The global phenomenon of invasive species is alive and well in Frederick County. An invasive species is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or may even be beneficial with respect to other species, invasive species adversely affect habitats and bioregions, causing ecological, environmental and economic damage.
The term “invasive species” can refer to any introduced organism, including insects, plants and fungi. Invasive species management is estimated to cost the US around $21 billion per year.
Global trade and the movement of people and goods have caused massive shifts in insect populations, introducing insect species to areas where they have no natural predators. Without predators, parasites and pathogens to keep them in check, invasive insect populations increase unimpeded.
Since the US, China, India and Brazil are large agricultural producers, they suffer the highest potential cost from invasive species. China has a whopping 283 invasive species, including 50 of the worst invasive species in the world, as classified by the International Union for Conservation of Nature. These species have been causing a great economic loss in China of about $29.3 billion (US) every year, and about 46.3% of them have invaded that region’s natural reserves.
In the US, the cost of invasive pests — including management, control and economic losses — in 2017 was estimated to be more than $13.6 billion dollars per year.
The enormous size of China and the US allows for a wide variety of invasive pests. Cropping systems range from subtropical to temperate environments, and this diversity supports a wide range of potential pest and disease species. In addition, they have active trading relationships with many countries worldwide, enabling links for the transport of pest and disease organisms to novel areas.
While the scale of the impact in China and the US is hard to comprehend, invasive species often have the worst impact on developing countries, as pests will ruin a proportionately larger part of their natural resources or, in catastrophic cases, eliminate them altogether.
Here in Maryland, we have learned to live with some invasive pests, such as the showy Japanese beetle, introduced in 1916. The adults of this “jewel beetle” feed on the foliage and fruits of several hundred species of trees, shrubs, vines and crops, while larvae feed on the roots of grasses and other plants, destroying the plants and even the soil. We have developed beetle bags, nettings, pheromones, sprays and many other tricks to manage them.
We are actively fighting other invasive pests, too, such as the emerald ash borer, which made its way to Frederick around 2008 and is still decimating our beautiful ash trees.
A relatively innocuous yet annoying invasive pest is the stink bug, which came to our region in 2009 and is known for oversharing its perfume.
The most critical invasive insect that we need to keep at bay here in Frederick County is the spotted lanternfly (Lycorma delicatula), a new invasive pest in the Mid-Atlantic. It has the potential to seriously affect our crops and has been detected in several states that border Maryland.
Sign up for the Frederick County Forestry Board’s spotted lanternfly workshop on Sept. 30, organized in partnership with the Washington County Forestry Board, if you want to learn all there is to know about this pest (register at frederick.forestryboard.org).
The Asian tiger mosquito (Aedes albopictus) came from northern Asia in the mid-1980s, hitching a ride on “lucky bamboo” plants, and has spread rapidly. The Asian tiger mosquito is an aggressive biter that feeds primarily during the day and has a broad host range, including humans, domestic and wild animals, and birds. It is a potential vector of encephalitis, dengue (all four serotypes), yellow fever, dog heartworm and West Nile virus. It is estimated that more than 100,000 residential properties in Maryland provide breeding sites for tiger mosquitoes. Public mosquito control agencies do not have the resources or the legal authority to remove and drain mosquito-breeding containers over such a large area, so it is imperative that every resident drain or remove water-holding containers from their properties.
The emerald ash borer (Agrilus planipennis) mentioned above is another “jewel beetle” that traveled from Northeastern Asia. Since its arrival in the US in 2002, it is estimated to have killed over 100 million ash trees. Females lay eggs in bark crevices on ash trees, and larvae feed underneath the bark to emerge as adults in one to two years. When the larvae of the beetle bore under the bark, they create tunnels as they eat and slice through the channels that transport water from the tree’s roots to the leaves. Once infested, unable to take up water, the tree dries out and dies. The emerald ash borer is widespread throughout Frederick County, and most ash trees have been killed unless they have ongoing emerald ash borer control, which requires injecting the tree every other year.
Gypsy moths (Lymantria dispar) are by far the most destructive pest of forest and shade trees in Maryland. The caterpillars eat the leaves of oaks and other hardwoods in May and June. Heavy populations of caterpillars will eat most or all leaves in a tree. Large outbreaks have affected hundreds of thousands of acres statewide, but the upside is that their populations show cyclic swings. The last time a gypsy moth infestation grew to damaging levels in Frederick County was 2009. Naturally occurring viruses and fungi are keeping populations in check, and these pathogens tend to be more prevalent when we experience a cool, wet spring.
The red imported fire ant (Solenopsis invica), or “RIFA” for short, is a major economic pest in the southeastern United States, but it has been spotted here as well, especially during warmer and drier years. It originates in lowland areas of South America, primarily Brazil and Argentina. RIFA threatens crops and plants and can girdle young trees. Large nests located in fields interfere with and damage equipment during cultivation and harvesting. Red imported fire ants respond rapidly and aggressively to disturbances, and ant attacks inhibit field-worker activities.
The hemlock woolly adelgid (Adelges tsugae) is a tiny insect of the order Hemiptera native to East Asia. It feeds by sucking sap from hemlock and spruce trees. In its native range, the hemlock woolly adelgid is not a serious pest because populations are managed by natural predators and parasitoids and by host resistance. Here, unless we treat the hemlock woolly adelgid with insecticide, it can kill a large adult tree in four years.
The Asian longhorned beetle is a very serious exotic pest that was introduced in solid wood packing material from China. It has the potential to cause more damage than Dutch elm disease, chestnut blight and gypsy moths combined because it attacks 29 species of deciduous hardwood trees. The beetle prefers species of maple, including boxelder, Norway, red, silver and sugar maples. Other known hosts include alders, birches, elms, horsechestnut, poplars, sycamore and willows. Fortunately, the Asian longhorned beetle does not spread very readily, and its populations are confined to small areas.
If you are interested in learning more about additional invasive species in our area, such as the euonymus leaf notcher, the Southern pine beetle and the shoot pine beetle, and how to protect our trees and crops from them, visit dnr.maryland.gov.
The Frederick County Forestry Board promotes the conservation, stewardship, and sustainable use of our forest resources and urban landscapes. We inform the public and vigorously advocate to retain or increase the integrity of our local, regional, and national forest ecosystems. Trees enhance our physical and mental well-being; improve the quality of our streams, lakes, and the Bay; help cool the environment; retain and improve soil; produce oxygen while consuming carbon dioxide; and provide shelter and food for wildlife. Please visit frederick.forestryboard.org for additional information and resources or to sign up for our free weekly Nature Note articles, tree plantings, Second Sunday Tree Walks, tree shelter exchange, and more.