against floating, invasive aquatic plants (Coetzee et al. 2011a) and against the
various hybrids in the Lantana camara L. hybrid-complex (Verbenaceae; Lantana;
Urban et al. 2011). More recently, herbaceous plants, vines and various subtropical
shrubs have been subjected to biological control (Moran et al. 2013).
For over a century, South Africa has been one of the five main countries
conducting research on and implementation of biological control of invasive alien
plants (McFadyen 1998). Since 1995, with major increases in funding from state
sources (Zimmermann et al. 2004) and the consequent involvement of many more
researchers, students, support staff (see also van Wilgen 2020, Chap. 2, Sect. 2.2),
and implementers, there have been an increasing number of innovative and successful projects, allowing South Africa to play a leadership role in the use of biological
control in the management of invasive alien plants (Moran and Hoffmann 2015;
Schwarzländer et al. 2018).
All the projects and programmes on biological control of invasive plants in
South Africa have been thoroughly documented in three sets of reviews (Hoffmann
1991; Olckers and Hill 1999; Moran et al. 2011), in Muniappan et al. (2009), and in a
recent overview of the entire South African biological control effort (Zachariades
et al. 2017). These compilations have been comprehensive in recording which agents
have been sourced, tested, mass-reared, released, established and redistributed
against each of the targeted, invasive plant species, and in recording their progress
and the extent of damage caused on the target host-plants. However, these accounts
have been less clear in summarising the overall achievements (i.e. outcomes) of
biological control programmes against invasive alien plant species and consequently, that is the primary purpose of this account.
19.2 Evaluating the Effectiveness of Biological Control
of Invasive Alien Plants
Across the world, many different approaches have been used to evaluate and express
the outcomes of biological control projects against invasive plant species (e.g. Syrett
et al. 2000; Morin et al. 2009). It has long been understood that the objective of
biological control “. . . is not the eradication [of the target plant species] but the
reduction of their densities to non-economic levels” (Huffaker 1964). In some
instances, the success of biological control is self-evident and before-and-after
photographic records (see, for example, Figs. 19.1, 19.2 and 19.3) suffice to make
the general point. Evaluations of biological control accomplishments against invasive alien plant species, during the earlier eras, were mostly descriptive and subjective. Thus, an apparent understanding of the outcomes of biological control was, and
often still is, based on ‘proxy-studies’ of the progress of the released biological
control agents themselves. These studies aligned with the expertise of the scientists
involved, who were overwhelmingly entomologists or, less often, pathologists, not
plant ecologists. Many of these studies were appropriate for short-term funding
cycles and provided excellent subject-matter for post-graduate student projects.
19 Biological Control Against Invasive Alien Plants
555
various hybrids in the Lantana camara L. hybrid-complex (Verbenaceae; Lantana;
Urban et al. 2011). More recently, herbaceous plants, vines and various subtropical
shrubs have been subjected to biological control (Moran et al. 2013).
For over a century, South Africa has been one of the five main countries
conducting research on and implementation of biological control of invasive alien
plants (McFadyen 1998). Since 1995, with major increases in funding from state
sources (Zimmermann et al. 2004) and the consequent involvement of many more
researchers, students, support staff (see also van Wilgen 2020, Chap. 2, Sect. 2.2),
and implementers, there have been an increasing number of innovative and successful projects, allowing South Africa to play a leadership role in the use of biological
control in the management of invasive alien plants (Moran and Hoffmann 2015;
Schwarzländer et al. 2018).
All the projects and programmes on biological control of invasive plants in
South Africa have been thoroughly documented in three sets of reviews (Hoffmann
1991; Olckers and Hill 1999; Moran et al. 2011), in Muniappan et al. (2009), and in a
recent overview of the entire South African biological control effort (Zachariades
et al. 2017). These compilations have been comprehensive in recording which agents
have been sourced, tested, mass-reared, released, established and redistributed
against each of the targeted, invasive plant species, and in recording their progress
and the extent of damage caused on the target host-plants. However, these accounts
have been less clear in summarising the overall achievements (i.e. outcomes) of
biological control programmes against invasive alien plant species and consequently, that is the primary purpose of this account.
19.2 Evaluating the Effectiveness of Biological Control
of Invasive Alien Plants
Across the world, many different approaches have been used to evaluate and express
the outcomes of biological control projects against invasive plant species (e.g. Syrett
et al. 2000; Morin et al. 2009). It has long been understood that the objective of
biological control “. . . is not the eradication [of the target plant species] but the
reduction of their densities to non-economic levels” (Huffaker 1964). In some
instances, the success of biological control is self-evident and before-and-after
photographic records (see, for example, Figs. 19.1, 19.2 and 19.3) suffice to make
the general point. Evaluations of biological control accomplishments against invasive alien plant species, during the earlier eras, were mostly descriptive and subjective. Thus, an apparent understanding of the outcomes of biological control was, and
often still is, based on ‘proxy-studies’ of the progress of the released biological
control agents themselves. These studies aligned with the expertise of the scientists
involved, who were overwhelmingly entomologists or, less often, pathologists, not
plant ecologists. Many of these studies were appropriate for short-term funding
cycles and provided excellent subject-matter for post-graduate student projects.
19 Biological Control Against Invasive Alien Plants
555