Two very different insects go by the common name potato bug. One is very destructive to crops, while the other does not cause as many problems. These two potato bugs are the Colorado potato beetle (Leptinotarsa decemlineata) and the Jerusalem cricket (Stenopelmatus fuscus).
This article addresses the Colorado potato beetle (CPB), a very destructive pest of potatoes and other crops in the nightshade family. At the end of the article, we’ll talk a bit about the harmless but scary-looking Jerusalem cricket.
Colorado potato beetles are found in most regions of the United States (except Hawaii, California, Nevada, and Alaska), southern Canada, and South America. They are also found in Europe and Asia. Because of their size and markings and their easily recognizable damage, it’s hard to mistake them for anything else.
How to Identify Colorado Potato Beetles
Adult potato beetles are about ½ inch long, easily visible to the naked eye. They are oval-shaped, with yellow-orange and black stripes on their backs and orange heads.
Larva are orange, and their backs are humped with two rows of black spots down each side. They can also be identified by the damage they cause – they chew holes in potato plants’ foliage and dine on tomato, pepper, and eggplant foliage.
Life Cycle
Adult beetles overwinter in the soil, about 6 to 10 inches down. They emerge in the spring when soil temperatures warm up to about 50°F(10°C), which is also the right time to start planting potatoes. When they emerge, they begin their search for food and mates.
They don’t migrate, but they can fly several miles to find food. They do not fly when air temperatures are below 70°F (21°C), so they walk to host plants in these conditions.
Females lay eggs on the underside of leaves in clusters of about 25. An adult female can lay hundreds of eggs in her lifetime.
Eggs hatch in 4-9 days. It may take up to two weeks for the eggs to hatch in cooler weather.
Larvae feed on foliage. They molt three times, growing bigger with each molt, and then pupate after the fourth instar (the period between molts is called an instar). The fourth instar is the period where it causes the most damage. Up to 75% of defoliation is caused during this stage. They drop to the soil to pupate, and in about ten days, the next generation emerges.
Depending on the weather and the climate, there can be two or more generations per year. The warmer your USDA zone, the more generations you can expect in a growing season.
Colorado potato beetles can go from egg to adult in 21 days, and adults, eggs, larva, and pupa can all be present simultaneously. In cooler climates, each stage of the life cycle can take longer, and you will see fewer generations.
What Kind of Damage Do They Cause
CPB adults and larvae eat the foliage of potato plants. Other plants in the nightshade family can also host larvae. This includes eggplant, tomatoes, peppers, ground cherry, and nightshade.
Left unchecked, populations can grow large enough to defoliate plants causing decreased yields and plant death.
Ways to Get Rid of Potato Bugs
CPB are resistant to many chemical treatments. It’s best to use mechanical or biological controls to manage their populations.
Remember that a good scouting program is your first line of defense in controlling insect pests. Once your potato plants start growing, look for the large adults, orange egg clusters on the underside of leaves, and the dark orange larva. It’s good to do this daily because populations can increase quickly.
Mechanical Control
Adult potato beetles are easy to see and can be picked off the plants. Wear gloves and drop them into a bucket of soapy water.
If you use a phosphate-free soap, you can then pour the water, bugs and all, into your compost bin.
Look for eggs on the underside of leaves. If you find them, scrape them off or crush them.
Biological Control
Potato bugs have many natural predators. Ladybugs, parasitic wasps, stink bugs, and soldier bugs will eat the eggs and larva. Chickens, box turtles, toads, and wild birds will dine on adults and larva. Bird species that eat both the adults and larva include wrens, sparrows, chickadees, finches, nuthatches, mockingbirds, swallows, and cardinals.
Bacillus thuringiensis (Bt), a beneficial microbe, has been shown to be effective against these pests. There are different strains, so be sure to read the label to know if a particular strain is effective against these beetles. Follow the instructions carefully.
Chemical Control
Potato beetles can quickly develop resistance to many chemical sprays. Check with your county extension service or master gardener program for advice about the effectiveness of specific pesticides in your area.
Neem oil can be used as a foliar spray. Use as directed, and don’t use it on sunny days because the oil can burn the plants.
Steps to Preventing an Infestation
Keep your garden free of solanaceae family weeds like nightshade and buffalo bur.
Rotate your crops. Plant tomatoes, peppers, potatoes, and eggplant in separate and different parts of the garden each year. These plants will attract the beetles to your property.
Invite birds to your yard with water, shelter, and nesting sites. They will help you buy eating the pests in your garden.
Planting early-harvest varieties of potatoes can allow you to get the harvest in before CPB can develop into a large and destructive population.
You can also use companion plants that can help repel potato beetles. Lavender, basil, dill, cosmos, parsley, onions and garlic, radishes, and petunias can be planted alongside your potatoes to help keep these pests away.
Jerusalem Crickets: The Other Potato Bug
Jerusalem crickets are found in the western United States and Mexico. It has a large head with black eyes, a long antenna, a big brown and black striped abdomen, and bent, jointed legs.
These bugs are enormous! They are usually about 2 inches long, and 3-inch long specimens are not uncommon.
They are nocturnal and slow-moving, spending the day beneath the soil surface or under rocks. They are considered beneficial because they eat garden debris, dead roots, and smaller insects. They also eat roots of vegetable crops and potato tubers but are not regarded as destructive pests. They are a food source for small hawks, barn owls, skunks, bats, rodents, and scorpions.
They have an incomplete life cycle – egg, nymph, and adult. Females often eat the male after mating and their reproduction rate is slow. It can take two years for a Jerusalem cricket to reach its mature size.
These insects go by many different names, including Jerusalem cricket, child of the earth (niño de la tierra), sand cricket, skull insect, earth baby, and potato bug. Contrary to its name, they are actually not crickets, not bugs, not from Jerusalem, and they also don’t eat potatoes much.
So why are they called potato bugs? It’s possible that they were given the name after farmers observed them in potato fields after tiling. And “Jerusalem!” is an old mild curse word, something you’d certainly shout out when surprised by this insect.
But for all their fierce appearance, they are harmless. They do not sting. If provoked, they can inflict a painful bite, but they are not venomous.
So leave them alone outdoors, and if one makes its way into your home, you can trap it and release it into the wilds of your backyard. Wear gloves, catch it under a glass, and then slide a piece of paper.
In fact, some people keep them as pets. If you do want this kind potato bug for a pet, buy them from a reputable dealer. Don’t collect them from the wild. The International Union for Conservation of Nature has listed some species of Stenopelmatus as vulnerable.
The other potato bug? Not a good pet.
