JUNE
2000

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

06-22-00

Colorado Beetles Bug Potato-Growers

Most people call them potato bugs. These striped, hard-shelled insects aren't really bugs; they're beetles. Potato beetles, to be exact. But they do bug anyone who grows potatoes. In fact, they are a major pest insect on potatoes grown almost anywhere in the United States, except California.

According to Metcalf, Flint and Metcalf, who wrote the widely used textbook Destructive and Useful Insects, the potato bug is the best-known beetle in America. That is because so many people have seen this destructive insect feeding on potato plants.

The yellow- and black-striped potato bug is officially known as the Colorado potato beetle. The name reflects the locality where the insect was first collected for scientific purposes. American pioneer entomologist Thomas Say collected some of these insects in the Colorado Territory in 1824 on a trip to the American West.

Say gave the insect its approved scientific name, Leptinotarsa decemlinata. The Latin basis for the scientific name means that it has slender or tiny (leptino) toes (tarsa). It also has 10 (decem) lines on its wing covers. So, we could call it the tiny-toed, 10-lined beetle, but the approved common name is the Colorado potato beetle.

When Say first found the beetle, it was feeding on buffalo burr. That plant is a sticky weed, so the insect was not a problem in its native area. However, as the pioneer settlers moved west across the continent, they brought the potato plant with them. The beetle found a new food plant in the cultivated potato, and it has been a pest ever since.

The Colorado potato beetle reached the Atlantic Coast in 1874. That means that the beetle traveled about 85 miles per year on its march to the sea from its Rocky Mountain-high homeland.

The insect spends the winter in the adult stage buried in the soil. When spring arrives, the adult emerges from its winter shelter to lay eggs on the new spouts of potatoes. The 500 or so eggs that each female lays hatch in about a week. The young insects are reddish-colored, hump-backed soft insects. The newly hatched insects feed for two to three weeks before becoming adults. Like the adults, the young beetles are leaf feeders. Frequently, high numbers of potato plants are quickly eaten by these pests.

Because of the damage the insect can do, gardeners try to kill as many of the beetles as they can. In the days before insecticides were available, hand picking was frequently used to remove the potato bugs.

Picking potato bugs is a job that most kids who grew up prior to 1960 had to do. Of course, picking the potato bugs off the plant was not enough. The insects had to be killed. Three methods were used.

Method number one is the squash method. In this approach, sufficient pressure is applied to the insect, which is held between the index finger and thumb, to smash it. This technique has the obvious drawback of getting the orangish innards of the insect distributed over your hands.

The second method is to drop the insect to the ground, and use the shoe-leather approach to grind it into the soil. Like method number one, the insect ends up being squashed but without the attendant mess to the fingers.

In method number three, the insect is dropped into a can of kerosene. The kerosene kills the insect upon contact. But you still have to pick the insects off the potato plant in order to drop them into the can.

Since insecticides have been widely used against the potato beetles, the beetles have developed resistance to many of the chemicals used in control. So, we are sometimes back to the old-time hand picking of potato bugs. This does at least three things. It saves using insecticides, gives the kids something to do, and allows them to say, “I had to pick potato bugs just like grandpa did!”

 

Writer: Tom Turpin
Editor: Olivia Maddox