Gardening in a changing climate
Pests
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Some new aliens out-compete our natives. Harlequin ladybird (Harmonia axyridis) arrived in 2004, and spread rapidly. It has a voracious appetite and a longer breeding period than native species.
Find out more and take part in a survey
Andrew Halstead, RHS Principal Entomologist, says the following:
Pest problems in Britain’s gardens are getting worse. Over the last 30 years at least 25 new pest insects and mites have become established. This is not all due to changing climate as some of these pests have come from distant lands where the climate is more extreme than that encountered in Britain. They have had the opportunity to colonise Britain thanks to the international trade in growing plants and plant produce.
However, there is evidence that some pests have benefited from recent longer, warmer summers and milder winters. Rosemary beetle and berberis sawfly have extended their range northwards in mainland Europe in recent years, so it is possible that their establishment in Britain is climate related. Euonymus scale and leek leaf-mining moth were formerly largely confined to coastal gardens but now occur well inland. Glasshouse pests, such as glasshouse thrips and fluted scale, are now surviving out of doors in sheltered gardens.
New insects in Britain currently swelling the entomology mailbag in the RHS Members’ Advice Service are horse chestnut leaf-mining moth, southern green shield bug, berberis sawfly and harlequin ladybird. The last mentioned is not all bad, as it is an effective predator of aphids on garden plants and street trees.
Recent insect pest arrivals
In recent years, a range of insects has been introduced to the UK and already established themselves as garden pests.
Lily beetle (Lilioceris lilii)
This pest first became established in Britain in 1940. It originates from southern Europe. RHS entomologists have monitored its spread since then through enquiries at RHS Garden Wisley. It spread slowly at first but accelerated during the 1990s - the hottest decade on record in Britain. It is now well established across southern England and each year spreads further north; it has now been reported in Scotland.
Find out about RHS research into lily beetle
Rosemary leaf beetle (Chrysolina americana)
A Mediterranean species that feeds on aromatic herbs and shrubs. It was accidentally introduced to Cheshire in 1963, and found on garden plants at RHS Garden Wisley in 1994 and since 2003. It is now common in London and the home counties on rosemary, lavender and thyme.
Find out about RHS research into rosemary leaf beetle
Berberis sawfly (Arge berberidis)
This defoliates Berberis and Mahonia, and is a native of central and southern Europe and Asia. It arrived in Essex, probably in 2000, and is now widespread in England.
Fuchsia gall mite (Aculops fuchsiae)
This
is a microscopic creature that has a profound effect on fuchsias. It was first discovered in Brazil as recently as the 1970s and it has since spread to other parts of the world, including California, France and the Channel Islands. The mite was found for the first time on the mainland of Britain in early September 2007.
Find out more
Southern green shield bug (Nezara viridula)
This
sucks sap of a wide variety of plants and is native to southern Europe. It arrived in London in 2003, and is now widespread.
Paper wasp (Polistes dominulus)
A native of mainland Europe. In 2004 it was found nesting in the roof of the orangery at Ham House in Richmond, Surrey; since 2006 it has been breeding outside at the Thames Barrier.
Hollyhock weevil (Rhopalapion longirostre)
This
attacks flowers and seedheads of Alcea rosea and is native to central and eastern Europe. It was found in southeast London in 2006 and is now spreading.
New species of vine weevil
Two species of weevil closely related to the vine weevil have become established in London and other urban centres. The weevils are likely to have been imported with plants from their native Mediterranean and appear to be thriving in southwest London gardens where they can cause extensive damage to the leaf margins of evergreen garden plants. Rising temperatures will mean that these species are here to stay and are likely to spread.
Future potential pests
Mediterranean fruit fly (Ceratitis capitata)
The larvae are a major pest of a huge range of fruit trees, soft fruits and berries. A native of tropical Africa, the fly was spread around the Mediterranean during the 19th and 20th centuries and was accidentally introduced throughout the world. Larvae are sometimes found in shop-bought fruit. It is still established in southern USA despite a high-profile and well-funded eradication scheme.
Termites (Reticulotermes grassei)
Large colonies live in logs and timber of houses and other buildings, including garden sheds and barns, excavating riddling galleries, which destroy the strength and integrity of the timber. It is a native of the Iberian peninsula and has already been introduced to Paris and other French towns and cities by movement of soil and infested timber. An outbreak in north Devon in the 1990s is thought to have been eradicated (monitoring at the site with baited wood traps is to continue until 2010).
Geranium bronze butterfly (Cacyreus marshalli)
The caterpillars feed on Pelargonium. A native of South Africa, it spread to Europe by transfer of horticultural material and is now well established. Found in the UK near Lewes, East Sussex in 1997, but does not yet appear to have overwintered successfully, except for a handful of individuals sheltered in glasshouses.
Rose jewel beetle (Coroebus rubi)
An important pest of roses in southern Europe but as far north as Paris. The larvae burrow just under the surface of the stems and branches, making long spiral galleries that interfere with the flow of nutrients and water between roots and leaves. It also breeds in bramble, allowing wild reservoirs to build up that are not easily treated or controlled.
Twelve-spot asparagus beetle (Crioceris duodecimpunctata)
A pest widespread in Europe; reports of introduced specimens were made in Bristol in the 19th century. Both adult and larvae feed on asparagus; the adult is red with black spots and, despite its narrow shape, could easily be overlooked as a species of ladybird.
Pear ‘tiger’ lacebug (Stephanitis pyri)
This insect sucks sap of the leaves of pear and apple trees, causing discoloration and defoliation. Native to Europe and Asia; common in northern France. Other members of this genus already established in the UK include: S. rhododendri on rhododendrons in early 20th century; and S. takeyai on Pieris japonica in 1999.
Pine processionary moth (Thaumetopoea pityocampa)
Native to mainland Europe, the large furry caterpillars feed gregariously in silk nests on pine trees causing major damage; the hairs are irritating, causing rashes and stinging. There was an outbreak at Royal Botanic Gardens, Kew, but it is thought to have been successfully eradicated.
Gypsy moth (Lymantria dispar)
This forestry pest of broad-leaved trees was a former resident, native to mainland Europe and East Anglian Fens until the 1850s. In recent years an Asian strain of gypsy moth has spread across mainland Europe, and an outbreak occurred in Redbridge, Essex, in 1995 although this has been eradicated by pest control.
Colorado beetle (Leptinotarsa decemlineata)
A major potato pest wherever it is established. A native of North America, it arrived in Europe in 1877, but was controlled until an outbreak in France in 1922; it is now increasing and spreading through most of Europe, except Britain and Ireland. Examples turn up in Britain from time to time but it has not yet become established. Our cold and wet climate was always thought to have previously prevented its survival here. Colorado beetle ‘wanted’ posters are still pinned up in UK police stations.
Found a new pest?
If you think you have found a new-to-Britain pest and are an RHS member, you can send or bring samples to the Members’ Advisory Service at RHS Garden Wisley, Woking, Surrey GU23 6QB, or samples can be sent to the Plant Health and Seeds Inspectorate, a division of Defra that is responsible for dealing with new plant pests and diseases. Write to: PHSI, Central Science Laboratory, Sand Hutton, York YO4 1LZ.
Samples of the insect should be sent with the host plant in a sealed polythene bag in a stout container. The covering letter needs to give details of where the plant is being grown, from where it was obtained and when the problem was first noticed. A contact telephone number should be provided.