Colorado potato beetle
A ⅜–½-inch yellow beetle with ten black stripes on its wing covers, and a plump, humped larva, brick red to salmon, with black spots down its sides. Adults and larvae eat the leaves of potato, eggplant and tomato, and can strip plants bare. Potatoes tolerate a good deal of leaf loss, but act before the larvae are large, because the last larval stage does most of the eating. In a garden, hand-pick adults, crush the orange egg clusters under the leaves, cover young plants, and plant potatoes somewhere new each year. The beetle is notorious for insecticide resistance, which has reached spinosad on some farms. Bt tenebrionis, the strain of Bt that kills beetles, works on small larvae, but we could not find a home-garden-sized product on sale.
Leptinotarsa decemlineata larvae and adult on potato foliage. Photo: pending.
Identification
Adults are oval, strongly domed and ⅜–½ inch long (⅜ in by UF/IFAS and Minnesota, ½ in by UMass). The thorax is yellow-orange and the wing covers are pale yellow, with ten narrow black stripes, five on each side. Larvae are humped and plump. Young ones are brick red with a black head, and older ones pink to salmon. All have two rows of dark spots down each side. They reach about ½–⅝ inch before dropping to the soil to pupate.
The eggs are yellow-orange ovals about 1.7 mm long, laid in clusters under the leaves. UF/IFAS gives 20–60 eggs as typical, UMass 20–35 and Minnesota 10–30. The false potato beetle (L. juncta) of the eastern US looks similar. Its larvae are paler, almost white, with one row of spots on each side instead of two, and the adults have a black spot on the upper leg. It lives mainly on horse-nettle and other wild nightshades.
Easily confused with
- Lady beetle eggsBeneficial — leave itLady beetle egg clusters look very like Colorado potato beetle eggs, but they are more yellow and smaller, about 1 mm, against 1.7–1.8 mm and more orange.
- Lady beetle larvaeBeneficial — leave itLong, spiny and alligator-shaped, black with bright spots. Colorado potato beetle larvae are plump and humped, brick red to pink, with two rows of dark spots on each side.
- False potato beetleHarmlessStriped like the real thing, but its larvae are almost white with one row of spots on each side, and the adult has a black spot on the upper leg. It lives mainly on horse-nettle and other wild nightshades.
Damage symptoms
Adults and larvae both chew the leaves, and the larvae feed almost continuously. The fourth and last larval stage does most of the eating: 75% of the feeding damage by Minnesota's figure, 85% by UMass's. Potatoes are more tolerant than they look. UKY puts the loss they can take without yield loss at up to 30% of the foliage, Minnesota says 30% before flowering, and UMass says 20% or more depending on cultivar and timing, though it gives 15% elsewhere on the same page. Once tubers are sizing, Minnesota drops that to about 10%. Eggplant is more sensitive: UMass says yields suffer beyond about 15% defoliation.
- Leaves chewed away, and in heavy attacks whole plants stripped to the stems
- Clusters of yellow-orange eggs under the leaves
- Humped red or salmon larvae feeding on the foliage
- Striped adults on young plants soon after potatoes come up
- Round exit holes in the soil where new adults have emerged
- Smaller yields when heavy defoliation comes while tubers are sizing
Lifecycle & degree days
Adults overwinter in the soil near last year's crop: 5–10 inches down in Minnesota, and up to 12 inches by UMass's figure. They emerge in late spring as potatoes come up, then feed, mate and lay eggs. Each female lays several hundred eggs over four to five weeks: 200–500 by UF/IFAS, up to 300 by UMass, and 500 or more by Kentucky's figure. The four larval instars take about three weeks in total, according to UF/IFAS. Minnesota says ten days in the mid-80s °F, but over a month near 60 °F. The larvae then pupate in the soil. There are one to three generations a year, depending on latitude. Northern New England has one. Southern New England and southern and central Minnesota generally get a second, which in New England appears in late July. Kentucky has two, and occasionally a partial third.
- Egg hatch
- 4–10 days; up to 2 weeks
- Larval stage
- About 21 days; 10 in the mid-80s °F, 30+ near 60 °F
- Egg to adult
- As little as 21 days (Kentucky)
- Eggs / female
- 200 to 500+, by source
- Generations / yr
- 1–3, by latitude
- Overwinters
- Adults, 5–12 in deep in the soil
Host crops
Potato is the preferred host, and eggplant is more sensitive to damage than potato. UF/IFAS also lists tomato, nightshade, ground cherry, henbane, horse-nettle, belladonna, tobacco and thorn apple. Its first recorded host was buffalo-bur, a weedy nightshade on which it was described from the Rocky Mountains in 1824. It moved onto potatoes around 1859 and reached the Atlantic coast by 1874.
Monitoring & action thresholds
UKY's rule is not to treat unless the average passes one beetle or larva per plant. UMass's commercial potato thresholds are per plant (per stalk once plants pass 18 inches): 0.5 adults, 2 small larvae, 1.5 large larvae, or 10% defoliation. For eggplant they are 4 small larvae or 1 large larva on plants under 6 inches, and 4 small or 2 large larvae on bigger plants. UMass advises scouting weekly, and again in 3–4 days when counts approach the threshold.
Start when the potatoes come up, since the overwintered adults arrive with them. Walk the rows weekly and turn leaves over to find egg clusters. Count adults, small larvae and large larvae separately, because UMass's thresholds treat each differently. Look again in 3–4 days when counts are close to the threshold. Watch for the first brick-red larvae: Bt and the softer sprays work best while larvae are under about ¼ inch.
Biological control
Several predators eat the eggs and larvae. The spined soldier bug is a voracious predator of both. It does not readily eat the adults, but in a 2018 study adult beetles fed 23% less when it was present, and in a greenhouse assay they laid 37% fewer eggs. The ground beetle Lebia grandis (ground beetles) ate the equivalent of 23 potato beetle eggs and 3.3 larvae a day in USDA laboratory tests, and its own larvae develop as parasitoids of the beetle. UMass also lists the twelve-spotted lady beetle (Coleomegilla maculata, see ladybugs), which eats the eggs, and the tachinid fly Myiopharus doryphorae. UMass says the fungus Beauveria bassiana suppresses populations, though not immediately. Bt tenebrionis kills first and second instar larvae, but we could not find a home-garden-sized product on sale. Novodor is labelled at farm rates in quarts per acre, and UMass reported Trident off the market in 2022.
Cultural controls
In a garden, rotation, barriers and hand-picking come first. UMass calls rotation the single most important tactic. On farms that means moving at least 200 yards (UMass), ¼ mile (Minnesota) or about 0.3 mile (UF/IFAS) from last year's crop, which is more distance than most gardens have. Minnesota still advises skipping potatoes for a year to reduce the local population.
- Hand-pick adults and larvae into soapy water, and crush the orange egg clusters under the leaves. UKY says picking the overwintered beetles on young plants in spring is particularly effective
- Cover young plants with row cover before any beetles appear
- Mulch potatoes and eggplant thickly with straw: fewer adults settle and fewer eggs are laid
- Grow early varieties that mature in under 80 days (Minnesota)
- Rotate potatoes, tomatoes and eggplant away from last year's bed, and skip potatoes for a year after a bad season
- On a larger scale, plastic-lined trenches beside overwintering sites trap walking adults in spring. UF/IFAS says trenches with slopes of 45° or more can catch 50% or more; UMass and Minnesota advise sides of 65–90°
- Some farms flame colonising adults while potatoes are under 5 inches tall (UMass), though Minnesota's 2020 on-farm trials found flaming did not reduce beetle numbers
Chemical, last resort
- SpinosadREI 4 h
Sources
UF/IFAS Featured Creatures EENY-146 (IN303), Colorado Potato Beetle (Jacques & Fasulo)
UMass Vegetable Program, Colorado Potato Beetle (updated 2 June 2022)
University of Minnesota Extension, Colorado Potato Beetles (Schuh, Hahn & Burkness, reviewed 2026)
University of Kentucky ENTFACT-312, Colorado Potato Beetle Management (Bessin, rev. 1/26)
Hermann & Thaler 2018, Predator presence and adult Colorado potato beetle, Oecologia 188: 945
Weber et al. 2006, Prey preference and host suitability of Lebia grandis, J. Insect Sci. 6
UC IPM, Relative Toxicities of Insecticides Used in Tomatoes to Natural Enemies (09/16)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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