Three-lined potato beetles are more likely to damage your tomatillos and cape gooseberries than your potatoes, which is why they are also known as tomatillo leaf beetles. But they will cause problems for your tomatoes and potatoes, too. Both adults and larval forms are voracious leaf eaters.
Originally from North and Central America, three-lined potato beetles (Lema daturaphila) are now found in many parts of North America, Australia, and South Africa. Although these pests are relatively rare, so far anyway, they can cause significant damage.
Three-lined potato beetle identification
As their name states, these invasive pests have three black stripes that run lengthwise on their mustard-colored to bright yellow wing covers. They are ¼” long and have an orange head and prothorax with two black spots. The prothorax is the bit just behind the head.
Larvae look like dark gray slugs with black heads and three pairs of prolegs. Three-lined potato beetle larvae have a nasty habit of covering themselves with their excrement to deter predators. I imagine it works. Eggs are oval and orange and laid in clusters on leaves.
Three-lined potato beetles look similar to western corn rootworms (Diabrotica virgifera) and striped cucumber beetles (Acalymma trivittatum), both of which are more likely to be found among your cucurbits and corn. Also, cornworms are smaller than three-lined potato beetles, while cucumber beetles are larger than both. Colorado potato beetles (Leptinotarsa decemlineata) may be found around potatoes and other nightshade plants, but their shape and color are different
Damage caused by three-lined potato beetles
Adults tend to travel and feed by themselves, so the damage they usually cause is minimal. As they eat, they may create holes in leaves, or they may remove entire leaves. The larvae, on the other hand, feed in groups and can cause considerable damage. Like other creatures who have evolved to eat members of the nightshade family, they are immune to the lethal tropane alkaloids found in the leaves of these plants.
All this leaf-feeding means less photosynthesis, weakened plants, and reduced crop size. It also makes plants more susceptible to other pests and several diseases.
Three-lined potato beetle lifecycle
These garden pests overwinter as adults or as pupae in the soil, depending on the local climate. Adults become active in late spring through the summer, laying eggs on host plants. The larvae usually hatch in early summer, though there can be two generations each year.
Three-lined potato beetle management
Hand-picking the caterpillars is your best defense since adults can fly. Simply pluck them from your plants and drop them in a container of soapy water or feed them to your chickens. Row covers can protect plants from three-lined potato beetles, and eliminating weeds in the nightshade family will make your garden less appealing to these pests.
You can grow a surprising amount of food in your own yard. Ask me how!
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