Control this Colorado opportunist: the potato beetle

By Gary Raham
Writer and Illustrator

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When the naturalist, Thomas Say, traveled across our state in 1823, he discovered a large, boldly striped beetle munching on the leaves of buffaloburs (Solanum rostratum). He called the insect Leptinotarsa decemlineata (fine-legged, 10-lined beetle). Because of an acquired taste on the beetle's part, however, and a human propensity for growing crops in vast monocultures, most people refer to it as the Colorado potato beetle. Perhaps you call it an expletive best left deleted--especially if it chooses to eat your potatoes, tomatoes or eggplants.

Take heart. You are not defenseless.

It's hard to blame the beetles for abandoning buffalobur, the apparent porcupine of weeds, and a plant that impales its seeds on tender portions of your hide to hitch a ride to fertile ground. When farmers trudged west in the 1880s, potato beetles cheerfully leapt from buffalobur to its tasty relative, the potato plant. Beetle populations exploded in weedless tracts that surely must have been their version of the Elysian fields. Fortunately for us, potato beetles are homebodies. They not only look like a Volkswagen, they fly like one, too, which is why 80 percent of the beetles in a field had parents in that same field the season before.

Therefore, your first defense against these six-legged tanks is crop rotation. Other defenses include insecticides-- both chemical and bacterial; natural enemies, like stinkbugs; other beetles; parasitic flies and the purchase of resistant crop plants.

To best use these measures, timing is critical. Certain defenses are best used at different stages in the beetle's life cycle. Adult beetles lay bright orange clusters of eggs on the underside of leaves, starting in June, but peaking in early August. Bright orange larvae hatch from these eggs and begin lunching on your plants. The young molt several times, producing four larval stages, or instars. When they've fed enough, they drop from the plant and pupate in the soil. In two weeks they transform into adults. The entire process can take a month, so two or three generations may enjoy your garden before the last adults eat for awhile, burp and find a quiet place to rest for the winter.

Chemical insecticides can create a beetle apocalypse, but other bad things happen: Resistant strains develop quickly, and the beetle's natural enemies, like stinkbugs and spiders, die in the blitz, too. Bacterial sprays containing Bacillus thuringiensis (Bt) specifically attack larval beetles. Apply the spray when larvae are abundant. In one study larval numbers peaked in mid-August, but much depends on temperature. A cool early season will delay the larval peak.

Take care not to step on two-spotted stinkbugs (Perillus bioculatus), as they feed on the potato beetle larvae. Tachinid flies also lay eggs in the larvae, which, after hatching, eat up their host from the inside out like the extraterrestrial in "Alien."

Here's another trick. Plant weeds near your crops. Not just any weed, of course--that would be too easy. Hairy nightshade seems to appeal to potato beetle taste buds. These serve as "traps" that attract adult beetles. Then enlist 10-year-old children, fresh from zapping evildoers in a video game, to dispatch them. At the same time they can squash any egg clusters and larvae they find. Lest you think Colorado has been unfairly colonized by this beetle, the East Coast suffers more because growing seasons tend to be longer and the beetles have become especially resistant to insecticides. Some beetles also took a cruise to Europe and have been known to force undeleted expletives out of farmers there.

Even the association of Colorado's good name to this beetle may be in error according to Whitney Cranshaw, CSU entomologist, in his book "Pests of the West." It seems some enterprising naturalists may have first described this potato-lover from deep within the Corn Belt.

Rumor is, it should have been called the Iowa potato beetle.

References:

Cranshaw, Whitney. 1992. "Pests of the West." Golden, Colo.: Fulcrum Publishing.

Cranshaw, Whitney and Kondratieff, Boris. 1995. "Bagging Big Bugs." Golden, Colo.: Fulcrum Publishing.

Raham, Gary. 1996. "Explorations in Backyard Biology, Drawing on Nature in the Classroom, Grades 4-6." Englewood, Colo.: Teacher Ideas Press.