Sensitivity of aquatic insect eggs to elevated fine sediment and phosphate concentrations in rivers

Insect populations are declining at an alarming rate, globally. Aquatic insects live as larvae in rivers before hatching as terrestrial flies, reproducing and laying eggs onto the water surface or marginal areas. Aquatic insects have a crucial functional role in the environment and are used to monitor stream impairment.
Despite the significance of aquatic insects, the majority of research is focused on the larval stage of these animals, with very little consideration of eggs. This is despite pollutants having potentially greater effects on early life stages that are typically the least mobile and most vulnerable to stressors. An exception is the work of Everall et al. (2018) who found eggs of the mayfly Serratella ignita were significantly impacted by chronic low dosages of fine sediment (FS) and orthophosphate (OP), well below legal thresholds in the UK and internationally. It is, therefore, essential that greater focus is given to the impacts of pollutants on insect eggs, rather than solely focusing on larvae. OP and FS are the leading cause of degradation to freshwater systems internationally. Legal thresholds of pollutants in rivers are largely based on larval tolerances and on annual average concentrations calculated from monthly measurements, not accounting for shortterm peaks in pollutant concentrations that could be highly significant.