and Rural Affairs (Defra), to monitor the arrival of brown marmorated stink bugs. It involves lacing a small piece of double-sided sticky plastic with a synthetically produced sex pheromone to attract the pest.

The Museum hosted a trap in its Wildlife Garden which, in summer 2020, caught a male stink bug. Another male was found on a pheromone trap in RSPB Rainham Marshes in Essex. These were the first two samples collected in 2020. At the end of the year, a resident in Surrey found one hibernating in her house.

'The trapping programme is more useful as a monitoring device than a controlling one,' explains Max. 'It's very difficult to control brown marmorated stink bug populations by killing individuals.

'Trapping is a good way of detecting the presence of the species which might influence your other behaviour, like bug-proofing your house or growing a different crop that is less susceptible to this pest.'

A team of UK-based researchers, including Max, Glen Powell at NIAB EMR and Andrew Evans from Scotland's Rural College (SRUC), have now published a scientific paper on the stink bug in the British Journal of Entomology and Natural History. The researchers looked at how global warming will change the likely spread and establishment of brown marmorated stink bug within Britain and predicted the bugs will inhabit London, as well as some parts of eastern England where it is the warmest.

Researchers at NIAB EMR are worried about the threat brown marmorated stink bugs pose to British crops. The species has a wide diet of over a hundred agricultural and ornamental flora species and could damage a large number of plants in gardens and on farms in the UK. Experts are currently researching how to manage this issue to avoid millions of pounds of economic damage.

Silhouette of stink bugs crawling on a window

Male stink bugs release an aggregation pheromone which attracts other stink bugs to form a mass gathering in one area. © Mike Lewinski/Flickr (CC BY 2.0).

The last invasive insect species to hit the headlines in the UK was the harlequin ladybird. Native to Asia, the ladybird was noticed by the public in 2004, eliciting both curiosity and caution. Soon after, they multiplied to all over the country and are now the most common ladybird species in the UK.

Invasive species like the harlequin ladybird and brown marmorated stink bug are able to enter the UK through increasing global trade, and they thrive due to climate change.

Stink bugs often hide in shipping crates and wooden pallets during winter, items which are frequently moved around countries. When spring arrives, the insects could be in a different country, and therefore have an opportunity to expand into a new part of the world.

At this stage, there isn't any evidence that shows the brown marmorated stink bugs have started to breed and establish populations in the UK, so monitoring via pheromone traps is crucial.

If further bugs are detected, NIAB EMR aim to follow this up with field sampling around sites of capture. Detection and monitoring of early populations allow NIAB EMR to alert growers of vulnerable crops, who can then put crop protection strategies into place.

Fortunately, the UK can benefit from existing research that has taken place elsewhere in the world, such as the USA, which will help in developing effective control strategies. One idea is to attract large number of stink bugs into a net trap using pheromone and then treat them with a plant-protecting product.

An annotated stink bug

Brown marmorated stink bugs can be easily mistaken for native shield bugs which also smell © Tim Haye/CABI

If members of the public think they have found a brown marmorated stink bug, NIAB EMR encourage them to first check online to make sure it hasn't been confused with a native species such the green shield bug, which turns brown over winter.

'There's also a sloe bug named after the fruit they use to make sloe gin,' adds Max. 'It's purplish brown and quite hairy under the microscope, which the stinkbug is not. But to the inexperienced eye, it would look very similar.'

If it turns out to be a brown marmorated stink bug, the scientists request that it is captured in a small container and posted to the Museum or NIAB EMR. Images of suspected stink bug can also be emailed to Max or NIAB EMR or for confirmation.

Max says, 'The insect fauna changes all the time. We have about 27,000 species of insects in the UK and about 5% of them have arrived here in the last few decades.

'It's only occasionally we get an invasive species that draws attention to itself by being a nuisance species or reaching very large populations. The last one was the harlequin ladybird, which was about 15 years ago. Now it's the stink bug.'

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