Fourlined Plant Bugs (Poecilocapsus lineatus: order Hemiptera; family Miridae) are native to North America. They have four black longitudinal lines on a yellow to yellowish-green background which is referenced by the common name and the specific epithet; lineatus is Latin for “lined.”
These black-lined plant marauders are one of the sneakiest, quickest hitting spring pests found in Ohio. Hordes of hungry nymphs and adults descend seemingly out of nowhere to cause extensive leaf damage, then they just fade away leaving behind their foliar wreckage.
Both the nymphs and adults have their piercing-sucking mouthparts coupled to exceptionally large salivary glands. The wicked combination allows them to inject huge quantities of a potent lipid enzyme into plants causing cells to rapidly collapse. They then feed on the resulting "cell slurry."
The damage appears as small, round, black sunken spots that commonly coalesce into extensive blackened areas. The symptoms are commonly mistaken for a plant leaf disease.
Fourlined plant bugs have one generation per season and their development from eggs to adults occurs over just a few weeks in the spring. It’s hypothesized that the plant bugs possess such a powerful enzyme in their saliva so they can swiftly convert healthy plant cells into a bug-guzzling cell slurry allowing the nymphs to quickly gain the necessary nutrients to support their rapid growth and development.
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.
Fourlined plant bugs may be found feeding on over 250 plant species in 57 plant families including woody ornamentals and herbaceous perennials. They have a particular affinity for members of the aster family (Asteraceae) as well as herbs, especially members of the mint family (Lamiaceae). High populations can produce significant plant injury.
Winter is spent as eggs deposited in vertical slits created by the females in their host plant stems. Thus, one of the most effective management options in herb gardens as well as landscape plantings of annuals and perennials is to closely inspect plants for oviposition scars later this season. Stems that show oviposition scars should be cut and destroyed to eliminate eggs.
Weed management is another important step in reducing localized fourlined plant bug populations. For example, I consistently see some of the heaviest damage on Teasel (Dipsacus spp.). The preference for these non-native weeds is so strong that I use the teasels to monitor localized fourlined plant bug population densities. Mowing to destroy teasel or other weeds showing feeding symptoms will eliminate them as repositories of bug eggs that will hatch next season.
Allen, C.C., and A.G. Wheeler. 1998. Role of Saliva in the Highly Destructive Fourlined Plant Bug (Hemiptera: Miridae: Mirinae), Annals of the Entomological Society of America, Volume 91, Issue 1, 1 January 1998, Pages 94–100, https://doi.org/10.1093/aesa/91.1.94
Wheeler, A.G., and G.L. Miller. 1981. Fourlined Plant Bug (Hemiptera: Miridae), a Reappraisal: Life History, Host Plants, and Plant Response to Feeding. Great Lakes Entomologist, Volume 14, Number 1, Pages 23-35