Professor University of Wisconsin-Milwaukee MILWAUKEE, Wisconsin, United States
Abstract: Declines in insect diversity and abundance have been reported from around the world, but the evidence for these declines has largely been drawn from local studies focused on specific taxa or pooled estimates from all taxa. Understanding how insects respond to climate change and other drivers across a large scale requires comprehensive, large-scale sampling with coordinated protocols. Here, we describe the phenology and abundance of insects collected in Malaise traps using a standardized protocol at 96 sites in open, grassy habitats across North America (N = 1041 samples). Over three years (2019-2021), we found strong regional differences in the phenology of insects and their response to temperature, even within the same taxonomic group, habitat type and time of season. Using standardized protocols and samples sizes similar to this study (131 samples/year), we estimate that 5 or 1% declines in insect abundance across North America could be detected with just 1 to 5 more years of sampling. Geographic and phenological variation has not been studied well, and it is a major source of controversy in previous analyses of insect declines that have aggregated studies from different locations and time periods. Our study illustrates that changes in insect abundance across North America will be difficult to detect unless studies incorporate knowledge of the phenology of specific taxonomic groups
