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
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
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".
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
In the beginning, the potato was not Irish, nor its enemy a "potato" beetle.
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Update: June 2012