FERA PLANT PEST FACTSHEET: Potato flea beetles (Epitrix species)

Potato tuber showing feeding damage by the larvae of a potato flea beetle - Image: Conceição Boavida Instituto Nacional de Recursos Biológicos, Portugal
Potato tuber showing feeding damage by the larvae of a potato flea beetle - Image: Conceição Boavida Instituto Nacional de Recursos Biológicos, Portugal

What are they?

Five species of flea beetle assigned to the genus Epitrix(Coleoptera: Chrysomelidae) feed on potatoes (Solanum tuberosum) in North America.

The common name ‘flea beetle’ derives from the ability of the adults to jump when disturbed. The adult beetles feed on the foliage producing small, scattered holes, which can occasionally be so severe to depress yield.

The larvae feed on the root system and some species feed on the tubers, which causes the most serious damage. The quality and value of the tubers is lowered and if the feeding damage is severe, it can render the whole crop unmarketable. Identification of Epitrix species is difficult and the identity of the species damaging tubers in North America has not
always been confirmed in the past, but E. tuberisGentner is generally considered to be the main culprit. It produces both superficial serpentine tunnelling, and deeper holes in the tuber flesh that are still evident after peeling.

Two North American Epitrixpotato flea beetles, E. cucumeris(Harris) and E. similaris Gentner, were recorded in mainland Portugal in 2008 (E. cucumerishas been known to be present in the Azore Islands since 1979). They were collected
from potato fields, where symptoms typical of Epitrixtuber damage (superficial lesions/furrows on the tubers) had been found.

This damage was first observed in 2004 in the north of the country (near Porto) but Epitrix was not identified as the cause until 2008. During this time the pest had spread to all potato growing regions in Portugal; a single adult beetle of E. similarishas also been found in Spain, close to the border with Portugal. Surveys are planned for 2010 to ascertain the status of Epitrixin Spain.

Why the concern?

Epitrixpotato flea beetles pose a serious threat to potato production in the UK. Potato tubers, or soil attached to the tubers, could carry the pest (as pupae or over wintering adults or possibly larvae) over long distances. The import of potatoes from infested areas in Portugal (and possibly Spain), therefore, provides a potential pathway of introduction to the UK. If Epitrix potato flea beetles are accidentally introduced to the UK, they are likely to spread relatively quickly as the adult beetles can fly.

Unless detected early, eradication would be almost impossible because the pests can feed on a wide range of hosts. Once established, control measures would be difficult and costly.

The yield of potato crops is apparently not affected in Portugal but the commercial value of the tubers is greatly reduced. The wounds caused by larval feeding, however, can reduce tuber storage capacity. Consignments with affected tubers have been downgraded and even rejected by processors and packers.

What are the host plants?

In general, Epitrix species complete their development on plants belonging to the family Solanaceae, including potato, tomato (Solanum lycopersicum), black nightshade (Solanum nigrum), cut-leaved nightshade (Solanum triflorum), thorn apple (Datura stramonium) and aubergine (Solanum melongena). The adults, however, can feed on the foliage of a wide range of unrelated plants including several crops and various common weeds, for example, cabbage (Brassica oleracea), cucumber (Cucumis sativus), beet (Beta vulgaris), lettuce (Lactuca sativa), maize (Zea mays), beans (Phaseolus spp.) and fat hen (Chenopodium album).

What does it look like and what are the symptoms?


Most adult Epitrix potato flea beetles are similar in appearance, being dark, tiny (1.5-2.0 mm long), oval, convex and hairy. This makes their specific identification difficult, particularly in the field.

Fig 1 - Epitrix similaris adult (image: Jean-Franc¸ois Germain, LNPV Montpellier)

There are two native Epitrix species (E. atropaeFoudras and E. pubescens(Koch)) in Britain but they do not feed on potato.

Adults chew minute, circular holes (1-1.5 mm diameter) on the leaves, producing a highly conspicuous shot-hole pattern.

Fig 2 - Potato flea beetle adults are about 2 mm (image: EPPO)

The tuber damage found in Portugal consists of shallow sub-epidermic wavy furrows that are removable by peeling the skin. No insects have ever been found inside the tubers.

What time of year have potato flea beetles been seen?


It appears that both adults and pupae can over winter in the soil and crop debris, and emerge in spring. The first peak in the population is in mid-June, the second in mid-August and the third in late September. Eggs are laid in the soil near the base of potato plants and newly hatched larvae move towards the root system and start to feed on the roots and tubers. Pupation occurs in the soil. It is considered that under favourable conditions, as in Portugal, there may be at least three generations per year. This may result in 20,000 individuals from each female in a single season.

How can Epitrixpotato flea beetles be controlled?


Avoid introduction of this pest

Once introduced, potato flea beetles are likely to be very difficult to eradicate unless they are detected very early and prompt action is taken. This is because they have a wide host range that includes several common weeds and they are very mobile.

The most effective way of preventing tuber damage is to avoid introducing these pests into the UK. The two most important pathways for spreading potato flea beetles are, seed potatoes with soil attached and ware potatoes with soil attached. This is because adult beetles, pupae and possibly larvae could be present with the tubers.

Imports from Portugal clearly pose a significant risk. Portugal is not believed to be a significant source of seed
potatoes for the UK, but the UK is an important Portuguese export market for ware potatoes, although the quantities imported have been small in recent years. 

Data from Eurostat indicates that between January and April 2009, only 106 tonnes of Portuguese ware were imported into the UK. Fortunately, imports of ware potatoes in recent years appear to have been mainly washed prior to export and this reduces or eliminates the risk of potato flea beetle survival. The risk posed by Spanish ware is not known because the status of potato flea beetles in Spain remains unclear. The UK, however, imports very large quantities of ware potatoes from Spain so vigilance is vital, especially given Spain’s close proximity to Portugal and the lack of official measures being taken there. Spain also has a long history of importing seed potatoes from Portugal.

Official measures in the event of an outbreak

In the event of an outbreak being found in the UK, official statutory action would almost certainly be taken to try and eradicate this very damaging pest. The exact action taken would depend on the particular circumstances of the outbreak but it is likely to involve measures such as destruction of the crop haulm (stems), the application of insecticide treatments and the controlled safe disposal of infested tubers.

Control of Epitrix potato flea beetles in countries where the pest is present (North America and
Portugal)

In North America control normally relies upon the application of a programme of insecticide treatments including seed treatments, in-furrow granular insecticides and foliar sprays. Many of the products used in the USA are, however, not available in the EU. The critical element of any successful control programme is to eliminate the first generation of adults before they have laid their eggs in the growing crop. Most farmers in British Colombia follow an Integrated Pest Management (IPM) programme.

This involves intensive monitoring of crops for adult beetles with foliar sprays applied when a particular threshold is reached. The alternative to IPM is to apply regular insecticide sprays prophylactically. Prior to the introduction of IPM, potato crops were routinely sprayed 7-10 times with broad-spectrum insecticides to control flea beetle and aphids. Epitrixpotato flea beetles are still damaging pests in North America and on occasions, can cause total crop loss.

In Portugal, the worst economic damage occurred in 2008 when whole consignments sent for processing in France, Spain and other countries were rejected. In 2009, growers applied additional early sprays of insecticides (mainly the neonicotinoid insecticide, acetamiprid and the synthetic pyrethroid, bifenthrin) and there were fewer reports of economic tuber damage.

Field observations suggest that if 2-3 insecticide sprays (1 additional early spray to the normal Colorado beetle spray programme) are applied the tuber damage is usually less than 2-3%. However when no insecticide sprays are applied, 80% tuber damage can commonly occur. In the UK, ware crops receive on average only one insecticide spray and if Epitrixpotato flea beetles were to become established, insecticide inputs would undoubtedly have to increase, especially for crops where even low levels of tuber damage is deemed unacceptable.  Other important elements of control include the maintenance of an adequate rotation between potato crops (3 years) and the control of volunteers and host weeds
during the intervening period.

Keep a good look out

If you suspect the presence of this pest or see a beetle that you suspect to be a potato flea beetle, trap it if possible, and immediately report the finding to your local Fera Plant Health and Seeds Inspector:

Tel: 01904 465625

Email: planthealth.info@fera.gsi.gov.uk

Web: www.defra.gov.uk/fera/plants/plantHealth

Authors

C. Malumphy, N. Giltrap and D. Eyre 

The Food and Environment Research Agency (Fera). February 2010
© Crown copyright 2010


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