Effects of thiamethoxam on Hypoaspis aculeifer: the role of predator–prey interactions and soil properties

Increasing agricultural production has led to a rise in the use of pesticides to control organisms that may cause production losses. Among the most widely used pesticides are neonicotinoid insecticides, such as thiamethoxam, which act on the nervous system of arthropods causing the death of both target and non-target organisms. Their toxicity assessment is usually conducted without considering predator–prey interactions and more realistic exposure pathways. In this study, the effects of thiamethoxam on the survival and reproduction of the predatory mite Hypoaspis aculeifer when exposed alongside the springtail Folsomia candida , their only food source, in two soil types, were evaluated. For the experiments,10–12 days old F. candida and 28–35 days old H. aculeifer were used. The organisms were exposed to concentrations ranging from 0.4 to 7.0 mg thiamethoxam/kg of dry soil in Tropical Artificial Soil (TAS) and 0.3 to 5.5 mg/kg in Concretionary Petric Plinthosol (FFc). After 28 days of exposure, H. aculeifer reproduction showed to be dependent on soil properties, with a EC 50 of 3.3 in TAS and 5.5 in FFc, and the prey content and nutritional quality. The number of juveniles produced in the control group was 91 times lower for organisms fed with F. candida , in comparison to mites fed with Tyrophagus putrescentiae, showing that F. candida may not be a suitable food in the conditions tested. Hence, although it is very important to consider predator-prey interactions in ecotoxicological assessments, and F. candida is mentioned in the OECD guideline as a suitable food for the ecotoxicological experiments using H. aculeifer , it is still necessary to refine the exposure conditions to allow an optimal predator species reproduction, and then be able to assess the impacts of contaminants. Once established, these experiments shall be employed in environmental risk assessment frameworks.