Organic farming fosters arthropod diversity of specific insect guilds – evidence from metabarcoding

Abstract

During the past decades, insect diversity, abundance and biomass has decreased throughout Central Europe, mainly due to agricultural intensification. Organic field management aims to counteract this negative trend. In order to investigate the effects of farming intensity on insect diversity, abundance, and biomass, we sampled insects from 2021 to 2023 on three organically and three conventionally managed meadows in southern Germany using Malaise traps. All individuals collected were subsequently analysed using metabarcoding, and BINs were determined. All identified taxa were then classified according to their characteristics and performance during the developmental and adult stage. All bulk samples were dried and weighted for the determination of biomass. BIN diversity of flying insects was 11% and biomass 75% higher on organically managed meadows compared to conventional ones. Although all functional guilds were more diverse on organic meadows, species overlap between management types was moderate and ranged from 60 to 76%, indicating that both, conventional and organic meadows harbour specific and species rich insect communities. Our trait-analyses showed that both habitat structure as well as resource availability strongly impacted the occurrence of species and diversity. The observed differences in diversity mainly result from the higher mowing frequency applied to conventionally managed meadows. Our study highlights that organic and conventional farming both have potential to maintain a high insect diversity and biomass in agricultural landscapes if some basic prerequisites for population survival are fulfilled.