Colorado Potato Beetle

Leptinotarsa decemlineata

Colorado potato beetle is a key pest of potato and eggplant throughout the Northeast and requires a combination of cultural, biological and chemical strategies for effective control. For information on management and control of this pest please see our Colorado Potato Beetle, Management article.

Increasing temperatures mean faster development and feeding rates. Cold, rainy weather slows both crop and insect growth, so eggs that are laid can pile up and then all hatch at once when it warms up. Knowing what to look for and getting out into the field to scout is key in determining when to use appropriate controls. CPB is also an important pest of eggplant, so these fields should be monitored as well. Good control of CPB in June will not only protect vulnerable crops throughout the growing season; it will also reduce the number of beetles in the next generation that will survive to feed on next year’s crops.

Identification:

Colorado potato beetles (CPB) are 1/2" long by 3/8" wide, oval with a rounded back, and each forewing is yellow with five black stripes. Eggs are bright yellow, elongated, laid in groups of up to 20-35 on the undersides of leaves. They may grow darker as they approach hatch. The larva is humpbacked, rusty-red with two rows of black dots along each side of its body, reaching about 5/8 inch long.

Life Cycle:

In the Northeast, CPB survives on solanaceous crops and weeds, including horsenettle, nightshade, eggplant, potato and tomato (primarily seedlings). CPB overwinters in the adult stage, primarily in soil (up to 12 inches deep) in the woods and brushy borders next to host crops, though some burrow into soil in the field. In spring the beetles search for food plants by walking from the field edges. Heavy feeding may occur on edges on non-rotated fields. If beetles do not find host plants via walking they will fly in search of food. Once host plants are found adults feed, mate and lay eggs. One female can lay up to 300 eggs. Eggs hatch in 7-10 days, depending on temperature. Feeding damage and larvae are easily seen on leaves. Larvae go through four molts (instars) before they pupate.  In the first instar, the larvae are about the same size as the eggs  and in the second instar they are about an eighth of an inch long.  Mature, fourth instar larvae are hump-backed and plump, and reach 5/8" long before they drop to the soil and pupate.  Adults emerge from pupae after 10-14 days leaving round exit holes at the soil surface. In southern New England there is second generation of eggs, larvae and adults, while northern New England there is one generation. Beetles fly out of fields in August, seeking overwintering sites at field edges.

Crop Injury:

Both adults and larvae cause feeding damage, but larvae damage is the most severe.  Because the fourth larval stage (instar) does 85% of the feeding damage it is critical to control larvae while they are small. Potatoes can tolerate 20% defoliation (or even more, depending on time of the season and cultivar) without reduction in yield. Eggplant is more sensitive to damage and can only tolerate up to 15% defoliation before yield is affected.

Monitoring & Thresholds:

• Potato: Scout every 3-4 days. Scout for beetles on 30 to 50 plants (or individual stalks later in the season). One recommended procedure is to walk the field in a V-shaped pattern and stop at 10 sites across the field. Randomize your selection of sites using a set number of paces, e.g. stop every 10 to 30 paces, depending on field size. At each location, select 3 to 5 plants (from when plants emerge until 12 to 18” tall); thereafter select 3 to 5 stalks at each site. Alternatively, select plants or stalks individually at random across the field. Count adults, large larvae (greater than halfgrown), and small larvae (less than half-grown) separately. A spray is warranted if any of the following thresholds are met:
  • 0.5 adults, 4 small larvae, or 1.5 large larvae per plant (or per stalk once plants are larger than 18” tall
  • 10% defoliation

Pay extra attention and be sure to scout again in 3-4 days if numbers are above 15 adults, 75 small larvae, or 30 large larvae per 50 plants/stalks. 

• Eggplant: A similar process can be used in eggplant. 
  • When plants are less than 6” tall: 2 small or 1 large larva per plant
  • When plants are more than 6” tall: 4 small or 2 large larvae per plant

There are no established thresholds for CPB in tomato, as it is not a preferred crop. 

Crops that are affected by this insect:

• Eggplant
• Potato
• Tomato, Field
• Tomato, Greenhouse