Leuven, 15/10/2024 – It's no secret fruit flies are attracted to beer. Setting aside a glass of beer is a common practice to lure pesky insects away from a summer barbeque. Research by Belgian and German scientists now shows that not all fruit fly species like the same beers. This discovery could lead to the development of better strategies to control harmful insects in agriculture.
Different beers, different fruit flies
Beer comes in many types and flavors. The uniqueness of a beer's flavor is the result of a specific set of ingredients and a meticulous brewing process. Scientists at the VIB-KU Leuven Center for Microbiology in Belgium, in collaboration with colleagues from the German Max Planck Institute for Chemical Ecology, and the Belgian company BioBest, have investigated which aromas attract fruit flies. The results show that, much like humans, flies prefer some types of beer over others. And that's more important than one might think…
The study concentrated on two types of fruit flies - the innocent Drosophila melanogaster, which can often be found circling overly ripe fruit at home, and Drosophila suzukii, which is a serious plague because it lays eggs in unripe fruit such as grapes and berries, leading to immense damage in agriculture.
"Across the world, D. suzukii causes millions in damages in fruit farming," explains Maria Dzialo, first author of the study."Because of climate change, the species is expanding its territory, with enormous economic and ecologic consequences."
Blonde or brown ale? A distinct preference.
At first sight, it might seem a bit strange to research the beer preferences of fruit flies. However, beer contains hundreds of natural aroma substances produced by plants and microbes, similar to the compounds that flies encounter in nature. Based on detailed chemical analysis of 250 Belgian beers, the scientists selected 45 beers with widely divergent aroma profiles to uncover which beers attract the most fruit flies. Tests revealed that D. suzukii has a distinct preference for hoppy blonde beers and tripel, while D. melanogaster prefers brown and amber beers, as well as fruity, high-fermentation beers.
"Blonde beers and tripels contain herby and hoppy aromas that are comparable to green, ripening fruit. Ales contain more esters, acids and phenols that are typically found in ripe fruits," explains Kevin Verstrepen, director of the VIB-KU Leuven Center for Microbiology. Both fruit fly types are attracted by beer scents that are also found in their natural habitats.
Chemical analyses confirm that yeast fragrances, such as pentylacetate (aroma of banana) and ethylacetate (sweet, fruity scent) are more attractive to D. melanogaster, while plant fragrances such as linalool (citrus and sweet scent) and geraniol (floral, fruity) are more to the taste of D. suzukii.
Brain activity reveals preference
Fruit flies detect smells through receptors in their antennae. Earlier studies have shown that attractive or repellent fragrances activate specific nerve cells expressing these receptors. While examining brain activity in response to specific beer aromas, the researchers identified measurable differences between the two species.
"For example, we observed stronger brain activity in D. melanogaster than in D. suzukii when exposed to geraniol", explains Silke Sachse from the Max Planck Institute for Chemical Ecology. "This activity occurred in a brain region responsible for aversion to scent. This suggests that geraniol could serve as a deterrent for D. melanogaster but won't have a repellent effect on D. suzukii."
Future perspectives for sustainable agriculture
These discoveries could lead to innovative solutions in managing annoying or harmful insects. Increasingly, insects are being controlled through sustainable methods, such as traps that do not rely on poisonous chemicals.
"By understanding which substances attract specific insects, we can develop targeted traps. This benefits both consumers and farmers while minimizing impact on other, beneficial insects," adds Professor Verstrepen. "For example, our experiments suggest that certain plants such as laurel and thyme could be deployed strategically to lure pests like D. suzukii away from fruit plants without using chemical agents. Tests in industrial greenhouse settings already confirmed that we can compose mixes of a few beer aroma compounds that attract more D. suzukii than D. melanogaster, showing the potential of our findings for pest control in biological agriculture."
The results of this study offer hopeful perspectives for more sustainable insect control measures. "And of course, it's also good to know which beers won't attract flies when you're out for a drink," says Verstrepen jokingly.
