CABI joins forces in first release of parasitic Asian wasp to fight devastating invasive fruit fly in Switzerland

CABI has teamed up with Agroscope and the phytosanitary office of the canton Ticino in the first experimental release of the parasitic Asian wasp Ganaspis brasiliensis to fight the invasive fruit fly Drosophila suzukii which has been devastating berry, stone fruit and grape crops in Switzerland.

The parasitic Asian wasp is the first exotic beneficial insect to be released for biological pest control in Switzerland since the Swiss Release Ordinance came into effect in 2008. Similar releases have also taken place this month in France and in the last three years in Italy and the USA.

Unlike already released parasitic wasps that target the invasive brown marmorated stink bug (Halyomorpha halys) in Zurich or the Comstock mealy bug (Pseudococcus comstocki) in Valais, G. brasiliensis was not previously present in Switzerland.

Scientists from CABI’s centre in Switzerland and colleagues from Agroscope – the Swiss Confederation’s centre of excellence for agricultural research – , and the phytosanitary office of the canton Ticino released around 1,000 adult Asian parasitic wasps in the Cantons of Jura and Ticino.

The Swiss Federal Office for the Environment has examined and approved the application for an experimental release permit submitted by Agroscope.

The aim is that the classical biological control agent will parasitize the larvae of D. suzukii – which is commonly known as Spotted Wing Drosophila (SWD) – and then reduce populations of the pest that attacks over 150 wild and cultivated fruits.

The release follows research conducted in 2022 – involving CABI and colleagues from Agroscope, the canton Ticino and the Institute of Agricultural Sciences (IAS) of ETH – that proved the safety of D. suzukii to tackle the SWD.

Unlike sympatric Drosophila species in invaded areas, D. suzukii females are able to lay eggs inside unwounded ripening fruits due to their specialized egg-laying organ. This is equipped with saw teeth, providing it with a unique niche virtually free from competition.

The resulting high abundance of D. suzukii has led to extensive damage, making it a major problem for fruit growers around the world including the Swiss high stem stone fruit industry for which significant economic losses have already occurred.

The invasive spotted-wing drosophila Drosophila suzukii laying eggs in a cherry (Credit: CABI, Tim Haye).

Following the latest release of the parasitic Asian wasp, the scientists will intensively monitor the area and determine whether it can become established in Switzerland and help reduce the SWD population in a safe and sustainable way.

Dr Dominique Mazzi is a scientist at Agroscope and was previously Head of the Drosophila suzukii Task Force which was set up in collaboration with the Research Institute for Organic Agriculture (FiBL) and other partners from research, extension, practice, and enforcement.

The aim of the task force was to develop sustainable pest-control strategies for farmers to protect Switzerland’s berries, fruits and vines from SWD.

Dr Mazzi said, ″Since Drosophila suzukii also infests fruit growing in the wild outside of agricultural production, large-scale, long-term measures are required to contain the unhindered reproduction of the invader there as well.″

The quest for such a beneficial insect began in 2015, when various research groups, including scientists from CABI, undertook initial studies in Asia. The researchers found the parasitic Asian wasp, a natural predator of the spotted-wing drosophila.

Dr Lukas Seehausen, Research Scientist, Risk Analysis & Invasion Ecology at CABI, said, ″Before a release of this type, years of studies on biosafety are required. The main focus of this is to analyse the risk of negative effects on domestic species.

″Our research findings have shown that Ganaspis brasiliensis is specialized in spotted-wing drosophila and that it is highly unlikely that it parasitizes larvae of native fruit flies.″