Abstract

Aquatic insects represent one of the most diverse and ecologically important groups in freshwater ecosystems, yet their thermal adaptations and responses to anthropogenic climate change remain poorly understood. This study examines thermal tolerance, physiological adaptations, and behavioral responses of aquatic insects across multiple taxonomic orders including Ephemeroptera (mayflies), Plecoptera (stoneflies), Trichoptera (caddisflies), and Diptera (true flies) in response to increasing water temperatures and habitat modification. We conducted laboratory thermal tolerance experiments, field surveys across temperature gradients, and molecular analyses of heat shock protein expression in 25 species from temperate and tropical freshwater systems. Results indicate significant interspecific variation in thermal tolerance, with critical thermal maxima (CTmax) ranging from 28.3°C in cold-adapted stoneflies to 42.7°C in tropical chironomids. Heat shock protein expression increased 3-8 fold above baseline temperatures, with HSP70 showing the strongest response. Field surveys revealed upstream range shifts averaging 127 m elevation per decade in montane streams, with cold-adapted species experiencing the greatest distributional changes. Behavioral thermoregulation, including vertical migration and microhabitat selection, emerged as critical short-term responses to thermal stress. These findings demonstrate that aquatic insects exhibit diverse thermal adaptation strategies, but many species, particularly cold-adapted specialists, face significant risks from continued warming. Understanding these thermal responses is crucial for predicting ecosystem-level impacts and developing effective conservation strategies for freshwater biodiversity.