The prospects of new biological controls to combat spotted-wing drosophila, a serious invasive pest causing extensive economic damage in berries and stone fruit, have moved a step closer thanks to two projects involving ENDURE partners.
In the search for natural enemies of spotted-wing drosophila (SWD or Drosophila suzukii ), experts at Swiss partner Agroscope have developed a method for detecting SWD genetic material in the stomachs of predators.
Meanwhile, INRA (France’s National Institute for Agricultural Research) has taken a different tack, working in conjunction with the Centre for Agriculture and Bioscience International in Switzerland and universities in Japan and China in the search for natural enemies in south-east Asia from where SWD originates.
There are good reasons for this focus on SWD. Unlike other fruit flies it does not target rotting fruit but attacks ripening fruit and berries, burying its eggs in them and rendering them unsellable. And over the past decade it has invaded large areas of the USA as well as several countries in Europe (Belgium, France, Italy and Spain). Estimates of the damage it causes run into millions of Euros per year.
Controlling this pest with other methods is difficult since it reproduces very quickly and its larvae are well protected inside the fruit. INRA also points to the problem caused by its polyphagous nature: it is possible for SWD to feed on a wide range of wild fruit in areas that are inaccessible to chemical treatments or preventative measures, providing a natural reservoir of this pest.
Agroscope notes that studies on native parasitic wasps as antagonists have already been conducted but “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.”
In tandem with the University of Innsbruck, Agroscope experts developed a molecular method using SWD genetic material (DNA) to identify its predators. Agroscope explains: “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.”
Following this method Argoscope researchers have been 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,” it adds.
INRA reports similar success in its Asian hunt for predators. Field research identified at least eight species of parasitoid hymenoptera, some of which were brought back to France and Switzerland for further investigation under high-containment conditions. These studies have examined the specificities of their parasitical behaviour.
INRA says the preliminary results are “rather encouraging” since one candidate from the Ganaspis genus shows a clear preference for attacking SWD during the period when fruits are maturing. A further evaluation will now be conducted before any application for authorisation to introduce this insect is filed.
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Last update: 24/05/2023 - ENDURE © 2009 - Contact ENDURE - Disclaimer