Environmental Engineering Reference
In-Depth Information
thistle family and that was acceptable based on the risk:benefi t analysis at that time.
Indeed, more recent studies on non-target impacts have shown that the doomsday
scenario for this 'cause célèbre' has been greatly exaggerated (Herr 1999), although
additional studies have revealed other unanticipated ecological risks when the
weevil proved to have indirect impacts on indigenous thistle insects (Louda
et al
.
2003). Given such controversies, this agent would not be released today, based
so much on the science
per se
but on the precautionary principle linked to public
perception and practitioner ethics. h is point is illustrated further with a recent
biological control project against giant hogweed in Europe (Box 6.3). Certainly,
there is no doubt that plant pathogens with a similarly wide range of hosts as the
thistle weevil must never be considered for classical biological control. Specifi city
has to be at a signifi cantly higher level based on co-evolution.
Box 6.3
Risk analysis and the precautionary principle—the case of the
giant hogweed
Although the European Union (EU) countries have been the source of almost
400 classical weed biocontrol agents (Julien and Griffi ths 1998), biological con-
trol of invasive alien plants using exotic natural enemies has yet to be imple-
mented in Europe. In an EU-funded project aimed at developing a sustainable
management strategy for the invasive and pernicious giant hogweed (
Heracleum
mantegazzianum
), a biological control component was included within an
ambitious multidisciplinary approach. The results of surveys in the Caucasus
region of Russia revealed a guild of natural enemies associated with this plant
which were absent in the western European invasive range. One fungal pathogen
in particular,
Phloeospora heraclei
, causing extensive and coalescing leaf lesions
showed promise since it impacted heavily on the fi rst-year plants—especially
the seedling stage—which are considered to be the most vulnerable stage for
biocontrol in a biennial plant species. Host-range screening of the Caucasus
fungus confi rmed this potential but, later in the centrifugal phylogenetic testing
sequence, symptoms were detected on the closely-related parsnip and coriander,
although not on the hogweed
H
.
sphondeylium
despite the fact that there are
European records of this pathogen on this host (Seier and Evans 2007). This was
perplexing because both in the UK and mainland Europe, there are no reports
of
P
.
hercalei
on the invasive giant hogweed, nor, apart from one isolated record,
on either parsnip or coriander even in the horticultural literature listing their
diseases. This suggests that there are special forms or pathotypes of the fungus
and, moreover, that these results are an artifi cial extension of host range (see
Wapshere 1989; Marohasy 1996).
However, because of the ground-breaking aspect of this project, in relation to
classical biological control and Europe, it has been decided to adopt the precau-
tionary principle and not recommend further action, concluding that none of
