Freshwater insect abundance trends vary between continents and families

With concern mounting that insect biodiversity is being harmed by human activities there is an urgent need for robust evidence to support or refute these contentions.  This is particularly critical in freshwaters which are widely considered among the most threatened ecosystems on earth.  In many high-income countries, river insect communities have been regularly sampled for decades for national water quality monitoring purposes.  Here, such data, from Europe, the Americas, Oceania, South Africa and South Korea, have been compiled and analysed using linear mixed-effects models to quantify trends in the abundance and prevalence of insect families.  Time series (>9-year span and with >9 sampling occasions) extended from 1965-2023 with the vast majority of being from Europe and most sampling effort occurring post-1985.  Across all time series, there were many more insect families with increasing than decreasing abundance trends; particularly among the Plecoptera, Trichoptera and Diptera.  Leuctridae, Glossosomatidae and Empididae were among the families with the most pronounced increases in abundance while those in decline included Capniidae, Uenoidae and Culicidae.  There was not a consistent pattern in trends of abundance across all locations for individual insect families, with different territories potentially being subject to different pressures or at different stages along the environmental degradation/recovery trajectory.  We produce a multi-family index of fitted trends using state-space models that propagate uncertainty associated with individual family trends.  Recovery trajectories are evident in Europe and Oceania but not so in South Korea or North America. The extent to which intrinsic biological traits can account for variation in trends between taxa was explored.  Insect families with a greater prevalence of omnivory and with a lesser prevalence of predation were more likely to be increasing in abundance. We demonstrate that re-purposing freshwater bioassessment datasets has potential to fill knowledge gaps on state and trends in the abundance of aquatic insects.