Biodiversity – With a wasp against the invasive cherry vinegar fly – News


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The spotted-wing drosophila is devastating in berry, stone and fruit growing. Now she should have an opponent.

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They like what we like: raspberries, strawberries – and especially cherries. Since the spotted drosophila was introduced to Switzerland in 2011, fruit farmers have complained about a 30 percent loss of income.

The worst affected are farmers who have standard fruit trees. Because you can’t span them with fine fly screens. According to Lukas Seehausen, a fruit fly specialist at the Cabi research institute in Delsberg in the Jura, cherries are lost quite often.

Legend:

A spotted-wing fly, perched on a grape.

KEYSTONE/DPA/Fredrik von Erichsen

“The high-stem fruit farmers are now so far that they want to give up,” says Seehausen. For them, it’s about thinking about sawing off such tall trees.

Bad for biodiversity

This would be a severe loss for a large number of animal and plant species. Because meadow orchards with standard fruit trees are now a rare habitat.

The reason why the drosophila is so harmful is that it can do something that others cannot. As Seehausen explains, it’s a fly that can lay eggs through the skin of fresh fruit.

In the end, it is not the fly that comes out, but the parasitic wasp.

The native fruit flies cannot do that. So large fly maggots can already feast on ripe cherries or raspberries.

The Battle of the Incarcerated

In order to change that, Seehausen releases the antagonist of the cherry vinegar fly – imported from Asia with official permission. These are tiny parasitic wasps, 1.5 millimeters in size.

This type of wasp also lays its eggs through the skin of the fruit – and further into the larvae of the spotted-wing drosophila: “Then the larva of this parasitic wasp develops in the larva of the spotted-wing drosophila. And in the end it’s not the fly that comes out, but the parasitic wasp,” explains Seehausen.

Invasive Species: The threat is global


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The spotted-wing drosophila is not the only invasive species causing global problems. A new report of the World Biodiversity Council shows that invasive species are increasing around the world. We currently know of around 200 species that are added every year, says Hanno Seebens from the Senckenberg Biodiversity and Climate Research Center in Frankfurt am Main. To date, that makes a total of more than 37,000 species that live in places where they are not actually native.

This number is likely to continue to rise in the future, according to Seebens. Because the drivers of the spread are known: These are, for example, international trade, but also private air travel or climate change. “All of these processes are increasing and have intensified,” says Seebens. “And there’s no reason to believe that it shouldn’t develop in the same way in the coming decades.”

Releases of such parasitic wasps in Canada and Italy gave cause for optimism, the fruit fly specialist continues. The number of cherry vinegar flies is reduced in this way – how quickly and to what extent exactly is still an open question.

Could slip vest cause problems?

But does it really make sense to fight invasive species with other introduced species? Couldn’t the newly introduced parasitic wasp cause problems for other species? This is exactly what Seehausen investigated. You can’t rule it out 100 percent, but: “Through the tests we’ve done, we can rule that out almost 99 percent.”

The researchers tested whether the parasitic wasps from Asia also damage native fruit flies. They didn’t – at least for the time being. Because that can probably only be clarified with certainty and finally much later.

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