“The classical form of biocontrol is specifically geared to invasive species management,” says Wyckhuys.
Biocontrol offers the option to go back to the region of origin of that pest, study the co-evolved natural enemies and choose the organisms that are highly effective at controlling them. “We don’t want to introduce an organism that is going to attack other organisms. We select an effective biocontrol that is highly specific,” says Wyckhuys.
Alternatively, in conservation approaches, predators that already exist within the environment are promoted by protecting their habitat. This can be done by increasing the amount of hedgerow or meadow around a field.
In a study on cabbage farming, where there was a high proportion of meadows surrounding a cabbage plot, numbers of cabbage-eating caterpillars were lower. This was likely due to the greater presence of parasitic wasps in those environments, the researchers say. However, in other instances, meadows promoted the presence of pest species like aphids and flea beetles. It’s not as simple as introducing more meadow to cut down on pests – the dynamics between farmland and wild land need to be carefully managed.
Conservation biocontrols like this are also limited to controlling pests which are native to their local environment. Like classical biocontrols, many pest species were first introduced to their environment by humans – they weren’t necessarily already there. As countries import seeds and crops from across the world, it is easy to assume that the odd accidental pest tagged along. Now, finding themselves in a new environment without a natural predator, they flourish.
Finally, in augmented approaches a pathogen or parasite is introduced to a crop at a key time – perhaps when pests begin to breed or lay eggs, or even before the pest arrives – so that the control species quickly nullifies their threat before their own numbers dwindle and they too die out in that area. The advantage of this approach is that you can be very specific with how you tackle the pest species.
“Augmented control is very popular in the European greenhouse sector,” says Wyckhuys. “In some areas pesticide use is zero.”
Greenhouses have been the domain of biocontrols for decades, even while chemical pesticides had their boom years. They have a big advantage of being a more or less closed system, so a predatory biocontrol is not going to fly away. Then there is the fact that greenhouse crops tend to be higher value – tomatoes, peppers and cucumbers sell for more per unit area than cereals, for instance.
In more recent years the popularity for biocontrols has spread to other sectors such as floraculture, viticulture and outdoor fruits like strawberries.
“In Canada we did a survey in 2017/ 2018, 92% of flower growers use biocontrol as the main pest control strategy,” says Buitenhuis. “It is an amazing success story and came about because of pesticide resistance, especially in Canada.”
Buitenhuis and Reid know that when large surface area crop farmers switch to biocontrols for their cereals and grains, the momentum will have swung back in their favour. “If an arable farmer decided that a biocontrol is usable on wheat or barley that is us cracked it,” says Reid. Likewise, Buitenhuis says that persuading countries like Colombia, Ecuador and Kenya to adopt such approaches would be “big wins”.
“It is coming,” says Buitenhuis. “Using chemicals only is not a long-term sustainable strategy.”
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