CSL Pest Risk Analysis for Eulecanium excrescens

CSL copyright, 2005

CSL Pest Risk Analysis for Eulecanium excrescens

STAGE 1: PRA INITIATION

1. What is the name of the pest? Eulecanium excrescens (Ferris) Hemiptera Coccoidea excrescent scale/ wisteria scale

Synonym: Lecanium excrescens Ferris

2. What is the reason for the PRA? A member of the public sent a sample of this pest to CSL in April 2002. The pest was on a tall and well established Wisteria sp., approximately 15 m high, in a domestic garden in SE London. The specimen was identified at CSL and confirmed by the British Museum of Natural History. This is the first record of this pest in Europe. The Plant Health and Seeds Inspectorate (PHSI) requested more information. A PRA was therefore conducted (June 2002). PHSI visited the site on 17th April 2002.

Note: CSL first became aware of the presence of the scale in 2001, when samples that had originally been sent to the Royal Horticultural Society were passed to CSL. However, the life stages present in these samples could not be accurately identified to species.

3. What is the PRA area? This PRA considers Europe and the Mediterranean as the PRA area, i.e. the EPPO region west of the Ural Mountains. Issues of particular concern to the UK are assessed in more detail.

STAGE 2: PEST RISK ASSESSMENT

4. Is the pest established in the PRA Area? There is nothing in the literature to suggest this pest is established in the PRA area. However, see 5.

5. Is there any other reason to suspect that the pest is already established in the PRA Area? Yes. Following the original finding, there have been reports of E. excrescens in ten other private gardens in Greater London. It may be more widely distributed.

6. What is the pest’s EPPO Status? (A1/A2 pest or Alert list ?) Not listed.

7. What is the pest’s EC Plant Health Directive status? Not listed. The UK informed the EU Standing Committee on Plant Health (SCPH) that E. excrescens had been found in London at the SCPH meeting of 30-31 May, 2002.

8. What are its host plants? Polyphagous - feeds on most deciduous temperate orchard trees, e.g. Malus (apple), Prunus (peach/cherry) and Pyrus (pear) (Essig, 1958). In the UK, E. excrescens has not been found in an orchard, only on ornamentals in private gardens where finds have been on Wisteria (Fabaceae), Prunus (cherry) and South African trumpet vine (Podranea ricasoliana: Bignoniaceae) (Malumphy in prep).

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9. What hosts are of economic and/or environmental importance in the PRA area?

9.1 Economic

Although primarily found on Wisteria in the UK, hosts in the USA of economic importance in the UK include, apple (Malus), almond (Prunus dulcis), apricot (P. armenaica), cherry (Prunus spp.), elm (Ulmus spp.), peach (P. persica), pear (Pyrus communis), sycamore (Acer pseudoplantus) and Wisteria.

9.2 Environmental

Although the orchard trees mentioned in 9.1 are hosts of economic importance they are also important in uncultivated environments.

10. If the pest needs a vector, is the vector present in the PRA area? No vector is required. This is a free living organism.

11. What is the pest’s present geographical distribution?

North America: USA (western and north-eastern USA [California, Connecticut, New York, Oregon and Pennsylvania] Essig, 1958; Gill, 1988) Central America: Absent - no records South America: Absent - no records Caribbean: Absent - no records Europe: Present - this is the first European finding. Africa: Absent - no records Middle East: Absent - no records Asia: Present in the Orient - no specific data from countries other than China (Deng, 1985). Oceania: Absent - no records

12. Could the pest enter the PRA area? Yes. E. excrescens has been found on Wisteria in a number of private gardens in south- central and south-west London (Westminster to Teddington). It is unknown how the pest was introduced.

13. Could the pest establish outdoors in the PRA area? Yes. When first seen in South Kensington in 2001, the population was very large (thousands of scales) indicative of a population that had been present for a minimum of three years. E. excrescens may be more widespread within London than is currently known. Further information on the status of E. excrescens in the UK could be obtained by carrying out a systematic survey of Wisteria and Prunus in the London area. Given that the scale is a large species (10-12 mm in length or diameter), populations should be relatively easy to detect.

The presence of E. excrescens in north-eastern USA (Connecticut, New York and Pennsylvania) and Oregon (the Pacific Northwest), and California, regions which have similar climates to much of the PRA area, suggests that E. excrescens could establish throughout much of Europe.

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CSL Pest Risk Analysis for Eulecanium excrescens

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It is possible that, in the UK, this species may be unable to establish outside the London urban heat island, other urban areas and the south-west, where winters are mild. In Southern Europe, where winters are warmer, survival during the winter will also be possible.

14. Could the pest establish in protected environments in the PRA area? E. excrescens is a pest of plants which are mainly grown outdoors.

15. How quickly could the pest spread within the PRA area? Natural dispersal is likely to be slow. However, first instars may disperse on air currents, e.g. caused by traffic in London. If transported via trade, it could spread undetected fairly quickly.

16. What is the pest’s potential to cause economic and/or environmental impacts in the PRA area? At present, in the PRA area, the organism only affects plants in private domestic gardens. It could slowly spread to the ornamental horticultural industry. Spread to fruit production within horticulture is likely to be even slower given the high value of such production, facilitating the use of more effective control methods.

In China, E. excrescens is regarded as a pest of Malus, Prunus and Pyrus (Deng, 1985). In California, E. excrescens is rare and not regarded as a pest of economic importance (Gill, 1988). There are no data from other US states. However, through feeding, E. excrescens does remove large quantities of sap, weakening the plant causing some leaf loss and slow dieback. Large amounts of honeydew are produced. Hosts are disfigured. Wisterias are very high value plants, often a main feature of gardens and buildings where they climb and cover south facing walls. Although detracting from the aesthetic appearance of the host, E. excrescens is unlikely to kill mature plants. Young, small plants would be more susceptible and could be killed. A parasitoid species has been detected attacking E. excrescens at one infested plant in London (Malumphy, in prep.). Thus natural enemies may be able to limit further damage.

Economic impacts can be assessed by estimating the cost of replacing contaminated individual host plants on a like for like basis. Wisteria plants in 13.5 litre tubs can be purchased for under £20. Larger plants, climbing buildings would be worth substantially more but could not be replaced on a like for like basis. The potential economic impact of this pest is likely to remain relatively small with negligible environmental or social impacts.

A parasitoid species has been detected attacking E. excrescens at one infested plant in London (Malumphy, in prep.). Thus natural enemies may be able to limit further damage.

17. What is the pest’s potential as a vector of plant pathogens? Not recorded as a vector.

STAGE 3: PEST RISK MANAGEMENT

18. What are the prospects for exclusion from the PRA area? Nil. E. excrescens is already present in at least eleven different locations in London. It has been in the UK for at least three years and may be more widespread. A survey would be required to determine its distribution in the UK.

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CSL Pest Risk Analysis for Eulecanium excrescens

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19. If the pest enters or has entered the PRA area, what are the prospects of eradication? Poor. It appears that this pest is established, at least in the London area in several private gardens.

20. What management options are available if eradication is not possible? Accurately determining the distribution of this organism and assessing its potential impact to UK (EU and EPPO) orchard crops is the key to deciding upon management action and whether eradication should be attempted.

Findings to date have only been in domestic private gardens. Consequently the options available for control or eradication are limited. Fatty acids could be used and plants could be pruned and debris burnt. Plant destruction is an option.

A summary of the potential regulatory impact of the pest risk management options described above (18. to 20.) is given in Table 1. Those bearing the costs and receiving the benefits are identified. The analysis of the management options assumes:

• That E. excrescens is not already present on plants at horticultural premises and is not present within the horticultural trade • That E. excrescens has been present in the UK for a number of years • That management to inhibit spread of E. excrescens would put obligations on private individuals whereas the PHSI could strongly advise treatments for gardeners without necessarily serving an official Notice.

SUMMARY OF THE PEST RISK ANALYSIS

Eulecanium excrescens is a polyphagous pest of economically important orchard trees in China. It has spread to the USA although it is not regarded as an economic pest in the US. The organism has been found at numerous sites in London and is likely to have been present in the UK since at least 2000. E. excrescens may be more widespread in the PRA area than is currently known.

E. excrescens produces large amounts of honeydew, and in the UK, E. excrescens is causing leaf loss and dieback. Hosts are being disfigured. Eradication would be difficult and is likely to lead to public objections.

Decisions on management action and, particularly, whether eradication should be attempted will depend on accurately determining the distribution of this organism and assessing its potential economic impact on all potential hosts in the PRA area.

This PRA has considered the implications, costs and benefits of the intervention of the Plant Health Service. Given that the organism is already present in London, exclusion is not possible. Eradication would be expensive for all parties involved and may be controversial. Pest spread could be inhibited in a number of ways. A broad approach impacting on the public would also impose burdens on the Plant Health Service and industry. Costs for such intervention would probably exceed the benefits resulting from the intervention. A softer approach would be to consider the organism as a Regulated Non-Quarantine Pest (RNQP). This would not impact on plants already infested but protect the horticultural trade by restricting movement of infested plants yet to be planted. 4 of 7

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CONCLUSION

Given the limited number of plant species at risk, the slow spread of the pest, the fact that natural enemies are present in the UK, and that well established mature plants are not likely to die, it is recommended that the Plant Health Service withdraw from conducting further work on this organism and opt to do nothing, considering the organism as an established exotic pest, with limited distribution.

Name of Pest Risk Analysts: Alan MacLeod, Lynne Matthews Address: Central Science Laboratory, Sand Hutton, York, YO4 1LZ, UK. Date: Text prepared based on information available on 8th August 2003. Editorial modifications made by Claire Sansford, 26th October 2004. REFERENCES

Deng, D. L.(1985) Anthribus niveovariegatus (Reolofs) - a natural enemy of Eulecanium excrescens Ferris. Plant Protection, 11: 2, 14-15. Essig, E.O. (1958) Insects and Mites of Western North America. Macmillan, NY, 1050pp. Gill, R.J. (1988) The scale insects of California. Part 1. The soft scales (Homoptera: Coccoidea: Coccidae), California Dept. of Food and Agriculture, Technical Series in Agriculture Biosystematics and Plant Pathology No. 1. Malumphy, C.L. (in prep). Eulecanium excrescens (Ferris) (Hemiptera: Coccidae), an Asian pest of woody ornamentals and fruit trees, new to Britain.

UNCERTAINTIES AND FURTHER WORK

Section of Uncertainties Possible further work that could PRA improve the PRA Taxonomy None. None. Pathway Sources of current infestations Check Wisteria imports specifically are unknown. for this pest Distribution Occurrence in other EPPO Contact other EPPO states to ask states is unknown. for information about presence of the pest. Hosts The complete host list is Obtain more references from the unknown. literature. Establishment Suitability of climate elsewhere Experimental data to determine the in the PRA area. It may be thermal biology of the pest. restricted to urban heat islands such as London. Spread Rate of spread if moved by air Check Wisteria imports and currents or in trade nurseries. Impact There are no specific data Experimental data to measure the available relating pest density effect on orchard crops in Europe. to host damage. Management Efficacy of home and garden Determine efficacy of products products available is unknown. available.

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Table 1: A summary of the potential regulatory impact of pest risk management options described in sections 18. to 20 of the PRA. Those bearing the costs and receiving the benefits are identified.

Option : (i) (ii) (iii) (iv) Do nothing Exclusio Eradication Inhibit spread Sector n e.g. RNQP. Plant Cost Nil. N/A High. Medium. Health already Domestic gardens will PHSI staff would be Service present. have to be surveyed. involved in inspecting (PHS) more plant material. Benefit High. N/A Low. Medium. PHS resources could already Only a few species are If considered as a be used on other more present. at risk, mature well RNQP, action would serious pests. established plants are only be taken on host not likely to be killed by planting material. the pest. This would avoid having to take action Public reaction could be against infested used to raise the profile plants already of Defra and general established, e.g. in plant health issues private gardens. Public Cost Low. N/A Low Low. Infested ornamental already (although potentially Plant owners could plants will continue to present. medium for owners of be obliged to treat or suffer damage. Plant infested plants). If destroy infested owners may choose to infested plants were plants. Replacement remove unsightly destroyed, plant owners costs would be borne damage though severe would suffer the loss of by consumers and pruning or even large, attractive plants would not be great. destroy plants. from their gardens. If treated as a Replacement costs Conducting "willingness RNQP, owners of would be borne by to pay" or "willingness to infested plants would consumers and would accept" studies would not be affected. not be great. indicate the value placed on Wisteria. Such values may be in the range of a few pounds to several thousand pounds if the plant is considered a particular feature of the house. Benefit Low. N/A Low. Owners of infested already No new plants would be plants will continue to present. infested. Owners of be able to enjoy the uninfested plants in the plants without official London area would impediment. benefit most from this course of action since they are closest to the existing infested plants.

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Business Cost Low. N/A Low. In time, E. excrescens already Slight increase in may spread into trade present. administration costs and cause damage. due to PHSI inspections. More costs incurred if treatment is required. Benefit Low. N/A Low. Medium. Costs associated with already By ensuring existing Trade is protected administration of present. populations are against uninhibited RNQP status are eradicated, businesses spread of the pest. avoided. are protected from any chance of spread of the pest into the horticultural trade.

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