The herbicide diuron and the insecticide imidacloprid are amongst the most frequently detected pesticides in French rivers, and each is known to affect many aquatic organisms. However, it is less examined whether and how both pesticides together might induce multistress conditions, which could induce indirect effects such as modification of biological interactions within freshwater microbial communities. This study was undertaken to determine the effect of diuron and imidacloprid alone and in combination on the feeding behavior of chironomid larvae. A first experiment measured the impact of the different contamination conditions at environmental concentrations (5µg L-1 for each pesticide) on the grazing rate of chironomids on three microalgae species, independently. Therefore, two diatom species, Gomphonema gracile (two different morphotype: normal (GG) and teratogen (GT)) and Planothidium lanceolatum (PL), and one green algae Pseudokirchneriella supcapitata (PS) were offered as food, during 24h. Protein and lipid contents in microalgae were analysed subsequently. Each pesticide condition elicited a different grazing rate in chironomids with regards to algal species and their nutritional quality, with a general preference for Gomphonema gracile with teratogen shape and Pseudokirchneriella supcapitata. In a second experiment (cafeteria), food selectivity of chironomids was determined under similar contamination conditions during 4h: Under diuron, larvae switched equally among microalgae, then were as mobile as in the control without pesticide. However, imidacloprid and the pesticide mixture condition altered chironomids' movements and grazing behaviour. In these experiments, we highlighted that chironomids feeding behaviour and food preferences are impacted by pesticides. Herbicide and insecticide exposure, alone or in combination, had contrasting effects on grazing, both directly on the larvae or indirectly (food selectivity according to its quality). Our study illustrates the value of considering the impacts of toxicants on target and non-target organisms across trophic levels to improve ecotoxicological risk assessment in an ecosystemic perspective.