A DEB-TKTD model for assessing the combined effects of imidacloprid, temperature and food availability on aquatic insects.

Mayflies and other aquatic insects are considered key species in environmental risk assessments of pesticides, particularly due to their sensitivity to neonicotinoids. While toxicity tests of pesticides are often conducted under laboratory controlled conditions, these organisms under environmentally relevant scenarios face numerous variable environmental factors including food availability, temperature, and chemical exposure. To investigate the influence of these environmental factors on toxicity, we developed Dynamic Energy Budget (DEB) based toxicokinetic-toxicodynamic (TKTD) models for Chironomus riparius and Cloeon dipterum exposed to the neonicotinoid insecticide imidacloprid. The models were parameterized using experimental data on feeding, mobility, and survival across various toxicant concentrations. Our findings reveal that, at constant exposure concentrations, the severity of effects is driven more by the duration of exposure (acute or chronic) than by the timing of exposure initiation. In batch exposure scenarios, the rate of decrease in toxicant significantly affects outcomes. Temperature primarily affects species sensitivity to the compound during short-term exposures, while food availability is more crucial in longer exposures. Survival to pupation/emergence is predominantly influenced by the toxicant concentration. C. riparius demonstrated sharp responses to concentration changes, while C. dipterum exhibited more gradual effects and heightened sensitivity to environmental variability.