What did we learn from meta-analyses about farmland arthropod conservation?

Quantitative evidence syntheses appeared in agroecological research in the early 2000 and gained momentum during the last decade for summarising the growing knowledge about the importance of farmland biodiversity conservation. Among other evidence syntheses, meta-analyses have a significant role in quantitatively synthesising findings of primary studies, typically in the frame of systematic reviews. Here we provide a global overview via a scoping review of the essential quantitative synthesis studies testing land-use extensification or diversification effects on arthropod biodiversity. Most meta-analyses showed a positive impact of the studied different extensification or diversification measures on arthropod species richness, with varying effects depending on the studied arthropod functional group, ecosystem, measure type, and landscape context. Our findings highlight a serious research gap from the tropics, envisage future directions of agroecological meta-analyses, and provide recommendations for insect conservation in farmland. Finally, we finish our review by emphasising the importance of closing the science-policy gap in order to support the transformative change in the European food system.