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Explora: Environment
and Resource Data should determine biocontrol success

words, the released seed-reducing agents in South Africa spp. Much greater effort is needed to gather data before
are not effective in reducing the number of seeds produced release or collect baseline data just after release.
by these invasive Australian Acacia spp. below a level where
biodiversity, ecosystem functioning, and management of the Acknowledgments
plants could benefit from. This is not surprising given that We would like to thank Michael Samways and two anonymous
these invasive plants are not seed-limited. reviewers for valuable feedback on the manuscript.
The question arises as to whether invasive management
that relies heavily on biocontrol agents to reduce the seed Funding
production of the target host is indeed adequate, and Ruan Veldtman’s salary is funded by The South African
should this not be monitored and tested? At present, in Department of Forestry, Fisheries and the Environment
South Africa, invasive plant species under biocontrol are (DFFE). This publication does not necessarily represent
considered less threatening than those species with no the views or opinions of the DFFE or its employees.
released agents. 21,24,27 However, if biocontrol does not reduce
the invasiveness in the high-density stands of their target Conflict of interest
host species, prioritizing mechanical control on species with The authors declare they have no competing interests.
no agents, may allow species under biocontrol to entrench
even further. Furthermore, this can also cause further loss of Author contributions
biodiversity and ecosystem functioning. This could lead to
inefficient use of conservation and management resources Conceptualization: All authors
in terms of managing invasions on the ground (e.g., Cheney Visualization: All authors
et al. ). In some cases, young invasive stands of Acacia spp. Writing–original draft: All authors
33
are not targeted as it is assumed that biocontrol will slow the Writing–review & editing: All authors
build-up of the population. 22,24,129 Consequently, instead of Ethics approval and consent to participate
targeting sparsely invaded areas first, established stands are
targeted. Over time, however, it is the sparse populations Not applicable.
that are increasing in density despite the presence of
33
biocontrol agents (i.e., Cheney et al. ). Indeed, there is a Consent for publication
strong relationship between weed impact and its landscape Not applicable.
density (Marchante et al. for A. longifolia specifically). 3
121
Both biological invasions and classical biological control Availability of data
have been recognized as unprecedented ecological and Not applicable.
evolutionary bio-geographical experiments. However,
130
classical biological control is a planned introduction of References
an alien organism and does not come without risks. 1. Seebens H, Blackburn T, Dyer E, et al. No saturation in the
17
The purposeful introduction of some classical biological accumulation of alien species worldwide. Nat Commun.
control species may thus be unwarranted, given the 2017;8:14435.
potential for non-target effects 124-126,113-133 and the likelihood doi: 10.1038/ncomms14435
of spontaneous geographic spread after establishment. 134,135
Going forward, countries that rely heavily on classical 2. Pyšek P, Hulme PE, Simberloff D, et al. Scientists’ warning
biological control for the management of weeds (South on invasive alien species. Biol Rev. 2020;95:1511-1534.
Africa, Australia, etc.) should invest in standardized, long- doi: 10.1111/brv.12627
term monitoring of the performance of released agents. 3. Cruttwell McFadyen RE. Biological control of weeds. Annu
If there are data at a scale larger than a single plant (i.e., at Rev Entomol. 1998;43:369-393.
the population scale), which quantitatively shows the doi: 10.1146/annurev.ento.43.1.369
control exerted by a seed-biocontrol agent of an Australian
Acacia spp. has reduced its invasive impact, we strongly 4. Hoddle MS. Restoring balance: Using exotic species to control
invasive exotic species. Conserv Biol. 2004;18(1):38-49.
encourage it to be published. Science can only progress
through the formulation and testing of hypotheses, and doi: 10.1111/j.1523-1739.2004.00249.x
here, of ecological processes. Hence, where to from here? 5. Hill MP, Moran VC, Hoffmann JH, et al. More than
We hope our review highlights the current problems with a century of biological control against invasive alien
evaluating the success of biocontrol of Australian Acacia plants in South Africa: A synoptic view of what has been

Volume 2 Issue 1 (2025) 15 doi: 10.36922/eer.5876