Invasive insect pests in home gardens and landscapes
Story and Photos by Dr. Blake Layton
When the first Americans arrived in North America, they brought non-native insect pests with them. Head lice and body lice were among the first of hundreds of species of non-native insect pests to invade our country and make it their home. During the first centuries after Columbus made his big discovery, many of our invasive insect pests came from Europe, such as gypsy moth, Hessian fly, bedbugs, balsam wooly adelgids, and honeybees, but non-native insects also came into the country from other parts of the world, most by hitching rides on merchant sailing ships. Yes, feral honeybees can be pests. They sometimes establish colonies in building voids and in rare situations even cause human fatalities.
During the past several decades, there has been a large increase in the number of new invasive insect species, with most of these coming from Asian countries. Things don’t come on a “slow boat from China” any more. They come on a fast ship or an airplane. The lengthy list of non-native insect pests to invade the U.S. from Asia within the last half-century includes pests such as Asian tiger mosquito, Formosan termites, Asian citrus psyllid, hemlock wooly adelgid, chilli thrips, Asian long horned beetle, and all but two of the pests discussed below. This is a two-way street. The U.S. has exported a few insect pests to Asian countries, but there is a large trade deficit!
When a non-native insect pest arrives in a new country and finds a suitable host and environment, it often develops higher populations and causes more economic damage than it does in its native land. This is because the pest insect often leaves many of its natural parasites, predators, and pathogens behind. Since kudzu bug was first detected near Atlanta in 2009, it has spread rapidly throughout the Southeast, often reaching huge numbers. Fortunately, a naturally occurring fungal disease and an introduced egg parasite are beginning to help control kudzu bugs in some areas.
In some cases, a new pest may also find a new host plant, one that is similar to its native host but does not have any natural resistance to the pest insect or any diseases it may vector. This often has devastating impacts. For example, red bay ambrosia beetle, along with the laurel wilt disease it spreads, has all but eliminated red bay trees (Persea borbonia) from their native range in coastal areas of the Southeast. A similar scenario occurred in the Smoky Mountain region with balsam wooly adelgid and Fraser fir (Abies fraseri) in the 1950s and 60s and, a bit more recently with hemlock wooly adelgid and hemlock trees (Tsuga spp.). These two adelgids do not vector a disease; they cause all this devastation on their own via toxins they inject into the tree when feeding. Asian citrus psyllid and the citrus greening disease it vectors have destroyed thousands of acres of citrus groves in Florida and other states, causing billions of dollars in losses, and making orange juice more expensive than it would be had this pest not gotten into the country.
Collectively, non-native insect pests that have become established in America cause tens of billions of dollars in economic losses each year, and we continue to get new pests all too frequently. Non-native insect pests adversely affect human health, livestock, homes, commercial buildings, agricultural crops, commercial fruits, vegetables, turfgrass, ornamental plants, and home gardens. Let’s focus on a few specific examples of the many non-native insect pests you might encounter in your garden and landscape. These are discussed in order of their arrival here, with three species arriving since the turn of the century.
Colorado potato beetle
(Leptinotarsa decemlineata)
This is an unusual example of an invasive insect – an insect that is native to one portion of the country where it was not a pest, but has invaded other portions of the country and become a serious pest. It’s not really the insect that’s the non-native here; it’s the host plant. Colorado potato beetle is native to Mexico and the western U.S., where it fed on a solanaceous weed known as buffalobur (Solanum rostratum). When European settlers came to the U.S., they brought Irish potatoes (Solanum tuberosum) with them. As the country expanded westward, settlers continued to transport and plant this important staple crop. It wasn’t until around 1859 that this little striped beetle figured out that it also liked potatoes and adapted to the crop. Then it simply followed the trail of potato patches back to the East Coast, and earned the common name by which we know it today. If you grow potatoes in your vegetable garden, this is one pest you know all too well. They like potatoes best, but will also feed on eggplant and tomatoes. Interestingly, false potato beetle (Leptinotarsa juncta), which is native to the eastern U.S. and feeds on horsenettle and a few other solanaceous plants, has never adapted to potatoes.
Red imported fire ants
(Solenopsis invicta)
As one of the best known, and most hated, non-native insect pests in the South, fire ants are a classic example of how non-native insect pests can enter the country and spread. They came here by boat from their native lands of South America, probably in soil that was used as ballast in the holds of ships and was off-loaded at the port of Mobile to make room for heavier cargo. This happened around 1930. Although black imported fire ants had already beat them here by a dozen or so years, red imported fire ants quickly became the dominant species.
Fire ants can spread on their own power when wind blows winged, reproductive swarmers miles away from the mound from which they emerged, but they can move farther and faster by human-aided transport. A potted plant that contains a small fire ant colony can quickly and easily be moved hundreds of miles in a single day. Fortunately, winter temperatures limit northern establishment and survival of fire ants. To see the current distribution of fire ants in the U.S., go online and search for the “Imported Fire Ant Quarantine Map.” Check with your local county extension office for information on how to control fire ants. Many safe, effective treatments are available, but fire ant control is a lot like mowing the grass. No matter how sharp you keep the mower blades or how short you mow the grass, it will grow back and have to be mowed again.
Silverleaf whitefly
(Bemisia tabaci, biotype B)
This tiny insect has so many big names. It is also known as Bemisia argentinifolii, poinsettia whitefly, sweetpotato whitefly, and even Bemisia tabaci Middle East-Asia Minor 1. Regardless of name, this whitefly is a major economic pest of U.S. vegetable and ornamental crops, causing billions of dollars in economic losses since it first appeared in the country around 1986. Yes, that’s billion, with a “b.” Estimated losses in California alone exceed $500 million. We have several other species of whiteflies, including the citrus whitefly that is so common on gardenias, but silverleaf whitefly is in a class by itself. Most of the direct damage is caused by the immobile nymphs feeding on the undersides of the leaves, removing plant sap and producing large amounts of honeydew and sooty mold, but silverleaf whitefly also vectors several serious viral diseases, and it is difficult to control because it is resistant to most insecticides. Now there’s even a biotype Q that’s even more resistant.
Silverleaf whitefly has hundreds of host plants, many of which are important ornamental, vegetable, or row crops. Although it is unable to survive outdoors through the winter in temperate climates, silverleaf whitefly thrives in greenhouses. Homeowners who experience heavy infestations of silverleaf whiteflies in their vegetable garden or landscape often have small greenhouses, keep indoor host plants such as poinsettias through the winter, or buy infested plants from nurseries in the spring. If you think you have silverleaf whiteflies, do your homework before attempting control. There are only a few effective treatments, and using the wrong insecticide will only make the problem worse.
Emerald ash borer
(Agrilus planipennis)
This is one of the most devastating forest pests to invade the country in recent years. Emerald ash borer (EAB) was first found in Michigan in 2002. Since then it has spread to all or part of 30 states, has killed hundreds of millions of ash trees (Fraxinus spp.), and continues to spread unchecked. Today, Florida and Mississippi are the only states in the eastern half of the country not infested (according to USDA.gov), but it’s just a matter of time. Although these shiny green beetles look like they would be easy to spot, they are only about ½ inch long. Most homeowners don’t realize they have an infestation until the crowns of their ash trees begin to die, and by then it is usually too late for effective treatment. The larvae kill trees by feeding on the cambium layer and girdling them.
Movement of firewood by recreational campers is one of the main ways this beetle was able to spread so far in only 15 years. Going camping this fall? Leave the firewood at home. Commercial insecticide treatments are available to preventively protect high value landscape trees, but are best initiated just before emerald ash borers reach the area (when EAB is detected within 30 to 50 miles). Click the following link to see the most current EAB distribution map. Check with your county extension office for information on treatment options.
Crapemyrtle bark scale
(Eriococcus lagerstroemia)
Crapemyrtles (Lagerstroemia spp.) are one of the most widely planted landscape trees in the South. They are beautiful, tough, come in a variety of sizes and colors, and they are, or at least were, relatively pestfree. Then came crapemyrtle bark scale. It was first detected in Texas around 2004, but has since spread to 11 Southeastern states. Distribution is still spotty, with only a few infested counties in each state, but expansion continues. Although female scale can’t fly, newly hatched crawlers can spread to nearby crapemyrtles by hitching a ride on birds, squirrels, or flying insects. Long-range movement occurs primarily by transport of infested crapemyrtles by homeowners, nurseries, or commercial landscapers. Before buying and transporting crapemyrtles, be sure – very sure – they are not infested with crapemyrtle bark scale.
Heavily infested trees will be black with sooty mold and limbs and branches will be encrusted with patches of white or gray felt-covered scales. Trees become so unsightly that some homeowners have cut infested trees, rather than keep them in their landscape. If you think you might have this pest on your crapemyrtles, report the infestation to your county extension office and ask for information on control. Soil-applied insecticide treatments containing active ingredients such as imidacloprid, dinotefuran, or thiamethoxam will give good control, but not 100 percent control. It is still too early to know what the ultimate impact of crapemyrtle bark scale will be; this largely depends on how good a job we, the green industry, do in preventing further spread.
Spotted wing drosophila (Drosophila suzukii)
Having problems with backyard blueberries and blackberries in the last few years? Berries that are sour, leaky, collapse when picked, dry up on the plant, or drop off the plant early? Spotted wing drosophila was first detected in 2008 in California. Now it is a major pest of small fruit such as blueberries, blackberries, cherries, and figs throughout the country, causing billions of dollars in losses for commercial fruit producers, and much disappointment and frustration for backyard gardeners.
Spotted wing drosophila are similar in size and appearance to the fruit flies you see in the house around over-ripe bananas; they even belong to the same genus. The difference is in the ovipositor, or egg-laying apparatus, of the female. Spotted wing drosophila females have a sharp, saw-like ovipositor, so they don’t have to wait for fruit to become over-ripe and soft before they can lay their eggs. They can lay eggs in unripe fruit or fruit that is just beginning to ripen, which means that the small white larvae, about ¼ inch long when fully grown, are present in fruit at harvest time. Effective treatments are available, but they have to be applied during harvest season, and this presents new challenges and costs for commercial producers. Most home producers are learning to live with the problem by picking sooner and more carefully, refrigerating fruit promptly, eating or processing fruit sooner, and lowering expectations for yield and quality.
Is Anything Being Done to Prevent Invasive Insects?
Yes, huge amounts of time and money are spent each year in this effort. APHIS-PPQ, USDA’s Animal and Plant Health Inspection Service – Plant Protection and Quarantine unit, is responsible for regulating international trade to prevent entry and establishment of non-native pests in the U.S. They do this by establishing and enforcing quarantines, inspecting incoming produce, and a variety of other ways. Individual states also conduct similar programs through their respective departments of agriculture. Granted, these efforts have not been able to stop entry of all non-native pests, but they have stopped thousands and slowed the spread of many others, and this has tremendous value to our country.
Do Your Part to Prevent Invasive Pests
There are many things citizens can do to help prevent introduction of invasive pests. The bottom line is to avoid moving live plants or animals, or any unprocessed parts of plants or animals, into the country, or from one part of the country to another. Don’t move firewood when camping. Don’t bring fruit back into the U.S. when visiting another country. Leave the potted plants behind when moving from one part of the country to another. Be aware of federal, state, and local quarantines, and comply with them. Cooperate with customs officials. The list goes on, but you get the idea. If this seems like excessive caution and too much trouble, just consider the adverse economic impacts non-native pests can cause. Billions of dollars is a lot of money.