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23.2 Pros of Biological Control
D. Babendreier
Since the spectacular success of the vedalia beetle Rodolia cardinalis which
was released to control a scale insect in California more than 100 years ago,
there is hardly any doubt that biological control can be a very effective strategy.
One of the most striking advantages is that, if biological control works,
then it virtually works forever. This means that it can be an extremely costeffective
pest control method, and the benefits may exceed the initial costs of
the projects by several orders of magnitude (Hoddle 2004). A clear advantage
of a successful biological control program is the saving of sometimes huge
amounts of pesticides, of which many are known to be harmful for numerous
non-target insects, vertebrates and even humans. For example, the biological
control program against alfalfa weevil conducted in the US reduced pesticide
use by 95 % from 1968 to 1983, and is saving farmers more than $ 100 million
each year in insecticide and application costs. Similarly, the use of biological
control agents against greenhouse pests altogether has saved substantial
amounts of pesticides. More than 100 species of beneficial organisms are
commercially available for control of nearly all important insect and mite
pests. As an example, we can take the parasitoid Encarsia formosa which is
successfully being used against whiteflies since more than 20 years. Special
advantages in augmentative biological control are that agents can be used
where pesticides are no longer efficient due to resistance, and also that the
growers of vegetables can make use of bumblebees for pollination, which
would be prohibited with the use of pesticides.
Probably the most impressive advantage of biological control is that it may
be the single one solution for restoration of ecosystems which have been
impacted by invasive species. For example, the invasion of purple loosestrife
(Lythrum salicaria) into North American freshwater wetlands has altered
decomposition rates and nutrient cycling, led to reductions in wetland plant
diversity, reduced pollination and seed output of the native Lythrum alatum,
and reduced habitat suitability for several specialized wetland bird species
(Blossey et al. 2001). After years of research in Europe, it was determined that
potential benefits outweigh risks, and four biocontrol agents were introduced
in 1992 and 1994. These species are attacking flowers, leaves and roots, and
this combination was predicted to enhance control. At some of the early
release sites, the attack by the host-specific insects has resulted in dramatic
declines of purple loosestrife and, often, the once monotypic stands of L. salicaria
are replaced by a diverse wetland plant community (Blossey et al. 2001).
There are clearly many more such success stories, of which only a very few
have been touched upon here. For a comprehensive review of successes in all
disciplines of biological control, I would like to refer to Gurr and Wratten
(2000).