The Potato Bug Is a Super Pest That's Hard to Control

The potato bug is not just any pest — it's an iconic pest of modern agriculture:

"This insect," wrote entomologist R.A. Casagrande in 1987, "resulted in the first large-scale use of insecticides on an agricultural crop ... influencing generations of agriculturists to depend upon this unilateral approach for managing this pest and others."

The Colorado potato bug has thwarted nearly every chemical we've devised to destroy it for the past two centuries — even the wildly toxic DDT. Scientists think their poison hardiness might be due to a tolerance to the toxins present in normally deadly (to us) nightshades — their regular breakfast, lunch and dinner — built up over millions of generations.

An adult potato bug is about the size of a grown-up human's pinky fingernail with a humped, hard shell and 10 orange and black vertical stripes running from head to tail. In fact, its species name, decemlineata, means "10 lines" in Latin. Larvae look a bit different — red and plump with black spots running down their sides.

Potato bugs eat all parts of a plant and will even burrow underground in early spring to eat the parts of a plant that haven't even emerged yet. You might have found potato bugs in your home garden, and some people deal with them by just going through and hand picking the adult insects off the plants early in the growing season before they start damaging or killing plants. Later, spraying insecticide or covering the plants with a fine netting might keep them at bay.

"Commercial producers rely on a variety of insecticides," says Ric Bessin, an extension entomologist at the University of Kentucky. "To manage resistance, these producers need to rotate modes of action of the insecticides they use to prevent or delay the development of insecticide resistance by Colorado potato bugs. This insect has shown tremendous ability to develop resistance to insecticides that have been used repeatedly against it."

Farmers have also found rotating fields where they grow their solanaceous crops can reduce the risk of a potato bug takeover.

Potato bugs overwinter in the soil and begin their year between 4 and 10 inches (10 and 25 centimeters) underground. When they emerge in the spring, they immediately start feeding on early crops or solanaceous weeds.

The females emerge and mate, laying their bright orange eggs in clusters on the undersides of the leaves of solanaceous plants. Each female can lay over 500 eggs in the first month of spring. Eggs will hatch in between four and nine days, depending on the air temperatures, and the larvae will begin to feed on the leaves.

"Initially the small larvae feed in groups near where the eggs were laid, but as they get older they begin to move apart," says Bessin. "The larvae pass through four growth states in two to four weeks, then drop to the ground to pupate in the soil. The next generation adult emerges in five to 10 days, and the cycle is repeated for the next generation."

How many generations of potato bugs can cycle through in a single season depends on the climate, but according to Bessin, where he lives in Kentucky, one year can spawn two generations of potato bugs.