The spotted-wing drosophila (SWD or Drosophila suzukii) is an introduced vinegar fly species that causes serious damage in Swiss crops. Unlike native vinegar flies, it can attack undamaged, ripening fruit and berries by laying its eggs in them. The affected fruit rots quickly, thus becoming unmarketable.

Tricky to control

Controlling SWD is difficult, since it reproduces very quickly and its larvae are well protected inside the fruit. In addition to physical control methods such as covering the orchards with nets, natural antagonists of SWD could also play a role in its control in the future.

Several studies on native parasitic wasps as antagonists have already been conducted. However, we remain largely in the dark as to which predators make a meal of SWD. Field observations do not readily yield an answer and laboratory feeding trials reflect the reality in the field only to a limited extent.

Who’s eating Drosophila suzukii?

Headed by Dr Jana Collatz and in collaboration with Prof. Michael Traugott and his ‘Applied and Trophic Ecology’ research group at the University of Innsbruck, Agroscope experts have developed a molecular method that utilises the genetic material (DNA) of Drosophila suzukii to identify its predators. For this, two short pieces of DNA (so-called ‘primers’) were designed which specifically bind to the DNA of the spotted-wing drosophila, but not to that of other vinegar-fly species. Now potential predators can be investigated: predatory arthropods such as insects and spiders are collected in the field and tested in the laboratory using the new method. When a predator has consumed an adult, larva or egg of spotted-wing drosophila, the DNA of SWD will also be contained in its stomach. In this case, the specific primer pair binds to the drosophila DNA. In a subsequent step, the bound piece of DNA can be replicated and made visible. If no Drosophila suzukii DNA is found in the predator’s stomach, no signal is generated.

Using this method, Agroscope experts were able to prove that earwigs, spiders, predatory bugs and a few rove beetles had eaten SWD. The method is easy to use and can contribute to the identification of further predators of Drosophila suzukii. This will allow us to better protect, or specifically promote, such predators.

References

Wolf S, Zeisler C, Sint S, Romeis J, Traugott M, Collatz J (2018). A simple and cost-effective molecular way to track predation on Drosophila suzukii in the field. Journal of Pest Science 91: 927-935, doi: 10.1007/s10340-017-0948-7

Which Predators Make a Meal of Drosophila suzukii?