Asian parasitoid wasp helps fruit growers combat the spotted-wing drosophila

The spotted-wing drosophila (Drosophila suzukii), originally from Asia, has been causing major damage in Dutch fruit cultivation for years. Since its arrival in Europe, this insect has put the cultivation of cherries, raspberries, strawberries and other soft fruits under pressure. Unlike native fruit flies, the female lays its eggs not in rotting fruit but in ripening, intact fruit still on the plant. The larvae feed from the inside, causing the fruit to rot quickly and become unsaleable.

“D. suzukii can multiply extremely rapidly in the Netherlands because it has no natural enemies here,” says WUR researcher Herman Helsen, who has been studying this pest for more than ten years. “The species has spread worldwide through trade and can live in the Netherlands on more than fifty plant species. This means it can reproduce almost anywhere in the landscape, which makes control difficult.”

The fly was brought to Europe in 2008 with imported fruit from Asia and was first recorded in the Netherlands in 2012. The humid climate, with mild winters and summers, turns out to be ideal for this species. Cherry growers in particular suffer from it: even with fine-mesh insect netting, pest pressure remains high. Just a few flies entering can already cause significant damage.

European parasitoid wasps do not know how to deal with D. suzukii. They search mainly on the ground, where larvae of native fruit flies develop in rotting fruit or plant debris. D. suzukii, by contrast, develops inside intact fruit on shrubs and trees, making it almost impossible to find. In addition, D. suzukii larvae possess a defence system that recognises and encapsulates the eggs of European parasitoid wasps, preventing their development.

The Asian parasitoid wasp Ganaspis kimorum can bypass this defence system. This wasp, originating from the same habitat as D. suzukii, actively searches with its antennae and ovipositor for young D. suzukii larvae inside the fruit. When it finds one, it inserts its ovipositor through the skin and lays an egg in the larva. As a result, the larva does not develop into a fruit fly but into a new parasitoid wasp.

Before this parasitoid wasp was released in the Netherlands, years of careful research were carried out. In laboratories in Switzerland and other countries, tests were conducted to determine whether Ganaspis kimorum targets only D. suzukii. The wasp recognises its host by specific odours emitted only from fruit infested with D. suzukii larvae. As a result, it ignores other fruit flies and leaves native insects unharmed. Only once this strong specialisation was convincingly demonstrated did Wageningen University & Research dare to take the next step.
In 2024, WUR submitted an extensive approval dossier to the Dutch government. Based on this, the authorities granted permission in early 2025 for a controlled introduction. “The release of insects is strictly regulated,” Helsen emphasises. “But this wasp has been thoroughly studied, is highly effective against the spotted-wing drosophila, and leaves native insects unharmed.”

In April 2025, the first parasitoid wasps arrived from Switzerland at the WUR laboratory in Randwijk, where they were further bred. In summer 2025, the first releases took place at several locations in the central Netherlands, mainly in areas with many wild blackberries and other ripening fruits - favourite breeding sites of D. suzukii.

Researchers expect the parasitoid wasps to reproduce on D. suzukii larvae and gradually spread. Because Ganaspis kimorum occurs in regions with climates similar to that of the Netherlands, its chances of survival are good. The development will be closely monitored over the coming years to see whether the wasp can establish itself permanently and to what extent it reduces the population of D. suzukii.

Does that mean the D. suzukii problem is solved? No, says Helsen: “This fruit fly managed to establish worldwide because there were no natural enemies outside Asia. By now introducing a specialised natural enemy, we can slow the growth of the D. suzukii population. This helps reduce pressure on crops, but additional measures in the field will still be needed.”
In the longer term, parasitoid wasps could perhaps also be deployed directly in fruit crops as part of sustainable pest management. This approach is already used successfully in greenhouse horticulture against other pests.

The project demonstrates how fundamental research, international collaboration and strict regulation come together in the search for sustainable solutions – with nature itself as a key ally.

WUR research into natural enemies of the spotted-wing drosophila offers promising prospects for biological pest control in fruit production. It reduces dependence on chemical crop protection products and contributes to more sustainable production.