In
this section:
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Quarantine
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Ptolemaic world
map, Johan Scotus, 1505. |
Over
the centuries, human beings have carried desirable plants with them
as they migrated around the world. Today most of our crop plants
are being grown where they are not endemic.
In
many cases we have been successful in introducing the crop species
without carrying along some of their pests, and we have been selecting
crops for perhaps hundreds of years in the absence of many of their
original pests. Since we have not been selecting for resistance
to these pests, some of the crops have lost what resistance they
may have had to their ancestral pests. Many of our crop plants
are now uniformly susceptible to endemic pests of their ancestral
stock. (For example, most potato varieties are susceptible to
the golden nematode.)
Opportunistic
pests. Some introduced pest species are opportunistscapable
of attacking host plants with which they have not coevolved. As
a result, the host plants have not evolved defenses to these pests
(e.g., the American elm and the Dutch elm disease pathogen, Ceratocystis
ulmi). Likewise, predators, parasites, and competitors may not
be well adapted to an introduced pest (such as with the gypsy moth).
Consequently, many introduced species that were minor pests in their
native habitats have become major, invasive pests in their new habitats.
Quarantine
reestablishes barriers. High-speed transport increases the likelihood of successful transport
of short-lived pests. Physical barriers to the spread of pests (oceans,
mountains, deserts, etc.) have been breached by the rapid transportation
of people and goods and the international movement of seeds, planting
stock, and soil. The purpose of quarantine is to reestablish
these barriers and to restrict movement of pests into areas where
they do not occur.
Quarantine
involves reducing the risk of pest introduction through the application
of specific technical measures within an established legal framework. International trade agreements recognize and support the sovereign
rights of nations to protect their agriculture and their natural
resources from the introduction of harmful pests, and these agreements
generally contain provisions for quarantine. These same trade agreements
also attempt to prevent countries from using phytosanitary restrictions
as disguised trade barriers.
International
organizations involved in quarantine
The
International Plant Protection Convention (IPPC)
is the internationally recognized organization responsible for setting
phytosanitary standards and coordinating plant protection around
the world. The IPPC has established guidelines
for national and regional cooperation in plant quarantine and
phytosanitary procedures. Regional plant protection organizations
(RPPOs) have been created to coordinate phytosanitary efforts within
their respective areas.
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Plant
quarantine inspector, Malaysia. |
The
RPPOs cooperate inter-regionally and also provide technical assistance
to the national plant protection organizations within their respective
regions, exchanging information and helping them to establish phytosanitary
measures consistent with international standards.
National
organizations involved in quarantine
Nearly
every nation of the world has its own national plant protection
organization, and nearly all are signatories to the International
Plant Protection Convention, agreeing to adhere to its provisions.
As an example of how a national plant protection organization functions,
we will use the Plant Protection and Quarantine Program (PPQ) of
the Animal and Plant Health Inspection Service ((APHIS))
. APHIS formerly
is a unit of the United States Department of Agriculture, that collaborates with the Department of Homeland Security.
APHIS/PPQ functions in close collaboration with the IPPC and NAPPO.
APHIS/PPQ
uses a systems approach to reduce the risk of introduction (or establishment)
of a pest. They evaluate the risk of introduction from various sources,
quantify the effectiveness of various risk mitigation measures,
and employ a combination of such measures. The goal is to have at
least two independent measures that have an additive effect in reducing
the risk of introduction of a pest. Developing specific measures
for a particular pest involves input from the grower (seller), the
shipper, the buyer, state regulatory officials, agricultural experiment
station researchers, and the growers that would be affected by the
introduction of the pest.
There
are four lines of defense in risk mitigation:
1.
Point-of-origin. Minimize the occurrence of the pest in the product to be shipped.
APHIS/PPQ works with the producers to develop and implement the
necessary pest control measures, inspects the crop in the field,
and issues phytosanitary certificates for the crops that meet the
risk mitigation criteria. APHIS/PPQ also works with and certifies
the major packers and shippers.
2. Point-of-entry. APHIS/PPQ, in cooperation with
U.S. Customs, inspects incoming agricultural products and also
nonagricultural cargoes that may harbor plant pests (e.g., ceramic
products packed in straw; crates made of wood with intact bark).
Based on the risk analysis for the particular commodity, APHIS/PPQ
may require post-entry treatment (e.g., fumigation, irradiation,
or hot water treatment) or, in the case of live plant introductions,
it may require post-entry quarantine, that is, holding and growing
out the plants in isolation plots. In some cases, the best option
may be post-entry destruction of the goods or returning them
to their point of origin. |
About 90% of the fresh produce entering the
U.S. and Canada from Mexico comes through this APHIS inspection
post in Arizona.
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Pests
are also introduced via the U.S. mail and international travelers.
APHIS/PPQ uses specially trained beagles (the "Beagle Brigade")
in airports and a few selected post offices to sniff out contraband
fruit and plants. |
Beagle
inspecting luggage at an international airport.
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3.
High risk zones. APHIS/PPQ
monitors for specific pests and conducts field inspections in areas
where there is a high probability of detecting newly introduced
pests (usually around points of entry). A good example is monitoring
Mediterranean fruit fly introductions in California, Texas, and
Florida by means of sex pheromones and bait traps. The purpose is
to detect low populations well before they are established and while
they can be eradicated.
4.
Regional inspection program. In
a program called the Cooperative Agricultural Pest Survey (CAPS),
APHIS/PPQ works closely with the research and extension personnel
in the state agricultural experiment stations to monitor pests and
biological control agents in the nations major crops. By collaborating
with the expert observers who are in the field almost daily, CAPS
attempts to detect introduced plant pests before they become well
established.
The
challenges of quarantine
Quarantine
is most effective where there are physical barriers to help keep
the immigration of pests to a manageable level. Oceans, mountains,
and deserts generally are effective barriers to pest movement, and
historically the time required for humans and cargoes to traverse
these barriers and the limited points of entry helped to reduce
the numbers of new pest introductions. But in these days of high-speed
transport, a pest can be transported thousands of miles in only
a couple of hours, rendering these physical barriers ineffective.
Furthermore, political boundaries do not always correspond with
physical barriers, and the pests do not respect legal border crossings.
Consider
the enormity of the job:
- huge
numbers of arriving cargoes, both agricultural and nonagricultural,
in a countrys airports and seaports;
- enormous
numbers of border crossings for roads and railroads;
- travelers
who cross the nation's borders every year, many of whom enter
through international airports in the center of the country;
- mail
that crosses borders every year.
No
wonder pests slip through. Every quarantine program must be prepared
to mobilize an effective eradication campaign quickly, and every
pest management program that relies on quarantine as a major tactic
must begin to prepare for the possibility that the pest cannot be
eradicated and will become established. At the very least, an
effective quarantine buys time to develop alternative control measures.
Once the pest population becomes well established in the quarantine
area and eradication is out of the question, the quarantine is no
longer useful.
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