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Mother nature has created thousands of species of insects from fleas to cockroaches to giant water beetles. And while we humans might not agree, all of them have their place in the natural order of things. Many species of insects spread pollen from plant to plant or flower to flower while other insects, like Ladybugs, are an aggressive and effective predator of the aphid and other juice-sucking parasites. Many species of birds, bats, fish and reptiles rely on insects as their major source of food. And yes, insects also feed on each other to survive. Yet even within this delicate insect hierarchy there are certain bugs, when left unchecked, that can cause serious harm to fields and crops. One of these is the “Leptinotarsa decemlineata”, more commonly known as the “potato bug”, or Colorado potato beetle.
The potato beetle is native to North America, primarily in the western regions around the Rocky Mountains. Its main source of food before settlers introduced cultivated potatoes was the buffalo bur, a wild-growing plant related to the potato family. The potato bug quickly became a voracious and destructive pest of not only potato crops, but also of tomotoes, peppers, eggplants, tobacco and other species belonging to the nightshade family.
Beetle species comprise about 40% of the entire insect population and come in many colours, shapes and sizes. They generally have hard wing covers, or “elytra”, making them appear as if it has its own body armour. Beetles can fly if necessary, but most aren’t very aerodynamic and generally remain in or around the areas where they hatched. All beetles metamorphosize from egg to larva to pupae and finally into an adult in a single season. Eggs are laid in clusters of 50-100 on the underside of leaves, in the soil or in plant debris found in and around gardens or fields. Larvae or grubs will appear after about 4-15 days, depending on temperatures, and then begin to voraciously feed on the nearest host plants.
Larvae and adult beetles both have very efficient chewing mouthparts equipped with sharp cutting edges. If left unchecked an infestation of leaf or plant-eating beetles, like the Colorado potato beetle, can decimate crops in a very short time, sometimes leaving behind nothing but stripped plant stalks. Most beetles are very resistant to sprays and repellents and after a few generations will build up a tolerance to a particular brand of toxin. In this respect the Colorado potato beetle is no different than its cousins, making it a real challenge to control.
While gardening laymen sometimes confuse the potato bugs with the Ladybug, one or two encounters with potato bugs will solve that problem. Adults are oval in shape, range in size from 6 to 11 mm and have 6 tan-coloured legs. Their shell, or hard elytra, is muted orange-yellow shade and usually shows 10 distinct vertical black stripes. The head is tan and also shows black markings. The Ladybug on the other hand, is smaller, its shell reddish in colour, and with spots, not stripes. Potato beetle larvae have orange-pink bodies, small black head and six legs and the main body has small black dots.
During the winter months adult potato beetles lie dormant under garden or field refuse and usually emerge sometime in May depending on the temperature and moisture conditions. Their first instinct is to find suitable plants on which to feed, then they mate and lay eggs. Once the larvae hatch they begin feeding. Many times larval infestation remains confined to a small area in a garden or field, but within that time frame they do much damage, often killing entire rows or patches of potato plants. While most beetles only produce one generation a year, there are some areas, like North Carolina, where 2 and sometimes 3 generations of beetles will hatch in a single year. After the larvae have gorged themselves for 2-3 weeks, they drop off the potato plant, burrow into the soil and go into their pupae or resting stage. After lying dormant for 5-10 days, adult potato bugs will emerge and the whole cycle begins again.
Because potato beetles built resistance to most sprays other methods of control are often more effective:
1) Clean up garden or field debris so the potato bugs have inadequate shelter to over-winter.
2) Don’t plant potatoes in the same spot every year.
3) Introduce some natural enemies of the potato beetle, like the Ladybug, the Stinkbug, or the Spined Soldierbug.
4) Alternate planting times. Heaviest potato beetle infestations usually occur in May. By planting early potato varieties in April the plants will be mature enough by May to sustain some leaf damage. With later potato varieties that sprout in June the beetles will already have migrated to another location to find food.
5) Hand-picking. While this control method might sound grotesque to people with bug phobias, it’s one of the most efficient and least harmful ways to control potato beetles. Slip on a pair of gloves, find an old soup can and pick off as many bugs as you can, then drop them into some kerosene, or a soap-based insecticide. Picking and squashing potato bugs might be an interesting way to keep the kids busy for a few hours -- as long as they aren’t too squeamish!
6) Chemical controls. While large scale potato producers sometimes have little choice in using chemical sprays like pyrethirns or organo-phosphates to control infestations, this should be a last choice for home gardeners. Before proceeding ALWAYS consult with a horticulturist at your local garden center or discuss the problem with a plant biologist. Timing, atmospheric conditions and temperatures and your location are critical when deciding on which herbicides or insecticides to use to control potato beetles.
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