Researchers deploy wasps in the fight against pests on cabbage

Flyvende gedehams: The wasp — or yellow jacket, as it is also called — is not a very popular guest. But maybe it can help us achieve more sustainable production of, among other things, cabbage. Photo: Creative Commons License

Grønåret Kålsommerfugl (2): The cabbage white butterfly belongs to the white butterflies. Here is a green-veined white butterfly. Photo: Christian Kjær.

Grønkål efter besøg af kålsommerfuglelarver: As a gardener, farmer, or ordinary home gardener, it can be a very sad sight to see your cabbage plants disappear like dew in the sun after an attack by cabbage white butterfly larvae. Photo: Creative Commons Licens.

Sukkerautomat i kålmark: WaspAlliance develops and sets up wasp nests around a cabbage field. With small sugar feeders placed in the fields, they lure wasps among the cabbage plants, where they can then eat the cabbage white larvae. Photo: Joachim Offenberg

Sukkerautomat med hveps: A wasp is leaving the sugar feeder after feeding on sugar. It is now lured into the cabbage field when the butterfly larvae start to act. Photo: Emma Lempert.

27 June 2025 by Hanne Bak

By Peter Bondo Christensen

If you have ever tried growing cabbage in your garden, you know that an entire cabbage plant can disappear like dew in the sun in a very short time.

It is the larvae of the cabbage white butterfly that voraciously munch on the cabbage leaves. Once they get started, the battle is basically lost. When they finish on one leaf, they simply move on to the next.

But researchers believe we can actively use wasps — also called yellow jackets — for biological control of these hungry larvae in open fields. Just as other predators are already used with great success to combat pests in greenhouses.

Plastic nets are currently one of the best tools
The cabbage white butterfly lays its eggs on the underside of cabbage and other cruciferous crops, such as rapeseed. When the eggs hatch, the caterpillars immediately start eating the plants.

Cabbage growers who do not use chemical sprays must cover plants with plastic nets, for example, to prevent butterflies from laying their eggs. In these efforts, they use up to one ton of plastic nets per hectare.

“That can leave plastic residues in nature, just as greenhouse gases are emitted during plastic production. If we can control the larvae biologically, we get a more sustainable production,” explains senior researcher Joachim Offenberg from the Department of Ecoscience at Aarhus University.

Joachim Offenberg leads the ‘WaspAlliance’ project, which over two years will investigate whether wasps can be actively released to eat the larvae of cabbage white butterflies on larger production fields.

“Already now, hives of bumblebees and honeybees are moved around to pollinate fields or plantations. Why couldn’t we do the same with wasps?” wonders Joachim Offenberg.

Annoying wasps become useful wasps
We know wasp nests best as the paper-thin cubes that hang under our eaves. The nests can contain thousands of wasps, and many of us call professionals if we want such a wasp nest removed.

Mortalin is one of the companies that respond to remove unwanted wasp nests. WaspAlliance has allied with them. When Mortalin removes a wasp nest, they deliver it to WaspAlliance. Here, researchers transfer the wasps to artificial nests — similar to beehives for honeybees.

Researchers then place the wasp nests on the edge of a cabbage field. Since wasps fly far and wide, researchers lure the wasps into the cabbage field by setting up small sugar feeders around the field. The researchers expect the wasps to attack the butterfly larvae once the wasps are drawn into the fields.

Wasps love butterfly larvae and eat many of them. Each wasp nest consumes up to 1.2 kilograms of larvae per season. And once the wasps have done their job, the nests can be moved to another field.

Joachim Offenberg has high hopes for the project: “Biological control has already outcompeted chemical control in indoor closed systems like greenhouses. It is obviously more difficult outdoors, but even a small step towards biological control will have a major impact on the goal of more sustainable food production.”

WaspAlliance has just launched a two-year trial in a kale field near Gl. Estrup by Auning.
At the field, managed by the Department of Food Science at Aarhus University, researchers led by Professor Hanne Lakkenborg are checking how effective biological control with wasps is for cabbage production compared to covering plants with plastic nets.

The research group from Ecoscience is also studying whether they can increase the number of wasps in the nests and whether the wasps are active during the same periods when the larvae cause problems for the cabbage plants.

“It is my hope that Danes will get a more positive impression of the little striped flyers and understand that they can actually be very useful to us by, among other things, providing us with pesticide-free vegetables, helping the climate, and reducing our plastic waste,” says Joachim Offenberg with a smile.

WaspAlliance is affiliated with ICROFS (International Centre for Research in Organic Food Systems) and has received funding from the Green Development and Demonstration Programme (GUDP) under the Ministry of Food, Agriculture and Fisheries.