Abstract

Herbicides are widely used in modern agriculture to control weeds and maintain crop productivity, but their persistence in soil raises concerns about unintended effects on non-target organisms. Pendimethalin, a dinitroaniline herbicide extensively applied to cereal and vegetable crops, is designed to target plant microtubules and is generally considered unlikely to pose genotoxic risks to animals. However, information on its sublethal effects on beneficial soil arthropods remains limited. In this study, we investigated the cytotoxic and histopathological effects of a commercial pendimethalin-based formulation on the ground beetle Pterostichus melas italicus, an ecologically relevant predatory species in agroecosystems. Adult males collected from an organic farm were exposed under laboratory conditions to soil treated at the recommended field dose and maintained for up to 7 days, corresponding to subchronic exposure. Individuals were sampled after 2 and 7 days, and the midgut and Malpighian tubules were analysed using histological and transmission electron microscopy. Exposure induced marked but non-lethal ultrastructural alterations, particularly in the Malpighian tubules, including reduction in the basal labyrinth, cytoplasmic vacuolisation, mitochondrial swelling, increased phagolysosome abundance, and nuclear karyorrhexis. These effects were transient under laboratory conditions and occurred without detectable impacts on survival, highlighting the Malpighian tubules as sensitive targets for the early detection of herbicide-induced physiological disturbances. However, the observed recovery may reflect compensatory physiological processes that could entail energetic costs and, under field conditions characterized by multiple concurrent stressors, potentially compromise physiological performance and predatory efficiency. Consequently, this study underscores the necessity of integrating sublethal ultrastructural biomarkers into environmental risk assessment frameworks for non-target beneficial insects.

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