Four-lined Plant Bugs (Poecilocapsus lineatus) are small and fairly attractive insects, but they are capable of quickly creating extensive damage to many herbs and ornamental plants in the garden. This is largely due to the powerful digestive enzymes contained in their saliva, which is injected into the plant tissue while they are feeding. Most of the damage occurs to the newest growth, on the tips of the plant, and often can be pruned off after the insect stops feeding and the eggs have been laid.

Feeding Damage

Four-lined plant bugs feed by inserting their stylet into plant tissue and sucking the juices out. As they do the tissue in this area quickly dies creating a small (about 1.5-2mm in diameter) roundish sunken spot that is silvery-brown and semi-transparent. Sometimes the center of the spot will eventually drop out altogether, resembling the feeding damage of flea beetles. The spots are pretty much uniform in size and shape which helps to distinguish the damage from a leaf spot disease which would have irregular spots with a border; however, these spots often coalesce creating a blotchier appearance.

The damage develops quickly, with only a few insects being able to create a lot of spots. If the numbers are high whole leaves may brown, curl or become distorted and growing tips may wilt.

Susceptible Plants

There are about 250 plant species that the four-lined plant bug feeds on. Many of those are from the Lamiaceae and Asteraceae families. They are particularly attracted to highly fragrant herbs and plants such as:

• Basil
• Bee balm
• Catnip
• Hyssop
• Lavender
• Lemon balm
• Marjoram
• Mint
• Oregano
• Rosemary
• Sage
• Salvia
• Thyme

Some other plants they like to feed on include:

• Azalea
• Blue mist shrub (Caryopteris)
• Chrysanthemum
• Chinese lantern
• Coreopsis
• Current
• Dahlia
• Deutzia *
• Dogwood*
• Forsythia*
• Gooseberry
• Honeysuckle
• Hydrangea
• Lettuce
• Liatris
• Maples
• Marigold
• Mint
• Morning glory
• Peppers
• Rhododendron
• Shasta daisy
• Sumac
• Viburnum
• Weigela*
• Zinnia 

*Favoured egg laying sites.

Fourlined Plant Bug Identification and Life Cycle

Nymphs begin hatching in late spring (mid to late May in my area). They are very tiny at the start about 1.27mm (1/20″). They start off bright red with black markings on their abdomen, changing to bright orange by the 5th instar stage. Their wings are black and barely visible at the first instar stage but grow larger as the insect matures and develop a yellow stripe down each wing. They mature very quickly completing their 5 instar stages in about 17 to 20 days.

Adults are a yellow green colour with 4 distinct black stripes that run downs the wings, (2 down each wing). Their heads are orangish, body and antennae are black, and the legs are yellow green with black marks. They are about 6 to 8mm (1/4-1/3″) long and about half as wide. Females tend to be slightly larger than the males. The adults are in flight for about 1 month during which time they mate and lay their eggs. The males die shortly after mating while the females live a bit longer.

Eggs are oviposited into the stems of the new growth, usually the upper 10-12cm (4-5″) of growth. The eggs are about 1.65mm long, pale yellow at the start and are laid in clusters deep within the plant tissue with only the tips appearing slightly visible. The eggs overwinter in these stems and come the following spring they begin maturing and turn red in colour.

Management and Control

While only a few of these insects can do a lot of damage it is considered cosmetic, and the overall health of the plant is usually not in jeopardy. There are a few things you can do however to help manage this pest and minimize the damage.

Manual control: Hand pick the insect and drop it into a container of warm soapy water. Four-lined plant bugs can move quickly either flying away or dropping from the plant. I find it tends to work best to hold the container of soapy water beneath them and quickly tap the insect into the container.

Fall cleanup: Since the insect tends to lay its eggs in the top 4-5″ of growth, prune this off in late fall to very early spring and dispose of the plant debris. This will remove the egg masses for next season.

Natural sprays: Dormant oil can be sprayed on ornamental trees and shrubs during dormancy to suffocate egg masses. Once the eggs hatch insecticidal soaps and horticultural oils can be sprayed directly on the nymphs.

Natural predators: There are a few natural predators of the four-lined plant bug that may help to keep the populations in check, such as a predatory wasp Cirrospilus ovisugosus, a jumping spider Phidippus clarus and several species of birds, big eyed bugs, damsel bugs and pirate bugs. See my article on beneficial insects to learn more about some of these predators and how to attract them to your garden.

Chemical sprays: In regions where homeowners are permitted, there are several chemicals listed for use against the four-lined plant bug. Use as directed and only when populations are high and damage extensive.

References:

Baker J., (2016- rev. Sept. 17, 2019). Fourlined Plant Bug. N. C. State Extension. https://content.ces.ncsu.edu/four-lined-plant-bug

Borden M. and Dale A., (n.d.). Featured Creatures fourlined plant bug. Entomology and Nematology Department, University of Florida. https://entnemdept.ufl.edu/creatures/veg/leaf/Poecilocapsus_lineatus.htm

Feather S., (Updated:  MAY 15, 2017). Four-lined Plant Bugs Are Active Now. https://extension.psu.edu/four-lined-plant-bugs-are-active-now

Hahn J. and Wold-Burkness S., (rev. 2019). Fourlined plant bug. University of Minnesota Extension. https://extension.umn.edu/yard-and-garden-insects/four-lined-plant-bugs

Staab C. and Pellitteri P. (Revised:  4/27/2004). Four-Lined Plant Bug. Wisconsin Horticulture Division of Extension. https://hort.extension.wisc.edu/articles/four-lined-plant-bug/

Photo credits: all photos taken by the author.

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