WenJun Zhang School of Life Sciences, Sun Yat-sen University, Guangzhou, China Network Biology ISSN 2220-8879 http://www.iaees.org/publications/journals/nb/online-version.asp 2027 17 1 76 101 International Academy of Ecology and Environmental Sciences Hong Kong 11 February 2026 26 May 2026 1 March 2027 insect decline butterflies wild bees ants functional extinction rate heterogeneity critical decoupling network robustness extinction debt ecological network resilience conservation early warning Global declines in insect populations have attracted attention, yet most assessments focus on counts and species richness rather than the erosion of ecological functions. Here, I ask when major terrestrial insect taxa (butterflies, bees, and ants) will cease to perform their roles at levels sufficient for ecosystem integrity. I synthesize data from 73 historical reports, 166 long-term surveys across 1676 sites, 40 additional studies, and systematic reviews of global change impacts. Using a Bayesian hierarchical approach that accounts for spatial and taxonomic heterogeneity, I estimate annual declines of 1.5-2.5% for butterflies, 1.8-3.5% for wild bees, and highly variable ant trajectories from local stability to 42-54% functional collapse in invaded areas. I introduce a multidimensional functional extinction threshold integrating three dimensions: minimum functional population, a network decoupling index quantifying keystone connectivity loss, and a functional performance baseline at 30% of historical levels. Building on critical slowing down theory, I propose the Critical Network Decoupling Hypothesis, in which ecological networks initially compensate via interaction redundancy, then enter a decoupling phase with rising variance and loss of synchrony among keystone species, culminating in abrupt functional collapse. I further propose the Life History Buffer Hypothesis to explain taxon-specific differences in decline timing based on generation time, dietary specialization, and sociality. Our models predict that specialized pollination by long-tongued wild bees will reach functional extinction thresholds between 2030 and 2050 in temperate regions, butterfly-mediated networks around 2060, and native ant seed dispersal in tropical forests between 2050 and 2080. I introduce the Functional Loss Acceleration index as a more sensitive early warning metric than conventional population trends. These findings call for a paradigm shift from species-counting to network function protection, providing a science-based early warning framework to prevent irreversible ecosystem function collapse. http://www.iaees.org/publications/journals/nb/articles/2027-17(1)/decline-rate-estimations.pdf