Climate, latitude, and land cover predict flying insect biomass across a German malaise trap network

Using data from the first year of a new, long-term, standardized German Malaise Trap Program coordinated by the German Long-Term Ecological Research network, we apply an ecological gradients approach to examine the effects of climate and land cover on flying insect biomass. We hypothesized that biomass would display a unimodal relationship with temperature, consistent with thermal performance theory, would decrease with precipitation due to reduced flying activity, and would decrease in areas with more heavily human-modified land cover. Flying insect biomass was quantified from malaise traps at 84 locations across Germany throughout the 2019 growing season. We used an AICc approach to parse drivers of temperature, deviation in 2019 temperature from long-term averages, precipitation, land cover, geographic coordinates, elevation, and sampling period. We further examined how effects of temperature on insect biomass change across space by testing for interactions between temperature and latitude. Flying insect biomass increased linearly with monthly temperature across all samples. However, positive effects of temperature on flying insect biomass declined with latitude, suggesting the warm 2019 summer temperatures in southern Germany may have exceeded local insect optimums, and highlighting the spatial variation in climate change-driven impacts on insect communities. Land cover explained less variation in insect biomass, with the largest effect being lower biomass in forested sites. Future work from this newly begun German Malaise Trap Program will add a multi-year dimension to this large-scale, distributed sampling network, with the aim of disentangling the roles of multiple drivers on flying insect communities.