No effect of Agri-Environment Schemes on radar-measured aerial insect abundance at landscape scale in England

Agri-environment schemes (AES) commonly represent the largest financial investment in biodiversity conservation at a national or international level, but evidence for AES intervention effectiveness remains equivocal. Here, we develop a novel and general method for assessing the impact of conservation interventions using Weather Surveillance Radar (WSR) to produce spatially explicit time series of aerial insect abundance over 1,597 km2 of agricultural land in England from 2015-2022. Using this dataset, we evaluated the landscape-scale causal effect of AES across 15 natural experiments involving paired AES and control sites. We find no natural experiment which indicates a positive causal effect of AES on aerial insect abundance at levels of expenditure ranging from £34 km-2 to £5,122 km-2. When considering all 1597 km2 of agricultural land covered by the radars, we also find a weak but significant negative correlation between AES and aerial insect abundance, with stronger, positive relationships between aerial insect numbers and the percentage cover of woodland and semi-natural grassland. Our results provide the most robust evaluation of the benefits of AES and indicate that AES are not working to conserve aerial insects, assuming that WSR accurately captures the landscape-scale abundance of insects from 500-700 m above sea-level. We demonstrate the utility of landscape-scale conservation impact assessment using WSR-measured insect abundance, a technique which may be broadly applicable to problems in insect conservation science.