not been recently or fully published, have been brought up to date (to 2019) from the
personal knowledge of one or more of the contributing authors.
Box 19.1 Opuntia stricta (Cactaceae) (Australian Pest Pear)
Invasion by Opuntia stricta (Australian Pest Pear) in the Kruger National Park
was rapid, with about 60,000 ha being infested by the turn of the century,
mainly through seeds being spread by baboons and elephants. An intensive
herbicide-based control programme failed to achieve its objectives and eventually biological control was adopted as a management process despite the park
management’s reluctance to have additional non-native species (i.e. biological
control agents) brought into a conservation area. Simulation models had correctly predicted that the release of the well-known cactus moth, cactoblastis, in
1988, would result in diminished invasion. But success was mainly due to the
release of a cochineal insect species (open circles), in 1997, that kills the pads/
cladodes (closed circles) and the plants. Long-term surveys over 20 years
showed that there was a rapid decline in the density of the cactus plants and
that the weed has now been permanently controlled well below an acceptable
threshold by biological control (Figure updated from Impson et al. 2011).
A system has been used in South Africa to describe overall success, i.e. outcomes
of biological control against invasive alien plants, at the plant population
(demographic) level, as ‘complete’, ‘substantial’, ‘negligible’, or ‘unknown’, and
which relies on long-term formal evaluations, or on expert-opinion on broad
categorisations of the reduced dependency on alternative control methods (chemical
or mechanical), as a result of the introduction of biological control agents. This
classification system was initiated by Hoffmann (1991). It has subsequently been
refined and elaborated by Hoffmann (1995), Anonymous (1999), Hoffmann and
Moran (2008), Klein (2011) and Zachariades et al. (2017), and has been widely
adopted internationally (McFadyen 1998). Using this ‘now-traditional’ descriptive
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M. P. Hill et al.
personal knowledge of one or more of the contributing authors.
Box 19.1 Opuntia stricta (Cactaceae) (Australian Pest Pear)
Invasion by Opuntia stricta (Australian Pest Pear) in the Kruger National Park
was rapid, with about 60,000 ha being infested by the turn of the century,
mainly through seeds being spread by baboons and elephants. An intensive
herbicide-based control programme failed to achieve its objectives and eventually biological control was adopted as a management process despite the park
management’s reluctance to have additional non-native species (i.e. biological
control agents) brought into a conservation area. Simulation models had correctly predicted that the release of the well-known cactus moth, cactoblastis, in
1988, would result in diminished invasion. But success was mainly due to the
release of a cochineal insect species (open circles), in 1997, that kills the pads/
cladodes (closed circles) and the plants. Long-term surveys over 20 years
showed that there was a rapid decline in the density of the cactus plants and
that the weed has now been permanently controlled well below an acceptable
threshold by biological control (Figure updated from Impson et al. 2011).
A system has been used in South Africa to describe overall success, i.e. outcomes
of biological control against invasive alien plants, at the plant population
(demographic) level, as ‘complete’, ‘substantial’, ‘negligible’, or ‘unknown’, and
which relies on long-term formal evaluations, or on expert-opinion on broad
categorisations of the reduced dependency on alternative control methods (chemical
or mechanical), as a result of the introduction of biological control agents. This
classification system was initiated by Hoffmann (1991). It has subsequently been
refined and elaborated by Hoffmann (1995), Anonymous (1999), Hoffmann and
Moran (2008), Klein (2011) and Zachariades et al. (2017), and has been widely
adopted internationally (McFadyen 1998). Using this ‘now-traditional’ descriptive
558
M. P. Hill et al.