Ecotoxicological effects and risk of novaluron-based insecticides and vegetable oil to non-target in-soil organisms

Insecticide application is the strategy mostly used to combat insect pests, especially in monocultures like soybean. There is an increasing demand for the development of more efficient, eco-friendly, and target-specific active substances (a.s.), like novaluron, which is an insect growth regulator acting in the inhibition of chitin synthesis. Several insect pests, like the fall armyworm, have been successfully combated using multi a.s. pesticides composed of novaluron and methomyl. Moreover, the application of these Plant Protection Products (PPPs) can be more efficient when adjuvants, like vegetable oil, are mixed before their application. However, there is a lack of knowledge about the risk posed by novaluron-based insecticides and the adjuvant vegetable oil, namely for soil non-target organisms. Aiming to fill this knowledge gap, laboratory reproduction tests were performed with the soil non-target invertebrate species considered in the data requirements for PPPs environmental risk assessment, i.e., the earthworm Eisenia andrei, the collembola Folsomia candida, the predatory mite Hypoaspis aculeifer, following standard guidelines. The toxicity-exposure ratio (TER) was used to estimate the risk based on a single application for soybean crops. Tested formulations with vegetable oil (Veget'Oil®) and novaluron (Rimon® 100 EC) presented no risk for all tested species, but the one with novaluron + methomyl (Voraz®) evidenced risk for all of them. Results indicate that the toxicity of novaluron-based insecticides can be more relevant when novaluron is combined with other a.s. Moreover, even when the risk of the novaluron pesticides is low, they should be seen with concern due to their considerable persistence in soil.