For the past two years, the ear-piercing groan of power saws and wood chippers has resounded through the residential streets of Chicago's Ravenswood neighborhood.
Like surgeons amputating a limb to save the rest of the body, workers chopping down trees here hope that their actions will prevent a more far-reaching calamity.
Asian long-horned beetles had infested the trees, and destroying the trees is the only way to prevent the pests from spreading. Officials believe the beetles crossed the ocean from China in wood shipping crates.
Because the beetles have victimized Chicago and New York, their damage has claimed a good chunk of the media spotlight.
But Asian long-horned beetles are just one example of thousands of pests-plant, animal and disease-that breach U.S. borders. They often are relatively innocuous in their native habitat; but once here, they disrupt the nation's ecological and economic well-being. Some of the other destructive species:
* Fire ants, native to Argentina, have infested much of the southern United States and can inflict a painful, sometimes fatal, sting (see sidebar, page 56).
* Formosan termites, native to east Asia, frequently are found in the Gulf Coast and can destroy trees and wooden structures rapidly.
* Africanized honeybees, known more sensationally as "killer" bees, have gradually spread north from Brazil to the United States. They attack more frequently and in greater numbers than typical domesticated honey bees.
* Leafy spurge, native to Eurasia, is now found throughout the United States except in the Southeast. It crowds out other vegetation and can make land unsuitable for grazing.
* Purple loosestrife, native to Europe, is found in most of the United States. It invades wetlands and crowds out native plants and animals.
Known as invasive exotic pests, these unwelcome visitors can be hard to detect at first and even harder to get rid of once they're established.
But even if these pests have not made themselves at home in the fields or landscapes you're responsible for (as far as you know), the problem affects you. It has become so widespread that just about everybody, whether involved in grounds care or not, is affected.
Preventing infestations is costly, and controlling them once they are here is costlier. Too often, there's little that can be done, and the consequences are devastating. One study has estimated that invasive pests drain $123 billion a year from the U.S. economy. This can take the form of reduced agricultural production and farm property values, contamination of grain, spread of disease, disruption of water supplies and power outages.
Sometimes, we lose things that are difficult to measure in dollars. Dutch elm disease has decimated the American elms that once graced the streets of U.S. cities. You can put a price on the treatments and tree removals, but not the loss of the graceful arches that once covered so many of our neighborhoods. Similarly, invasive species threaten endangered native organisms and habitats in ways that are not easy to define in terms of dollars, but troubling nonetheless.
In response to the growing problem, President Clinton signed an executive order in 1999 that created an Invasive Species Council. It will devise a plan to prevent invasive species from entering the United States.
"There are a lot of bioinvasive hitchhikers from around the globe and now is the time to take action," says U.S. Interior Secretary Bruce Babbitt. "The costs to habitats and the economy are racing out of control."
How do they get here? Exotic pests penetrate the country's borders like dam water through a leaky dike-and there just aren't enough fingers to plug all the leaks. The United States, sitting between two oceans, has always faced a problem with species invading from distant continents, but the dimensions of the trouble have mushroomed in recent years. Global trade has increased, international travel has become more common, and the speed of modern transportation has effectively shrunken the Earth. The result: More non-native species are going along for the ride, and more of them are surviving the journey.
They come from all directions in nearly every imaginable way. The uninvited pests arrive hidden in ship ballasts, in wood packing crates, in the wheel wells of airplanes, in the luggage of uninformed tourists.
Some are brought to the United States intentionally for controlled study, then escape to the wild. Some are imported here to provide some benefit-kudzu, for example, for erosion control (see sidebar, page 52)-and end up being a nuisance or worse. The reasons some species are brought here can be whimsical. A Congressional Research Service report on non-native species noted that starlings were imported as part of an effort to bring all of the birds mentioned in Shakespeare's works to the United States.
Sometimes, an invasive species makes it into the country through conventional means because nobody recognizes it as troublesome. In 1999, Home Depot stores were selling pond plants from Holland. The plants were prohibited "noxious" weeds, but Dutch and American officials didn't make the connection. Thousands of plants were sold before a knowledgeable shopper recognized the mistake. Home Depot has cooperated fully with officials, who have managed to track down most, but not all, of the plants sold to consumers.
What makes solving the problem even more difficult is that some species may be present for years or decades before their presence is detected or any problems become evident.
Industrious immigrants In their native habitats, exotic pests often amount to no more than a minor nuisance. There, they are kept in check by other organisms-parasites, predators or competitors. Such ecological balances evolve over time.
In a new environment, however, the organisms that kept the pest in check are lacking. Without any checks on population growth, the pest's numbers grow exponentially. Thus, kudzu is able to become the "vine that ate the South;" Japanese beetles are the worst turf pest in the eastern UnitedStates; Fire ants are spreading like.well, you know; and gypsy moths render thou sands of square miles of forest leafless (see sidebar, page 58).
This explosive growth threatens natural habitats. If an organism reproduces uncontrollably, it takes the place of something else. Zebra mussels are a severe threat to many native mollusks. Fire ants are displacing native ant species unaccustomed to such competition. Melaleuca, a tree species originally planted in Florida for its ornamental value, is turning huge swaths of the Everglades into single-species stands. Purple loosestrife, also planted for its ornamental value, is doing likewise in wetlands around the country.
Circling the wagons Prevention is the best medicine when it comes to dealing with exotic pests. Thousands have become established in the United States, and once a pest becomes established, it's here to stay.
That's why all people entering the United States through customs must declare (and surrender, usually) plants, unprocessed foods, soil, seeds, flowers and similar materials to customs agents. People who knowingly bring uninspected plants or plant products into this country are subject to stiff penalties. Similarly, commercial shipments must submit to rigorous inspections.
The U.S. Department of Agriculture, through its Animal and Plant Health Inspection Service (APHIS), uses more than 1,300 inspectors at ports of entry. Their "Beagle Brigade" dogs sniff out agricultural products in much the same way that drug-sniffing dogs ferret out narcotics. Despite this vigilance, many tourists and smugglers still manage to get restricted materials into this country. Their cargo frequently carries unwanted invaders.
For example, tourists bringing undeclared fruits and vegetables into the U.S. mainland from tropical destinations are probably to blame for repeated problems in California and Florida with Mediterranean fruit flies. Eradication efforts are successful, but the flies return in subsequent invasions (see sidebar, page 20).
The mode of entry isn't always obvious. Cargo ships from Europe flushing their ballast water apparently introduced the zebra mussel into the Great Lakes region (see sidebar, page 54).
"The ocean serves as a highway in transporting these invasive species into U.S. waters," says Undersecretary of Commerce James Baker. "Every minute, 40,000 gallons of foreign ballast water is dumped in U.S. harbors-this water contains a multitude of non-indigenous organisms which could alter or destroy America's natural marine ecosystems."
Containing the problem When prevention doesn't work, the next line of defense is an elaborate system of monitoring and control. This typically involves, among other detection methods, closely monitored pheromone traps (which use sex attractants to lure insects) in vulnerable areas.
If an exotic pest shows up in a trap, officials carry out a predetermined plan of attack to eradicate the pest before it gets out of hand. Time is critical. As any pest control professional can tell you, large-scale eradication isn't feasible.
A similar strategy can be useful for pests such as the gypsy moth and Japanese beetle (see sidebar, page 48) that have become established but have not yet reached all potential habitats. Battling localized infestations that establish themselves ahead of the main front considerably slows the spread. Quarantines and inspections help deter the spread of pests that travel to distant areas by way of commercially shipped ornamental plants.
Biological control-in which a species that preys on or causes disease in an invasive species is introduced into the environment-is a favorite option. Researchers frequently travel to the native habitat of the target pest to discover which predators and parasites prey on it (see sidebar, page47).
Scientists are more than a little cautious about introducing one exotic species to combat another. If the first one got out of hand, there is a risk it will happen again. Scientists must make sure the biological control agent they plan to use will not go after more than justthe target pest.
For example, parasitic flies that prey on fire ants, a current research focus, must be carefully screened to ensure they do not attack native ants as well. Likewise, any insect that feeds on a target weed must have such a finicky palate that it will not attack native or otherwise desirable plants.
University of Nebraska researchers recently demonstrated that this can happen during research on rangeland ecology. They discovered that a weevil that was imported and released to control an exotic weed, the musk thistle, had developed an appetite for native thistles as well.
Sometimes, biological control simply does not work. In most unsuccessful attempts, the biocontrol agent could not establish itself (perhaps it could not tolerate the climate) or it became established but did not provide significant control.
Depsite the potential pitfalls, there have been some shining successes using biological control. For example, in California in the early 1990s, scientists successfully controlled the ash whitefly-which became a major pest of ornamental trees within just a few years of its introduction-by releasing a parasitic wasp. Over a century earlier, the cottony cushion scale threatened the U.S. citrus industry. The small but voracious Vedalia beetle was imported and quickly reduced the cottony cushion scale to minor-pest status.
There oughta be a law Government agencies have begun to focus more attention on the problem of invasive pests, but it's not always clear who has jurisdiction. The Congressional Research Service report on non-native species notes that within the federal government, numerous departments-Agriculture, Commerce, Defense and State-and agencies have responsibilities related to the issue.
No comprehensive law addresses imports of non-native species, and many regulations are left to states. But as the problem has evolved in recent years, officials have begun to act.
In 1998, Sen. John Glenn (D., Ohio) authored the Nonindigenous Aquatic Nuisance Prevention and Control Act. It established the interagency Aquatic Nuisance Species Task Force and regulates where ships can release ballast water. The Act takes aim at potential aquatic invaders that might gain a foothold as zebra mussels or sea lampreys did.
In response to the Asian long-horned beetle infestations in Chicago, New York and elsewhere (see sidebar, page 50), U.S. Secretary of Agriculture Dan Glickman imposed a moratorium on wood packing materials, causing a minor row in trade relations with China.
The most notable federal action was the executive order President Clinton signed last year initiating a federal effort to combat invasive exotics. Glickman, Babbitt and Baker will chair the Invasive Species Council, which will develop a comprehensive strategy within 18 months for combating invasive species.
Meanwhile, Clinton's 2001 budget proposal calls for $28.8 million to battle exotics. (Unfortunately, the same budget proposes eliminating federal money for some domestic quarantine programs, such as for the imported fire ant.)
In Congress, the House has recently held hearings on the Plant Protection Act (H.R. 1504), introduced by Rep. Charles Canady (R-Fla.). A similar bill (S.B. 910) has been introduced in the Senate by U.S. Sen. Larry Craig (R-Idaho).
Ben Bolusky, executive vice president of the Florida Nurserymen & Growers Association, testified before the Agriculture Committee's Livestock and Horticulture Subcommittee that the proposed bill "would streamline and consolidate the federal statutes under which APHIS operates, as well as modernize some of the old statutes. This would give APHIS a clear statutory framework to prevent entry and establishment of invasive pests. In addition, it would enhance the penalty authority of APHIS."
The proposal calls for increased penalties for introducing invasives. "Civil penalties for smuggling and other willful violations are so low that they can be viewed as nothing more than the cost of doing business," says Bolusky. "For instance, if you're talking about a $50,000 or $100,000 shipment ofproduce, a $500 fine is hardly a disincentive."
Putting some teeth into the regulations should help APHIS deal more effectively with illegal importation.
Some regulations addressing invasives-such as "noxious weed" lists-have been on the books for years. The lists specify plants that can't be sold, exported or imported (unless a permit is obtained) because some characteristic of them is deemed so troublesome that it must be prevented from spreading.
The USDA maintains such a list. States compile their own inventories, often including weeds not found on the federal list. Federally listed noxious weeds are illegal to sell or transport anywhere in the United States without a permit. State-listed weeds are restricted, but only within the borders of the specific state.
Kudzu and purple loosestrife, for example, are not federally listed and are legal to sell and transport in some states despite their prohibition in others.
How much regulation? As awareness of invasive pests grows, you can expect to see more regulation. This brings mixed reactions from members of the Green Industry. Most agree that more needs to be done about invasives, but they also fear prohibitions that are too strict.
Douglas Fender, executive director of Turfgrass Producers International, points out that the Alien Plant Working Group (AWPG) (Washington, D.C.) includes many popular ornamentals and several of the major turfgrasses on its list of invasives. The AWPG discourages the use of the listed plants.
"We as an organization are not opposed to bans on species demonstrated to have a negative effect," says Fender. "But let's use science, not emotion. We need to use definitions that make sense and make sure we know what we're doing before we throw anything away.
"I fear a series of erosive-type actions that would start at higher government levels. For example, contracts for projects receiving government money might prohibit the use of 'invasive' species. Then they would attach a list [such as AWPG's list] for reference."
In that scenario, construction projects might be prohibited from landscaping with, among other species, burning bush, crape myrtle, butterfly bush, cotoneaster, Austrian pine, Norway spruce, Bradford pear and Kentucky bluegrass or bermudagrass turf. These are all popular landscape ornamentals or turfgrasses that have been used for decades, but now appear on the AWPG list. The list even includes plants promoted elsewhere as being environmentally friendly for their drought tolerance or other low maintenance qualities, such as some ornamental grasses.
Jil Swearingen, an entomologist and IPM coordinator with the National Park Service, chairs the AWPG. Taking a conciliatory stance, Swearingen notes, "We don't want this to be a big fight with the nursery industry. We are trying to be partners in the whole effort. If I were in the [nursery] industry, I might be reacting the same way. But there are strong reasons to list these plants. We all need to understand that there is a problem."
Swearingen explains that it is easy to react too quickly when a plant appears on some group's list of invasives. "Plants may be invasive in some areas or habitats but not others and that needs to be taken into consideration. If someone feels there are plants on the list that shouldn't be, then we need to have a discussion about that. We know that throwing up a list for the whole United States is not that meaningful for a particular environment or area."
Nevertheless, Swearingen is adamant about truly problematic plants, even widely planted types. English ivy is one example. "We need to be doing something about it. Just because it's already widespread, doesn't mean we shouldn't stop selling it. Why do we keep using a plant like that when there are so many other suitable plants out there? It really makes it hard to maintain our national parks and native habitats the way they're supposed to be," says Swearingen.
A common suspicion in the green industry is that the invasives issue is being driven, at least in part, by proponents of native plants, someof whom tend to label any non-native species as automatically "bad," and anything native as "good." However, the primary concern of Swearingen and others involved in the effort is preservation of native habitat. Swearingen concedes that there are some people with motives that extend beyond native-habitat preservation. However, she explains, "By and large, the people I've worked with in this effort are concerned about out-of-control plants that are wreaking havoc. This stuff really is damaging our native ecosystems and literally changing the whole landscape of America. That's our main concern."
Officials concede that even if scientists and government regulators were able to end all pest invasions today, we would still have to spend years combating the problems caused by the thousands of non-natives that have already slipped through the cracks into the United States.
The difficulty in solving the problems with invasives is testimony to the power and ingenuity that nature can put forth. The battle against non-native species may be forever an uphill struggle, but unless we continue to fight, the forces of nature may roll over us and do irreparable damage to our habitats and our economy.
A.K.A.: Ceratitis capitata
Origin: Many tropical countries
Extent of infestation: Not currently established in continental United States; infestations common in California and Florida.
Damage: Immature stages (maggots) infest large number of fruit and vegetable crops.
How it got here: Via plant material brought to the United States by tourists or fruit smugglers.
No other pest better symbolizes the modern-day problem of exotic pests than the Mediterranean fruit fly, or the Medfly, as it's familiarly known. California and Florida, the primary battlegrounds of the war against the Medfly, share three characteristics that make them vulnerable. They are major ports of international travel, they possess climates favorable to the Medfly and they are major agricultural states.
International travelers (as well as those disembarking from Hawaii, where the fly has been resident since the early 1900s) ensure that a steady stream of tropical fruits and vegetables-some of it infested with Medflies-arrives each day from exotic lands. Inspectors do their best, but some Medflies slip through.
Extensive inspection and monitoring ensure that no infestation will go unnoticed for long. If a Medfly shows up in one of the thousands of traps that officials constantly monitor, a virtual war is declared on the fly, using as weapons a combination of sterile male flies and pesticide applications in and around the infested area.
Since California's first outbreak in 1975, infestations have become more frequent. Nearly every year in the last decade California officials have had to battle the Medfly, with costs for each bout ranging into the tens of millions of dollars. However, with California's agriculture industry worth about $25 billion annually, there's a lot at stake. The cost of fighting the Medfly is money well spent.
Controversy over spraying malathion created a political drama during a 1981 Northern California infestation. Citing environmental concerns, Gov. Jerry Brown refused to allow malathion spraying, instead opting for a strategy of destroying fruit and releasing sterile male flies (some of which, it turned out, were not so sterile).
This pleased conservationists and some municipalities that were resistant to malathion spraying. However, it put Brown at odds with politically powerful agricultural interests. They spurred members of the California congressional delegation to petition U.S. Secretary of Agriculture John Block to assume federal control of the outbreak. Block had already threatened a quarantine of California fruit, as had some Asian trading partners. Brown was forced to back down and allow spraying.
California continues to fight, and win, its war with the Medfly. The cost has been in the hundreds of millions of dollars-not cheap, but cheaper than the alternative.
Whenever a new pest becomes established, the first strategy to try is classical biological control. Free of the predators and parasites that normally would keep its numbers in check, the pest is able to reproduce exponentially. The obvious answer is to restore balance by importing the natural enemies of the offending pest.
This strategy is not always as easy as it sounds. The biocontrols-parasitic flies and wasps and predatory beetles are some of the most common types-may not be able to survive the climate here as well as the targeted pest. Sometimes, they do manage to gain a foothold, but just don't do enough.
Other times, they may be a little too effective. If they pose a threat to native species in addition to the target pest, release is out of the question.
Nevertheless, classical biological control has worked impressively in some instances.
* The cottony cushion scale, an imported pest that threatened to devastate the American citrus industry, was brought under control rapidly by Vedalia, a small beetle with a huge appetite for scale insects. This occurred in the 1880s but remains one of the most outstanding successes in biocontrols.
* Klamath weed was becoming a serious problem in California, but is now little more than an incidental roadside weed thanks to the beetle Chrisolina quadrigemina.
* The ash whitefly, after its 1988 arrival in California, became a serious pest of several ornamental trees, especially ash and pear. California officials imported a tiny wasp from Europe (also the origin of the ash whitefly) and brought the infestation under control in just 2 years.
In each of these instances, the pest was not eradicated, but merely reduced to tolerable levels. The pests and their natural enemies will continue to coexist indefinitely at relatively low population levels. Not all attempts at biocontrol are such clear-cut successes. But these stories show why, when an outbreak erupts, one of the first calls many scientists make is to their travel agent.
What are the risks that biolgocial control will backfire and that the newly released organism itself will become a menace? Scientists thoroughly assess the potential for this before releasing any imported organism. Nevertheless, some risk exists.
In 1993, researchers from the University of Nebraska studying rangeland ecology came across a species of weevil they had not encountered previously. They soon identified it as a species that had been intentionally released in the 1960s and 1970s to control musk thistle, a plant native to Europe and Asia that has become a serious weed in the United States.
By 1996, it was clear that the weevil's numbers were increasing considerably, even though musk thistle did not grow in the researchers' study sites. The weevil apparently has developed an appetite for native thistles and attacks several species, including the Platte thistle, whose limited range makes it vulnerable to population declines.
In addition, the weevils appear to be outcompeting a native insect that also feeds on thistles. This insect has two generations per year, the second of which feeds on other, late-season thistles. If it declines, the late-season thistles could become new weed problems.
The complexity of ecological relationships makes predicting outcomes such as this exceedingly difficult. As careful as scientists may be, classical biological control will always entail some risks.
A.K.A.: Popillia japonica
Extent of infestation: Roughly the eastern half of the United States.
Damage: Adults feed on many horticultural and ornamental crops; immagure stages (grubs) are serious turf pests.
How it got here: Accidentally imported with nursery products in the early 1900s.
The Japanese beetle is arguably the most serious turf pest in the United States. It also causes serious economic and aesthetic damage to food and ornamental crops. Its destructive potential has never been a secret to entomologists, who tried in vain to eradicate the pest during the first stages of its establishment in New Jersey early in the 1900s.
In the 1940s, researchers introduced milky spore disease to combat the Japanese beetle. Milky spore is a disease caused by Bacillus popillae, a bacterium that infects the immature (grub) stages of the Japanese beetle. Milky spore, like its intended target, is an imported organism. It has all the attributes of a good biological control-it is self perpetuating, it is specific to the target pest and, most importantly, it works well enough to make a practical difference.
Early efforts with milky spore were successful and worked best when applied on an area- or community-wide basis. Japanese beetle numbers dropped significantly in parts of the Northeast after milky spore's release. However, entomologists have noticed that milky spore's effectiveness seems to be decreasing.
This may be due to decreased virulence on the part of the bacterium, or perhaps the Japanese beetle is evolving some resistance to the bacterium. In any event, milky spore, though still used, is not quite the solution it once was. Japanese beetles continue to spread, and are now making their way across the Midwest.
Plant quarantines, which mandate inspections and limit shipments of nursery stock, have helped slow the march, because nursery products seem to be the primary mechanism of spread. The American Nursery and Landscape Association's Craig Regelbrugge says: "In the mid-1970s, the federal government [revoked] the federal quarantine on nursery stock because they argued that the pest had essentially reached its favorable ecological limits in the eastern half of the country. They left the field open for Western states to quarantine as they wish.. We argued against it, fearing a proliferation of inconsistent state quarantines. We were right."
The nursery industry, through ANLA, has responded by working with the National Plant Board (consisting of plant regulators from the states) to establish a Japanese beetle Harmonization Plan and create consistent regulations among states. This effort is voluntary and has been fairly successful. The plan sets standards for inspection, treatment and plant-stock certification, all of which vary according to whether the nursery stock originates in an infested area, and whether it is destined for an area susceptible to Japanese beetle outbreaks.
So far, this strategy has helped prevent the pest from becoming established in horticulture-rich states such as California, though occasional flare-ups have been eradicated.
A.K.A.: Anoplophora glabripennis
Extent of infestation: Isolated outbreaks in Chicago and New York.
Damage: Destroys a variety of deciduous hardwood trees.
How it got here: Late 1990s via wood used in shipping crates.
Asian long-horned beetles must have a savvy publicity agent. When this invasive pest made its move to America, it began to do its damage in two of the country's largest cities, New York and Chicago.
Officials believe the pest arrived in the United States by way of wooden shipping crates from China, where it's known as the starry sky beetle. It has attacked healthy trees in the Greenpoint section of Brooklyn and the Ravenswood neighborhood of Chicago.
The beetle destroys hardwood trees such as maples, horsechestnut, poplar, willow, elm, mulberry and black locust. The pest eats trees from the inside out and spreads quickly from tree to tree.
Pesticides are of limited use for eradication. The only surefire method to eliminate Asian long-horned beetles is to destroy the trees they have infested. In the meantime, tree climbers and workers in bucket trucks scour the areas where the pests have been found to look for signs of their presence: entrance and exit holes on tree branches.
To prevent continuing introductions of the beetles, the federal government has also restricted the use of untreated wooden shipping crates from China. This prompted Chinese officials to accuse the United States of using the infestation as leverage in trade relations. U.S. Agriculture Secretary Dan Glickman responded by citing the very real danger the beetle represents to U.S. forests and urban landscapes.
A.K.A.: Pueraria Iobata
Origin: China, Japan
Extent of infestation: Southeastern United States.
Damage: Aggressive, prolific weed overtakes native habitat, necessitates control measures.
How it got here: Imported intentionally in the late 1880s for erosion control, forage and ornamental use.
Kudzu has achieved near-cult-like status. Poets write about it. Blythewood, S.C., holds an annual kudzu festival. You can treat alcoholism with it, make baskets from it, graze livestock on it and even plant it as an ornamental (one of the reasons it was first imported). Memorials even commemorate locations significant in kudzu's history. Despite these accolades, a kudzu infestation is something you wouldn't unleash on your worst enemy.
Kudzu goes by several colorful names-"mile-a-minute vine," "foot-a-night vine" and "the vine that ate the South." Kudzu has firmly taken root in Southern lore. Southerners warn you not to turn your back on your children because the vine has been known to kidnap the little ones.
The vine was used as an ornamental in the United States as early as the late 1800s. It was touted as a nutritious forage plant (which it is) in the 1920s, and in the 1930s and 1940s the U.S. government promoted the plant to control erosion. It even employed the Civilian Conservation Corp to establish stands of the vine.
In retrospect, kudzu clearly falls into the "What were we thinking?" category of exotics. It now inhabits many states, growing as far north as New York, and as far west as Texas. However, the deep South, with its warm, humid climate, remains kudzu's stronghold.
In its native China and Japan, kudzu does not thrive nearly so well. In the United States, however, kudzu's consuming growth rate allows it to swallow buildings, power poles, abandoned cars and even trees.
Kudzu is difficult to kill even with the most effective herbicides. Mowing, burning, and chopping are all ineffective. The vine simply re-grows from its enormous root system.
Another potential control measure is grazing livestock. Goats apparently thrive on the stuff and can control it quite well (proving that goats' appetites are as insatiable as they are indiscriminate). However, short of turning several states into giant goat farms, no effective, practical tools exist for reining in this beastly vine.
Kudzu is a prime candidate for biological control. But researchers haven't found the right organism. Perhaps the most promising research comes from the U.S. Department of Agriculture's Agricultural Research Service. Researcher C. David Boyette has identified a fungus that aggressively infects kudzu. The pathogen, Myrothecium verrucaria, is already commercially available, but is not registered by the Environmental Protection Agency for controlling kudzu. Boyette is working toward that goal.
Until then, Southerners will continue their love-hate relationship with kudzu, celebrating, cursing and grudgingly admiring the vine that ate the South.
A.K.A.: Dreisenna polymorpha
Origin: Mediterranean region
Extent of infestation: Waterways in Great Lakes region, and the Mississippi and Ohio river systems.
Damage: Fouls waterways, intake pipes, sides of vessels; displaces native mollusks.
How it got here: Via cargo ship ballast water flushed into Lake St. Clair, in 1985 or 1986.
Relatively new on the scene is the zebra mussel. Scientists believe it arrived in 1985 or 1986 in Lake St. Clair of the Great Lakes region. It apparently traveled in ballast water from a European freighter. The mussel has spread rapidly and now inhabits waters throughout much of the Great Lakes and the Ohio and Mississippi river systems (see maps, at left).
This nasty mollusk has astounding reproductive potential. Populations build up on just about any available surface-boat hulls, pilings and, of course, the bottoms of lakes and rivers. The mussels can form thick layers several deep and become as dense as several hundred thousand per square meter.
This creates several problems. Not only does this displace native mollusks, but it also results in "biofouling:" scientists' way of saying that things are getting mucked up. Especially troubling is the mussel's ability to clog water intakes and pipes. Power plants, municipal water providers, industrial plants, golf courses-anyone pulling water from an infested source is finding that they have a new maintenance problem. Great Lakes businesses and governments now spend tens of millions of dollars annually to prevent zebra mussels from clogging water intakes. Officials estimate that this mollusk has the potential to cause up to $5 billion in damage by 2002.
A few control options exist, but all have drawbacks. Chlorine does the job in pipelines, but relatively high levels are needed, which may create water-quality problems depending on how you're using the water.
Some waterfowl, and a few fish, consume zebra mussels, but they don't eat enough to make a significant difference. Plus, zebra mussels excel at filtering out water-borne contaminants (perhaps the only positive quality they possess), which then build up in their tissue. Waterfowl that consume zebra mussels can develop reproductive problems because of these contaminants, so this method of control is not being pursued.
The threat from zebra mussels (as well as the sea lamprey, an exotic species that threatens U.S. and Canadian fisheries) has become so severe that Sen. John Glenn of Ohio recently authored the Nonindigenous Aquatic Nuisance Prevention and Control Act. One result of the Act is that freighters entering the St. Lawrence Seaway must exchange ballast water in the open ocean. This should reduce the chance of another aquatic invader taking hold.
Additionally, The U.S. Fish and Wildlife Service is constructing a barrier in the Chicago Ship Canal to reduce the chances of organisms spreading from the Great Lakes to the Mississippi basin (and vice versa).
A.K.A.: Solenopsis invicta
Extent of infestation: Much of the southern United States
Damage: Injury to livestock, wildlife and public health
How it got here: Via ship ballast water (date not certain).
The damage caused by some invasive pests may not be evident to the casual observer, but the harm inflicted by red imported fire ants is painfully clear, especially to anyone victimized by their nasty bites.
Since they turned up in the United States-some say as early as 1918, while others put the date as late as 1940-words typically used to describe the ants include vicious and ferocious.
Researchers believe the fire ants came to the United States in ballast water that was released in the Gulf Coast. With no natural enemies here, they have flourished. Fire ants have spread across several hundred million acres in the Southeast and in the last few years have been detected in California. Estimates of the damage they cause are as high as $2 billion a year.
Besides their painful, sometimes fatal, stings, fire ants can cause significant damage by getting into electrical systems, causing power outages, short circuits and fires. (No one is sure what attracts them to electrical systems.) Recently, trout kills have been reported in some river fisheries in Texas. Apparently, the trout consumed large numbers of the ants that had fallen into the river, and the ant venom then took its toll.
For such a destructive pest, it is fitting that one of the most promising weapons in the effort to control fire ants is a fly that makes an ant's head fall off. A phorid fly, Pseudacteon tricuspus, imported from South America, attacks by depositing an egg on an ant. The resulting larva moves into the ant's head and eventually releases an enzyme that causes the head to fall off.
A second biological control being used to rein in the spread of the ants is Thelohania solenopsae. This microorganism infects fire ant colonies and causes disease. Research indicates that the microorganism doesn't harm plants or native ants.
A.K.A.: Lymantria dispar
Extent of infestation: Northeastern United States, southeastern Canada.
Damage: Outbreaks defoliate huge swaths of forest.
How it got here: Imported in the late 1800s by a French artist with an amateur interest in silk-producing moths; caterpillars escaped from his cages.
Residents of the northeastern United States are all too aware of the nightmarish effects that gypsy moths bring. Severe outbreaks can defoliate entire forests in a matter of weeks. Such devastation has made the gypsy moth one of the most unwanted insect pests.
French artist Etienne Leopold Trouvelot imported the insect from France in the 1800s. He was interested in the possibility of using the gypsy moth for silk production in the United States. His efforts failed and, unfortunately, so did his cages. Some of the caterpillars escaped, and their legacy is the overwhelming problem that we battle today.
Andrew Liebhold, a U.S. Forest Service researcher in Morgantown, W.Va., says several controls are available for the gypsy moth, and some of them are fairly effective by traditional standards. However, there is no hope of eradication, and the moth is gradually expanding its range westward.
The standard approach of classical biocontrol has not been very successful with the gypsy moth. "Biological control agents have been a success in the sense that they have become established," says Liebhold, "They just haven't done a good job of keeping populations down."
In fact, says Liebhold, "the system of predators and parasites present in the moth's native ranges in Europe and Asia is not too different from what we've established here." In that light, it's not surprising to learn that the gypsy moth is prone to outbreaks even in its natural habitat (though they seem to be more severe in the United States).
What all this means is that a cure to the gypsy moth problem is unlikely. However, the U.S. Forest Service recently has taken another tack, which they have dubbed "Slow the Spread" (STS).
According to Liebhold, the moth seems to flare up in localized infestations just ahead of its established range. These outlying infestations grow and gradually coalesce, thus enlarging the moth's range in leapfrog fashion. Researchers believed if these "outposts" could be eliminated whenever they popped up, the rate of spread could be slowed. And it could-by about 50 percent, as it turns out. Liebhold notes that the unabated advance of the moth consumes about 12 miles a year. STS keeps that to around 5 to 6 miles a year. The Forest Service has moved the program from pilot status to a full-fledged nationwide effort.
While it may seem futile to continue fighting a war that has already been conceded, there is much to gain. The losses from gypsy moths are enormous. Delaying the moth in this manner may gain areas far away from the advancing front decades of freedom from this pest.
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