Preserving the U.S. Capitol Grounds with Beneficial Insects

Over the next month, hundreds of trees, shrubs and herbaceous plants will be planted and will bring new life and interest to the Capitol campus. Decisions about what will be added to the diverse collection of plants at the U.S. Capitol Grounds are more complex than meets the eye. A team of gardeners, arborists, a landscape architect and other specialists all play a role in selecting what plants will be planted. A central driver in this process is the Capitol Grounds mission to preserve the historic integrity and aesthetics of the landscape. In today's complex urban environments, this means that we must consider new plant species that offer increased resilience to pests and pathogens that have emerged since the development of the historic Capitol campus landscape by Frederick Law Olmsted in 1874.

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Newly designed and planted tear drop beds provide habitat for generalist insect pest predators, while preserving the historic design intent created by Olmsted. Plants include woodland and creeping phlox, beardtongue, liverwort and mountain mint.

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Merissa Reynolds, Capitol Gardening Division Assistant Supervisor, places immature green lacewing larvae on garden phlox leaves to encourage their growth and establishment in the newly designed and planted tear drop beds.

Newly designed and planted tear drop beds; Merissa Reynolds, Capitol Gardening Division Assistant Supervisor, places immature green lacewing larvae on garden phlox leaves to encourage their growth and establishment.

As new and existing insect pests impact the health of plants located throughout the 274-acre Capitol campus, the Capitol Grounds team continues to explore innovative, ecologically minded solutions to address campuswide plant health care challenges. One of those challenges is the effective management of scale pests. Scales are sap-feeding insects with protective waxy coverings that commonly attack ornamental trees and shrubs.

In their natural surroundings, scale populations are kept in low numbers by natural predators that feed on them. However, recent research has shown that scale pest outbreaks are becoming more frequent, especially for built urban environments like those throughout the Washington, D.C., region.

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Green lacewing adults are generalist predators of common plant pests and are reported to feed on non-native, invasive CMBS crawlers among other soft-bodied insect pests.

The arrival of a new, invasive scale species — the Crapemyrtle Bark Scale (CMBS, Acanthococcus lagerstroemiae) — has further exacerbated plant damage caused by scale pests. CMBS is a recently introduced pest from Asia that mainly attacks crapemyrtles (Lagerstroemia spp.). While this non-native scale will not destroy crapemyrtles, heavy infestations negatively impact tree health and flower abundance and cause unsightly growth of a dark fungus called sooty mold. More than 400 crapemyrtles currently planted across the Capitol campus are susceptible to CMBS attack and subsequent damage.

With more than 1,000 different insect scales reported in the U.S., how does the Capitol Grounds team effectively manage to control for CMBS and other scale pests?

Taking an ecological approach to pest management, Capitol Grounds utilizes two innovative control practices — Conservation and Augmentative Biological Control.

In Conservation Biological Control, the aim is to integrate landscapes designed for their aesthetic quality while also incorporating plant species that support populations of natural predators to plant pests. In recent years, Capitol Grounds has used strategic planting initiatives to increase landscape function, resiliency and sustainability. These efforts have also reinforced the role the arboretum takes in managing urban forests to create landscapes that support the conservation of plant and animal species in urban ecosystems. Where possible, Capitol Grounds seeks to plant species that not only offer seasonal floral display, but also provide important habitat for existing pollinator and beneficial invertebrate communities.

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Beardstongue, Penstemon digitalis, is well-known for providing habit to natural enemies, as shown by the newly parasitized green peach aphids on the leaf tips of newly established plants at the northwest garden bed of Capitol Square.

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Photo by

Thomas Hatzenbuhler

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Green lacewing eggs on a placement card for an infested plant.

Dr. Emily Mueller and Merissa Reynolds scout the undersides of leaves for aphid pests and their natural enemies; Newly parasitized green peach aphids on Beardstongue, Penstemon digitalis; Green lacewing eggs on a card placed on an infested plant.

One example of supporting the environment through the recruitment of beneficial insects is the recently designed tear drop beds at the pedestrian entrances at the western most boundary of the U.S. Capitol Grounds. Native plants were selected to provide seasonal nectar resources for generalist insect pest predators such as wasps, spiders, beetles and other beneficial insects.

The other approach to controlling insect plant pests in our landscapes involves the release of additional populations of natural pest predators, known as Augmentative Biological Control. This practice is particularly effective with managing invasive insect species like CMBS because natural predators are not yet accustomed to this non-native insect in the environment. For example, Capitol Grounds will implement early releases of a generalist predator, the green lacewing (Chrysoperla rufilabris), which feeds on a wide variety of insect pests such as scales, aphids, and thrips, to help suppress pest populations across campus. While this Integrated Pest Management (IPM) practice is not currently being implemented on the grounds of the U.S. Capitol, Capitol Grounds will be joining other AOC jurisdictions, including the U.S. Botanic Garden and the Library Buildings and Grounds staff, in the use of augmentative biological controls such as green lacewings to help sustainability control plant pests such as CMBS.

Written by AOC Capitol Grounds and Arboretum's Dr. Emily Mueller, Plant Health Care Specialist, and Melissa Westbrook, Urban Forester.

Join Us to Learn More

In commemoration of Earth Day 2023 and in support of the Architect of the Capitol's commitment to environmental conservation, Capitol Grounds and Arboretum will host an event featuring these ecological-based pest management approaches.

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Garden beds that promote beneficial insects like pollinators and natural enemies of plant pests provide abundant, season long floral nectar and pollen resources, which are often provided by mixtures of both native and cultivated plant species.

WHEN: Friday, April 21, 2023, at 11 a.m.
WHERE: Please meet us at the tear drop garden bed on the corner of Northwest Drive and 1st Street NW near Peace Monument.

Trained professionals from the Capitol Grounds garden team will provide an overview of the importance of native plant designs for biological pest control. Attendees will have the opportunity to see the release of beneficial insects and learn about the different life stages of the generalist green lacewing.