Adult Colorado potato beetles are oval with hard convex yellowish-white wing covers marked with lengthwise black stripes. Adults are about ⅓ inch long. Larvae are humpbacked grubs reddish to salmon-colored with black heads and two rows of black spots along both sides of the body.
Adults and grubs chew on the leaves of potato-family plants—potatoes, eggplants, tomatoes, and peppers. A heavy infestation can defoliate a plant.
Potato beetles emerge from the soil in spring at about the same time that potato shoots emerge. The beetles walk to host plants then climb up the stalks to feed. Adults mate and females lay rows of bright orange eggs on the undersides of leaves.
Humpbacked grubs hatch from eggs after 5 to 15 days, depending on how warm the weather is. They feed in groups at first then spread out to cover an entire plant. Larvae progress through four distinct growth stages (instars) over a 10-day period. About 13 days after hatching the prepupae drop to the soil and burrow to a depth of several inches, then pupate. The adults emerge in a few weeks to continue the life cycle, or, if the weather is chilly, delay emergence until spring.
There are one to three generations per year.
Potato beetles can be found throughout North America and Canada, except the South.
Target Plants: Eggplants, peppers, potatoes, and tomatoes (these are members of the nightshade family, also called the tomato family or potato family).
Feeding Habits and Damage: Adults and grubs feed on leaves; a heavy infestation can defoliate a plant.
Organic Controls: Mulch well with a 1-foot layer of clean hay or straw. Handpick eggs and crush them (eggs resemble ladybug eggs but are larger and more orange). Handpick larvae and drop them in soapy water. Apply rotenone, spinosad, or neem as a last resort if the infestation is bad (these natural insecticides will also kill beneficial insects so apply in the evening when beneficial insects are less active).
Organic Control Calendar: Here is what you can do seasonally to control Colorado potato beetles:
- Before planting: Plant an early maturing potato variety. Pull out nightshade-family weeds in spring before beetles emerge; these weeds can serve as food sources and egg-laying sites. Rotate tomato family crops from one place to another in your garden each year; this will make it harder for beetles to find the crop. Plant nectar crops to attract beneficial insects such as spindled soldier bugs; soldier bugs feed on potato beetles.
- At planting time: Plant early maturing varieties of potatoes about one month earlier or later than usual; early potato crops will near harvest by the time beetles emerge and begin to feed. Put 4 inches of straw around crops; beetles find it difficult to traverse straw. Cover plants with row covers at planting time and seal the edges to exclude emerging beetles. Begin looking for beetles on plants as soon as potatoes sprout in the garden. Check leaf undersides for clusters of bright orange eggs. Look for humpbacked grubs and dark spots of excrement on foliage.
- While crops develop: Colorado potato beetles emerge from the soil at about the same time that potato shoots emerge in spring. The beetles walk in search of host plants then climb up the stalks to feed. Collect and destroy eggs, larvae, and beetles. Be sure you don’t destroy lady bugs or their eggs by mistake. Remove beetles from plants with a handheld vacuum cleaner. Use spinosad, Beauveria bassiana, or Bt to kill larvae. As a last resort, spray pests with spinosad or neem.
- After harvest: Remove all spent nightshade-family crops, weeds, and debris from the garden after harvest. Plan to plant tomato-family crops in a different bed next year to slow the progress of beetles.
Natural Predators: Insect predators include beneficial nematodes which burrow inside beetles to reproduce; they release bacteria that kill beetles. Chalcid, trichogramma, and Colombian wasps parasitize the eggs of beetles. Assassin bugs, ground beetles, lady bugs, soldier bugs, and stinkbugs are predators. Animal predators include many birds including Baltimore orioles, bluebirds, cardinals, chickadees, grosbeaks, juncos, purple finches, and robins,
Scientific Name: Leptinotarsa decemlinata