Biological control – better known as biocontrol – leverages natural processes such as biostimulants and predation to manage pests and diseases. A recent talk by applied entomologist Dr Francois Bekker of the Department of Conservation Biology and Entomology at Stellenbosch University focused on biocontrol based on pathogens, parasitoids and predators.
Bekker was addressing the audience at SATI’s 2025 Table Talk event in Paarl. His key message to growers? Biocontrol takes some work, but the benefits outweigh the costs.
The pros and cons
Biocontrol is generally considered to have a lower environmental impact than conventional chemicals. Most biocontrol agents are species-specific. For example, parasitoid wasps tend to lay their eggs in a very narrow host range, so they pose no threat to non-host species. In contrast, pesticide applications don’t discriminate between beneficial and harmful insects. Furthermore, our markets don’t view biocontrol agents as risky to consumers, operators or the environment. Given the current pressure on conventional chemicals, biocontrol is a potentially valuable extension to a grower’s arsenal.
Bekker also listed several drawbacks of biocontrol. Unlike chemicals, which rapidly reduce pest numbers, biocontrol agents act more slowly and can’t eradicate pests. The situation in the vineyard is similar to that on the savannah: the lions don’t eat every impala. And although more impalas mean more lions, impala numbers increase before lions do. As biocontrol is, by definition, biological, it has variable effectiveness. “And – a very important point – it’s complex to implement,” cautioned Bekker. “If someone tells you it’s easy, don’t listen to them.”
“If someone tells you it’s easy, don’t listen to them.”
Regulation: friend or foe?
Regulation is often seen as an obstacle to innovation. Bekker provided a different perspective, quoting from Martin Wohlfarter, Senior Global Regulatory Affairs Specialist at Koppert B.V., who pointed out that regulation can be a catalyst to ensure innovation is effective, safe, and scalable.
“I get a lot of questions about why there should be registration for mass-produced parasitoids and predators that occur naturally,” said Bekker. “Setting aside the fact that it’s illegal to sell unregistered products, there are three reasons for registration.”
The first, explained Bekker, is quality control to ensure that mass-reared predators and parasitoids are safe, effective and contaminant-free. The second is that companies must submit data to support their efficacy claims when applying for registration, so registration supports evidence-based pest control.
“The third is environmental risk,” said Bekker. “Even native species can disrupt ecosystems if misused, and registration helps assess and manage these ecological risks.”
“Registration helps assess and manage eco-logical risks.”
He presented a short review of registered and non-registered biocontrol products for table grapes. The registered products include viral, bacterial, and fungal agents for use against a range of pests, including mealy bugs, mites and various moths. The non-registered products included fungi, nematodes, and many predators and parasitoids. Bekker pointed out that some of the predators don’t occur south of the Sahara. “So is this an incorrect identification? Or is a foreign species being distributed in our vineyards and the rest of agriculture?” he asked. Other non-registered products don’t even specify which species they contain. To Bekker, this raises concerns about quality control and the risks of ecological impacts or low efficacy.
What should growers consider?
Bekker used mealy bugs to illustrate the questions growers should ask when considering biocontrol. “This framework can be applied to any other pest in table grapes,” he said. There are several mealy bug species found on South African table grapes, and numerous parasitoids and predators attack them, according to a 2004 publication by Prof. Vaughn Walton (based on his postgraduate research) and the late Dr Ken Pringle.
Mealy bugs lend themselves to biocontrol because of their rapid reproduction and sedentary habits – they are literally sitting prey for parasitoids and predators. Pests that mainly reproduce outside the vineyard, continuously immigrating to infest vines, could be less amenable to biocontrol.
The existence of natural enemies suggests that biocontrol could be effective against mealy bugs. However, it must also be cost-effective, so growers need to take the value of their crop into account. For example, the high value of table grapes justifies greater expenditure on crop protection. It matters how much damage or infestation is tolerable. Although mealy bugs do little damage to leaves, their presence on fruit is unacceptable for aesthetic and phytosanitary reasons. Therefore, biocontrol may not offer a standalone management tool.
The perennial nature of table-grape vineyards and the ubiquity of mealy bugs also influence the choice of biocontrol agent. Theoretically, it should be possible for well-adapted biocontrol agents to establish in vineyards.
Lastly, for biocontrol to succeed, growers need access to pesticides that won’t annihilate the biocontrol agents. Fortunately, these are available for mealy bugs.
The ideal natural enemy
“The ideal natural enemy is a good coloniser,” said Bekker. “It must be able to multiply quickly, in synchrony with the host, to keep up with your pest populations. Also, you don’t want something that you release into your orchard, and it just flies away.”
If the natural enemy sticks around, it should then be good at locating and either predating or parasitising prey. For example, mealy bug adults have a waxy layer, and many mealy bug colonies are guarded by aggressive ants. Successful enemies must overcome these defences.
As vine mealy bugs are the most common mealy bugs on grapevines, biocontrol agents that target this species are preferred. However, for some pests – such as mites – non-specific biocontrol agents can be helpful because the biocontrol agents can multiply on other food sources, switching to mites in outbreak situations.
Whatever biocontrol agent is selected, it must be adaptable to the climate where it’s released, and designing a spray programme that accommodates it must be feasible. A highly sensitive biocontrol agent will likely be impractical, regardless of how adept it is at finding and killing pests.
Bekker mentioned three biocontrol strategies. The first, conservation, is simply protecting the natural enemies that are already present. This requires correct identification during scouting and adapting spray programmes accordingly.
Augmentation entails releasing predators or parasitoids. “Inoculative releases involve releasing low numbers so that they can establish populations,” elaborated Bekker. “Inundative releases are when there are large numbers of pests, so you release large numbers of predators or parasitoids to get an immediate knock-down.”
Take-home message
Growers must understand that biocontrol is knowledge-intensive, said Bekker. “But that doesn’t mean you shouldn’t do it,” he stressed. “Educate yourself. There are more than enough resources, and independent technical advisers you can talk to.”
He acknowledged that there is a significant gap in registrations, resulting in a lack of robust efficacy data for many products. Therefore, growers must be prepared to question their suppliers and ensure that claims about products are supported by evidence.
Bekker reminded the audience that industry-funded research also generates data and helps to drive developments in biocontrol. The mealy bug research mentioned above is an example of this. In conclusion, Bekker made it clear that, despite the challenges, biocontrol is worth pursuing. “We need to learn how to navigate it, and to innovate,” he said. “But I’m positive about the future of biocontrol in South Africa.”
