How Agroscope researchers are developing biological control strategies against the invasive Japanese beetle. An on-site visit of the EU project IPM Popillia in the Piedmont region.

In the morning of 6 July 2022, a white van turns into a dirt track in the village of Landiona in the province of Novara. After a few metres it stops. A man and a young woman get off and walk to the small wood at the edge of a field. The man is Dr Giselher Grabenweger, an entomologist at Agroscope, the federal government’s centre of excellence for agricultural research, and coordinator of the EU project IPM Popillia. The young woman, Tanja Sostizzo, is a staff member and PhD student in the Popillia team. The two left early in the morning from the Ticino to inspect their field trial in Piedmont. «The best time for you to visit our experimental field in Italy is during peak flight time of the Japanese beetles, then we can show you what we are doing,» Giselher Grabenweger suggested when we met him at Agroscope in Zurich in April for a preliminary discussion.

«You have to fight
both beetles and larvae,
otherwise the population
will always recover.»

That’s why we await the entomologist and his colleague on this hot summer morning at their experimental field near Landiona. «Sorry we’re late,» the two arrivals greet us from afar and then lead us to the first of three low wooden racks at the edge of the grove. A plexiglass pane is mounted on the rack, which bears a small hole, where a capsule emits lures to attract the Japanese beetles. The beetles fly against the pane and fall into an open tub. The tub contains a thick layer of substrate covered with spores of an entomopathogenic fungus. They crawl over the fungus carpet to the edges of the tub, infect themselves with fungal spores and fly away. In a few days they will die from the fungal infection, but until then they should infect as many conspecifics as possible. The strategy of controlling pests with certain types of fungi has long been used in Switzerland with great success against the native cockchafer, which is related to the Japanese beetle. «We have gained experience in the development and application of this method at Agroscope over many years, so it was only reasonable to test it also against the Japanese beetle,» says Giselher Grabenweger. Field trials like this one in Piedmont and another in the Ticino will show whether this control strategy works. «We installed the insect traps here at the end of June. The location between the edge of the forest and a new blueberry plantation is ideal. During the flying season, someone from the team now comes by every week, checks whether the traps are intact and takes samples of beetles and the fungus substrate,» the entomologist explains as he and his colleague inspect the first of the three traps. «There are very few beetles in there, so we probably have to replace the substrate. And the capsule with the attractant also seems to have dried out,» comments Giselher Grabenweger, while Tanja Sostizzo starts collecting beetle samples from the traps, from the blackberry bushes at the edge of the forest and the blueberry bushes in the field. In the laboratory in Zurich, they will be examined by her doctoral colleague Magdalena Wey to see whether and to what extent the beetles are infected with the fungus. Meanwhile, Giselher Grabenweger looks at the other two traps. Everything fine, they work perfectly.

The beetles

After about three quarters of an hour, the inspection is completed. We get into our car and follow the white van along the country road towards the north-east. After ten kilometres, it turns onto a dusty dirt road and stops behind a farm at the edge of a large field planted with blueberry bushes. Many farmers in this area produce berries in addition to rice, maize or soya, as these bring in a good income. The field belongs to a farmer who practices organic farming and allows access to his plantations, Giselher Grabenweger explains to us as we walk with him through the blueberry field. Thousands of beetles are sitting on the bushes. They cling to the branches like grapes, eat leaves and berries, copulate and swarm out or fall to the ground when we shake the branches. The air above the field seems full of beetles. «The farmer stopped harvesting blueberries two weeks after the beetle flight started. The beetle infestation became so severe that it was no longer worth picking the few ripe berries that were still intact,» the entomologist explains. PhD student Tanja Sostizzo has unloaded large plastic containers from the van and starts collecting beetles. The blueberry plantation here serves the researchers as a kind of control field and complements their field experiments. A part of the collected beetles will be used in the laboratory in Zurich to examine which proportion of the population is infected by the fungi. A second part will be infected in the lab to observe the fungus’ efficacy. Lab experiments are done under strict quarantine conditions.

The larvae

Experiments to control the pest with fungi are not limited to the beetles themselves. The scientists are also targeting their larvae in the soil. Since 2020, Giselher Grabenweger and his team have been conducting trials on three fields in the Piedmont and one in the Ticino with fungi that are supposed to attack the grubs underground and kill them. The team is using native fungal strains from Switzerland and the Piedmont for this purpose. After one Japanese beetle season, the first results are available, which Giselher Grabenweger summarises as follows: «We can say that we actually had little success with the experiments using fungi against the larvae. For whatever reason, the grubs are very resistant to the fungi we used, even at a high number of spores. Quite in contrast to the adult beetles. The beetles are very susceptible and both the laboratory and semi-field trials show that the beetles can be decimated very well with the fungi.» This year, Giselher Grabenweger wants to verify these results with another series of field trials he and his team set up in the Piedmont and the Ticino.

«There are regulatory
mechanisms in the soils
that we do not know yet.»

However, controlling the beetles alone will not be enough, explains the entomologist, while Japanese beetles are constantly swarming around our heads. «The problem is: if you want to achieve a really significant reduction in the population, you have to act against both, beetles and larvae. That means you also have to find something to treat the grubs, otherwise the population will always recover. And at the moment it looks like nematodes rather than fungi could be efficient against the grubs.» Right at the beginning of the project, the insect specialists in the IPM Popillia consortium agreed on a dividing project work. While the Agroscope team focuses on controlling the larvae and beetles with fungi, the Italian colleagues from the federal agricultural research institute CREA* concentrate on trials with nematodes. These now appear to be promising against the grubs. «That is the great advantage of such EU projects. You can work together with many excellent colleagues, complement each other and thus save a lot of work for the individual scientist,» says Giselher Grabenweger.

Interactions in the soil

The field and laboratory trials of Giselher Grabenweger and his team are one of two «work packages» for which Agroscope is responsible within the IPM Popillia project. The aim is to provide a toolbox of effective, integrated control measures against the Japanese beetle as quickly as possible, and thus prevent its spread to other areas of Europe. The second «work package», for which molecular biologist Dr Jürg Enkerli and his team at Agroscope are responsible, deals with the complex interactions between the microorganisms, the entomopathogenic fungi and their host larvae, as well as the conditions in the different soils and soil types. For the researchers, it is still a mystery why the Japanese beetles multiply explosively in certain soils, but can hardly develop in other plots that lie nearby. «Apparently, there are regulatory mechanisms in the soil that influence this and which we do not know yet. My colleague Jürg Enkerli is on the trail of these together with doctoral student Noëmi Küng,» Giselher Grabenweger explains and laughingly adds: «I am the fire brigade and he works on fire prevention.» In fact, Jürg Enkerli’s «work package» links applied and basic research. The knowledge he gains from the IPM Popillia project will be of importance far beyond the control of Japanese beetles.

«If you keep on searching
long enough, you can
actually find a natural
antagonist to every pest.»

In the meantime, a car has stopped at the edge of the field and a man in a red T-shirt gets off. It is Giovanni Bosio from the phytosanitary service of the Piedmont region. He also needs a few more bugs, he says with a laugh as he greets us. He and Giselher Grabenweger know each other well, because the phytosanitary service is an important partner of the IPM Popillia consortium in Piedmont. They observe the current development of the beetle infestation in the region very closely, search for suitable trial fields and arrange contacts with the farmers.

By now it is noon and the sun is burning relentlessly on the rice and blueberry fields. Tanja Sostizzo empties the last bottle of collected Japanese beetles into the large collection container, stows the approximately 20 litres of crawling beetle mass well secured in the cooling box and closes the back door. Giselher Grabenweger starts the engine and the white van rolls along the dusty dirt road back towards the Ticino. There is still much more to do there today.

*CREA: Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria

Interview with Giselher Grabenweger (in German)