Four-Lined Plant Bugs

Four-lined plant bugs are sap suckers. This means they have piercing mouthparts, similar to their cousins, tarnished plant bugs and capsid bugs. Small populations can be ignored, but things can get out of hand. 

​Four-lined plant bugs (Poecilocapsus lineatus) are traditionally found east of the Rocky Mountains, but that can always change.

Four-lined plant bug (Judy Gallagher) CC BY 2.0

Four-lined plant bug identification

Four-lined plant bugs look like small beetles, but they lack the characteristic hardened wing covers. They are greenish-yellow with four distinct black stripes running the length of their wings. The head is orangish-brown, with prominent red eyes, and they average ¼” long or a little more. Newly hatched nymphs are bright red with black wing pads. If you flip one of those nymphs over, you’ll see black spots on the abdomen. As they mature, nymphs turn more orange, and a stripe develops on the wing pads.

Four-lined plant bug leaf damage (Whitney Cranshaw, Colorado State University, Bugwood.org) CC BY 3.0 US

Damage caused by four-lined plant bugs

Adults and nymphs feed on basil, cucumber, currants, gooseberry, lavender, mint, oregano, peppers, and sage. They also suck the vital fluids from several flowers and woody shrubs, including azalea, butterfly bush, dogwood, geraniums, Shasta daisy, and zinnia. As they pierce plant cells and siphon out sugary liquids, dark, round, sunken spots appear. Those spots range from 1/8” to 1/16” in diameter. Those spots may turn black or translucent. After a few weeks, the dead plant tissue falls away, leaving holes in leaves. These holes are commonly mistaken for leaf spot disease. If leaf holes have discolored edges, they are more likely to be bacterial or fungal disease than insect feeding. Distorted growing tips may also occur.

Four-lined plant bug (young and late nymphs) feeding on catnip, with visible damage to new growth. (Matthew Borden, Bartlett Tree Experts, Bugwood.org) CC BY 3.0 US

Four-lined plant bug lifecycle

Four-lined plant bug nymphs emerge in late spring and start feeding on the upper side of leaves. One month later, they molt and become adults. Those adults continue eating as they look for a mate. Females then cut 2” vertical slits into stems where they lay six or more banana-shaped eggs. Adult feeding continues through mid-summer. The next spring, those eggs hatch, and the cycle continues.

Four-lined plant bug management

Unless the infestation is severe, you don’t need to do anything about four-lined plant bugs. Monitor your plants for signs of infestation as you work in the garden. Don’t be surprised if one of these pests falls to the ground if you surprise them. They tend to panic that way, even though they can fly. They are also known to try hiding from us behind stems as we pass by. And they move quickly.

If four-lined plant bug infestations become troublesome in your landscape, you can reduce their numbers by removing the aboveground portion of host plants in autumn and tossing them in the compost pile. Composting destroys many eggs before they have a chance to hatch. Treat severe nymph infestations with insecticidal soap or neem oil. These treatments aren’t very effective against adults. I have no idea why.