SLU news

Spread of the invasive pest Drosophila suzukii is monitored with help of hobby growers

Published: 13 November 2019

The fruit fly Drosophila suzukii that is a major pest on soft summer fruits such as blueberries and raspberries is spreading in Sweden. But how far has it spread? In a citizen science project, Paul Becher together with Isabella Kleman have investigated this. In 2018, traps were distributed to hobby growers and the fly was found as far up as Stockholm. This year, a new project has started to see if Drosophila suzukii has spread even further north.

Drosophila suzukii, commonly called the spotted wing drosophila, is a fruit fly that originates from southeast Asia and became a major pest species on soft-skinned fruit in America and Europe. D. suzukii infests fruit early during the ripening stage, in contrast to other Drosophila species that infest only overripe fruit. Therefore, it is a serious economic threat to soft fruit such as cherries, blueberries, raspberries, blackberries, peaches, nectarines, apricots and grapes.

Detected in Sweden 2014

D. suzukii was first detected in Sweden 2014 and since then regular monitoring has been carried out, but focus has mainly been on the southernmost parts of Sweden.

– In an effort to map the distribution in other parts of Sweden, we conducted a citizen science monitoring project in 2018. Hobby growers organised in allotment associations across the country were contacted regarding the project, and 8 associations participated, says project leader Paul Becher.

Easy-to-use traps were distributed

Last year, single use D. suzukii traps were sent out, ten to each participant, with the containers and packaging needed to return the trapped insects. With the help of private contacts and travelling to place traps a total of 21 locations were sampled.

– We could see that D. suzukii was present not only in Skåne but also in several locations further north up to, and including, Stockholm, says field assistant Isabella Kleman.

– We did however not find D. suzukii in the few sampled locations in Dalarna, Västmanland and Värmland. The hobby growers were informed of the results, and some showed an interest in participating in a second monitoring effort in 2019, says Paul Becher.

Drosphila suzukii is spreading in Sweden

For the 2019 monitoring project, focus was placed on the middle areas of Sweden, just north of the northernmost findings of D. suzukii in 2018. Participants from the previous year were contacted, and with the help of the Swedish hobby gardeners’ association (Fritidsodlingens riksorganisation) an additional 25 interested participants in the areas of interest were found, adding up to a total of 37 participants.

– Traps were sent out during September. By now most of the trapped insects have been sent back and counting is underway. So far, D. suzukii has been found in multiple new locations. It would seem that the fly is still on the move, unfortunately increasing its area of distribution considerably since last year, concludes Isabella Kleman.


Contact

Portrait photography of a man.Paul Becher

Researcher at the Department of Plant Protection Biology

paul.becher@slu.se
Telephone: 040-415305
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