Tarnished and four-lined plant bugs
Click for larger image Tarnished plant bug adult (Hemiptera)

Two of the most damaging insects on perennial plants are the tarnished plant bug, Lygus lineolaris, and the four-lined plant bug, Poecilocapsus lineatus. These two plant bugs can cause serious problems because they have such a wide variety of host plants. The four-lined plant bug feeds on 250 plant species which are mostly herbaceous. The tarnished plant bug is a problem on a wide variety of ornamental flowers.

Symptoms and Diagnosis

Damage varies slightly from the two plant bugs. The four-lined plant bugs cause small (1/16 inch), discolored areas on leaves where they suck out cell juices. Injured areas will turn black or become translucent, and after several weeks, the dead tissue may drop out, leaving small holes. The adults feed on the upper surfaces of leaves and are voracious feeders. The topmost leaves will generally be the first to be injured.

Damage from the tarnished plant bug is in the form of distorted foliage or disbudded plants. This damage is caused by the overwintered adults which attack swollen and opening buds in the early spring. The disbudding will cause the plant to be short and bushy. If the attack takes place after shoot elongation begins, the tip will often turn black and die, or it will be so damaged that shoot stunting or distortion occurs. Stems frequently break at the injured area.

Life Cycle

The four-lined plant bug overwinters as eggs inserted into a slit near the top of tender shoots. Nymphs emerge from the eggs in May. Nymphal coloring varies from bright red to yellow. The species requires about 30 days to complete nymphal development. Forewings of adults are yellow, but may turn bright green. However, the four black stripes that give the insect its name remain distinct. This species normally has one generation a year.

Adults of the tarnished plant bug overwinter as adults in leaf litter. Beginning in the spring, they lay eggs mainly in the stems and flowers of herbaceous plants. After hatching, the young nymphs usually remain to feed on the same plant until they mature. The nymph is green or pale yellow and grows rapidly. Adults are capable flyers and readily move from place to place. There may be two to five generations per year. In midsummer, a life cycle may be completed in about 25 days. By late summer, populations can become very abundant.

Integrated Pest Management Strategies

1. Live with the damage. Since damage is often cosmetic, some damage can be tolerated. Often, natural predators will keep the insects under control.

2. Remove leaf litter. To limit problems in coming years, clean up leaf litter to avoid overwintering sites for tarnished plant bugs.

3. Prune out egg masses. Learn to identify the egg masses of four-lined plant bugs and prune them out in winter.

4. Use insecticidal soaps. If populations are high enough, spraying with an insecticidal soap may be necessary. Because the tarnished plant bug can go through many generations in a single year and cause great damage to a plant, it is best to initiate control when it first appears.

5. If necessary, use chemical insecticides. Plant bugs can be controlled with malathion, and carbaryl (Sevin).

Organic Strategies

Strategies 1, 2, and 3 are strictly organic approaches. For an organic approach to Strategy 4, consult the Organic Materials Review Institute (OMRI™) for appropriate insecticidal soap products.

More images:

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Tarnished plant bug nymph (Hemiptera)
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Feeding damage on oregano (Origanum vulgare hirtum) caused by toxic saliva of the four-lined plant bug (Hemiptera)
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Four-lined plant bug adult (Hemiptera) on oregano (Origanum vulgare hirtum); note the hinged wingtips characteristic of plant bugs in the family Miridae.
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Feeding damage on oregano (Origanum vulgare hirtum) and adult four-lined plant bug (Hemiptera), Poecilocapsus lineatus
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Four-lined plant bug adult on oregano Origanum vulgare hirtum), Poecilocapsus lineatus
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Four-lined plant bug adult on oregano Origanum vulgare hirtum), Poecilocapsus lineatus; note piercing-sucking beak
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Four-lined plant bug adult on oregano Origanum vulgare hirtum), Poecilocapsus lineatus: note characteristic hinged wingtips
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Tarnished plant bug (Hemiptera) on Brassica spp.
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Tarnished plant bug (Hemiptera) on Brassica spp.