Fourlined plant bug
Published in Yard & Garden Brief October 2002
Fourlined plant bugs, Poecilocapsus lineatus, are common pests of many herbaceous perennials including chrysanthemum, mint, Chinese lantern, liatris, basil, and shasta daisy as well as fruits, especially currant and gooseberry. They may also feed on woody ornamentals such as azalea, dogwood, forsythia, viburnum, amur maple and sumac, and they feed occasionally on flowering annuals, including marigolds.
Adult fourlined plant bugs overwinter as eggs laid in clusters into a slit near the top of canes of currants, brambles and other woody plants. The eggs hatch in late May or early June in central Minnesota (including the Twin Cities.) When nymphs first hatch, they are bright red with black wing pads then change to yellow with black blotches on their abdomens and black wingpads with a yellow stripe on each. Adults are greenish yellow with four black stripes down the wings. When disturbed they rapidly run or fly away. Fourlined plant bugs are active for about a month; there is one generation each year.
Fourlined plant bugs feed by inserting their needle-like mouthparts into leaves and removing chlorophyll. Their damage appears as small round, depressed spots which may be brown or black. The spots may become clear and after several weeks the affected tissue drops out leaving small holes. Nymphs as well as adults can injure plants.
Small to moderate numbers of fourlined plant bugs normally do not seriously harm plants and treatment is not necessary to protect the plants' health. Tolerate and ignore fourlined plant bugs when possible, especially if you have not seen much damage in recent years.
Moderate to large populations of fourlined plant bugs can be destructive to plants, especially herbs and mint. If you wish to preserve the plants' appearance or if feeding is extensive, treatment is warranted. To manage fourlined plant bugs, spray a labeled insecticide, such as acephate (Orthene), diazinon, chlorpyrifos, carbaryl (Sevin) or malathion as soon as you see damage in May or June. The earlier you detect fourlined plant activity, the better your chances of minimizing plant injury. When choosing an insecticide, be sure the chemical is cleared for use on those plants you wish to treat.
Insecticidal soap is a less toxic option to consider, especially on herbs since there are few insecticides labeled for use on herbs. Unfortunately, insecticidal soap is generally not very effective against mobile insects such as fourlined plant bugs. Results may not be as good as other insecticides.
Caution: Read all insecticide label directions very carefully before purchasing and again before using. Information on the label should be used as the final authority.