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

Authors: DUNN, PETER - University Of Wisconsin; AHMED, INSIYAA - Us Army Corp Of Engineers (USACE); ARMSTRONG, ELISE - Siena Heights University; BARLOW, NATASHA - Birds Canada; BARNARD, MALCOLM - Baylor University; BELISLE, MARC - Universite De Sherbrooke; BENSON, THOMAS - University Of Illinois; BERZINS, LISHA - University Of Saskatchewan; BOYNTON, CHLOE - Canadian Wildlife Service; BROWN, T - Trinity College; CADY, MELISSA - Us Fish And Wildlife Service; CAMERON, KYLE - Birds Canada; CHEN, XUAN - Salisbury University; CLARK, ROBERT - University Of Saskatchewan; CLOTFELTER, ETHAN - Amherst College; CROMWELL, KARA - University Of Montana; DAWSON, RUSSELL - University Of North British Columbia; Denton, Elsie

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2023
Publication Date: 3/21/2023
Citation: Dunn, P.O., Ahmed, I., Armstrong, E., Barlow, N., Barnard, M.A., Belisle, M., Benson, T.J., Berzins, L.L., Boynton, C.K., Brown, T.A., Cady, M., Cameron, K., Chen, X., Clark, R.G., Clotfelter, E.D., Cromwell, K., Dawson, R.D., Denton, E.M., et al. 2023. Extensive regional variation in the phenology of insects and their response to temperature across North America. Ecology. 104(5). Article e4036. https://doi.org/10.1002/ecy.4036.
DOI: https://doi.org/10.1002/ecy.4036

Interpretive Summary: Decline in insect abundance is one of the novel challenges of the Anthropocene, yet sufficient studies do not yet exist in most locations to document or explain it. This paper compiles data from 96 sites over the course of three years in open grassy habitats in North America, all of which were collected in a consistent fasion. We found that temperature and region were the most important predictors of insect abundance, with eastern regions and warmer temperatures generally having more insects. While most insects increased in biomass throughout the season, Nematocerans, small flies such as midges and mosquitos decreased at later dates, and true bugs showed no response in abundance to date. We also estimated the sample size that would be necessary to detect a both a 1% and 5% decline in insect population. A study of a similar size and geographic would require at least 5 years of data to detect such a decline (5%), or 8 years (1%).

Technical Abstract: Climate change models often assume similar responses to temperatures across the range of a species, 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, the 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 ~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.