The Effects of Temperature Variation on the Sensitivity to Pesticides: a Study on the Slime Mould Dictyostelium discoideum (Protozoa)

Slime moulds live in agricultural ecosystems, where they play an important role in the soil fertilization and in the battle against crop pathogens. In an agricultural soil, the amoebae are exposed to different stress factors such as pesticides and weather conditions. The use of pesticides increased up from 0.49 kg per hectare in 1961 to 2 kg in 2004, and the global greenhouse gas emission has grown 70 % between 1970 and 2004 leading to a global fluctuation of average surface temperature. Therefore, the European Directive 2009/128/EC has led to a new approach to agriculture, with the transition from an old concept based on high use of pesticides and fossil fuels to an agriculture aware of biodiversity and health issues. We studied the effects of temperature variations and pesticides on Dictyostelium discoideum. We measured the fission rate, the ability to differentiate and the markers of stress such as the activity and presence of pseudocholinesterase and the presence of heat shock protein 70. Our results highlight how the sensitivity to zinc, aluminium, silver, copper, cadmium, mercury, diazinon and dicofol changes for a 2 °C variation from nothing/low to critical. Our work suggests considering, in future regulations, about the use of pesticides as their toxic effect on non-target organisms is strongly influenced by climate temperatures. In addition, there is a need for a new consideration of the protozoa, which takes into account recent researches about the presence in this microorganism of classical neurotransmitters that, similar to those in animals, make protozoa an innocent target of neurotoxic pesticides in the battle against the pest crops.