Several studies have taken place throughout the years focusing on the toxicity of several chemicals to organisms when using food level ranges. Barry et al. (1995) reported that the toxicity of esfenvalerate to Daphnia carinata was increased as food concentration decreases, a synergistic effect also observed by Takahashi and Hanazato ( Takahashi and Hanazato, 2007) when daphnid sensitivity to carbaryl was tested using high and low food levels, while the opposite trend was observed when the toxicity of endosulfan increased with higher food concentrations. For the same pesticide, esfenvalerate, a study by Beketov and Liess (2005) on the survival and reproduction of the mayfly C. dipterum, showed that with lower food levels, sensitivity to the chemical was increased. It was also reported an increasing sensitivity of Daphnia magna and Daphnia cf. longispinaclones to the herbicide propanil when food supply was decreased ( Pereira and Gonçalves, 2007 and Pereira et al., 2007). Antunes et al. (2004) reported that lindane toxicity to daphnids depends on the food level, while it suggested that further studies needed to be carried out using food as an important factor for evaluating the toxicity of chemicals. Results from the present study are in accordance with most of the studies using pesticides and low food levels, indicating an increasing sensitivity of the daphnids with decreasing food levels and increasing chemical concentration. However, studies like Barry et al. (1995) show that the pattern of combined effects of chemicals and food levels could mainly depend on the chemical. In addition, Jeon et al. (2010) stresses out that the importance of particles presence in theenvironment, such as food and clay, which can play a significant role in regulating the toxicity of several chemicals.