Exotic Pest Invaders
Nature exists in a tenuous balance, having evolved over millions of years so that the organisms found within a given ecosystem, both plants and animals, generally tolerate the presence of each other, and a remarkable percentage of the time even rely on each other for their survival. Even though many insects feed on plants, mammals, or other insects, they do so without threatening the existence of that other group in a properly running habitat. While plants compete for nutrients and space, in a natural setting no plant species is likely to completely overrun the other kinds around it. Major changes would normally be caused by some other effect, such as the many climate changes our Earth has experienced over the eons, volcanic eruptions, continental drift, polar shifts, or perhaps the occasional asteroid slamming into the planet.
As humans perfected the ability to travel throughout the world, and now even to other planets, it became increasingly common for organisms living in one part of the world to be transported to other regions. If they managed to survive in the new habitat, tolerating the environmental conditions there, finding food and others of their kind to mate with, they could be the precursors of vast populations of their own kind. Since the beginnings of human migration to North America tens of thousands of other living things have also come along for the ride, and now are so widespread and common within our borders that most people do not even realize they are foreign invaders. If you stand along a roadside you may have difficulty spotting very many native plants, as the vast majority of stands of grasses and wildflowers are species which originated in Europe, Africa, or Asia. The 3 primary pest bird species – pigeons, English sparrows, and Starlings – all were imported from Europe. Rodents such as the Norway and Roof Rats, House Mouse, and the nutria have been introduced from other parts of the world.
Most of the pest insects you find living within your homes may be exotic invaders, including bed bugs, German Cockroaches, European Earwigs, Hobo spiders, and many, many others. Even something as common and annoying as the lowly House Fly is believed not to be native to North America, but at some point in human history managed to make its way here with the movement of people. In their native habitats they may have been simply another bug living in harmony, but they found a new habitat that did not include the predators, parasites, or other competition that kept them under control. More recent imports to the U.S. include Formosan Termites, Red Imported Fire Ants, Gypsy Moths, Japanese Beetles, or “Killer” Bees, and many others. Those who live in parts of the country where these insects are common easily understand the extraordinary impact they can have. However, it is not slowing down, and today the U.S. faces serious consequences from many new invaders that have the potential to destroy major segments of our agriculture and our forests. Let’s look at a few of them.
Florida seems to bear the brunt of these problems, due perhaps to the subtropical climate there that supports year-round breeding and survival of so many animals and plants. Hawaii is another tropical setting that has suffered tremendous changes to its ecology due to the invasion of organisms from other places. Florida seems to be besieged by exotic plants and animals, with new kinds discovered routinely. The weed kudzu has overwhelmed thousands of acres of forests, water hyacinth chokes many square miles of waterways, and at least 5 dozen more imported plants are causing environmental damage in that state. Four dozen kinds of reptiles and 4 kinds of toads and frogs, including the Green Iguana, numerous geckos, the Giant Toad and Cuban Treefrog are now established and changing the environmental balance of Florida. There are nearly 200 species of exotic birds, 31 species of mammals, and untold numbers of insects and other arthropods living in Florida today that do not belong there. A devastating disease of citrus, called Citrus Greening, has taken a terrible toll on the citrus industries in Florida, and has the potential to completely wipe it out.
Where did all of these exotic imports come from, and how did they get to North America? During the early decades of human migration to the “new world”, emigrants commonly brought along those things they felt they would need for survival. In particular they were concerned with the availability of food, so they brought plants and seeds with them, and many of these plants spread rapidly in a new climate that did not include the natural controls that kept them in control in their native habitats. Quite often their bags of seeds were contaminated with the seeds of unwanted plants, and the introduction of serious weeds began there. This is how “tumbleweed”, or Russian Thistle, arrived in North America. Even the “native” honeybees, brought along for the honey and the wax used for making candles, are not native to North America. In fact, there is no native honeybee in North America, but the honeybee has lived here so long we have now forgotten that fact. In the 1900’s we began more and more to recognize the serious consequences of this uncontrolled movement of living things around the world, and began to regulate the importation of plants and animals.
You might think that today, with the environmental awareness so many of us have and the publicity these exotic pests are given, that people no longer would intentionally import plants or animals without the assurance that they will not cause problems, but if anything the trade in exotic things is increasing. The internet allows us to purchase anything from anywhere, and with agriculture officials and inspections already stretched too thin, there is absolutely no way to intercept everything that is mailed. Border inspections generally are on the “honor” system, which is a failure when it comes to people choosing to discard what should not be brought back from their vacation to Hawaii or South America. A recent outbreak of Mediterranean Fruit Fly in northern California was shown to be flies of a strain now found in Hawaii, and the presumption is that someone returning from a vacation there snuck some infested fruit back in their suitcase, perhaps choosing not to believe all the warnings against such an illegal practice.
While Florida may be one of the hardest hit states, let’s discuss some of the exotic pests found in California, as it is this state the author of this article is most familiar with. The economic impact of these pests, once found, is enormous, and yet very few people understand the impact beyond the inconvenience of being told they can’t ship some fruit or nuts to their friends. The Medfly discovery is a good example, being found in September 2007 in a small agricultural town near Sacramento. This fly is known to infest over 350 different kinds of food crops, including walnuts and almonds. By terrible timing the discovery occurred right in the midst of the harvest of these two nut crops, major crops in the county of the infestation. A quarantine was immediately put into effect that prohibits the exportation of any nuts out of the infested area, and this could result in tens of millions of dollars of lost food resources for the growers in that area. All possibly because someone snuck an infested papaya in from Hawaii.
California also is dealing with a tiny moth from Australia, called the Light Brown Apple Moth, a species whose larva feeds on several hundred different plants, ranging from food crops to landscape ornamentals to weeds to forest trees, including most varieties of pines and redwoods. At the time of writing this the moth occurs in 9 counties along the central California coast, where agriculture and plant nurseries abound. All of the plant materials in these counties are quarantined and may not be exported. Another pest recently found in California is the Asian Long-horned Beetle, a large tree-eating beetle currently destroying hardwood forests in the northeastern U.S.. It was discovered resting on the outside walls of buildings where wooden pallets from China were then discovered to be infested with the beetles. This particular insect has the ability to completely kill entire forests of hardwood trees.
The list for California for 2007 is daunting, and the state Department of Agriculture is doing the best it can to discover, contain, and eradicate the many insects, weeds, crabs, fish, and plant pathogens that threaten the agriculture and environment of that state. The list includes northern pike, northern snakehead, mitten crabs, green crabs, Asian long horned beetle, emerald ash borer beetle, diaprepes weevils, soybean rust, stem rust of cereals, plum pox virus, vine mealybug, glassy winged sharpshooter, marmorated stinkbugs, channeled apple snails, golden nematodes, Mediterranean fruit fly, Mexican fruit fly, olive fruit fly, light brown apple moth, yellowstar thistle, scotch broom, and Japanese dodder. These are just a tiny sampling of the exotic pests that have invaded the state, and there is no end in sight. The cost to the general public is staggering, in lost food production, lost forests, lost waterways, and lost species of native animals that cannot out-compete the invaders. The states with major ports of entry are likely those hit the hardest, but every state deals with this tragedy.
The list is endless it seems, but there must be a lesson here that can be learned. While many of the imported pests enter in materials of commerce, and cannot be controlled by the average person, many of them are being brought in by people deliberately avoiding the regulations regarding importation of living things from other parts of the world. People are sneaking in seeds or parts of plants so that they can propagate the plants themselves. They are sneaking in reptiles or birds in suitcases. They may have so enjoyed some fruit or vegetables on their vacation in Tahiti that they just had to share some with their friends at home. The consequences of this activity, as we are seeing, potentially can destroy the agriculture that produces the food we eat. It can destroy the waterways and the forests we enjoy. It can bring in pests that bite us, such as new species of mosquitoes like the Asian Tiger Mosquito or Ochlerotatus japonicus, two new species now spreading rapidly in the eastern U.S.
It is hoped that the American public can be provided with the information on this growing environmental disaster, and cooperate by leaving plants and animals behind when they vacation outside the U.S. By understanding the intolerable impact these exotic pests can have on our lives and livelihoods it is hoped that we all can cooperate with the control efforts made to eradicate them. We can become familiar with the pests of interest, and if we find something out of the ordinary we can immediately report it to the local county department of agriculture. It may be nothing important after all, or it may be something with a serious potential that can be caught in the early stages of its invasion, and eliminated before it is too well established ever to be eradicated.