Ecotoxicological effects of a matrine-based botanical insecticide on edaphic invertebrates in a tropical soil

Botanical insecticides are gaining space as crop protectants due to their safety profile (e.g., perceived lower toxicity to non-target organisms and increased biodegradability) compared to synthetic pesticides. In this line, matrine - a quinolizidine alkaloid obtained from the roots of a Chinese medicinal plant ( Sophora flavescens Aiton) – stands out due to its potency against arthropod pests of agricultural relevance. However, its potential ecotoxicological effects toward non-target soil invertebrates are still poorly understood. In this context, this study aimed to assess the ecotoxicity of a matrine-based commercial formulation (Matrine®) on the survival and reproduction of earthworms ( Eisenia andrei Bouché), enchytraeids ( Enchytraeus crypticus Westheide & Graefe), and collembolans ( Folsomia candida Willem). The avoidance behavior of earthworms ( E. andrei ) exposed to soils spiked with the matrine-based botanical insecticide was also assessed. Ecotoxicological assays were performed in a clayey loam soil (Oxisol) from Brazil following ISO protocols. Matrine-based formulation reduced the reproduction of all tested species, but the magnitude of the effects varied among species. Earthworms were the most sensitive organisms (EC 50 = 173.8 mg kg −1 ), followed by enchytraeids (EC 50 = 408.4 mg kg −1 ) and collembolans (EC 50 = 1418 mg kg −1 ). The earthworm's avoidance behavior (LOEC = 9.3 mg kg −1 ) was more sensitive than survival (LOEC >600 mg kg −1 ) and reproduction (LOEC = 75 mg kg −1 ). These findings warn of the hazards of a widely used botanical insecticide toward non-target soil organisms in a natural tropical soil.