Where Do Four-Lined Plant Bugs Come From?

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I’ve come to expect seeing some damage each spring from our native Four-Lined Plant Bug (Poecilocapsus lineatus, family Hemiptera).  However, their wreckage appears to be particularly heavy this season in some parts of Ohio.  The question “where did they come from” is common when hordes of hungry insect pests descend seemingly out of nowhere onto plants to cause extensive damage.

 

 

Life Cycle and Damage

Four-lined plant bugs have one generation per season and their development from eggs to adults occurs in the spring.  Both the adults and nymphs are heavy feeders; however, the nymphs produce the most significant damage because they feed over a longer period as they develop through five instar stages.

 

Four-Lined Plant Bug

 

Four-Lined Plant Bug

 

Like many plant-feeding hemipterans, the bugs inject enzymes into the plant to cause cells to collapse.  They then feed on the resulting "cell slurry."  The damage appears as small, round, black sunken spots that may coalesce into extensive blackened areas on infested leaves.  The symptoms are commonly mistaken for a plant leaf disease.

 

Four-Lined Plant Bug

 

Four-Lined Plant Bug

 

This sucking insect feeds on over 250 plant species including woody ornamentals and herbaceous perennials.  They seem to have a particularly affinity for herbs, especially members of the mint family (Lamiaceae) and high populations can produce significant plant injury.  Although they can damage many annual vegetables, we seldom see significant injury in Ohio because vegetable gardens are usually planted after the bugs have completed much of their spring development.

 

 

Where Do They Come From?

Adult four-lined plant bugs deposit eggs into 2 – 3” long vertical slits they create in the stems of their host plants.  The eggs overwinter and hatch in the spring to launch another round of damage.  Therefore, the answer to the question, “where do they come from?” may be that they never left!

 

One of the most effective management options is to cut and destroy the stems of infested plants in the fall to remove eggs.  I’ve observed this strategy to be very effective in herb gardens.  Conversely, I’ve watched populations continue to rise in herb gardens where a good fall clean-up program is not applied.

 

Four-Lined Plant Bug

 

Given the wide host range, you may also need to inspect nearby weeds.  For example, I’ve observed over the years that some of the heaviest damage can be found on Teasel (Dipsacus spp.).  In fact, the preference for these non-native weeds is so strong; I use the teasels to monitor localized four-lined plant bug population densities.  Mowing right now to destroy teasel or any other weeds showing feeding symptoms can help to remove them as an annual source for four-lined plant bugs in landscapes and herb gardens.