Systematic Continental Scale Monitoring by Weather Surveillance Radar Shows Fewer Insects Above Warming Landscapes in the United States.

Anthropogenic change is predicted to result in widespread declines in insect abundance, but assessing long-term trends is challenging due to the scarcity of systematically collected time series measurements across large spatial scales. We develop a novel continental-scale dataset using a nationwide network of radars in the United States to generate a 10-year time series of daily aerial insect density and assess temporal trends. We do not find evidence of a continental-scale net decline in insect density over the 10-year period included in this study; instead we find a mosaic of increasing and declining trends at the landscape scale. This spatial variation in density trends is associated with climatic drivers, where areas with warmer winters experience greater declines in insect density and areas with cooling winter trends see increases in density. Winter warming has a stronger negative effect on density at higher latitudes. After assessing temporal trends, we also use the 10-year dataset and atmospheric variables to model insect aerial abundance, finding that on a typical summer day approximately a hundred trillion (1014) flying insects are present in the airspace, representing millions of tons of aerial biomass. Our results provide the first continental-scale quantification of insect density and its response to anthropogenic warming and demonstrate the utility of weather surveillance radar to provide large-scale monitoring of insect abundance.