Potato Beetles

The Colorado potato beetle (Leptinotarsa decemlineata) is a striped leaf beetle that feeds on potato plants. It is the most damaging insect pest of potatoes in many parts of the world. It is also known as the Colorado beetle, the ten-lined potato beetle and the ten-striped spearman.

Colorado potato beetle Quick Facts

Common name	Colorado potato beetle
Scientific name	Leptinotarsa decemlineata
Kingdom	Animalia
Phylum	Arthropoda
Class	Insecta
Order	Coleoptera
Family	Chrysomelidae
Genus	Leptinotarsa
Type	Insect (leaf beetle)
Diet	Leaves of potatoes, tomatoes, eggplants and other nightshades
Habitat	Potato fields, vegetable gardens and wild nightshade plants
Native range	Mexico and the southwestern United States
Size	About 10 mm (3/8 in)
Colours	Creamy yellow with 10 black stripes
Special feature	Has become resistant to many insecticides

What Does It Look Like?

The adult beetle is about 10 mm (3/8 inch) long, oval and dome-shaped. Its wing covers are creamy yellow with ten black stripes, five on each side, which is where its scientific name comes from: decemlineata means ‘ten-lined’. The area behind its head is orange-yellow with black spots.

The eggs are bright yellow-orange and laid in clusters on the undersides of leaves. The larvae look quite different from the adults. They are soft, plump and humped, brick-red at first and then pink or orange as they grow, with black heads and two rows of black spots along each side.

A close relative, the false potato beetle, looks very similar, but it feeds mainly on wild nightshade plants rather than potatoes.

Where Did It Come From?

The Colorado potato beetle is native to Mexico and the southwestern United States, where it fed on a wild spiny plant called buffalo bur. The American naturalist Thomas Say first described it in 1824 from beetles collected in the Rocky Mountain region.

When settlers began growing potatoes in the West in the mid-1800s, the beetle switched to this new food. It spread east across North America within a few decades. It then crossed to Europe, where it became established in France in the 1920s and spread across much of the continent and into Asia.

What Does It Eat?

Both adults and larvae eat the leaves of potato plants. They also feed on related plants in the nightshade family, such as tomatoes, eggplants and peppers. The large, older larvae do most of the damage.

A few holes in the leaves do little harm, but large numbers of beetles can strip a plant to bare stems. Potato plants can usually cope with losing some leaves early in the season, but losing many leaves while the potatoes (tubers) are growing can greatly reduce the harvest.

Life Cycle

The Colorado potato beetle goes through complete metamorphosis: egg, larva, pupa and adult.

• Spring: Adults that spent the winter buried in the soil come out in spring, usually around the time potato plants appear. They walk or fly to the plants to feed and mate.
• Eggs: Each female can lay several hundred eggs in her lifetime, in clusters of about 20 to 40. They hatch in about four to ten days, depending on temperature.
• Larvae: The larvae feed for about two to three weeks and pass through four growth stages, called instars. They grow from about 1.5 mm to about 13 mm long.
• Pupae: Fully grown larvae drop to the ground and dig into the soil to pupate. About one to two weeks later, the new adults emerge.
• Late summer: As the days get shorter, new adults feed for a while and then dig into the soil, often at the edges of fields, to spend the winter in a resting state called diapause.

In cooler places such as the northern United States and much of Europe, there may be one or two generations a year. In warmer areas there can be three.

A Champion at Beating Pesticides

Farmers began using chemical sprays against the Colorado potato beetle in the 1860s, which makes it one of the first insects ever controlled this way. Over time, the beetle has become resistant to dozens of different insecticides, starting with DDT in the 1950s. Not every population is resistant to every chemical, but this ability to adapt is why farmers now try to use many different methods together.

Natural Enemies

Many animals and microbes help keep Colorado potato beetles in check:

• A ground beetle, Lebia grandis, eats the eggs and larvae, and its own larvae feed on the pupae.
• Ladybugs, lacewings and predatory stink bugs, such as the spined soldier bug, eat eggs and young larvae.
• Some tachinid flies lay their eggs on the beetles, and their larvae develop inside them.
• A fungus called Beauveria bassiana can infect and kill the beetles, and it is sold as a natural pest control product.

How to Protect Your Potatoes

Gardeners can usually manage this beetle without harsh chemicals:

• Rotate crops: plant potatoes as far as possible from where potatoes, tomatoes or eggplants grew last year.
• Check plants often. Hand-pick adults and larvae into a container of soapy water.
• Look under the leaves and crush the yellow-orange egg clusters.
• Cover young plants with row cover fabric, sealing the edges, to keep beetles out.
• Spread a thick layer of straw mulch around plants, which seems to make it harder for beetles to find them and helps their predators.
• Avoid unnecessary sprays so that natural enemies can do their work.

In Britain and Ireland, the Colorado potato beetle is not established and is a notifiable pest. If you think you have found one there, report it to the plant health authorities right away.

Related: Leaf Beetles · salmon

Colorado potato beetle FAQs