Forest Preserve District of Cook County, Illinois
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Potato Beetles
Nature Bulletin No. 522   March 22, 1958
Forest Preserve District of Cook County
Daniel Ryan, President
Floyd A. Swink, Naturalist
David H. Thompson, Senior Naturalist

POTATO BEETLES
Until a little over a hundred years ago the Colorado Potato Beetle was a well-behaved harmless insect. It was unimportant because it fed on the buffalo bur, a close relative to the potato, a tough stickery weed that grew along the eastern foothills of the Rocky Mountains. Then. suddenly, it discovered a new diet in the white man's gardens and adopted the tender-leaved cultivated potato as its favorite food. It spread rapidly on potatoes and we have been fighting it ever since. Now, this pest is among our best-known beetles. In addition to the potato it occasionally attacks other plants of the nightshade family -- tobacco, tomato, eggplant, pepper and petunia.

This is the story. With the opening up of the West following the Mormon migration to Utah in 1847 and the California gold rush of '49, the pioneer settlers planted potatoes. By 1855 potato growing reached westward to the native home of the beetle, and the insect then began to spread eastward along the trails the pioneers traveled. Perhaps by hitchhiking, and perhaps by flying with westerly winds, it spread about 85 miles a year. It reached Nebraska in 1859, Illinois in 1864, Ohio in 1869, and the Atlantic coast in 1874.

The adult beetles and, especially, their voracious larvae stripped the plants of leaves and growing tips. Their ravages caused the loss of entire crops or so weakened the plants that their underground tubers were small and watery. In those early years there was no control, other than hand picking, usually by children, until after 1865 when Paris green, a compound of copper and arsenic, came into use as a poison. Today, with the use of DDT and other sprays, control is much more effective.

When the beetle reached our Atlantic coast in 1874, it caused great alarm abroad. Within the next year or two almost every European country forbade the importation of American potatoes. Their potato- growing regions remained free of the pest until after World War I when it appeared near Bordeaux, France, where there had been large concentrations of American troops and supplies. Now it is widespread in continental Europe and requires control.

The dome-shaped, 3/8-inch adults are yellow with five black stripes on each wing cover and black spots on the thorax. In late spring, after hibernating deep in the soil, they fly about actively seeking potato plants. The females soon begin to lay clusters of bright yellow eggs on the undersides of the leaves. From these hatch soft-bodied, hump- backed larvae -- brick-red with two rows of black dots down each side. These feed ravenously and molt four times while growing to a length of a half inch or so, then crawl into the soil and pupate. From this resting stage, a new brood of adults appears and, before the end of summer, they produce a second generation.

At the slightest disturbance the adult beetle folds its legs, drops to the ground and "plays possum". If picked up, an ill-smelling yellow juice oozes out of the body which is believed to be distasteful to most birds and natural enemies. Toads eat them and so does the rose-breasted grosbeak -- sometimes called the "potato-bug bird".

Before our potato patches were invaded by the Colorado potato beetle, the name "potato bug" was used for a long slender beetle with two black stripes on each wing cover. The adult of this beetle feeds on potatoes but it lays its eggs in the ground and its predatory young feed on grasshopper eggs. Now, a minor pest, it is called the "old-fashioned potato bug".

In the beginning, the potato was not Irish, nor its enemy a "potato" beetle.


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