Four-lined plant bug in home gardens
The four-lined plant bug, Poecilocapus lineatus, is a common insect found in Minnesota gardens. It has an extensive host range, feeding on over 250 species of plants, including herbaceous perennials, woody ornamentals, fruits, vegetables, and annual flowers.
Four-lined plant bug nymphs are bright red to orange in color with black wing pads and dots on their abdomen when they first hatch. Later instars have black wing pads with a yellow strip on each. Adults are greenish-yellow with four black strips running longitudinally down the wings. The head is orange-brown and the legs are yellow-green. Both nymphs and adults have piercing-sucking mouthparts.
Four-lined plant bugs are most commonly encountered on herbaceous perennials including chrysanthemum, Chinese lantern, liatris, and shasta daisy. They also feed on herbs, including mint and basil. They may also be found feeding on woody ornamentals, such as azalea, dogwood, forsythia, viburnum, amur maple and sumac, and flowering annuals, such as zinnia and marigold. Berries such as currant and gooseberry are attractive to four-lined plant bug and although less common on vegetables, they can be a pest on peppers.
Four-lined plant bug eggs hatch in late spring and nymphs begin feeding on the upper side of leaves. After feeding for about four weeks, the nymphs molt into adults. Adults will continue to feed and then mate, laying banana shaped eggs in vertical slits measuring two to three inches along the plant's stem. They are usually not laid individually but instead are laid in groups of six or more. The eggs will overwinter and hatch in late May or early June just after the plant's foliage emerges. There is only one generation per year.
Both four-lined plant bug adults and nymphs can injure plants. They feed by inserting their needle-like mouthparts into leaves and removing chlorophyll. This feeding produces dark, round, sunken spots, about 1/16 to 1/8 inch wide. The spots may become clear and after several weeks the affected tissue drops out leaving small holes. If feeding occurs on new growth, wilting may result.
This feeding damage may be misidentified as a leaf spot disease. However, four-lined plant bug feeding leaves spots similar in size and shape, unlike damage caused by fungi and bacteria which often cause spots that vary in size and have discolored outer margins.
In most cases, four-lined plant bug feeding only affects the appearance of plants. Moderate to large populations of four-lined plant bugs can be destructive to plants, especially herbs.
Start to monitor susceptible plants in late May and early June for damage and insects. When looking for four-lined plant bugs, look carefully as they may drop to the ground or hide when disturbed.
Small to moderate numbers of four-lined plant bugs normally do not seriously harm plants and treatment is not necessary to protect the plants' health. Tolerate and ignore four-lined plant bugs when possible, especially if you have not seen much damage in recent years.
Cut down host plants in the fall to remove eggs that may have been inserted into them. Be sure to bury or compost removed plant material or remove residues from the landscape area.
If you wish to preserve the plants' appearance or protect edible plants, especially herbs, an insecticide treatment is warranted. The earlier you detect four-lined plant bug activity, the better you can minimize plant injury.
When choosing an insecticide, be sure the chemical is cleared for use on those plants you wish to treat and on edible herbs pay attention to the pre-harvest interval. Insecticidal soap can be effective against the immature nymphs. However, the insects must be contacted directly and there is no residual so treatment may need to be repeated.
There are a variety of contact residual insecticides that are available which are longer lasting. Use them judiciously as they are broad spectrum and can kill a variety of insects, including natural enemies. Examples of contact residual insecticides are permethrin, bifenthrin, lambda-cyhalothrin, acetamiprid, and carbaryl.