Vienna Study: Fruit Fly Species Diversity Drops by Around Half Over Three Decades

Two Species Dominate the Traps

According to the researchers, it is striking that two species now dominate the populations. The most frequently found was Drosophila mercatorum with around 8,800 records, followed by D. melanogaster with about 6,700 specimens. According to the team, this shift is accompanied by a loss of rarer species.

Kapun explained that the populations in the Vienna urban area are "dominiert von Generalisten mit starker Affinität zum Menschen". This refers to species that are well adapted to human-shaped habitats and displace other, more sensitive species.

Generalists Displace Rare Species

For the research team, the observed differences in species abundance and community composition reflect "bedeutende ökologische und biologische Veränderungen". Such shifts are considered in biodiversity research as an indicator of stress on urban ecosystems.

Citizen Science as a Method

The study deliberately relies on the help of ordinary citizens. Citizen scientists took over setting up the traps, collecting, and returning the samples. Kapun emphasized that long-term monitoring of Drosophila – supported by citizen science – would represent an "effektiven und anpassungsfähigen Ansatz zur Erfassung von Veränderungen der Biodiversität in einer sich rasant wandelnden Welt".

The authors see the project as a template for future monitoring programs. Through broad participation, large amounts of data can be gathered over the years that would be difficult to collect with purely scientific staff alone.

A Signal for Urban Ecosystems

The findings from the Vienna team are also part of a larger picture: internationally, studies also show that insect populations in cities and agricultural landscapes are declining. According to Kapun, fruit flies are particularly well suited as bioindicators because they are sensitive to environmental changes and can be recorded using simple methods.

NHM Vienna announced that it would continue the "Vienna City Fly" program in the coming years and expand it to other regions. The goal is to document the development of insect diversity over the coming decades and compare it with earlier data series.