Tarnished Plant Bug: Piercing Plant ParasiteDecember 30, 2021
Some of the most formidable foes in the garden are plant omnivores because they are not reliant on just one host. The tarnished plant bug (TPB), Lygus lineolaris (Palisot de Beauvois), is one such pest that is a nuisance in gardens and can cause significant economic losses to commercial farmers and plant nurseries.
Plant bugs are a large, diverse order of insects that fall within either the families of Lygaeidae or Miridae. The Miridae family, which includes the tarnished plant bug, includes over 10,000 species with 2,000 found in North America. TPBs feed with their distinctive piercing-sucking mouthparts that insert into plant tissues and inject their toxic saliva. The toxic substance kills plant cells near the feeding site and causes browning and scarring of the plants.
Tarnished plant bugs prefer to feed on parts of plants that have high rates of cell division, such as on buds or flowers. Their damage can cause reduced vegetative growth, termination or deformation of young fruits and flowers and overall stunted development of the plant.
The geographic distribution of the tarnished plant bug is astounding due to their ability to fly long distances and their flexibility of hosts. They have been found as far north as Alaska and Newfoundland and as far south as Central and South America.
Tarnished Plant Bug Overview
Adult tarnished plant bugs are 1/4 inch in length with flattened dark brown bodies and white or yellow markings along their backs and wings. Summer adults are lighter in colour than overwintered adults. Adult bugs have a distinct yellow v-shaped marking behind their heads and yellow triangles on the tips of their wings. Tarnished plant bug eggs are cream-coloured and curved with one flat edge where new nymphs emerge. Tarnished plant bugs undergo five nymphal instars that start with pale green nymphs that gradually develop into their adult size and colour. Nymphs in the early stages of their five nymphal instars may be confused for aphids, but they move much more quickly and do not have cornicles, or rear-pointing parts, that protrude from the abdomen of aphids.
Life Cycle of Lygus Bugs
TPBs have three developmental stages: eggs, nymphs, and adults. Depending on climate conditions, the tarnished plant bugs may have two to three generations per year. Their life cycle starts with overwintered adults laying eggs in early spring. Tarnished plant bug nymphs emerge in five to seven days and when the temperatures reach above 50 degrees Fahrenheit. Both adult stage bugs and nymphs feed on plant tissue but those in an immature stage are particularly voracious and cause more pervasive damage. Their development can take as little as 12.5 days to as much as 40 days to reach full adulthood depending on temperature, humidity, and daylight. Adults begin to lay eggs a few days after reaching maturity. Females on average can lay over 90 eggs with some even being able to lay 140 in their lifetime.
TPBs overwinters among leaf litter, clover, debris, bark, and wooded areas. In springtime, these overwintered adults will lay eggs inside plant tissue of stems or leaf ribs so that only a small part of the egg protrudes from the plant. During their peak growing season in the summer, they can be found on the tips of plants where they typically feed in an upright position. Adult bugs also have the ability to fly.
What Do Tarnished Plant Bugs Eat?
An astounding 700 plant species have been identified as host plants for tarnished plant bugs, out of which 130 are economically important species for agriculture and forestry. Affected vegetable crops and fruits include cotton, strawberries, asparagus, potatoes, beans, stone fruits, and carrots to name a few. Cut flowers and nursery plants are also susceptible. Even conifer seedlings, such as loblolly pines, cannot escape the appetite of these pests. In addition to domesticated host plants, many native plants especially those with aster-like flowers are also hosts. Tarnished plant bugs are early colonizers of meadows and weeds that have reached their flowering stage.
How to Control Tarnished Plant Bugs
Tarnished plant bugs are mobile and generalist feeders that have developed resistance to many conventional pesticides. It will take continuous population monitoring, coupled with using integrated pest management techniques, to keep their population under control.
Organic or Chemical Control
Historically, the tarnished plant bug has been viewed as a secondary pest and treated in large agricultural fields with broad-spectrum pesticides. However, in recent years, researchers have found that some TPB populations have developed resistance to commonly used pesticides such as pyrethroids, carbamates, and organophosphates. Many pesticides on the market approved for home use are unfortunately not effective against TPBs.
TPBs have many natural enemies such as parasitic wasps and many other native and introduced predators. These biological control agents have been used in commercial farms and the USDA is exploring new microbial biopesticides such as entomopathogenic fungi in response to the rising pesticide resistance issue. Novel chemical controls that act as insect growth regulators also hold promise for the future. At this time, more research is needed to find an effective and integrated use of chemical and biological control. However, minimizing your use of pesticides can still encourage the natural predation of TPBs.
Weed control is an essential component to managing the tarnished plant bug population, especially since many weeds are hosts. Remove or mow weedy patches near susceptible fruit trees, strawberry plants, nursery stock, etc. Also, avoid planting cover crops like clover and alfalfa near these plants. Limiting the overwintering habitat of TPBs can make a significant impact on their population in subsequent years.
Preventing Tarnished Plant Bugs
Prevent tarnished plant bug population growth by frequently monitoring their numbers. You can install white sticky traps around your crops or tap on plants over a tarp or a plate to count the number of bugs to get an idea of their infestation density. Floating row covers can be an effective way to create a physical barrier and deter any adult bugs from landing on plants to lay eggs. Make sure to remove the floating row covers when flowers bloom to allow for pollination. Early flowering and early maturing cultivars tend to also be more successful in the presence of this pest.