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Biological Control: Important Tool
for Managing Invasive Species
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The U.S. Department of Agriculture has long
worked to exclude and manage invasive species. But globalization of trade and
travel has allowed unprecedented spread of foreign plants and animals. The
damage caused by these invasive pests costs an estimated $122 billion annually
in control, loss of resources, and damage to property.
At least 14 federal laws and other actions have been passed during the last
century to deal with invasive weeds, insects, and other pests. The latest and
most comprehensive, Executive Order 13112, was signed by President Clinton in
February 1999.
Since 1881, biological control—the deliberate use of one living organism
to control another—has been one of the tools used to stem the spread of
introduced pests. Properly conducted biological control works because it uses
carefully selected and tested natural enemies (for example, insects, mites, or
pathogens) of the target pest.
Leafy spurge, for example, is not a problematic weed in its Eurasian homeland.
But once in the United States, free of the hundreds of insects and diseases
that naturally limit its growth, it has spread over millions of acres. By
introducing some of the weed's natural enemies, scientists help reestablish
controls on the weed. The key is to be selective in choosing these natural
enemies—introducing only those that are acceptably specific and damage a
susceptible stage or part of the weed.
Concern about introducing any species, potentially beneficial or otherwise, is
warranted. That's why for over 120 years, biological control ecologists have
developed and modified a series of tests that take several years to complete
before a biological control agent is proposed for release.
First a weed is selected as a target for biological control because it is
perceived as a significant domestic problem. Then scientists study the plant in
its homeland to identify the weed's natural enemies.
Once a promising candidate is identified, many "host-specificity
tests" are conducted to determine whether the agent will significantly
damage the weed and whether it might also damage crops or native plants. The
goal is to find an organism that feeds and reproduces entirely or primarily on
the target weed, significantly damaging it and reducing its ability to compete
with other vegetation.
If an agent passes these tests, the findings are submitted to the Technical
Advisory Group for Biological Control Agents of Weeds, an independent group
that advises USDA's Animal and Plant Health Inspection Service on whether to
approve the release of the agent. If an agent is approved, it is first imported
to quarantine facilities. There, scientists confirm that the correct agent was
imported and that no unwanted parasites or diseases have come along for the
ride.
Dozens of researchers both here and abroad—in
ARS and other state and federal agencies
and universities—participate to identify, test, and import each biological
control agent for each weed. The first two stories in this issue of
Agricultural Research demonstrate the cooperation necessary between
overseas and U.S. laboratories to bring biological control projects to
fruition.
Despite the extensive precautions, biological control, like all integrated pest
management strategies, is not a panacea and is not risk-free. But that doesn't
mean we should not proceed. The consequences of inaction are far greater than
the risks, as million of acres of rangeland, cropland, and wildlife habitat are
affected each year.
The very few examples of nontarget damage from weed biological control agents
receive widespread attention. However, the most recent catalog of biological
weed control projects notes that there are only eight examples worldwide of
agent damage to nontarget plants, "none of which has caused serious
economic or environmental damage and the majority of which were anticipated by
routine testing before release."
This catalog contains data on more than 350 biological control agents released
against 133 weeds in more than 70 countries in the last 120 years.
Further, the vast majority of this nontarget damage is short term and
insignificant. For example, an agent may nibble on a nontarget plant but can't
complete its life cycle on the plant and dies off without reproducing.
To further improve the practice of weed biological control projects, ARS
recently revised its policy. Now, each project is considered to last at least
20 years, even though individual components may take only 3 to 5.
Biologically based integrated weed management (biological control with cultural
control/revegetation) is the basis of our programs. Chemical and mechanical
strategies are still vital in many instances and may be used in combination
with biological control.
ARS is also committed to long-term monitoring of the effects of agents on
target weeds and on potential nontarget species closely related to target
weeds.
Finally, ARS continues to lead in fostering partnerships with other federal and
state agencies, universities, overseas groups, private organizations, and
landowners. The invasive species problem is too vast for anyone to tackle
alone.
Biological control takes many years to succeed. But it is often the best,
safest, and most cost-effective approach to long-term management of widespread,
invasive weeds. Sometimes it is the only practical approach.
Ernest S. Delfosse
ARS National Program Leader for
Weed Sciences |
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"Forum" was published in the
March 2000
issue of Agricultural Research magazine.
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