Stoneflies (Insecta, Plecoptera) of the Midwest, USA: species checklist derived from nearly 170 Years of collection records.

BACKGROUND: The landscape in the Midwest, USA (limited to the states of Illinois, Indiana, Iowa, Michigan, Minnesota, Ohio and Wisconsin) has undergone dramatic shifts from the historic natural settings to agricultural and urbanised landscapes over the past two centuries following European colonisation. These shifts have restructured community assemblages and species distributions of aquatic insects, particularly stoneflies, an insect order susceptible to regional and local extirpations following anthropogenic, climatic and environmental alterations. Within the Midwest, species extirpations at a broad scale have been documented for multiple states, including Illinois, Indiana, Michigan and Ohio. Illinois and Minnesota appear to have lost endemics to extinction. To better understand how species distributions have shifted over the past two centuries, we have compiled records of species occurrences from the mid-19th century to the present day. NEW INFORMATION: In preparation for a comprehensive assessment of the Midwest stonefly fauna, we present a species occurrence dataset composed of approximately 50,000 records. This dataset spans from the early 1860s through 2025. These data have been compiled from 26 regional natural history museums, a review of published literature records and collecting efforts by the authors since 1987. This dataset presents occurrence records for 157 regional species from 41 genera, representing nine of ten Nearctic stonefly families. Of these species, 21 are new state records, including three species recorded for the first time within the Midwest region. The new state records include two from Illinois, two from Indiana, one from Iowa, one from Michigan, nine from Minnesota, five from Ohio and seven from Wisconsin. Overall, these updates bring the total known richness for Illinois to 85, Indiana to 93, Iowa to 47, Michigan to 71, Minnesota to 65, Ohio to 109 and Wisconsin to 68. State richness declines along east-west and south-north gradients. The five most species-rich families were Perlidae (n = 42), Perlodidae (n = 38), Capniidae (n = 21), Chloroperlidae (n = 15) and Nemouridae (n = 15). The contemporary Midwest fauna is diminished compared to historical community richness and composition, through both regional and state extirpations and extinctions. Despite intensive contemporary collection efforts throughout the region, 13 species are known solely from historical collections. Each Midwest state experienced extirpations. The greatest losses occurred in Illinois, with 16 species that were absent in collections made after 1970. This was followed by Indiana (n = 9), Michigan (n = 8), Ohio (n = 8), Minnesota (n = 7), Wisconsin (n = 2) and Iowa (n = 1). The greatest losses were within the families Perlidae and Perlodidae, with 17 and eight species extirpated from at least one state by 1970, respectively.