the initial safe introduction of biological control agents, as candidate species have to
be rigorously tested to assess the risk of them having any adverse impacts on native
flora and fauna.
South Africa first utilised this technique over a century ago, when Dactylopius
ceylonicus (Cochineal Insect) was released in 1913 to control Opuntia monacantha
(Drooping Prickly Pear), which was then highly invasive along the coast between
the Western Cape and Durban (Moran et al. 2013). Despite the lack of precautionary testing, this introduction was a resounding success and resulted in rapid
and permanent control of the host. Since that time, South Africa has become a
global leader on the field of biological control and is now considered one of the
top five countries in the world with regards to research in this field (Zachariades
et al. 2017).
In the early years, the target plants were mostly invasive Cactaceae and the
biological control agents introduced were ones whose effectiveness had already
been proven in other countries. Later projects have targeted new hosts, for which
the experimental testing had to be conducted in South Africa, and by 2018 a total of
93 species of insect, mites or plant pathogens had been released against 59 host
plants species, with 25 additional plant species under investigation (Zachariades
et al. 2017).
A few invasive invertebrates have also been targeted for biological control,
the most common control agents in these cases being wasp parasitoids. For
example, Megalyra fasciipennis is a pupal parasitoid that has been introduced
to control invasive Eucalyptus Longhorn Borer Beetles (Phorocantha species)
(Gess 1964), while Cotesia plutella is a parasitoid introduced to control Plutella
xylostella (Diamondback Moth), a major pest of cabbages and other plant species
in the family Brassicaceae (Nofemela and Kfir 2005). The solitary regional
example of a nematode biological control agent, Beddingia siricidicola, was
also introduced from Europe to control Sirex noctilio (Sirex Woodwasp) (Hurley
et al. 2007).
Biological control agents that control invasive invertebrates have sometimes
arrived accidentally. Thus, Psyllaephagus bliteus (a eucalypt gall wasp parasitiod),
which is a classical biological control agent in many countries for the control of the
Redgum Lerp Psyllid, Glycaspis brimblecombei, seems to have arrived in
South Africa (and indeed other regions globally) without intervention, presumably
as larvae within imported host populations (Bush et al. 2016). Conversely, the
populations of some invasive invertebrates can also sometimes be brought under
control by host-switching in native predators and/or parasitoids. For example,
populations of the invasive Pieris brassicae (Large Cabbage White Butterfly),
fluctuate dramatically between years and appear to be effectively controlled by an
unidentified, but probably native, braconid wasp (Apantles species), which attacks
the caterpillars, as well as by a native pteromalid wasp, Pteromalus puparum, which
attacks the pupae (Picker and Griffiths 2011; Prinsloo and Uys 2015). Similarly,
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be rigorously tested to assess the risk of them having any adverse impacts on native
flora and fauna.
South Africa first utilised this technique over a century ago, when Dactylopius
ceylonicus (Cochineal Insect) was released in 1913 to control Opuntia monacantha
(Drooping Prickly Pear), which was then highly invasive along the coast between
the Western Cape and Durban (Moran et al. 2013). Despite the lack of precautionary testing, this introduction was a resounding success and resulted in rapid
and permanent control of the host. Since that time, South Africa has become a
global leader on the field of biological control and is now considered one of the
top five countries in the world with regards to research in this field (Zachariades
et al. 2017).
In the early years, the target plants were mostly invasive Cactaceae and the
biological control agents introduced were ones whose effectiveness had already
been proven in other countries. Later projects have targeted new hosts, for which
the experimental testing had to be conducted in South Africa, and by 2018 a total of
93 species of insect, mites or plant pathogens had been released against 59 host
plants species, with 25 additional plant species under investigation (Zachariades
et al. 2017).
A few invasive invertebrates have also been targeted for biological control,
the most common control agents in these cases being wasp parasitoids. For
example, Megalyra fasciipennis is a pupal parasitoid that has been introduced
to control invasive Eucalyptus Longhorn Borer Beetles (Phorocantha species)
(Gess 1964), while Cotesia plutella is a parasitoid introduced to control Plutella
xylostella (Diamondback Moth), a major pest of cabbages and other plant species
in the family Brassicaceae (Nofemela and Kfir 2005). The solitary regional
example of a nematode biological control agent, Beddingia siricidicola, was
also introduced from Europe to control Sirex noctilio (Sirex Woodwasp) (Hurley
et al. 2007).
Biological control agents that control invasive invertebrates have sometimes
arrived accidentally. Thus, Psyllaephagus bliteus (a eucalypt gall wasp parasitiod),
which is a classical biological control agent in many countries for the control of the
Redgum Lerp Psyllid, Glycaspis brimblecombei, seems to have arrived in
South Africa (and indeed other regions globally) without intervention, presumably
as larvae within imported host populations (Bush et al. 2016). Conversely, the
populations of some invasive invertebrates can also sometimes be brought under
control by host-switching in native predators and/or parasitoids. For example,
populations of the invasive Pieris brassicae (Large Cabbage White Butterfly),
fluctuate dramatically between years and appear to be effectively controlled by an
unidentified, but probably native, braconid wasp (Apantles species), which attacks
the caterpillars, as well as by a native pteromalid wasp, Pteromalus puparum, which
attacks the pupae (Picker and Griffiths 2011; Prinsloo and Uys 2015). Similarly,
192
C. Janion-Scheepers and C. L. Griffiths