Biologically Based Technologies for Pest Control Page: 81
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Chapter 4 Risks and Regulations 81
A major difficulty with attempting to order the
levels of risk, of course, is that there will always
be exceptions. Organisms within categories des-
ignated as high risk may prove relatively innocu-
ous, while those that fulfill the criteria as low-
risk BBTs may cause unexpected harm. A regu-
latory system that incorporates reliance on risk
categories, therefore, must also include flexibil-
ity and substantial safeguards to ensure the rec-
ognition of such exceptions.
An advantage of a risk hierarchy is that it
facilitates matching the required pre-use evalua-
tions to the likely level of risk posed by a BBT.
Evaluation schemes that take into account the
variable levels of scrutiny required by different
potential risks are called tiered testing. These
systems preclude unnecessary testing and wasted
resources. APHIS and EPA use tiered testing to
varying degrees. The first tier provides maxi-
mum opportunity for the identification of any
adverse effects. BBTs that pass the first tier are
not subject to further testing. Second and third
tier testing are used to reveal possible mitigating
factors (21 9).
Testing for Host Specificity
Host specificity measures the degree to which a
biological control agent is restricted to its target.
It provides information on the range of organ-
isms a biological control agent will affect
through feeding, reproduction, or other interac-
tions. Scientists use information on host specific-
ity to try to identify the organisms likely to be
attacked by candidate control agents in the
release environment. Testing of host specificity
began for biological control agents targeting
weeds in the 1950s. Initially, the potential agent
was tested only on the agricultural crops growing
in the region into which the control organism
was considered for introduction (21 9).
More predictive frameworks have since
replaced the crop-testing method, often placing
greater emphasis on nontarget threatened and
endangered species and other plants of ecologi-
cal value. Many biological control practitioners
advocate use of the centrifugal/phylogeneticNatural enemies imported for research on the biological control
of weeds are held in quarantine prior to release.
Agricultural Research Service, USDA
approach, which involves testing plants of
increasingly distant relationship to the target
until the host range is circumscribed. The centrif-
ugal approach is not without its problems, how-
ever. For one, it assumes that related plants are
more likely to be attacked, whereas, in reality,
sometimes widely unrelated plants are attacked
(220). This may be more a problem among
pathogens than among insects (159). In addition,
the centrifugal approach may overlook some
important variations in resistance and suscepti-
bility of individual hosts (328).
The relatedness procedure, the newest
approach to host specificity, is a subtractive pro-
cedure that involves selecting plants to be tested
on the basis of their evolutionary relationship to
the target organism, as well as their distribution,
climatic preferences, seasonal occurrence,
regional weather patterns, life cycles, and other
information available in the scientific literature
(73). The approach is weighted to favor those
potential hosts most closely related to the target
organism, but it tests representatives from all
other levels of relationship as well. The method
has been applied successful y in Australia for the
host-specificity testing of Uromysces heliotropic,
a fungal agent for the biological control of the
weed, common heliotrope, Heliotropism euro-
paeum (139,140,73).
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United States. Congress. Office of Technology Assessment. Biologically Based Technologies for Pest Control, report, September 1995; [Washington D.C.]. (https://digital.library.unt.edu/ark:/67531/metadc39770/m1/87/: accessed April 26, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.