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Pros and Cons of Biological Control 415
most promising agents are those which exhibit high levels of host and habitat
fidelity, and maximal impact on the target species, ensuring at the same time
minimal impact off target. Host range assessment is essential to all of the
abovementioned documents, and many recent introductions have already
been accompanied by appropriate host range tests. Therefore, there is reason
to expect that polyphagous predators such as H. axyridis will no longer be
released as biological control agents into foreign countries in the future or, if
so, then only after a thorough assessment of possible risks.
23.7 Conclusions
The vast majority of non-native species pose no threat to native biota in the
new environment. However, a small number are highly invasive. In parallel, by
far most introductions of classical biological control agents of both weeds and
arthropods have not caused any harm to the environment, only a small number
leading to unwanted non-target effects. It should be stressed, however,
that those negative cases which have been documented to date (1) mostly
result from projects conducted relatively early in the history of biological control
and (2) most often relate to the introduction of vertebrate top predators
in arthropod biological control. Nowadays, biological control is conducted in
a much more reasonable manner and, as Frank (1998) noted correctly, it may
not be appropriate to criticize today’s biological control for disastrous introductions
of the distant past.
However, adding species to ecosystems (new environments) can have complicated
consequences and, undoubtedly, a variety of factors can influence
host use by biological control agents under field conditions. This means that
precluding any negative effects of new biological control introductions will be
notoriously difficult, if at all possible. To reduce this potential as far as possible,
host range testing and general risk assessment procedures must be conducted.
Fortunately, much progress has been made in terms of regulation of
biological control agents and methods to be used for assessing potential
effects before introduction into new environments. In fact, the predictive
power of the outcome of biological control introductions (in terms of realized
host range) is rather good, assuming that sound ecological studies have been
conducted beforehand (Babendreier et al. 2005). Saying this, I would even like
to suggest that the large experience and the many data available from the purposeful
introduction of biological control agents could be used more intensively
to the benefits of invasion biology in general.
In this chapter, I provided some examples of detrimental environmental
effects stemming from introductions of biological control agents but also
showed that many deliberate introductions for biological pest control have
resulted in long-term ecological and economic benefits. Altogether, I suggest