Butterflies have a hard time in the cultural landscape that is used intensively in many places. However, the switch to organic farming can help moths and other insects, as a study from southern Germany has now shown. Accordingly, the number of species and the frequency of butterflies in the area of organically farmed fields are 60 percent higher than in conventional fields. Obviously, the rare and endangered species benefit particularly strongly.
Researchers have long been observing a drastic decline in insects in Germany and throughout Europe. According to a long-term study published in autumn 20178, the biomass of flying insects in German nature reserves has decreased by 76 percent in 27 years. The number of butterflies in field-close meadows has decreased by two thirds, as another study showed in 2019.
Insect survey in organic and normal farming
Now researchers with Axel Hausmann from the Munich Zoological State Collection are adding another interesting aspect to these findings. Because they have investigated whether and how the insect population of meadows differs from conventional or organically farmed fields. In contrast to the previous studies, they not only used one parameter – biomass, number of animals or biodiversity – as an indicator of insect diversity and frequency, but also captured all of these parameters. This was made possible by a combination of two catching methods: the classic malaise traps for insects flying during the day and light traps for nocturnal arthropods. All catches were weighed for biomass determination, counted and assigned to a species using DNA barcoding. The traps were active from April to October 2018.
The evaluation showed clear differences between the insect populations in the environment of organic and conventionally cultivated fields. “Our data reveal a higher biomass and a greater biodiversity in organic agriculture and twice the amount of endangered nocturnal butterflies compared to conventional locations,” report Hausmann and his colleagues. The total biomass of insects in organic farming was 2.6 times higher than in the area of conventionally cultivated fields. The number of species was ten to 30 percent higher, depending on the location of the trap.
Especially butterflies and endangered species benefit
The differences were particularly pronounced in the butterflies: With the light traps, the scientists caught a total of 256 moth species on the ecological sites and 222 on the sites near conventional fields. The frequency was also higher: one and a half times as many moths were trapped in organic farming. The differences in the Malaise traps were even more pronounced: “The ecologically managed field environment brought 4.3 times more butterflies than the traps near the conventional fields,” the researchers report.
The evaluations also showed clear advantages for rare and endangered species of butterflies: With 30 species, the scientists found twice the number of endangered butterfly species from the Red List on the organically farmed areas than on the conventionally managed areas. “Our data show that red list species mainly occur in close ecological fields,” said Hausmann and his team. “This is in line with studies showing that more specialized species, which are often on the red list, are particularly hard hit by the intensification of agriculture.”
These results only come from a small pilot study with few areas. That is why the researchers next want to continue and expand their sampling as part of a five-year research program. Nevertheless, her study already provides indications that organic farming helps to reduce the loss of species in agricultural areas.
Source: Bavarian State Natural Science Collections; Technical article: Ecology and Evolution, doi: 10.1002 / ece3.6166