Pictured Above: Hugo Bester
Macadamia farmers across South Africa are hailing the parasitoid wasp, Trissolcus basalis, as a deadly strike weapon in their war on stinkbugs. Improved nut quality is proof of the insect predator’s success, they say.
While Trissolcus basalis might be just half the size and width of a housefly, the parasitoid wasp is punching way above its weight in the fight against the stinkbugs so prevalent in South Africa’s macadamia orchards.
Lyle Wichmann, who has orchards inland of Zinkwazi Beach on the KwaZulu-Natal North Coast, says in the three years since he introduced the wasps into his 20- to 30-year-old trees, unsound nut percentages have dropped from 4%-6% of his annual harvest to less than 1%.
Pictured: Lyle
“Our initial attitude to pest control in our orchards – which had been severely neglected before I took over – was to go harder with chemical spraying. And yes, we would knock down the stinkbugs and other pests, but they would be back within days of the application,” he said.
Dr Brent Chiazzari, who is the Farmers Agri-Care Crop Advisor for that region, said the exponential growth in bio-security measures to control pests in the domestic orchards had taken off in the country since 2021. “Farmers are responding to international pressure to reduce harmful chemical use in their orchards in compliance with international certification standards such as Global Gap and the European Union’s Green Deal. They are also seeing the benefits of biosecurity on the growth of beneficial insect populations inside and outside their orchards.”
Dr Brent Chiazzari
Wichmann said a wake-up call for him personally was standing in his orchard during flowering and hearing nothing, just silence. “Now, it’s the opposite. The orchards are humming and buzzing with life,” he said.
So how do these tiny black wasps with four transparent wings go about their business, and why are they in the frontline in the fight against stinkbug infestations in macadamia orchards?
Hugo Bester, Technical Advisor for Koppert Southern Africa – a Dutch-based biological pest control company – opens a video on his smartphone, showing a small black-winged insect darting back and forth over a cluster of pale stinkbug eggs on the back of a macadamia tree leaf. “Look how excited she is,” Bester says. “She’s laying an egg in each of the stinkbug eggs; in a few days the eggs will start to discolour, which indicates that the stinkbug nymph is dead and the Trissolcus basalis larvae are feeding on them.”
The female wasp guards her brood until they hatch, and as soon as they do, the newly emerged males and females will mate, ready to start their lifecycle all over again. Because the insect is a strong flyer it distributes well in the orchard, Bester adds.
He then demonstrates how the wasps – branded as Greenshield – are transported by courier directly to farmers in small cardboard “bottles” from Koppert’s South African laboratories in Lanseria.
The deliveries are synced with other synergistic soft and targeted pest control methods, including sprays and drenches. “All of us work as a team to make sure the different remedies are delivered at the right time and in the right way. Timing is key,” he said.
Each bottle contains a “sugar patch” as food for the little creatures and is sealed with a white paper disc. Every bottle has a rubber band attached.
Bester removes the seal revealing a small hole, makes a loop with the rubber band, and attaches the container to a branch halfway up the macadamia tree. “One bottle contains 100 wasps, enough to cover 1ha. Ideally the tube is placed in the shade of the tree canopy, wedged between branches, and first prize is to have them near a batch of stinkbug eggs, but that’s not essential,” he said.
But timing the release was crucial.
Parasitised Eggs
“We recommend the first release in August and September depending on the season and the cultivar. The presence of stinkbug adults or eggs is not essential, but rather helpful, to build parasitic wasp populations. The wasps should be released in the middle of each hectare block every four to six weeks at 100 insects per hectare.”
Chiazzari hailed the wasps as integral to biosecurity strategies in macadamia orchards as they effectively controlled the egg phase of the stinkbug’s life cycle. “Greenshield is not a stand-alone control method of stinkbugs. We still use compatible chemical sprays in our arsenal to control the pest, but they are key,” he said.
Bester added that chemical sprays were necessary, particularly in the first year, to lower the stinkbug pest pressure.
The list of compatible chemicals includes:
Thiamethoxam
Pymetrozine
Imidacloprid
Methoxyfenoxide
He said scouting remained a vital part of a successful pest control programme. “Scouting for parasitised and non-parasitised eggs can indicate the success of the Greenshield releases. The non-parasitised eggs are cream-coloured while the parasitised eggs are brown or black,” he noted.
Wichmann said another plus factor was since the release of the wasps into his orchards, he had been able to slash the active ingredients in the chemicals he used. “I used to apply products with about four to five active ingredients, now it’s one or two. That is a huge cost saving and its better for the environment,” he said.
Dustin Cooper, whose seven- to eight-year-old orchards are also in the Darnall/Zinkwazi area, said in his mind the wasps were like security guards patrolling his orchards. “I think about them chipping away at the stinkbug numbers in the background. I might not be able to see them, but I know they are there. Doing their work. Guarding the trees,” he said.
Written by Colleen Dardagan
