6. Likelihood of Introducing Nonindigenous Organisms
81
are being used. Our quantitative assessments are probabilistic and estimate the
likelihood of introduction using scenario analysis and Monte Carlo simulation.
Probabilistic assessments contain more detailed and rigorous appraisals of the
likelihood that nonindigenous species will be spread. We conduct probabilistic
assessments—as opposed to less rigorous, qualitative assessments—for a variety
of reasons including trade with a bilateral trading partner (a country with which
the United States has special trading relationship), controversy, large domestic
industry, or potential for significant impacts.
We have estimated the biological risks associated with trade in a variety of
agricultural commodities. Because different exporting areas typically have unique
collections of agricultural pests, separate assessments may be needed for each
unique combination of commodity and export area. To illustrate the use of the
concepts described below, examples are provided from four probabilistic assessments conducted to estimate the likelihood of bad events. The first addresses risks
associated with the importation and sale of self-contained bumblebee hives for
crop pollination, two involve importation of fresh fruits, and the last involves a set
of assessments conducted to support decisions regarding domestic quarantines
and regulations to limit spread of Karnal Bunt disease of wheat. Although probabilistic methods had been used previously by other staffs in USDA, their first use
in PPQ was in the 1994 assessment conducted in support of issuance of permits
for importation of bumblebee hives (unpublished).
Bumblebees
Wild bumblebees play a significant role in pollination of both wild plants and
crops. In the past decade, there has been increased interest in managed colonies of
bumblebees, Bombus spp. (Hymenoptera: Bombidae), for crop pollination. This
development followed a breakthrough in the ability to mass produce bumblebee
colonies. In the early 1990s, APHIS began to receive requests for permission to
import European species of bumblebees such as B. terrestris. Releases of nonindigenous species have been authorized in various countries; B. impatiens, a species native to eastern North America, is now established in Europe following
releases for crop pollination. Agricultural officials in the United States and
Canada have worked together to ensure that only Bombus species native to North
America have been authorized for release here. Bumblebees for crop pollination
are delivered as self-contained cardboard “hives” that are simply opened within a
greenhouse or grove to allow exit and entrance of worker bees; we estimate that at
least 1 million hives were shipped worldwide during 1995.
Qualitative risk assessment conducted in support of permit decisions regarding
importation of nonindigenous bumblebees indicated that both economic and environmental risks were too high to allow introduction of bumblebees not native to
North America. Not only do workers compete for limited resources, queens compete for nest sites and sometimes fight to the death over suitable nest sites (Heinrich 1979). Aggressive nonindigenous species could place pollination of crops
81
are being used. Our quantitative assessments are probabilistic and estimate the
likelihood of introduction using scenario analysis and Monte Carlo simulation.
Probabilistic assessments contain more detailed and rigorous appraisals of the
likelihood that nonindigenous species will be spread. We conduct probabilistic
assessments—as opposed to less rigorous, qualitative assessments—for a variety
of reasons including trade with a bilateral trading partner (a country with which
the United States has special trading relationship), controversy, large domestic
industry, or potential for significant impacts.
We have estimated the biological risks associated with trade in a variety of
agricultural commodities. Because different exporting areas typically have unique
collections of agricultural pests, separate assessments may be needed for each
unique combination of commodity and export area. To illustrate the use of the
concepts described below, examples are provided from four probabilistic assessments conducted to estimate the likelihood of bad events. The first addresses risks
associated with the importation and sale of self-contained bumblebee hives for
crop pollination, two involve importation of fresh fruits, and the last involves a set
of assessments conducted to support decisions regarding domestic quarantines
and regulations to limit spread of Karnal Bunt disease of wheat. Although probabilistic methods had been used previously by other staffs in USDA, their first use
in PPQ was in the 1994 assessment conducted in support of issuance of permits
for importation of bumblebee hives (unpublished).
Bumblebees
Wild bumblebees play a significant role in pollination of both wild plants and
crops. In the past decade, there has been increased interest in managed colonies of
bumblebees, Bombus spp. (Hymenoptera: Bombidae), for crop pollination. This
development followed a breakthrough in the ability to mass produce bumblebee
colonies. In the early 1990s, APHIS began to receive requests for permission to
import European species of bumblebees such as B. terrestris. Releases of nonindigenous species have been authorized in various countries; B. impatiens, a species native to eastern North America, is now established in Europe following
releases for crop pollination. Agricultural officials in the United States and
Canada have worked together to ensure that only Bombus species native to North
America have been authorized for release here. Bumblebees for crop pollination
are delivered as self-contained cardboard “hives” that are simply opened within a
greenhouse or grove to allow exit and entrance of worker bees; we estimate that at
least 1 million hives were shipped worldwide during 1995.
Qualitative risk assessment conducted in support of permit decisions regarding
importation of nonindigenous bumblebees indicated that both economic and environmental risks were too high to allow introduction of bumblebees not native to
North America. Not only do workers compete for limited resources, queens compete for nest sites and sometimes fight to the death over suitable nest sites (Heinrich 1979). Aggressive nonindigenous species could place pollination of crops