Impacting on fruit quality and marketable yield, the Spotted Wing Drosophila (SWD), Drosophila suzukii, has become a widespread and economically damaging pest of soft fruit and orchard crops. Here Biobest IPM and Pollination Specialist David Abeijon, together with Paco Lozano – from the Biobest Academy – explain why early detection plays a vital role in effective control strategies.
Originating from South-East Asia, SWD belongs to the vinegar fly family and has become an invasive pest of fruit crops in most parts of the world, especially Europe and North America. Extremely well adapted to a wide range of fruit crops, including raspberries, blueberries, strawberries and cherries, SWD can cause complete crop loss.
What to look out for
In contrast to the ‘common vinegar fly’ (Drosophila melanogaster), SWD attacks healthy ripening fruits. Equipped with serrated ovipositors, the females penetrate the fruit skin to lay their eggs. They leave behind tiny holes, with breathing tubes protruding, which can be seen with a magnifier.
Protruding breathing tubes clearly visible on elderberry
Decomposing fig
The larvae emerge after 1-3 days and develop inside the fruit, feeding on the pulp. Causing soft sunken spots, affected fruits soon start to wilt and decompose and sometimes exude fluid. In addition to direct damage, affected fruits are susceptible to secondary diseases such as grey mould. The pupae, which appear around two weeks later, can often be seen protruding from the fruit.
Early detection key
To achieve reliable and sustainable control, early detection of the pest is vital. With no available biological solutions, growers must rely on effective and low persistence chemical pesticides. Timing of application is crucial, as effective strategies rely on keeping the pest controlled while minimising any negatives effects on established IPM strategies and locally occurring beneficials.
Tools for optimum results
“The most effective SWD monitoring tool is the red bowl-shaped Droso Trap, combined with the liquid food bait - Dros’Attract.
Picture: Dros’Attract and Droso Trap
These traps have been shown to attract more Drosophilids than other colours and shapes. In combination with Dros’Attract, the most effective food bait, captures results are over three times higher compared to when apple cider vinegar (ACV) is used.
Equally important, the combination of Droso Trap with Dros’Attract produces early captures leading to significantly earlier SWD detection in the crop – up to seven weeks sooner than with ACV (see graph below).
How to monitor?
Adult SWD hibernate in winter host plants, present in the surroundings, lying in wait for the next season.
In cases of recurrent infections, Biobest advises carrying out perimetrical monitoring as a key component of the overall preventative strategy.
For best results, traps should be placed approximately 1-1.5m above the ground, at the height SWD pest tend to fly. The adults prefer dark and humid places so trap numbers should be increased in these areas. In bushy crops, such as raspberries and blueberries, traps should be sited in the shade of the crop canopy. Each Droso Trap should be charged with 200ml of Dros’Attract and refill every two weeks.
Recognising SWD captures
The Droso Trap has been designed with small openings, to minimise non-Drosophilidae catches such as flies and wasps. However, the common vinegar fly can still be caught.
Fortunately, it is relatively easy to distinguish between the two species using visible characteristics; male SWD have spotted wings, female SWD do not have spots but do have strong serrated ovipositors.
Male SWD with spotted wings
Female SWD – no spots but strong serrated ovipositor