As a PhD student at the aquatic research institute Eawag, Elena Gimmi closely studied the tripartite relationship between the black bean aphid (Aphis fabae), a tiny parasitoid wasp (Lysiphlebus fabarum) and the bacterium Hamiltonella defensa. She was supervised by Prof. Christoph Vorburger and Prof. Jukka Jokela. Vorburger’s research group has been following the interplay between the three different organisms for years. Laboratory experiments showed that the bacterium H. defensa lives in the body of the bean aphid as a symbiont. It receives “board and lodging” from the aphid and, in return, protects it against parasitic wasps, the larvae of which devour the aphid. The bacteria presumably produce toxins which kill the eggs of the wasp.

Comprehensive range of data obtained in the field – despite Covid

Elena Gimmi has tested predictions obtained from basic laboratory research in wild populations under natural conditions for the first time. She examined in particular the patterns and seasonal dynamics in the resistance of the aphids. “I found it exciting and challenging to compare known results from laboratory testing with observations obtained from the real world,” says the environmental biologist.

The centrepiece of Gimmi’s work was a large-scale field study conducted over a two-year period. In three different areas around Zurich, Gimmi tracked the abundance of the bacteria in the aphids on a monthly basis. Over the same period of time, she also investigated how the risk of the aphid being parasitised by the wasp changed. “It was clear from the start that a lot of things could essentially go wrong. However, thanks to a combination of persistence and luck, the original plans for my thesis turned out quite well,” says Gimmi in retrospect.

“A tremendous amount of time and effort went into the field work. This was reflected in the high quality of the data collected, which allowed us to ascertain a significant number of new and important findings.”

Christoph Vorburger

Christoph Vorburger emphasises: “A tremendous amount of time and effort went into the field investigations. This was reflected in the high quality of the data collected, which allowed us to ascertain a significant number of new and important findings.” However, the important second year of the field project was put at serious risk by the Covid pandemic. The researcher quickly set up a home laboratory for the study of small insects with the help of her father and engaged her brother as a field assistant. This ensured a continuous flow of data and made it seem as though there had never been any lockdown. Vorburger: “That really was a great effort and I am also very grateful to Elena’s family for their support.”