First field estimation of greenhouse gas emissions from European soil-dwelling Scarabaeidae larvae targeting the genus Melolontha

Arthropods are a major soil fauna group, and have the potential to substantially influence the spatial and temporal variability of soil greenhouse gas (GHG) sinks and sources. The overall effect of soil-inhabiting arthropods on soil GHG fluxes still remains poorly quantified since the majority of the available data comes from laboratory experiments, is often controversial, and has been limited to a few species. The main objective of this study was to provide first insights into field-level carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) emissions of soil-inhabiting larvae of the Scarabaeidae family. Larvae of the genus Melolontha were excavated at various grassland and forest sites in west-central and southern Germany, covering a wide range of different larval developmental stages, and larval activity levels. Excavated larvae were immediately incubated in the field to measure their GHG emissions. Gaseous carbon emissions of individual larvae showed a large inter- and intra-site variability which was strongly correlated to larval biomass. This correlation persisted when upscaling CO₂ and CH₄ emissions to the plot scale. Field emission estimates for Melolontha spp. were subsequently upscaled to the European level to derive the first regional GHG emission estimates for members of the Scarabaeidae family. Estimates ranged between 10.42 and 409.53 kt CO₂ yr^-1, and 0.01 and 1.36 kt CH₄ yr^-1. Larval N₂O emissions were only sporadically observed and not upscaled. For one site, a comparison of field- and laboratory-based GHG emission measurements was conducted to assess potential biases introduced by transferring Scarabaeidae larvae to artificial environments. Emission strength and variability of captive larvae decreased significantly within two weeks and the correlation between larval biomass and gaseous carbon emissions disappeared, highlighting the importance of field measurements. Overall, our data show that Scarabaeidae larvae can be significant soil GHG sources and should not be neglected in soil GHG flux research.