19.4 Additional Considerations, Caveats and Conclusions
Since 1995, and the advent of support from the Working for Water programme
(Zimmermann et al. 2004), biological control of invasive plants in South Africa has
gained enormous momentum, and many of the outcomes summarised in this chapter
owe their successes to this. Much has been achieved, but some additional points and
caveats need to be recorded:
1. Although in this account we have purposely not dealt with the details of the
biological control agents that have been used against invasive plant species in
South Africa since 1913, all the candidate agents have been subjected to
internationally-accepted procedures for safety-testing (usually host-specificity
trials): none of the eventual releases have resulted in unexpected consequences,
or in damage to non-target plants. Over the years, in South Africa, 70 entities
(species and their biotypes) of candidate biological control agents, under consideration in quarantine for prospective use against invasive alien plants, have been
‘shelved’, i.e. not released pending further developments or investigations, and
65 have been ‘rejected’ and the cultures destroyed, not usually because of issues
with facilities or funding, but because of doubts about their safety (Zachariades
2018b). Klein (2011) has put this into perspective: “It is of particular significance, in terms of safety practices and standards, that all the rejections were
advocated and implemented by the researchers themselves, mostly following
discussions within the South African weed biological control fraternity. No
formal release applications from the researchers have been rejected by the
regulatory authorities.”
2. An integral feature of the biological control of invasive plants is dealing with
conflicts of interest, i.e. where a potential target plant species is problematic in
some circumstances or areas, but also has beneficial attributes. Acacia mearnsii
De Wild. (Fabaceae; Black Wattle), for example, is a major problem in the
Western and Eastern Cape provinces, especially in riparian areas, and was
mooted for biological control in the early 1970s. This proposal met with strenuous objections lodged in 1977 by the wattle growers who, in other parts of the
country, cultivate A. mearnsii and, to a lesser extent, two other closely-related
wattle-species as the basis of lucrative timber production and tannin extraction
industries. Previous initiatives and experience with other invasive Acacia species
in South Africa led to the proposal that seed-destroying agents be released that
reduce the reproductive capacity (‘invasiveness’) of their hosts, but that do not
retard the vegetative growth. After protracted discussions and negotiations with
the wattle-growers, the first biological control agent was released against
A. mearnsii in 1993 (Impson et al. 2011). These precedents explain the frequent
use of seed-destroying species in projects for biological control of invasive alien
plants in South Africa. In some instances, as with the proposed biological control
of two species of invasive Pinus species (Pinaceae; pine trees) in South Africa,
attempts at biological control were abandoned, largely because of a failure to
overcome conflicts of interest (Moran et al. 2000; Hoffmann et al. 2011).
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M. P. Hill et al.
Since 1995, and the advent of support from the Working for Water programme
(Zimmermann et al. 2004), biological control of invasive plants in South Africa has
gained enormous momentum, and many of the outcomes summarised in this chapter
owe their successes to this. Much has been achieved, but some additional points and
caveats need to be recorded:
1. Although in this account we have purposely not dealt with the details of the
biological control agents that have been used against invasive plant species in
South Africa since 1913, all the candidate agents have been subjected to
internationally-accepted procedures for safety-testing (usually host-specificity
trials): none of the eventual releases have resulted in unexpected consequences,
or in damage to non-target plants. Over the years, in South Africa, 70 entities
(species and their biotypes) of candidate biological control agents, under consideration in quarantine for prospective use against invasive alien plants, have been
‘shelved’, i.e. not released pending further developments or investigations, and
65 have been ‘rejected’ and the cultures destroyed, not usually because of issues
with facilities or funding, but because of doubts about their safety (Zachariades
2018b). Klein (2011) has put this into perspective: “It is of particular significance, in terms of safety practices and standards, that all the rejections were
advocated and implemented by the researchers themselves, mostly following
discussions within the South African weed biological control fraternity. No
formal release applications from the researchers have been rejected by the
regulatory authorities.”
2. An integral feature of the biological control of invasive plants is dealing with
conflicts of interest, i.e. where a potential target plant species is problematic in
some circumstances or areas, but also has beneficial attributes. Acacia mearnsii
De Wild. (Fabaceae; Black Wattle), for example, is a major problem in the
Western and Eastern Cape provinces, especially in riparian areas, and was
mooted for biological control in the early 1970s. This proposal met with strenuous objections lodged in 1977 by the wattle growers who, in other parts of the
country, cultivate A. mearnsii and, to a lesser extent, two other closely-related
wattle-species as the basis of lucrative timber production and tannin extraction
industries. Previous initiatives and experience with other invasive Acacia species
in South Africa led to the proposal that seed-destroying agents be released that
reduce the reproductive capacity (‘invasiveness’) of their hosts, but that do not
retard the vegetative growth. After protracted discussions and negotiations with
the wattle-growers, the first biological control agent was released against
A. mearnsii in 1993 (Impson et al. 2011). These precedents explain the frequent
use of seed-destroying species in projects for biological control of invasive alien
plants in South Africa. In some instances, as with the proposed biological control
of two species of invasive Pinus species (Pinaceae; pine trees) in South Africa,
attempts at biological control were abandoned, largely because of a failure to
overcome conflicts of interest (Moran et al. 2000; Hoffmann et al. 2011).
566
M. P. Hill et al.