Usually, by mid-December, in South Africa, table grape and wine grape farmers time the final release of beneficial wasps to deal with mealybug in their vineyards: some around De Doorns have been using them for twelve years and have told him, says Brahm Jonker of FieldBugs, that they completely ceased their chemical mealybug programme.
Right: The pupae of Anagyrus and Leptomastix wasps are sold in packs of 200, 250 and 500
Word has spread, and this month FieldBugs was pleasantly surprised by the high and early demand from citrus farmers for predatory wasps: usually they start their biological programme only in January.
"Citrus farmers are telling us that they're not doing the hard spraying against thrips they'd normally have done in January. They can't take the risk in terms of residue levels, and that means," Jonker explains, "that the window to release beneficial insects opens up earlier, without the risk posed to the wasps by the January thrips spray of previous years."
The insecticide spinetoram is from this year banned within the European Union and its residue levels on fruit from third-party countries are under close scrutiny.
To meet the unexpected demand ("If we only knew to expect it six months ago!" he says) their two insectaries in Tzaneen and Piketberg are mass-rearing mealybugs around the clock to use as hosts for the wasps that will be sent out to growers just before hatching.
Anagyrus and Leptomastix wasps are released in orchards of citrus, grapes, apples, pears, persimmons, pomegranates and papayas in the order of thousands of hectares, he says, and farm scouts are encouraged to keep their eyes peeled for beneficial insects, not only pests anymore. Beneficial insects have taken on the dimensions of a commodity within the orchard.
The current bottleneck in supply will be resolved by the second week of the new year
"Twelve years ago, when I first began working in orchard biology, beneficial insects were hardly a consideration. Today, however, farm scouts are well-trained and actively monitor for them. For some farmers, beneficial wasps are old news, but many others are using them for the first time."
He remarks that interest from up north, and specifically Zimbabwe, Zambia, and Mozambique, has grown by leaps and bounds during 2024.
First commercial season for Leptomastix wasp
In the insectaries of FieldBugs located both in the north and south of the country, rooms upon rooms are dedicated to rearing mealybugs on butternuts, which serve as hosts for the beneficial wasps. By adjusting temperature and humidity within these insect factories, the ideal conditions are created to maximize mealybug populations, which are then harvested and parasitized by Leptomastix.
The current bottleneck in supply will be resolved by the second week of the new year.
The Leptomastix wasp, using many more species of mealybugs for egg-laying than the well-known Anagyrus wasp
The Anagyrus genus is cosmopolitan and widely used as a beneficial insect for mealybug control. FieldBugs exports permitted Anagyrus species to growers in the USA and Europe during specific times of the year.
FieldBugs' unique addition to its arsenal is the Leptomastix wasp, whose name reflects its insectivorous nature. The indigenous wasp was identified years ago by Stellenbosch University and others. The many mealybug species it uses as hatchery, instead of only a few, confers an advantage over Anagyrus, making it especially valuable, he says. "While Anagyrus parasitizes only four local species of mealybugs, research has shown that Leptomastix lays its eggs in sixteen different mealybug species."
He continues: "Apple and pear farmers, certain table grape growers, and producers of persimmons, pomegranates, and papayas previously had no effective way to use parasitoids as biocontrol agents - until Leptomastix came along."
Could Leptomastix with its wider mealybug species range one day replace Anagyrus wasps? Time will answer that one, Jonker says, but field results and customer feedback have been excellent. It is as yet only commercially available through FieldBugs.
He adds that they plan to export Leptomastix wasps to growers of a wide variety of crops in Turkey, where it's in high demand, and other countries like the United States, Australia, and Europe.
Biological mealybug control is supplanting chemical methods on some South African fruit farms
Anagyrus-Leptomastix combo proves popular
"We offer both the Anagyrus and Leptomastix in individual packs of 200, 250 or 500 pupae, but something that has proved popular among our clients – especially those who are well acquainted with Anagyrus by now, but haven't yet tried Leptomastix – is a combination of the two wasp species in a 50:50 ratio. There is no antagonism between the two species and they don't compete in the orchard."
Some farmers apply the biodegradable cylinders containing parasitized mealybug pupae by hand at a rate of two to eight dispensers per hectare depending on the pest pressure, while others decide to release it from overhead by drone. Labour costs and drone costs are roughly equal; the latter is quick and would result in more uniform coverage.
"Large farming groups are starting to explore biological pest management, aiming to familiarize their production managers with the integration process, release timing, and required quantities. As a result, they're designating specific blocks on various farms to test out beneficials."
Jonker observes that it's a gradual process. Some farmers get unnerved when they notice mealybugs in the orchards after the release of beneficial insects, but they need to learn to trust the process. "FieldBugs consultants support and teach growers and their scouts to gauge the levels of predation, a reliable indicator of success, and they remain onboard with advice and support during the growing season."
For more information:
Brahm Jonker
FieldBugs
Tel: +27 82 077 5940
Email: [email protected] / [email protected]
www.fieldbugs.co.za