Weird Nature The Most Damaging Invasive Species in the World  

1.1k votes 108 voters 4.3k views 102 items

List Rules Vote up the things that you believe are the most damaging invasives through direct or indirect experience.

Ecosystems on our planet are, as we have learned over and over as a species that seems to live outside them, much more fragile than we've given them credit for. Sometimes it only takes the introduction of one species to upend the whole boat. This can happen naturally... say a flood or a windstorm blows an invader into a new biome that is not prepared for it... but it is usually humans that are responsible for bringing these invaders in. Sometimes it is by accident, and other times we do it to solve a problem that we, ourselves, have created; then going on to make it so much worse. Insects and viruses can be carried across oceans by boats, on livestock or even our clothing. Animals can be imported as pets and then let loose... or imported as a possible resource, and then found to be deeply destructive and impossible to control. Island ecosystems are deeply vulnerable, often having completely endemic, carefully balanced food chains and interspecies relationships. The introduction of a single new animal can, and has, completely upended that balance. Large-scale agriculture is also vulnerable to a single invader that it has no defense against. We can struggle to right these human-caused wrongs, but often find ourselves helpless in the face of an imbalance we have no way to fight. This is a list of the most destructive invasive plants, animals and diseases on Earth. Vote up the ones that you have experienced the impacts of, either directly or indirectly.

list ordered by

22 2
Zebra Mussel is listed (or ranked) 1 on the list The Most Damaging Invasive Species in the World
Zebra Mussel

Origin: E. Europe and W. Russia

Another ballast water hitch-hiker, the fingernail sized Zebra mussel arrived from Europe in 1988 and established a colony in the great lake region. They soon spread their way through the lakes, down the Mississippi and throughout the eastern US. Ravenous filter feeders, they rapidly deplete the water of food, out-competing the native organisms. They cluster by the millions, clinging to every solid surface. They create a costly problem for power plants, cities and residents when they clog water intakes. They kill native mussels and they slice open the unsuspecting feet of any swimmer or pet that steps on them. There has yet to be found an efficient way to control them, but researchers have tried special paint that keeps them from adhering to docks and pipes. There has been some experimentation with ion emitters that the mussels seem not to like, but for the most part nothing has worked yet.

37 6
Kudzu is listed (or ranked) 2 on the list The Most Damaging Invasive Species in the World

Origin: Japan

Going by several not-so-flattering nicknames, Kudzu is well known to areas that is is not native to. It's hard to miss, as it covers everything. The Kudzu vine is native to Japan, but arrived in the US in 1876 when it was featured at an expo as a hardy, fast growing vine that could fight soil erosion. Well. They weren't wrong about that part. Also known as the 'mile a minute' vine and the 'the vine that ate the south', Kudzu has been spreading across the country at 150,000 acres a year. In the right conditions, a length of vine can grow a foot in a single DAY. The vines themselves grow up to 100ft long and the plant can smother trees, houses, power lines and whatever else that can't move out of the way. It is drought and frost tolerant and practically unstoppable. Nothing can compete with it, and thus, it wins. This invasive easily sits in the top 10 of the worst case scenarios that happen when an organism has no natural barriers built into its ecosystem.

30 4
Red imported fire ant is listed (or ranked) 3 on the list The Most Damaging Invasive Species in the World
Red imported fire ant

Origin: Brazil and Argentina

Originating in Argentina and Brazil, there are few that have never heard of the fire ant, one of the worst invasives in the world. In the US, it is thought that the first ant arrived in Mobile, Alabama via cargo ship somewhere between 1933 and 1945. In Australia it is believed to be closer to 2011. It has since caused billions of dollars in damage to the areas it now infests. The ants thrive in urban areas, so their presence may deter outdoor activities, but more damagingly, nests can be built under structures such as pavements and foundations, which may cause structural problems, or cause them to collapse. They also can damage equipment and infrastructure and impact business, land, and property values. As the workers are attracted to electricity, they can swarm electrical equipment and destroy it. In agriculture, they can damage crops, damage machinery, and threaten pastures. They are known to invade a wide variety of crops, and mounds built on farmland may prevent harvesting. They also pose a threat to animals and livestock, capable of inflicting serious injury or killing them, especially weak or sick animals. So far, the only ways of controlling these ants has been found to be baiting and pesticides. Due to its capability for damage, the ant has become one of the most studied insects on earth.

15 1
Asian Citrus Psyllid is listed (or ranked) 4 on the list The Most Damaging Invasive Species in the World
Asian Citrus Psyllid

Origin: SE Asia

This is a bad one. First detected in 1998 coming in from imported plants from Asia, this little insect survives by feeding on the sap of citrus leaves. As it eats, it injects its toxic saliva into the plant... a saliva that often carries Huanglongbing or HLB disease, which infects the tree and causes the citrus fruits to be discolored. The poor tree then goes on to die in 3-5 years, reducing orange production. This disease has already forced the Florida citrus market to grow indoors and went from over 80 citrus companies in Florida alone to only 35 firms; leaving trees, people and their livelihoods devastated by this bacterium. It reached California in 2008 and has resulted in quarantines and restrictions. A year later, it was found in Georgia, South Carolina and Louisiana. 2012, it arrived in Texas.  While some research has found some footing in the war against Citrus Greening disease, it remains a real and terrible threat to the entire Orange growing industry.

14 1
Northern snakehead is listed (or ranked) 5 on the list The Most Damaging Invasive Species in the World
Northern snakehead

Origin: Asia and Africa

Looking like a mutant crossbreed between a python and an eel, the aptly named Snakehead competes with native species for food and habitat. No one really knows how it got into the US waterways, but it is now the most feared fish in Chesapeake Bay watershed. During all life stages, snakeheads compete with native species for food and habitat. When young, they eat zooplankton, insect larvae, small crustaceans, and the young of other fishes. As adults, they become voracious predators, feeding on other fishes, crustaceans, frogs, small reptiles, and sometimes birds and small mammals. Beyond their ability to wreak havoc on ecosystems, there is also concern for the snakehead’s potential to transfer pathogens to native fishes, because snakeheads can carry diseases and parasites that have the potential to be harmful. Snakeheads are now on the list of injurious wildlife under the Lacey Act.

22 4
Asian tiger mosquito is listed (or ranked) 6 on the list The Most Damaging Invasive Species in the World
Asian tiger mosquito

Origin: Northern Asia

This small, striped day-biter has been in the news in recent years in California, having newly arrived to join the phalanx of ultra-annoying mosquito species that already live there. Previous to California, it was first found in the US in 1985 in Texas. Since that time they have been spreading rapidly and unabated across the country. They prefer warm weather, so they have been identified in every county in Georgia, Florida, South Carolina and Tennessee, as well as many counties in surrounding states. They breed in small puddles of standing water near human habitation, in diverse places, varying from cemetery vases to junk piles. Like other invasive species, the Asian tiger has out-competed native mosquitoes, such as Aedes aegypti, the yellow fever mosquito, but that's not necessarily good. The tiger mosquito can spread diseases too, such as West Nile, dengue fever or Eastern equine encephalitis. In fact, its habit of staying close to where people live and biting multiple hosts in the daytime, make it an even more efficient vector for some diseases. Stay safe by following standard anti-mosquito protocols; including removing any standing water source from near your house if possible, no matter how small.

7 0
Yellow crazy ant is listed (or ranked) 7 on the list The Most Damaging Invasive Species in the World
Yellow Crazy Ant

Origin: West Africa

Called "crazy" because of their frenetic movements, these long-legged ants have invaded ecosystems from Hawaii to Zanzibar. On Christmas Island in particular they have formed massive, multi-queen super colonies and have decimated the red land crab populations. They prey on a variety of arthropods, reptiles, birds and mammals on the forest floor and canopy. To make things even worse, they are 'ranching' ants, cultivating herds of scale insects for their honeydew and which cause forest die back, and even the death of large forest trees. These changes create a cascade of negative impacts, including weed invasion, significantly altering the forest landscape. The species has been known to occupy agricultural systems such as cinnamon, citrus, coffee and coconut plantations. Because the ant has generalized nesting habits, they are able to disperse via trucks, boats and other forms of human transport - making their onward spread an almost certainty.

12 1
Carp is listed (or ranked) 8 on the list The Most Damaging Invasive Species in the World

Origin: Europe and Asia

Originally from Europe and Asia, the common carp has been cultured far and wide as a valuable food source for over 2,500 years. It is the third most introduced species in the world. They are an aggressive, omnivorous fish known for consuming resources to the point of depletion. This carp is one of the most damaging aquatic invasive species due to its wide distribution and severe impacts in shallow lakes and wetlands. On top of the fact that they outcompete native fish, their feeding also disrupts shallowly rooted plants muddying the water. They release phosphorus that increases algae abundance and they cause a decline in water quality that then causes declines of aquatic plants needed by waterfowl and fish. In the US, many people do not consider this fish to be an invasive because it has been around for so long and they also enjoy it as a sporting fish. In some countries, however, control methods are employed that include barriers, harvesting, traps and water level manipulation as well as electric barriers, bubble curtains and sonic barriers.

16 2
Red Lionfish is listed (or ranked) 9 on the list The Most Damaging Invasive Species in the World

Origin: South Pacific

Most would agree that the lionfish is one of the most beautiful fish in the sea. It seems as if it were designed as jewelry. However, looks aside, it is an exceedingly destructive invasive species. It first appeared in coastal Florida waters around the 80s, probably the result of exotic animal stocking of aquariums. Once free in its new, fresh ecosystem it began preying on many important commercial fish. Lionfish now inhabit reefs, wrecks, and other habitat types in the warm marine waters of the greater Atlantic. Adults are primarily fish-eaters and have very few predators outside of their home range.  They eat the herbivores that eat algae from coral reefs. Without these herbivores, algal growth goes unchecked, which can be detrimental to the health of coral reefs.

22 6
Emerald Ash Borer is listed (or ranked) 10 on the list The Most Damaging Invasive Species in the World
Emerald Ash Borer

Origin: Asia

The emerald ash borer is a menace that, while sparkly, creates devastation the ash trees left in its wake. The adults do little damage for the most part, however, once they bore nickel sized holes, they deposit their larval offspring behind to carve wiggly, damaging tunnels through the bark and disrupting the tree's ability to transport water and nutrients. It is thought to have arrived in the US in wood packing material carried on cargo ships from Asia around 2002. As of May 2018, it is now found in 33 states, and the Canadian provinces of Ontario, Quebec, and Manitoba. Ash trees lose most of their canopy within 2 years of infestation and die within 3-4 years. If you find it, please report it to your local authorities. The only ways to control this beetle are with pesticides, removing the tree, or the experimental biocontrol method of the parasitoid braconid wasp, which will lay its eggs in the beetle and kill it.

19 4
Brown marmorated stink bug is listed (or ranked) 11 on the list The Most Damaging Invasive Species in the World
Brown Marmorated Stink Bug

Origin: China

This damaging and hard-to-eradicate insect is believed to have first arrived in the US in packing crates or on machinery shipped from China. The first documented specimen was collected in Allentown, Pennsylvania, in September, 1998.  Not only does it smell bad - hence the name - but it has the ability to eat its way through a variety of crops, from cotton to apple. It has an uncanny and unfortunate ability to avoid pesticides. Once introduced to an area, this pest can take years to build up enough population to destroy an entire crop... somewhere between 8 and 10 years depending on the local climate and situation. Once established, however, the numbers can explode and new populations can spread, partly because the climate of the US is paradise for the stink bug. In fact, there does not appear to be any environmental limiting factors that are slowing their spread across the United States. They also are extremely mobile insects capable of moving from host to host without causing disruption in their reproductive processes. Currently it is estimated that BMSB populations will continue to grow and spread to other states, especially during unusual periods of warm weather.

22 8
Feral Pig is listed (or ranked) 12 on the list The Most Damaging Invasive Species in the World
Feral Pig

Origin: Eurasia

Considered one of the most outright destructive invasive species of all time, these pigs were originally brought to the US for domestication from Europe and Asia. Some escaped captivity and took to the new environment easily. Prolific breeders, they can produce four to eight babies per litter. Feral swine are highly adaptable, but prefer habitats with an abundant supply of water and dense cover. They are aggressive and pose serious ecological, economic, and health threats. They are extremely destructive to fields, fences, and facilities. Their wallows can affect ponds and wetlands, muddying the water and destroying aquatic vegetation. They can strip a field of crops in one night and pose a threat to ground-nesting birds and some endangered species. To make it even worse, they can transmit diseases and parasites, such as pseudorabies, brucellosis, and tuberculosis, to livestock and people. It is estimated that they do at least 1.5 billion dollars worth of damage a year - conservatively. A quarter of that alone is in Texas.

15 2
Formosan Termite is listed (or ranked) 13 on the list The Most Damaging Invasive Species in the World
Formosan Termite

Origin: Taiwan

Originating from Taiwan or perhaps China before that, the first Formosan Termite probably arrived in the US via ship. It was first reported in a Houston shipyard in 1965 and has since spread across the southern US. Sometimes called the super termite, this little bastard is one of the most destructive insects in the US. This particular species can tear through wood like a buzzsaw - faster than any other species.It is known to consume over 50 living plant species as well as structural lumber, plastics, asphalt and even thin metals. Not only is it an aggressive eater, but it is also territorial. They are very expensive pests to deal with. In Hawaii for example, annual costs to control them exceed $100 million dollars and in Florida, $60 million. Physical barriers such as special sand or wire mesh installed under buildings at the time of construction are used where Formosan subterranean termites are troublesome, but such barriers are very expensive. Expensive or not, a sobering statistic: once established, Formosan subterranean termite has never been eradicated from an area.

17 4
Black Rat is listed (or ranked) 14 on the list The Most Damaging Invasive Species in the World
Black Rat

Origin: SE Asia

Originally from tropical Asia a long, long time ago, the black rat is most likely one of the first invasive species to ever be inadvertently distributed by humans. It is thought to have reached Europe by the first century A.D. before spreading across the globe on European ships. Since then, the black rat has thrived in just about every region of the world, and has adapted with ease to rural, urban, and suburban environments alike. Unfortunately, its success as a species alongside other rat species, has caused dramatic population declines and even extinction of countless bird, reptile, and other small vertebrate species all around the world.

17 4
Africanized bee is listed (or ranked) 15 on the list The Most Damaging Invasive Species in the World
Africanized Honey Bee

Origin: African/European Hybrid

The Africanized honey bee is a slightly unusual case, a bit of a Frankenstein's monster. It's a species cross-breed between aggressive Tanzanian bees and docile European honey bees. This was done as a way to try and increase honey production, however, the result was a very angry honey bee. That would have been the end of the story, but unfortunately in 1957, a beekeeper in charge of the hybrids accidentally released 26 Tanzanian queens in Sao Paolo, Brazil. These queens went out, found some european honeybees and multiplied. These hybrids are aggressive and hyper-territorial. They out-compete any native bees in the region they occupy. Africanized honeybee swarms have been known to invade regular honey bee hives, kill the European honey bee queen and install their own leader. They are less likely to store honey like the domesticated bees and they are quick to abandon a hive. The bees first infiltrated the U.S. in 1990 and have since spread to the southern parts of many states, including California, Nevada, Utah, Arizona, New Mexico, Texas, Oklahoma, Louisiana, Arkansas and Florida. Despite what fun TV movies of the week might make you think, their sting is no more toxic than any normal honey bee, however, because of their intense aggression, they have been known to swarm easily and sting many times, making them a threat to humans as well as honey production. 

11 1
New Guinea Flatworm is listed (or ranked) 16 on the list The Most Damaging Invasive Species in the World
New Guinea Flatworm

Origin: New Guinea

Native to New Guinea, this flatworm was accidentally introduced to the soil of many countries. It was also deliberately introduced into two Pacific islands in an attempt to control an invasion of the Giant East African Snail. It has since grown to have a detrimental impact on biodiversity has earned a spot on the '100 worst invasive alien species' list. This worm is spread by humans, reproducing quickly. When it comes into a new habitat it will quickly adapt and eat any snail or invertebrate it can find. The flatworm has had multiple impacts on the ecosystems it has been introduced to. In the Pacific Islands, several native land snails have either gone extinct or their numbers have drastically reduced. It is such an efficient and invasive species that it has caused the decline and extinction of gastropods on several islands and consumes more endemic land species than other species. It even outcompetes other predatory flatworm species. Currently, there are no known methods for controlling the population of P. manokwari. This makes the eradication of the invasive species especially difficult.

14 2
Mediterranean Fruit Fly is listed (or ranked) 17 on the list The Most Damaging Invasive Species in the World
Mediterranean Fruit Fly

Origin: Sub-Saharan Africa

In 1929, the first infestation of the Mediterranean Fruit Fly - or Medfly - in the US were recorded in Florida. Since that time, this pest has continued to attack more than 260 different fruits, vegetables and nuts. These flies lay their eggs in the fruit and the larvae then feed off the flesh of the crop. Even worse, the tunnels that the larvae make leave the fruit or vegetable vulnerable to bacteria and fungi which cause it to rot. And, to add insult to injury, the maggots then attack the roots, stems and buds of the plant. They can be painstakingly eradicated by keeping a close eye for even a single fly and, once ID is positive, increasing the number of traps and pesticide. Any infected soil has to be treated and all fruit stripped from any known host trees, bagged and removed to a landfill. There has also been some success with the release of sterile flies that will eventually neutralize the population.

15 3
Chestnut blight is listed (or ranked) 18 on the list The Most Damaging Invasive Species in the World
Chestnut Blight

Origin: Asia

One of the few fungi on this list, Chestnut Blight first came to the US fro Asia in the 1900s carried in on infected plants. The disease is transferred in a variety of methods such as air, wind, and animals. Hosts become infected by open vulnerable wounds that are moist, creating an ideal environment for chestnut blight. Once established the fungus forms yellow-orange fruiting found on the older areas of the cankers on the host tree. The American Chestnut tree, unable to develop adequate defenses, has been found to be particularly susceptible to this fungus. As a result, large forested areas have been devastated by infection from chestnut blight resulting in the loss of trees in large quantities. Sadly there is no effective method of treating chestnut blight. Once a tree contracts the disease (as they all eventually do), there is nothing to do but watch it decline and die. The prognosis is so bleak that when experts are asked how to prevent chestnut blight, their only advice is to avoid planting chestnut trees altogether. The tree has been declared all but extinct, however there are still efforts to save the species. The Chinese Chestnut is immune and attempts to cross pollinate with the American tree by hand is underway. It could be many decades before we know if the transgenic species will be successful.

19 7
Burmese Python is listed (or ranked) 19 on the list The Most Damaging Invasive Species in the World

Origin: Southeast Asia

This invasive story sounds like science fiction. Burmese Pythons are not animals you think of when you think of Disneyworld and caftan-dressed grandmas on the beach... but they have become a top predator in Florida. Living off bountiful native populations of deer, raccoon, marsh rabbits, bobcats and possum, these stealthy hunters have declined those populations by up to 99 percent in some cases. That is staggering. Pythons take to Florida's climate like a snake to a swamp, and because they have no natural predators there other than humans and alligators, they are happily increasing their numbers. They are creating this problem because they are a popular pet, and many people who like snakes for pets get them. Once they get too big (a thing that Pythons DO), they get dumped in the swamp by their idiot ex-owners. It is estimated that 99,000 Burmese Pythons were imported to the US between 96 and 2000. If even only half their owner dumped them, that's a lot of pythons. Ironically, they are considered a 'threatened' species in their homeland. Currently, these snakes continue to make Florida their home despite efforts to control their population. They are stealthy and very hard to find and kill, thus, they will only continue to wreak havoc on Florida's ecosystem.

13 2
Asian Gypsy Moth is listed (or ranked) 20 on the list The Most Damaging Invasive Species in the World
Asian Gypsy Moth

Origin: Eurasia

Now one of North America's most devastating pests, the Gypsy Moth originally lived in Europe and Asia. In the late 1860s it is thought to have arrived in Boston and has wreaked havoc on North American forests since. Due to its unending appetite and ability to multiply quickly, this moth causes incredible damage to forests, nurseries, vegetation along creeks and rivers, and trees and shrubs in yards and parks. Because of the defoliation, it alters wildlife habitat and affects the quality of life in communities that experience repeated outbreaks. The USDA estimates that the economic cost of gypsymoths has averaged $30 million a year for the past 20 years. Gypsy moth controls include cultural, mechanical, and chemical controls; natural predators; and silvicultural practices. Unfortunately, because it's a nonnative pest, gypsy moth has few natural controls and none capable of preventing its eventual establishment.

18 7
Feral Cat is listed (or ranked) 21 on the list The Most Damaging Invasive Species in the World
Feral Cat


While the house cat may seem like a strange addition to this list, consider: being a domesticated animal, it is not a native species to any of the habitats it currently impacts. It is listed here as a feral cat, but even your cuddly home companion has an astounding impact on the ecosystem you live in. The domesticated cat is a major threat to native amphibians, reptiles, birds and small mammals, many of which are endangered. In New Zealand alone it is considered to be responsible for the decline of 76 bird species. In Australia it has caused the extinction of some species on islands and is thought to have contributed to the disappearance of many ground-dwelling birds and mammals on the mainland. When introduced to small, fragile island ecosystems, the impact is even higher;  causing  or contributing to 33 (14%) of the modern bird, mammal and reptile extinctions recorded by the International Union for Conservation of Nature (IUCN) Red List. Today, more than 100 million feral and outdoor cats function as an invasive species with enormous impacts - even well-fed cats will hunt and kill. Domestic cats are easily one of the worst, most-damaging invasive species in the world.

6 0
Killer Algae is listed (or ranked) 22 on the list The Most Damaging Invasive Species in the World
Killer Algae

Origin: Indian Ocean

With the fun name "Killer Algae", you know it's going to delightful. An invasive marine alga that is widely used as a decorative plant in aquariums, it was originally found in the Indian ocean. A cold-tolerant strain was inadvertently introduced into the Mediterranean Sea in wastewater from the Oceanographic Museum at Monaco, where it has now spread over more than 13,000 hectares of seabed. It forms dense colonies that prevent the establishment of native plants and excludes almost all marine life, affecting the livelihoods of local fishermen.  It contains a toxin that is not harmful to humans but may be lethal to certain species of fish and invertebrates and may interfere with the eggs of some marine organisms.  The plant appears unpalatable to general herbivores, and seems to grow unrestrained and develop into a dense, uniform carpet that blankets an area and persists from year to year.  Other marine life leaves the area, and there are even indications that it may kill off many microscopic organisms.  It has displaced rich habitats like eelgrass beds that sustain a complex food chain leaving the area unable to sustain a variety of life forms.  

6 0
Big-Headed Ant is listed (or ranked) 23 on the list The Most Damaging Invasive Species in the World
Big-Headed Ant

Origin: Mauritius

Considered one of the world's worst invasive ant species, the big-headed ant is very aggressive and very good at multiplying because they employ more than one queen. Scientists have found them in more than 1,600 sites across the globe. When they arrive at a sufficiently warm destination, it spells almost certain doom for native ants, spiders, beetles, and other invertebrates that are unaccustomed to their brand of aggressive warfare. As the name implies, this ant's colonies include soldiers with disproportionately large heads. These giant, muscle-bound noggins power their mandibles, which they use to attack other ants and inverterbrates and cut up prey. They also harvest seeds and harbor phytophagous insects that reduce crop productivity. It is also known to chew on irrigation, electrical wire and telephone cables.

6 0
Rainbow trout is listed (or ranked) 24 on the list The Most Damaging Invasive Species in the World

Origin: North America

One of the favorite sport fish in the world, these natives of North America can now be found on every continent in the world except Antarctica. Intentionally introduced all over to "improve" fish stocks, they are extremely competitive for resources and have been found to negatively impact native species. This adaptibility is made worse by their abilty to hybridize with other species, a fact that has led to the near-extinction of many other types of fish. Additionally, they have introduced whirling diesease to many populations, a parasite that causes fish to swim erratically and have a hard time eating. While some areas have eradication efforts underway, others are still stocking these fish for sport fishing and aquaculture despite the impacts on native fish.

6 0
Tree Privet is listed (or ranked) 25 on the list The Most Damaging Invasive Species in the World
Tree Privet

Origin: SE Asia

Originally from SE Asia, there are about 50 subspecies of this very tall shrub that has made its way across the world as an ornamental hedge. It has become a serious nuisance in most areas it has invaded. Like most of the worst invasives, it's damaging potential is partly attributable to its dense foliage, which reduces light reaching the forest floor and prevents the regeneration of light-demanding plants. It is a rapid grower, high seed recruiter and has the ability to tolerate high shade conditions. It is highly invasive in the Mascarene Archipelago, Mauritius and La Reunion. On the oceanic islands that it has invaded, it disrupts primary forest regeneration and threatens native floral biodiversity. It has high fruit production and a lack of natural biocontrol in regions where it has invaded. It can only be controlled by hand pulling when the plant is young, and the entire root must be removed or the plant will regrow. There has also been some success with chemical options, but no biological controls have yet been found.