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Explora: Environment
and Resource Data should determine biocontrol success

initial agents (T. acaciaelongifoliae and U. morrisii) were if pre-release data on the invasive plant were collected,
released in South Africa but surprisingly no further data which would make it possible to quantitatively measure the
were published. Therefore, the defined success within these change in distribution of the target host. Surprisingly, these
review articles (that little to no seeds or plants survive, data are still not collected before agent release as a standard
which has resulted in a reduced area of coverage and rate practice, despite the strength it would provide to statistical
of spread) has remained as a qualitative notion within the evaluations of control. 19
scientific literature as quantitative evidence lacks for all Hill et al. 5,p.568 states that “If there are any doubts about
of the biocontrol programs on invasive Australian Acacia what has been achieved with biological control against
spp. For example, Zachariades et al. 12,p.1 state that “We invasive alien plants in South Africa over the years, the
used published literature, unpublished work and personal fundamental counterfactual question is: what would be
communication to assess the status of biological control the extent of the alien plant invasions if there had been no
of IAPs [invasive alien plants],” essentially emphasizing biological controls?’” Similarly, Impson et al. 16,p.8 states that
successful control of Australian Acacia spp. through “While there is no definitive confirmation that the inclusion
released agents. Despite this claimed success, many of biological control on A. cyclops in South Africa has brought
established Australian Acacia spp. still occupy a large about the changes in its pest status, it is not unreasonable to
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area in South Africa and are still increasing in densities. deduce that the introductions of D. dielsi and M. servulus
Furthermore, area managers do not see environmental were not a wasted effort and that biological control is almost
gains in invasive impact reduction even when agents are certainly contributing to the decline of the pest.”
present. 33
These and similar statements underpin the assumption
The above-mentioned then draws into question the that biocontrol has an effect and that proof should be
cost-benefit analysis that has been done for invasive provided to prove the opposite. Fundamentally, this
Australian Acacia spp. using biocontrol. If no changes the null hypothesis of no effect to the alternate
120
quantitative information on the extent of biocontrol for effect. Therefore, this implies that the alternate hypothesis
these plants is available, they can only be based on expert should be used during statistical testing. This violates
opinion. The cost-versus-benefit of biocontrol agent a basic principle of scientific inquiry. The dangers of
introduction on Australian Acacia spp. was calculated as making a type 1 versus type 2 error in the question of
1:3726. 22,120 Considering the bias toward the perceived whether biocontrol agents are effective are as such. If it is
success of biocontrol agents, the estimates on impact assumed that there is a significant effect but there is none,
reduction were likely inflated (because experts perceive the control program will not recommend any further
and recommend biocontrol agents as effective), providing control action. However, if a type 2 error is made, there
a skewed perception of cost-benefits of using biocontrol. is a significant effect, but this is recorded as there is none,
This is based on statements that biocontrol is more cost- and control actions will be further explored. Consequently,
effective than other control measures in terms of being based on sound scientific practice, the current approach
self-perpetuating and reducing the extent of invasion and of biocontrol programs on invasive Australian Acacia
rate of spread of the targeted host plants. However, the spp. implicitly risks being affected by a type 1 statistical
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effectiveness of other control methods versus biological error. Based on the evidence that has been provided so far,
control has not been formally compared in terms of cost this is the general approach that has been followed with
relative to benefit. biocontrol programs in South Africa. However, if sound
Recently, the seed banks of invasive Australian Acacia scientific practice is followed, the burden of proof should
spp. have been used to provide a method to assess the impact be demonstrating that biocontrol has a significant effect.
of seed-reducing biocontrol agents in the southwestern 4. Consequences of believing without
part of South Africa. 13-15 Using quantile regression and
using tree diameter as an indication of stand age, seed seeing
bank development over time could be demonstrated. These The implications of Acacia spp. seed biocontrol not being
data show that insect seed-reducing agents have similar effective but believed as being effective are four-fold. First,
deficiencies to an introduced fungus, namely slow rates of the apparent success of biocontrol of invasive wattles has
dispersal and population growth 10,50 relative to the rate of been used to lobby for the release of more agents. 10,12,109
seed bank accumulation of their Australian Acacia hosts. In fact, after the release of T. acaciaelongifoliae and U.
13
How could there be such a big gap between perceived morrisii, six seed-feeding beetles and six more gall formers
success and what empirical data is showing to be the have been released (Table 1). During this whole exercise,
contrary? However, such a debate would be unnecessary not one pre-release study has quantified the reproductive

Volume 2 Issue 1 (2025) 13 doi: 10.36922/eer.5876