alien species, exotic pests, bio-pollution, non-indigenous species, or invasive
alien species, are common names that categorize non-native animals, microbes, diseases, or
plants that are pests. These pests are not native in areas in which they cause problems and they
are considered "invasive" because they invade and establish populations in new areas and the
resulting uncontrolled population growth and spread causes economic or environmental
problems.
On the other hand, some species that are native to a country can be invasive if they are moved to
another part of the same country. For example, in California, the glassy-winged sharpshooter is
a serious pest of grapes because it spreads a bacteria that kills grapes. Interestingly, the glassywinged sharpshooter is native to the USA and is found naturally in Florida, Louisiana,
Mississippi, and Texas. However, this insect is not native to California and it was accidentally
moved on ornamental plants from the Southeast USA to California in the late 1980's. Once
established in Southern California, populations of this pest grew to very high densities and it
spread into many different areas of California where grapes and other crops are grown.
Here are a couple of pictures of a few Invasive Species.
The Glassy-winged sharpshooter.
The Avocado thrips.
THESE ARE JUST A COUPLE OF INVASIVE SPECIES ABOVE.
Speciation is an evolutionary process by which new ecological species arise. Due to various
natural processes including geographical separation and drift, some species are becoming
separated. Because of this the consequences are: under changing environmental and climatic
conditions and due to natural selection, new species are established. These are extremely
slow processes that take many centuries to happen.
During the last few centuries people started moving over large distances at an accelerating
pace and shipping a larger volume of commodities to far-away destinations. This increasing
of massive and rapid movement of people and goods has been facilitating the transport of
various plants, animals and organisms to completely new, non-indigenous environments.
Upon encountering new ecosystems, many of these deliberately or accidentally brought
organisms may die, because they cannot survive in foreign environmental conditions.
Invasive species are most commonly defined as a non-native plant, animal or other organism
that dominates the encountered ecosystem and impairs its function and structure. Invasive
species displace or damage native plants and animals, often causing serious threats and
causing economic and public health effects. The lack of a natural competitor in this new
ecosystem allows invasive species to be successful and resistant enough to survive in a
foreign environment.
It is important to remember that biological invasions are a fundamental and integral aspect
of nature and have always been present in the history of life on Earth. What is of concern
however, is the extraordinary rate at which the invasions are now taking place. This requires
global attention and action.
Invasive species cause a wide diversity of economic and environmental problems which almost
always arise from uncontrolled population growth and spread in the area which has been
invaded. Economic problems arise from the costs required to control invasive species, to reduce
their rate of spread, or the need to inspect agricultural products that are being exported that may
accidentally move the invasive pest to a new area.
These economic impacts are most severe in agricultural systems and urban areas where people's
livelihoods or quality of life are affected. For example, successful invasions by agricultural pests
results in greater costs to farmers who must control the new pest, often with
pesticides. Consequently, food costs more to produce because of increased pest management
expenses, and the risk to the environment, such as accidental pollution of water and air with
pesticides, increases too. An example of a recent serious economic threat to California citrus
growers is the Asian citrus psyllid.
Invasive species can cause major environmental problems too, especially in natural or wilderness
areas. These problems are often largely unnoticed or ignored because there is no obvious and
readily identifiable stakeholder group, such as home owners or avocado growers, that is being
adversely affected.
The Asian citrus psyllid.
: In this approach potentially invasive species are not allowed to
enter a new area.
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Often this practice is part of protecting a country's borders
through the enforcement of quarantine laws, inspection of imports for hitchhikers, or the banning of the importation and sale of certain plant and animal
species that are likely to cause problems.
: In some instances, an invasive species may be detected at a
very early stage of the invasion. When populations are small and highly
localized it may be possible to eradicate populations of this pest so it no
longer lives in the country or area in which it was detected. Eradication was
recently achieved in California for the killer alga, Caulerpa taxifolia. .
In this situation the invasive species has successfully invaded
and high populations are now spread over large areas making exclusion and eradication
impossible. Several options are available for dealing with the invader and include:

: This approach employs management strategies
that can be manipulated to disadvantage the invasive species so its
reproductive capacity or its ability to spread is reduced. For example, the
damage caused by some invasive agricultural pests can be lessened by using
crop varieties that are resistant to a plant disease, planting dates are altered
so the crop is not growing when an insect pest is present to attack it, or mulch
is added to the soil to promote the growth of beneficial organisms that kill the
pest.
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In this instance no management plan is developed or enacted
and the invader is left to spread unchecked. This may occur because there is
no stakeholder group (e.g., citrus growers) that is adversely affected by the
invasive species. This situation typically arises in national, state, and county
parks where invasive weed species are left to spread to new areas.
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: Invasive weeds, insects, mites, and plant
diseases have all been controlled to varying levels with pesticides. These
compounds can provide rapid control of an invasive species over very large
areas. However, they are often expensive to apply, need repeated
applications, and pesticide residues may be found on food, in water supplies,
or in the air which raises concerns over human safety.
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: As the name suggests, integrated pest
management, or IPM, integrates a variety of control strategies to control an
invasive pest. For example, IPM of an invasive weed may employ a herbicide
(i.e., chemical control) to knock the weed populations down. This is followed
by the establishment of herbivorous natural enemy (i.e., biological control)
that eats the recovering weed population and helps to keep the weed
population from rebounding. Once the weed population is suppressed by
herbicides and natural enemies, mulches are added to the soil to suppress
weed seedling regrowth and native trees are planted in the mulch to shade out
the weed.
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This approach reassociates natural enemies with the
invader in the new area in which the pest is causing problems. Natural
enemies like predators, parasites, and pathogens have been used most
commonly to successfully control invasive weeds, and insect pests. This form
of pest control can be very safe if the correct natural enemies are used, and
once established, effective natural enemies can provide permanent control of
the invasive species.
(N.B.) We can all take some responsibility for reducing the problems caused by invasive
species. Some very simple steps include: careful selection of garden plants, use species that are
not likely to be invasive. Check for with your local garden center or on-line for recommended
plant species for your area.