The Suzuki fruit fly has gained a new natural enemy in the Netherlands. Researchers at Wageningen University & Research (WUR) have released Asian parasitic wasps for the first time as biological control agents against this invasive pest. "This is an important step towards a more manageable population," says researcher Herman Helsen.
© Herman Helsen, WUR - NFO
The parasitic wasp lays an egg in the larva of the Suzuki fruit fly, which lives under the skin of fruit
"At several locations in the central Netherlands, we release parasitic wasps of the species Ganaspis kimorum. This parasitic wasp originates from Asia and is an important natural enemy of the Suzuki fruit fly there." The parasitic wasps were brought to the Netherlands from Switzerland in April and propagated at the WUR lab in Randwijk. They are now being deployed in areas with many wild blackberries and other ripening fruit, which are preferred breeding sites of the Suzuki fruit fly. There, researchers expect the parasitic wasps to reproduce on the Suzuki larvae and gradually spread. Ultimately, this should result in a smaller Suzuki population and reduced pressure on fruit crops. Releases will continue until 2026 at several locations in the Netherlands.
Strict rules for introduction
"The release of insects is strictly regulated," Helsen stresses. "Ganaspis kimorum has been studied for years in laboratories in Switzerland and other countries. This wasp is very effective against the Suzuki fruit fly and leaves other, native insects unharmed." In 2024, Wageningen University & Research submitted a comprehensive authorisation dossier. Based on this, the Dutch government granted permission for a controlled release early this year.
Exotic fly is pest for fruit growers
The Suzuki fruit fly (Drosophila suzukii) is native to Asia and reached Europe and the United States via fruit shipments in 2008. In the Netherlands, the species was first recorded in 2012. Unlike native fruit flies, the female lays her eggs in intact, ripening soft fruit, such as cherries, strawberries, and raspberries. The larvae feed inside the fruit, causing it to rot quickly and become inedible. The Dutch climate, characterized by humid conditions with mild winters and summers, is ideal for this fruit fly, making it a serious pest for fruit growers and allotment holders.
Clever parasitic wasp knows how to find larvae
The females of the released Asian parasitic wasps lay their eggs in young Suzuki larvae inside fruit. To do this, they actively search for ripening fruit still on the bush or tree. As they move over the fruit, they use their antennae and ovipositor to detect larvae inside. Once they find one, they pierce the skin with the ovipositor and lay an egg in the larva. As a result, it develops not into a fruit fly but into a new parasitic wasp.
Suzuki fruit fly outsmarts European parasitic wasps
European parasitic wasps are largely ineffective against the Suzuki fruit fly. They usually hunt for prey on the ground, where native fruit fly larvae develop in rotting fruit or plant waste. The Suzuki fruit fly, however, is found in intact fruit on bushes and trees, and is therefore rarely encountered by these wasps. Moreover, Suzuki larvae have a defence system that recognises and encapsulates the eggs of European parasitic wasps, preventing them from developing. Ganaspis kimorum can bypass this defence and locate larvae in fruit still hanging on the plant.
© Herman Helsen, WUR - NFO
A Suzuki fruit fly lays an egg under the skin of soft, ripening fruit, such as cherry, strawberry, and raspberry
Good survival prospects for parasitic wasp
Ganaspis kimorum is found in large parts of Asia, including areas with a climate similar to that of the Netherlands. Researchers, therefore, expect it to overwinter successfully. Because the wasp depends on the Suzuki larvae, releases are carried out in places with long-term ripening fruit, and thus a stable fruit fly population. Next year, these locations will be checked to see if the parasitic wasp has established itself.
Not a cure-all, but an important step
Will this solve the Suzuki problem? No, says Helsen: "This fruit fly has established itself worldwide because it has no natural enemies outside Asia. In the Netherlands, there are more than 50 plant species on which it can live. This allows it to reproduce anywhere in the landscape, creating a constant influx into orchards and making control difficult. By introducing a specialised natural enemy, we can slow population growth. This helps reduce crop pressure, but additional measures in orchards remain necessary."
Application in fruit crops
In the future, parasitic wasps may also be used directly in fruit crops as part of sustainable pest management. In greenhouse horticulture, this method is already used successfully against other pests. For use in fruit crops, it is important that parasitic wasps can be produced efficiently and cost-effectively. Wageningen University & Research is studying this in collaboration with Koppert, a producer of biological control agents. Using natural enemies such as ichneumon wasps aligns with the broader search for green alternatives to chemical crop protection.
Source: NFO