The concept of alien invaders has fascinated us for decades. Movies such as The Day the Earth Stood Still, The Thing, and Predator all have a common theme: Alien invaders aren’t a good thing.
Alien invaders are real, and here on our planet, but they aren’t from outer space. They’re insects from across the globe that enter the U.S. via produce shipments, as stowaways on equipment and packing materials, or as hitchhikers on ships’ hulls and decks and in aircraft landing gear. Some even enter the country as pets or research subjects.
U.S. Department of Agriculture (USDA) inspectors do their best to prevent new invasive pests from entering the country by conducting routine inspections and quarantines of imported shipments, but there’s simply no way to catch every one. Shipments are enormous, and a solitary insect has its choice of hiding places. Egg masses are even easier to overlook.
Many invasive insects have been in the U.S. for so long that they’ve become part of the landscape. Let’s focus on three of the newest alien insect invaders that are causing major problems across the country.
Brown Marmorated Stink Bug
Our first alien invader was identified near Allentown, Pennsylvania, in 1998, although officials suspect it arrived a few years earlier in shipping containers from China or Taiwan. As of January 2018, brown marmorated stink bugs (Halyomorpha halys) have been positively identified in 44 U.S. states, including Hawaii, plus four Canadian provinces. They’re most common on the East and West Coasts, for now. Brown marmorated stink bugs resemble native stink bugs: shield-shaped, about 5/8-inch long, and mottled brown in color. They have brown and white antennae, and dark-brown and white beading along the sides and back of their abdomens.
In most U.S. regions, stink bugs produce 1 to 2 generations a year, although they can produce up to six generations in California and Florida.
Stink bugs feed on a variety of fruits, vegetables, ornamental plants, and weeds, using their piercing mouthparts to suck plant juices from the stem or fruit. Feeding damage on plants includes sunken, wet-looking spots, spongy tissue, rot spots, and scars; this renders crops unsalable.
These bugs also have a (not so) secret weapon: a volatile chemical defense, the source of their “stink,” which they release when threatened or crushed. More than just a nuisance, the stink can cause nausea; sinus and eye irritation; and even reddened, irritated areas of chemically burned skin. A stink bug’s defense effectively convinces birds and other predators to pick something else for their next meal.
Stink bugs have another behavior that quickly wears out their welcome: They gather into large groups in fall, looking for sheltered places to hibernate. In their native territory, they crawl into south-facing crevices in sandstone cliffs. Here, they make do by crawling through gaps and cracks in houses, garages, and sheds. They seem to prefer tight spaces where they have contact on at least two sides, and shelter in insulation, storage boxes, power tool motors, construction materials, or anywhere they can find close quarters. They also tend to emerge from hibernation on warm winter days, entering living spaces and swarming lights and windows.
To date, the best control is trap and disposal. Shelter-style traps are effective in fall when stink bugs begin to swarm. These traps can be made with sheets of corrugated cardboard spaced 1/8-inch to 3/8-inch apart with wooden shim wedges or paint sticks, and hung outside where stink bugs congregate. Manage these winter wanderers by using lights positioned over water traps. Large clusters of stink bugs can be vacuumed up for removal, but their released stink may ruin the vacuum cleaner. Spraying with insecticide will knock down any stink bugs present at the time, but will do little to later arrivals, and will add unhealthy toxins to the home environment.
Adult stink bugs can fly, and can spread slowly on their own power. However, they’ve expanded their territory faster by stowing away in shipments that unknowingly give them rides beyond their current areas of residence. Stink bugs are blamed for millions of dollars of damaged produce each year. Mid-Atlantic apple growers estimated apple losses of $35 million in 2011 — never mind damage to pears, plums, cherries, corn, beans, okra, and more.
Emerald Ash Borer
Another invader made its appearance in Canton, Michigan, in 2002. Since then, it’s been identified in 35 states, from Colorado to New Hampshire to Georgia. Ironically, little is known about this invader in its native range of China, Mongolia, Russia, and the Korean Peninsula, because it’s so insignificant.
The emerald ash borer (Agrilus planipennis) isn’t much to look at: a slim beetle with big eyes and short antennae, about 1/3-inch in length. The only thing that stands out is its color, a brilliant, metallic, emerald green. The even less remarkable larvae are skinny, cream-colored grubs that reach a little longer than an inch, although they’re rarely seen. In fact, the most common visible indication of emerald ash borers is a small D-shaped hole made in the bark of an infested ash tree by newly emerging adults.
As its name implies, the emerald ash borer feeds on ash (Fraxinus) species. Adult borers feed on ash leaves in the canopy for a few weeks, causing minor damage. The larvae cause the real damage, burrowing through the bark to reach the inner layers of living tissue. There, they spend the next year or two feeding on the inner bark, creating extensive labyrinthine galleries and girdling infested trees. Once an ash is infested, there’s no saving it; the tree will be dead in 3 to 5 years. At that point, the only thing to do is to remove the tree and use it for firewood.
Healthy, individual trees can be protected with treatments of systemic insecticides, which work well in urban and suburban settings. In rural areas and forests, though, this treatment just isn’t practical. (No organic remedies have yet been developed.) The best way to control borers is to stop their spread. Infested trees should be removed, both for safety and to reduce the population of borers. The trees should then be replaced with non-ash species.
While adult borers are capable of flight, they don’t travel far. They rely on us for long-distance travel. The country’s first borer is suspected of arriving in Michigan on wooden shipping crates from China. Since then, borers have traveled from place to place on camping firewood and lumber.
To help stop hitchhiking borers, firewood, especially ash firewood, should never be transported any distance. Most infested areas have quarantines in place, including bans on moving firewood, and fines from $100 to $10,000 or more depending on state and federal regulations.
Emerald ash borers have the potential to destroy every ash tree in North America. While European and Asian ash species have built-in protections from emerald ash borers, our native species are completely vulnerable. The USDA estimates a potential lumber loss of $20 billion to $60 billion because of the potential deaths of 300 million ash trees in North America. Asian parasitoid wasps are being trialed for release in North America, but to date, the best control is removal of infested trees, restricted transportation of infested wood, and treatment with systemic insecticides on an individual basis.
Spotted Lanternfly
Spotted lanternflies (Lycorma delicatula) were first discovered in 2014 in eastern Pennsylvania, near Allentown and Reading. They likely arrived as eggs on a shipment of stone from Asia. Native to northern India, Nepal, China, and Vietnam, they’ve become a serious invasive on the Korean Peninsula, where they were first identified in 2004. In the five years since they’ve been discovered in the U.S., spotted lanternflies have spread to 13 counties in southeastern Pennsylvania, along with New York, New Jersey, Maryland, and Virginia. While most sightings outside Pennsylvania have been of single adult specimens, breeding populations have been confirmed in Virginia, and possibly in New Jersey.
Spotted lanternflies are conspicuous plant hoppers, an inch in length, with a 1-1/2-inch wingspan, and a width of about 1/2-inch when resting. They fly poorly, weakly fluttering to a new perch, but are surprising jumpers that can leap up to 6 feet. At rest, they are pale-gray with a faint pink cast, their wings polka-dotted and patterned with tiny black “bricking.” They have small red cheek spots and black eyes. They flash their wings to reveal shocking red, white, and black underwings and a black abdomen seamed with yellow.
In late fall, spotted lanternflies lay egg masses on any available flat surface, from tree trunks to park benches, barrels, and trailers. The eggs are covered with a gray, putty-like, waxy weatherproofing. They hatch from May into June. The early nymphs are black with white polka dots, developing bright-red markings later.
Lanternflies feed on a wide variety of plants, from oak and walnut trees to apples, grapes, hops, and vegetable crops. They’re sap suckers, drawing enormous amounts of fluid out of their hosts, enough to weaken and kill them, especially when feeding in swarms numbering in the thousands. They also produce excessive amounts of honeydew, a sugary liquid waste that stains anything parked beneath a feeding swarm and fosters fungal outbreaks.
There’s still a chance to stop spotted lanternflies, and possibly even eliminate them. Their spread seems tied to another aggressive invasive species, the tree of heaven (Ailanthus altissima). Adult lanternflies seek out trees of heaven, and seem to require at least one meal from the plants. Entomologists speculate they use it for a chemical defense, similar to monarchs feeding on milkweed. Penn State University recommends removing most trees of heaven in areas prone to lanternflies, and treating individual male “bait-trees” left standing with a systemic insecticide. Trees of heaven tend to grow in colonies with extensive root systems, which means they’ll regrow rapidly after being cut down. Trim back regrowth when it appears or dig out the root systems. Better yet, pull young seedlings as soon as you spy them.
When you see a spotted lanternfly, catch and kill it if possible, and send a photograph to your state extension office for positive identification. Do the same for suspected lanternfly egg masses, then scrape them into a jar of rubbing alcohol to kill them. Nymphs tend to climb up and down their host tree trunks daily, and can be captured with sticky band traps applied to the trunk. Care must be taken to cage the traps with chicken wire or hardware cloth to prevent the incidental capture of woodpeckers, flickers, squirrels, and other non-target species. In quarantine areas, visit your state extension web page for lists of banned materials that can’t be transported out of the area. Keep car windows closed while in the quarantine area, and inspect vehicles, trailers, and loads before leaving. Knowingly transporting lanternflies or restricted materials without proper permitting can carry fines of up to $20,000.
While it’s too early to supply comprehensive damage estimates for spotted lanternflies, the potential for economic damage is staggering. According to Bloomberg reporting, one vineyard owner north of Philadelphia lost $100,000 worth of grapevines in 2017. That’s just one grower! Pennsylvania hosts a wine industry of about $4.8 billion, New York another $4.8 billion, and Virginia an additional $1.37 billion. A lot of vines are at risk, and other vulnerable crops include apples, hops, and hardwoods.
These three insects are by no means the first invaders in the U.S., nor are they likely to be the last. They’re simply outstanding examples of the hazards we must keep a wary eye out for in the hopes we can stop, or at least slow, these alien invasions before it’s too late.
Andrew Weidman lives in Lebanon, Pennsylvania, in an area affected by all three invasive insects covered in this article. He works alongside the Backyard Fruit Growers to stop the spread of spotted lanternflies to other parts of the country.
