Environmental Engineering Reference
In-Depth Information
systems is to prevent the entry of new organisms that can have a negative impact
and, as such, the release of biological control agents is contrary to most quarantine
measures. Just because an organism is labelled as a biological control agent does
not automatically mean that it will be safe or benefi cial in all circumstances. Even
though an organism may have been used successfully and safely as a biological con-
trol agent in a particular target area, it does not necessarily mean it will be safe in
another ecological area. An example of this is with the highly successful use of the
prickly pear moth,
Cactoblastis cactorum
in Australia to control prickly pear (Dodd
1940), where, even 70 years after initial release, it is still controlling prickly pear in
that country. This same species of moth has accidentally entered the USA where it
is an invasive pest (Hight
et al
. 2002; Vigueras and Portillo 2002; Zimmermann
et al
. 2002), and threatens species of cacti in their area of origin and livelihoods of
subsistence farmers. This does not discount from the usefulness of this species as
a safe biological control agent, provided appropriate non-target testing has been
undertaken as well as consideration of the possible affects of this species in areas
outside of the release areas, i.e. ability of this species to disperse (or be transported)
to other geographic areas. Hence, when releasing biological control agents, if a
country has land borders with another country or is in close proximity to another
country, then potential impact of the biological agent in those areas should be
considered.
1.4.3.2 Plant introductions
Plants have been introduced around the world in an attempt to improve prod-
uctivity in many areas. However, signifi cant numbers of these plants have either
not been particularly useful or become invasive weeds. For example, in north-
ern Australia, 463 pasture species of legumes and grasses were introduced for
pasture improvement between 1947 and 1985; only four species proved useful
with no invasive consequences, 17 species were proved useful as well as having
weedy characteristics that caused problems for some sectors, and a further 60
species are considered invasive and as having no useful characteristics (Lonsdale
1994).
1
Other examples of species introduced for commercial reasons include
pines, acacias, and eucalypts, which form the basis of commercial plantation
industries in many countries. However, in some areas outside of their native
ranges, these introduced species have become invasive. For example, in South
Africa in climatically suitable areas all three groups have become invasive
(Rouget
et al.
2002).
Many ornamental plants that have been deliberately introduced into various
areas around the world have become highly invasive. Some continue to be promoted
in various areas as ornamental species. Part of the problem is that the combination
of hardiness and attractiveness makes them desirable in horticulture because they
require little maintenance to produce sometimes spectacular fl oral displays. One
1
These fi ndings eventually resulted in a weed risk assessment system for the introduction of plants into
Australia (Pheloung
et al.
1999).
