Extensive regional variation in the phenology of insects and their response to temperature across North America

Peter O. Dunn, Insiyaa Ahmed, Elise Armstrong, Natasha Barlow, Malcolm A. Barnard, Marc Bélisle, Thomas J. Benson, Lisha L. Berzins, Chloe K. Boynton, T. Anders Brown, Melissa Cady, Kyle Cameron, Xuan Chen, Robert G. Clark, Ethan D. Clotfelter, Kara Cromwell, Russell D. Dawson, Elsie Denton, Andrew Forbes, Kendrick Fowler, Kevin C. Fraser, Kamal J. K. Gandhi, Dany Garant, Megan Hiebert, Claire Houchen, Jennifer Houtz, Tara L. Imlay, Brian D. Inouye, David W. Inouye, Michelle Jackson, Andrew P. Jacobson, Kristin Jayd, Christy Juteau, Andrea Kautz, Caroline Killian, Elliot Kinnear, Kimberly J. Komatsu, Kirk Larsen, Andrew Laughlin, Valerie Levesque‐Beaudin, Ryan Leys, Elizabeth Long, Stephen C. Lougheed, Stuart Mackenzie, Jen Marangelo, Colleen Miller, Brenda Molano‐Flores, Christy A. Morrissey, Emony Nicholls, Jessica M. Orlofske, Ian S. Pearse, Fanie Pelletier, Amber L. Pitt, Joseph P. Poston, Danielle M. Racke, Jeannine A. Randall, Matthew L. Richardson, Olivia Rooney, A. Rose Ruegg, Scott Rush, Sadie J. Ryan, Mitchell Sadowski, Ivana Schoepf, Lindsay Schulz, Brenna Shea, Thomas N. Sheehan, Lynn Siefferman, Derek Sikes, Mark Stanback, John D. Styrsky, Conor C. Taff, Jennifer J. Uehling, Kathleen Uvino, Thomas Wassmer, Kathryn Weglarz, Megan Weinberger, John Wenzel, Linda A. Whittingham

Climate change models often assume similar responses to temperatures across a species range, but local adaptation or phenotypic plasticity can lead plants and animals to respond differently to temperature in different parts of their range. To date, there have been few tests of this assumption at the scale of continents, so it is unclear if this is a large-scale problem. Here, we examined the assumption that insect taxa show similar responses to temperature at 96 sites in grassy habitats across North America. We sampled insects with Malaise traps during 2019-2021 (N = 1041 samples) and examined the biomass of insects in relation to temperature and time of season. Our samples mostly contained Diptera (33%), Lepidoptera (19%), Hymenoptera (18%), and Coleoptera (10%). 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. For example, biomass of nematoceran flies increased across the season in the central part of the continent, but it only showed a small increase in the northeast and a seasonal decline in the southeast and west. At a smaller scale, insect biomass at different traps operating on the same days was correlated up to about 75 km apart. Large-scale geographic and phenological variation in insect biomass and abundance 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 large-scale predictions about changes in insect populations, and their causes, will need to incorporate regional and taxonomic differences in the response to temperature.