Recently reported insect declines have raised both political and social concern. Although the declines have been attributed to land use and climate change, supporting evidence suffers from low taxonomic resolution, short time series, a focus on local scales, and the collinearity of the identified drivers. In this study, we conducted a systematic assessment of insect populations in southern Germany, which showed that differences in insect biomass and richness are highly context dependent. We found the largest difference in biomass between semi-natural and urban environments (−42%), whereas differences in total richness (−29%) and the richness of threatened species (−56%) were largest from semi-natural to agricultural environments. These results point to urbanization and agriculture as major drivers of decline. We also found that richness and biomass increase monotonously with increasing temperature, independent of habitat. The contrasting patterns of insect biomass and richness question the use of these indicators as mutual surrogates. Our study provides support for the implementation of more comprehensive measures aimed at habitat restoration in order to halt insect declines.

Among the many concerns for biodiversity in the Anthropocene, recent reports of flying insect loss are particularly alarming, given their importance as pollinators, pest control agents, and as a food source. Few insect monitoring programmes cover the large spatial scales required to provide more generalizable estimates of insect responses to global change drivers. We ask how climate and surrounding habitat affect flying insect biomass using data from the first year of a new monitoring network at 84 locations across Germany comprising a spatial gradient of land cover types from protected to urban and crop areas. Flying insect biomass increased linearly with temperature across Germany. However, the effect of temperature on flying insect biomass flipped to negative in the hot months of June and July when local temperatures most exceeded long‐term averages. Land cover explained little variation in insect biomass, but biomass was lowest in forests. Grasslands, pastures, and orchards harboured the highest insect biomass. The date of peak biomass was primarily driven by surrounding land cover, with grasslands especially having earlier insect biomass phenologies. Standardised, large‐scale monitoring provides key insights into the underlying processes of insect decline and is pivotal for the development of climate‐adapted strategies to promote insect diversity. In a temperate climate region, we find that the positive effects of temperature on flying insect biomass diminish in a German summer at locations where temperatures most exceeded long‐term averages. Our results highlight the importance of local adaptation in climate change‐driven impacts on insect communities.

Changes in climate and land use are major threats to pollinating insects, an essential functional group. Here, we unravel the largely unknown interactive effects of both threats on seven pollinator taxa using a multiscale space-for-time approach across large climate and land-use gradients in a temperate region. Pollinator community composition, regional gamma diversity, and community dissimilarity (beta diversity) of pollinator taxa were shaped by climate-land-use interactions, while local alpha diversity was solely explained by their additive effects. Pollinator diversity increased with reduced land-use intensity (forest < grassland < arable land < urban) and high flowering-plant diversity at different spatial scales, and higher temperatures homogenized pollinator communities across regions. Our study reveals declines in pollinator diversity with land-use intensity at multiple spatial scales and regional community homogenization in warmer and drier climates. Management options at several scales are highlighted to mitigate impacts of climate change on pollinators and their ecosystem services.

1. Climate and land-use change are key drivers of environmental degradation in the Anthropocene, but too little is known about their interactive effects on biodiversity and ecosystem services. Long-term data on biodiversity trends are currently lacking. Furthermore, previous ecological studies have rarely considered climate and land use in a joint design, did not achieve variable independence or lost statistical power by not covering the full range of environmental gradients.2. Here, we introduce a multi-scale space-for-time study design to disentangle effects of climate and land use on biodiversity and ecosystem services. The site selection approach coupled extensive GIS-based exploration (i.e. using a Geographic information system) and correlation heatmaps with a crossed and nested design covering regional, landscape and local scales. Its implementation in Bavaria (Germany) resulted in a set of study plots that maximise the potential range and independence of environmental variables at different spatial scales. 3. Stratifying the state of Bavaria into five climate zones (reference period 1981-2010) and three prevailing land-use types, that is, near-natural, agriculture and | 515 Methods in Ecology and Evoluঞon REDLICH Et aL.

Sexually dimorphic traits in insects are rapidly evolving due to sexual selection which can ultimately lead to speciation. However, our knowledge of the underlying sex-specific molecular mechanisms is still scarce. Here we show that the highly conserved gene, Doublesex (Dsx), regulates rapidly diverging sexually dimorphic traits in the model parasitoid wasp Nasonia vitripennis (Hymenoptera: Pteromalidae). We present here the revised full Dsx gene structure with an alternative first exon, and two additional male NvDsx isoforms, which gives important insights into the evolution of the sex-specific oligomerization domains and C-termini. We show the sex-specific NvDsx expression throughout development, and demonstrate that transient NvDsx silencing in different male developmental stages dramatically shifts the morphology of two sexually dimorphic traits from male to female, with the effect being dependent on the timing of silencing. In addition, transient silencing of NvDsx in early male larvae affects male genitalia tissue growth but not morphology. This indicates that male NvDsx is actively required to suppress female-specific traits and to promote male-specific traits during specific developmental windows. These results also strongly suggest that in N. vitripennis most sex-specific tissues fully differentiate in the embryonic stage and only need the input of NvDsx for growth afterwards. This provides a first insight into the regulatory activity of Dsx in the Hymenoptera and will help to better understand the evolutionary and molecular mechanisms involved in sex-specific development in this parasitoid wasp, which can eventually lead to the development of new synthetic genetics-based tools for biological pest control by parasitoid wasps.Significance StatementIn insects, male and female differentiation is regulated by the highly conserved transcription factor Doublesex (Dsx). The role of Dsx in regulating rapidly evolving sexually dimorphic traits has received less attention, especially in wasps and bees. Here, we mainly focused on Dsx regulation of two sexually dimorphic traits and male genitalia morphology in the parasitoid wasp, Nasonia vitripennis. We demonstrate that Dsx actively regulates male-specific tissue growth and morphology during specific developmental windows. These findings will help to better understand the molecular mechanisms underlying the rapid evolution of sexual differentiation and sexually dimorphic traits in insects, but may also be the starting point for the development of new tools for biological control of pest insects by parasitoid wasps.