Earthworms as Integrative Bioindicators of Soil Health in Agroecosystems under Chemical and Plastic Stress

Agricultural soil health assessment continues to focus heavily on chemical fertility despite the fact that soil functioning is highly mediated by biological communities and the structures they form. The earthworms are the only useful indicators in that they are sensitive to disturbance and also control aggregation, porosity, residue turnover, nutrient mineralization, and microbial habitats. This review is a synthesis of evidence on earthworms as integrative bioindicators of the state of agroecosystems under synthetic pesticides, plastic residues and microplastics, and biopesticide-based management. Web of Science, Scopus, PubMed, and Google Scholar were searched systematically to identify studies published between 2000 and early 2026 that correlated earthworm measures with soil functions. Recent synthesis shows that earthworms are involved in approximately 6.5 percent of the world grain production and 2.3 percent of the legume production, highlighting their agronomic importance (Fonte et al., 2023). In pesticide research, the most common negative effects are reproduction, behavior, growth, and biochemical biomarkers; a general hazard assessment found negative responses in 87.7% of earthworm survival parameters, 82.7% of reproduction parameters, and 80.6% of behavioral parameters in laboratory exposure conditions (Gunstone et al., 2021). In the case of microplastics, a recent meta-analysis of 2,124 observations of 102 articles revealed a decrease in survival and growth, increased oxidative stress, and impaired gut microbial diversity, and biodegradable polymers were not necessarily less harmful than conventional plastics (Zhong et al., 2026). In comparison, existing data on biopesticides tends to indicate reduced non-target interference at recommended concentrations, but formulation impacts and multiple applications are not well-investigated. The literature suggests that abundance and biomass continue to be valuable field diagnostics, but reproduction, avoidance behavior, and function-related measures like aggregate stability and enzyme activity give earlier and more mechanistic warning signals. It is suggested to use an earthworm-based indicator panel in intensified tropical and subtropical agroecosystems, especially in the context of Indian agroecosystems where pesticide inputs and agricultural plastics are becoming more and more co-located.