Asian ladybird beetles originally were released in the U.S. as a means of pest control for crops, but they quickly spread in distance and numbers and now threaten their native look-alikes by out-competing them for food -- and they're just one of 466 invasive insect species you might encounter in your lawn and garden, according to the Center for Invasive Species and Ecosystem Health.
Some invasive species are mere castaways, sightseers hitching rides on imported cargo, and offer little cause for concern. Others, though, are decimating forests and wreaking havoc on the environment.
The Asian long-horned beetle, for example, is believed to have arrived in the U.S. in wooden packing materials in cargo shipments from China. This black-and-white spotted beetle attacks hardwood trees and has hit New York and New Jersey especially hard, damaging maple trees as the larvae bore through the woody trunks.
"Each region suffers different kinds of invasions, often requiring concerted efforts by the entire community to eradicate or control," says Danny Ledoux, author of "Pest Control Simplified for Everyone: Kill, Repel, or Mitigate Pests With or Without Pesticides." "This mass effort makes an invasive species difficult to control because insects do not honor legal boundaries as to whom they wish to infest and destroy. They destroy wherever plentiful food exists, making your garden a likely target -- and any living organism that competes to eat, contaminate or destroy food requires prompt and effective control tactics."
Invasive species tend to flourish in disturbed or unbalanced ecosystems, and the most destructive are those with few natural predators in their new environments. Chemical and organic pesticides offer some protection against these unwanted visitors, but often, they already have gained a foothold in the local ecology by the time the problem is identified.
When an invasive species threatens indigenous wildlife or attacks crops, it takes a determined effort on the part of governmental agencies, farmers and homeowners to tame the damage. To help stem the invasion, abide by government-sanctioned quarantines, and report interlopers when you see them. Also, promote biodiversity in your own backyard.
Five of the worst invasive insects that homeowners may encounter:
--Asian citrus psyllid. "In citrus-growing states, the tiny Asian citrus psyllid poses a serious threat to both commercial and homegrown citrus trees," says Lance Walheim, garden expert for Bayer Advanced and author of "Lawn Care for Dummies." "The insect itself causes minor plant damage; the disease it carries is far worse. Huanglongbing disease, also known as citrus greening disease, causes trees to produce green, misshapen and inedible fruit and generally kills the tree in just a few years. Worldwide, it is the most destructive disease of citrus, and there is no cure."
Walheim cautions that homeowners should be aware of these pests because homeowners "may be on the front line when it comes to containing them. Do anything you can to protect valuable trees you already have planted on your landscape and prevent the movement of the pest."
Abide by quarantines, which are in place in all the citrus states, and check your trees often. Look for blotchy leaves, yellow shoots, twig dieback and fruit that stays green even when ripe.
"In Southern California, homeowners are encouraged to report pest findings and protect their trees by applying Bayer Advanced Fruit, Citrus & Vegetable Insect Control. If insects are actually found on specific trees, the state will treat the trees," Walheim says.
--Asian tiger mosquito. These pesky pests arrived as stowaways in tire shipments from Japan, and though they don't attack crops or native plants, Asian tiger mosquitoes are one of the most dangerous invasives in the U.S.
"Although the Asian tiger mosquito doesn't cause damage to gardens, it is an important vector of disease and inflicts painful, itchy bites," says entomologist Jim Fredericks, director of technical services for the National Pest Management Association. "It can transmit yellow fever, West Nile virus, St. Louis encephalitis and La Crosse encephalitis."
The best form of control is to reduce their breeding areas. Like all mosquitoes, these invaders lay eggs in water -- and their larvae thrive in even small bodies of standing water.
"Gardeners can reduce the potential for Asian tiger mosquitoes in their yards by removing sources of water that these insects use for breeding sites -- clogged rain gutters, flowerpots, buckets, birdbaths, etc.," Fredericks says.
--Formosan subterranean termite. Originally from the Far East, it has been nicknamed the "super-termite" -- and for good reason. Colonies can top 1 million members in the wild, and they have a voracious appetite. Though colonies in the U.S. are generally smaller, they consume wood at an alarming rate and can cause extensive structural damage to a home in a very short period of time.
"Formosan termites can cause extreme damage in only one year, compared with the five to seven years of their counterparts," says Greg Baumann, technical services director for Orkin. "Homeowners should look for signs of activity while working in the garden -- damaged wood, piles of wings and termite tubes around trees."
Any wood that has started to break down or decay is fair game, Baumann says, so don't store unused lumber in the yard, and replace pressure-treated landscape timbers every three years. Also, be mindful of local infestations and work with a quarantine mindset.
"Avoid transporting wooden objects, such as railroad ties and landscaping timbers, from areas that are infested," Fredericks says.
--Emerald ash borer. Originally from eastern Asia, this bright metallic beetle has an appetite for ash trees, and in the U.S., it has caused extensive woodland damage across the Midwest and Northeast.
As the larvae tunnel into the trees, the canopy of the ash tree dies back, and new smaller shoots grow at the base of the tree. Then the bark splits, revealing the telltale S-shaped burrows and D-shaped exit holes of the larvae.
The U.S. Department of Agriculture and several state governments have instituted a quarantine program to stop the spread of the emerald ash borer. Those in the affected states -- check http://www.StopTheBeetle.info for a map -- are asked not to move firewood, which may harbor the beetles' eggs and larvae. Instead, homeowners and campers are asked to "burn it where you buy it."
Homeowners also should be cognizant of any ash trees on or near their property and report beetle damage to their local wildlife authorities.
--Red imported fire ants. Native to South America, these reddish-brown ants are now common in the southwestern U.S. and pose a serious public health hazard.
The ants out-compete native species for food and attack the eggs and young of many bird and reptile species, but they also attack humans. When disturbed, they work together en masse to inflict painful, venomous stings that often result in a visit to the emergency room.
"These insects aren't much of a threat to the garden, but gardeners should beware of them," Baumann says. "They inflict a painful bite, which can be fatal. Homeowners should always wear shoes and protective gear on their hands when gardening."
Be on the lookout for large soil mounds, indicating an active colony, and keep them at bay by treating mounds to maintain healthy turf.