ONE of the latest alien insect pests to breach UK border controls – such as they are – is set to make a right old stink.

This is the brown marmorated stink bug (Halyomorpha halys), a sap-sucking bug with a shield-shaped body. The brown-coloured shield bug is a serious pest of a wide range of fruit trees, including apple, pear, plum, peaches and nectarines, leaving brown stains on the fruit which ruin their marketability.

There is a large number of native shield bugs in the British Isles, with many like the forest shield bug (Pentatoma rufipes) belonging to the same insect family (Pentatomidae) as Halyomorpha halys. However, none are regarded as economic insect pests.

However, there is no doubting the pest potential of the brown marmorated stink bug, which emits an unpleasant almond-like smell as a defence mechanism against predators. Its intrinsic sweet marzipan-like odour has been described by Max Barclay, entomologist at the Natural History Museum, as “oily, toxic and clingy”. It is certainly toxic for the wine-making industry, because if sufficient beetles invade and infest bunches of wine grapes, their chemicals will contaminate the wine to destroy the delicate flavours which make or break a vintage. Observers claim this insect has the capacity to cause real damage to the UK’s rapidly expanding grape-growing and wine-making industry.

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This alien invasive insect pest is clearly of interest to arborists who are regularly called upon to manage fruit tree orchards. However, like other insects with highly invasive pest potential and credentials, it has a very wide plant host range including a large number of forest tree species.

Forestry Journal: Catalpa (Indian bean tree) is a host for the brown marmorated stink bug. Like this fine specimen seen in flower in Parliament Square, London, right under the nose of David Lloyd George.Catalpa (Indian bean tree) is a host for the brown marmorated stink bug. Like this fine specimen seen in flower in Parliament Square, London, right under the nose of David Lloyd George.

Halyomorpha halys is a native of East Asia (China, Japan, Korea and Taiwan) but had already spread its wings far and wide before arriving in southern and eastern England. Having arrived in North America in the late 1990s, the pest is now spread through 41 states of the USA and is also widespread in Canada. North American distribution covers more than 100 different plant hosts including ash, lime (Tilia), buckthorn, crab apple, dogwood, walnut, mulberry and Indian bean tree (Catalpa).

The invasion of continental Europe started somewhat later – around 10 years ago – but the plant host range in Europe already covers over 50 different species across more than 30 plant families. With regard to trees, this includes Indian bean tree (Catalpa bignonioides), Rowan or mountain ash (Sorbus aucuparia) and common dogwood (Cornus sanguinea). Even common ash (Fraxinus excelsior), much persecuted by pests, has not escaped this nasty-smelling insect.

Entomologists warned for years that it was only a matter of time before the insect arrived in the UK. Its presence has now been confirmed at three sites in London, the Home Counties and Suffolk, but experts believe it is more widely spread across south-east England, worsening with a warming climate and impossible to eradicate.

The question is: how did this insect pest get into the UK? Despite the egg and nymph (larval) forms found on a variety of fruit and vegetables, experts believe cold-chain conditions for fresh food commodity trade greatly diminish probability of the pest being spread in this way. Transnational trade in nursery stock is regarded as a potential route for the introduction of the pest in its nymph (juvenile) form.

However, the most likely route of introduction into the UK is as adult beetles hitching a ride on wooden crates or pallets used in international trade, which is how the Asian Longhorn beetle (Anoplophora glabripennis) arrived in Kent.

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