Colorado beetle

North American black and yellow striped beetle that is a pest on potato crops. Although it was once a serious pest, it can now usually be controlled by using insecticides. It has also colonized many European countries.

Classification

Life cycle The Colorado beetle spends the winter in the adult state, buried deeply in the soil. In late spring or early summer it works its way to the surface and flies in search of potato crops, travelling several kilometres if necessary. On reaching a crop the beetles feed upon the potato leaves, and the females lay clusters of eggs on the leaves, mostly on the underside. Each female lays about 500 eggs over a period of about five weeks.

In a few days the eggs hatch into grubs, which also feed upon the potato leaves. The larvae are a bright pink or red colour and both beetles and grubs leave a black and rather messy excrement (frass) on the leaves. After about three weeks the grubs are fully grown, and descend into the soil, where they turn into pupae. Ten to 15 days later they undergo a further and final change into adult beetles. Towards the end of July and during August these beetles come up to the surface, feed, and, if the weather is warm, lay eggs that produce a further generation of beetles before the leaves die off in the autumn. With the end of summer the beetles burrow down into the soil again, and stay there for winter.

Crop damage During the early part of the 19th century the beetle was an obscure weed-feeder found on the slopes of the Rocky Mountains. Its staple diet was native weeds such as the ‘buffalo bur’ (Solanum rostratum). It was not until the mid-19th century, when the potato was introduced as a crop by pioneer farmers, that the beetle became an important pest.

The effect upon the potato crop depends upon the number of beetles and grubs present. When there are many the plant is completely stripped of leaves, and no tubers worth digging are formed. It is by the destruction of the plant that the pests do damage; they do not burrow into the tubers themselves.