Invasive Alien Species in Northern Ireland

Lepinotarsa decemlineata, Colorado beetle

Lepinotarsa decemlineata (Say)
The Colorado beetle is an unmistakable black–striped bright yellow–orange beetle which has become a major pest of the cultivated potato plant (Solanum tuberosum (L.)) in North America and Europe. It belongs to the leaf beetles or Chrysomelidae, and although accidentally imported on a regular basis with agricultural produce from other parts of Europe has never become established in either Britain or Ireland. With a warming climate, however, the potential for its eventual establishment is high.
The adults measure 10–12mm long and are yellowish–orange with five broad black stripes down the back and black spots on the foreparts. They amble about on the ground or on foodplants but can also fly. The reddish larvae are around 12mm long when fully grown and have black spots down the sides. The abdomen appears strongly inflated compared to the fore-body and gives the larva a characteristic appearance.
Country of origin
There has been some dispute about where exactly the Colorado beetle originated. What is certain is that it is a mountain insect first discovered by Thomas Nuttal in 1811 and described in 1824 by Thomas Say from specimens collected in the Rocky Mountains on buffalo–bur, Solanum rostratum Ramur. Whether it came originally from Colorado is debatable and some authors think its country of origin is in fact central Mexico.
Even its association with the cultivated potato was not realised until it was reported attacking potato crops in Nebraska as late as 1859.
Location in Ireland
Not so far recorded in Ireland other than as an occasional accidental import. In May 2005 a large number (about 80) were imported to Belfast from Italy with a shipment of parsley. This was one of 28 incidents reported by Defra for 2005, involving a variety of crops from potatoes (6) through frozen beans (5) to radish (2) and parsley (1).
Life cycle
Colorado beetles overwinter as adults. These dig into the soil to a depth of about 7–10cm and emerge in the spring. Sprouting potato plants are used as a food source and having fed they mate.
Females deposit eggs on the surface of the host plant’s leaves, usually on the undersurface protected from direct sunlight. An egg mass may contain from 10 to 40 eggs, and most adult females deposit over 300 eggs during a period of four to five weeks. Eggs hatch in four to five days depending in part on temperature and humidity.
The larval stages (four) last for about 21 days. During this time the larvae feed continuously on the leaves of the host plant, stopping only to moult. When feeding and moulting have finished they drop into the soil where they burrow and construct a spherical cell to metamorphose into yellowish pupae. The pupal stage lasts from five to 10 days. There may be one to three generations in a year, depending on climate and latitude.
Wildlife and habitat impacts
None at present.
As well as cultivated potato, there are reports of Colorado beetles feeding on other members of the nightshade family (Solanaceae) including eggplant, tomato, pepper, tobacco, black nightshade, deadly nightshade, thorn apple, Cape gooseberry, henbane, and its first recorded host plant, buffalo–bur.
Potentially it could damage any of these as wild or garden plants. Of the possible wild hosts only henbane (Hyoscyamus niger), black nightshade (Solanum nigrum) and deadly nightshade (Atropa belladonna) occur in the wild in Ireland but all are local and/or rare.
Human impacts
This species can be a significant pest of the cultivated potato and has an importance outweighing its economic significance because of the history and iconic status of the potato in Ireland.
Baker et al. (1998) predict, using the CLIMEX computer program that in the UK the pest could extend its range by 120 per cent with a 400 km shift of its northerly limit to include 99 per cent of the ware and seed potato area. This would include parts of Ireland.
Key vectors
The main method of spread is with agricultural produce from European markets. It can occur on produce with which it is not normally associated. The example of parsley from Italy has been given above.
What you can do as an individual
Members of the public have a role to play here by reporting suspected occurrences to the Department of Agriculture’s Service Delivery Group, or to AFBI (Agri–food Biosciences Institute, formerly Science Service of DARD, at Newforge Lane), or to CEDaR, Botany Department, Sciences Division, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down BT18 0EU. Tel: 028 9039 5256, email damian.mcferran[at]
Advice to specific groups relevant to this species
Apart from the reporting of any suspected occurrences to regulatory authorities, no further action is recommended.
Management measures
Colorado beetle has been established in mainland Europe for about 80 years and all attempts to eradicate it have so far failed. It is currently controlled by pesticides but there has been much research on genetically modified potatoes which produce ant–feedants.
Since 1993 the British Isles has been given Protected Zone status within the European Plant Health Directive. This is aimed at excluding the Colorado beetle by import controls as a first line of defence, backed by eradication measures should pockets of insects become established.
Early potatoes are most unlikely to be affected by Colorado beetles but second earlies and ware potatoes could also be affected. The main risk, however, appears to be to organic potatoes, judging by results from the near–Continent.
Further information
Pope R.D. and Madge R.B. (1984). The ‘when’ and ‘why’ of the ‘Colorado potato beetle’. Bulletin of the Entomological Society of London 8: 175-177.
Baker R.H.A., MacLeod A., Cannon R.J.C., Jarvis C.H., Walters K.F.A., Barrow, E.M. and Hulme M. (1998). Predicting the impacts of a non–indigenous pest on the UK potato crop under global climate change: reviewing the evidence for the Colorado beetle, Leptinotarsa decemlineata. Brighton Crop Protection Conference Pests and Diseases, Vol. III, 979-984. BCPC, Surrey, UK.
Text written by:
Dr Roy Anderson