6. Likelihood of Introducing Nonindigenous Organisms
83
States. Over the past few decades, avocado producers in Mexico, along with
Mexican agricultural officials, have developed comprehensive pest control programs, and Mexico has been exporting avocado fruit to many countries around the
world for several years. In the early 1990s, Mexican agricultural officials again
requested authorization to export fresh avocados to the United States, and shipments have been allowed into Alaska under certain conditions since 1993. Then in
1994, the Mexican government formally requested that APHIS further amend its
import regulations to allow importations into the northeastern United States. We
conducted a complete risk assessment including a probabilistic assessment of the
likelihood of introduction for nine species of arthropod pests. Fresh avocado fruit
from Mexico can now enter the United States, subject to certain restrictions. For
example, fruits are enterable only from certain regulated export groves, they may
be imported only during the months of November through February, and they may
only be imported into 19 northeastern states.
Domestic Regulation of Wheat to Limit the Spread of
Karnal Bunt Disease of Wheat
In March 1996, Karnal Bunt, a disease of wheat caused by the smut fungus Tilletia
indica, was first detected in the wheat-growing regions of Arizona. The wheat
harvest in Arizona was scheduled to begin in May. Because much of the grain and
seed produced in Arizona is shipped to other wheat-producing areas of the United
States, we had to consider the consequences of various regulatory actions. For
example, much of the grain produced in Arizona is shipped to flour mills in the
Midwest that produce semolina for pasta. Some of the seed is shipped to northern
states for planting, and some is shipped to grain elevators in other states, where it
is stored until it is exported to foreign countries. Regulation of grain destined for
mills is complicated by the fact that roughly 25% of mill products are used as
animal feed, and spores of T. indica are capable of surviving the digestive systems
of both birds and mammals. Manure from these animals is used to fertilize fields,
including wheat fields. In a series of probabilistic risk assessments (USDA
1996a–d), we considered risks associated with 24 different program options by
describing each option with a specific scenario.
Probabilistic Risk Assessment: Estimating the
Likelihood of “Bad Events”
Our probabilistic assessments focus on the likelihood that plant pests will be
spread if particular activities are authorized. However, the word probabilistic in
this context refers to the fact that the input parameters and model output are
expressed in probabilistic terms. That is, estimates of the likelihoods of bad events
are expressed in probabilistic terms, with each estimate having an associated
83
States. Over the past few decades, avocado producers in Mexico, along with
Mexican agricultural officials, have developed comprehensive pest control programs, and Mexico has been exporting avocado fruit to many countries around the
world for several years. In the early 1990s, Mexican agricultural officials again
requested authorization to export fresh avocados to the United States, and shipments have been allowed into Alaska under certain conditions since 1993. Then in
1994, the Mexican government formally requested that APHIS further amend its
import regulations to allow importations into the northeastern United States. We
conducted a complete risk assessment including a probabilistic assessment of the
likelihood of introduction for nine species of arthropod pests. Fresh avocado fruit
from Mexico can now enter the United States, subject to certain restrictions. For
example, fruits are enterable only from certain regulated export groves, they may
be imported only during the months of November through February, and they may
only be imported into 19 northeastern states.
Domestic Regulation of Wheat to Limit the Spread of
Karnal Bunt Disease of Wheat
In March 1996, Karnal Bunt, a disease of wheat caused by the smut fungus Tilletia
indica, was first detected in the wheat-growing regions of Arizona. The wheat
harvest in Arizona was scheduled to begin in May. Because much of the grain and
seed produced in Arizona is shipped to other wheat-producing areas of the United
States, we had to consider the consequences of various regulatory actions. For
example, much of the grain produced in Arizona is shipped to flour mills in the
Midwest that produce semolina for pasta. Some of the seed is shipped to northern
states for planting, and some is shipped to grain elevators in other states, where it
is stored until it is exported to foreign countries. Regulation of grain destined for
mills is complicated by the fact that roughly 25% of mill products are used as
animal feed, and spores of T. indica are capable of surviving the digestive systems
of both birds and mammals. Manure from these animals is used to fertilize fields,
including wheat fields. In a series of probabilistic risk assessments (USDA
1996a–d), we considered risks associated with 24 different program options by
describing each option with a specific scenario.
Probabilistic Risk Assessment: Estimating the
Likelihood of “Bad Events”
Our probabilistic assessments focus on the likelihood that plant pests will be
spread if particular activities are authorized. However, the word probabilistic in
this context refers to the fact that the input parameters and model output are
expressed in probabilistic terms. That is, estimates of the likelihoods of bad events
are expressed in probabilistic terms, with each estimate having an associated