Three-Lined Potato Beetle

Three-Lined Potato Beetle are found on plants in the family Solanaceae, including potato, tomato and relatives. They are uncommon on potato, rare on tomato, but very common on tomatillo Physalis ixocarpa.

Adults are 7-8 mm long (1/4 inch) orange-yellow, with three lengthwise black stripes. The females lay orange-yellow eggs in groups, usually on the undersides of leaves, by veins.

Mature larvae are 1/3 inch long with a black head, thorax and legs, and a pale yellowish or grayish body. The body of the larva is kept moist and sticky by a secretion and its back is usually covered with a coating of its own excrement.

Life Cycle: Overwintered beetles emerge in early spring and feed on solanaceous weeds, migrating to eggplant, potato, and tomato plants when they are available.

Females deposit eggs in clusters of 6–10 on the undersides of leaves. Eggs hatch in about two weeks and young larvae feed at first in a row side by side, beginning at the edge of the leaf and moving backward as they devour the tissue. Older larvae separate, migrate throughout the plant, and feed individually. Larvae become full grown in about two weeks. There are two generations each year.

Damage: Potato, tomato, and sometimes eggplant are attacked by the three-lined potato beetle, Lema trilinea White. Adults and larvae chew irregularly shaped holes in the leaves, feeding along the margin of the leaf or in the central area, and occasionally may devour all leaf tissue except the mid-vein. Larvae generally feed on the lower surface, but may feed anywhere on the plant.

Control: Hand picking of eggs, larvae, and adults is effective but difficult due to their size and activity. Eggs may be difficult to find, and adults and larvae can migrate large distances, even across rows to other plants. Also, they will readily climb back up the plant and resume feeding if just knocked off and not destroyed.

Floating row covers, cheesecloth, or other similar materials are an effective barrier to the beetles while the plants are small. However, these materials can be expensive and are generally not economically justified.

Because damage is sporadic and population levels seldom reach economic levels, pesticides are usually not necessary for this pest. However, if an insecticide is used, obtain thorough coverage of foliage to ensure adequate control of both adults and larvae. Pesticides used for other insects, such as the Colorado potato beetle, are also effective against the three-lined potato beetle. Read and follow all pesticide label directions, restrictions and precautionary.