Fourlined plant bug feeding injury can easily be confused with disease symptoms

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Several people have sent in samples or photographs showing lots of little round, brown spots on the foliage of their favorite plants caused by the fourlined plant bug, Poecilocapsus lineatus (Miridae).

This pretty little bug has been recorded feeding on 250 plant species, most of which are herbaceous plants. The insect gets its common name from its four black stripes present on its front wings. This insect can cause extensive damage to the leaves of its host. Like all plant bugs, the fourlined plant bug has piercing mouthparts that are inserted into the leaf to suck out plant juice. In doing so, the bug injects saliva that contains enzymes that kill the plant tissue directly around the feeding puncture. Both fourlined plant bug nymphs and adult bugs cause characteristic necrotic spots, which might be confused with disease symptoms. This bug overwinters in the egg stage. The eggs hatch in early to mid-May in Michigan. Nymphs require 30 days or so to develop into adults. There are two to three generations each year, but most damage I have experienced in my garden has been caused by the first generation. The fourlined plant bug attacks the upper leaves first, and only a small number of these recreational feeders are required to cause extensive damage. It is best to spray these insects when they are first noticed. Picking these fast moving, elusive bugs by hand can be very frustrating. Any spray applied during bloom may damage the flowers.

See what the nymphs look like at

Leaf damage
The round necrotic spots
caused by fourlined plant
bugs. Photo credit: John A.
Virginia Polytechnic
Institute and State University.
Courtesy of

Fourlined plant bug
A pretty little fourlined plant bug does
some pretty ugly damage.
Photo credit: Whitney Cranshaw, Colorado State University.
Courtesy of

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