Combined toxicity of pesticides and heavy metals on Rhizoglyphus robini (Acari: Acaridae)

Abstract

Abstract This study investigates the combined effects of heavy metals (lead and nickel) and three pesticides (abamectin, propargite, and chlorpyrifos) on the bulb mite, Rhizoglyphus robini (Acaridae). Toxicity bioassays were conducted to determine the heavy metal ratios (HMR) and the LC 50 of pesticide alone divided by LC 50 of pesticide with heavy metal pretreatment. The results revealed that exposure to lead and nickel enhanced the toxicity of propargite and chlorpyrifos but significantly reduced the toxicity of abamectin, indicating an antagonistic effect. Specifically, for propargite, lead increased toxicity by 2.67-fold and nickel by 1.73-fold. For chlorpyrifos, lead increased toxicity by 1.75-fold and nickel by 1.17-fold. In contrast, for abamectin, lead and nickel reduced toxicity by 0.82-fold and 0.86-fold, respectively (HMR < 1), confirming an antagonistic interaction. Biochemical analyses showed that lead exposure significantly increased cytochrome P450 activity, while nickel reduced glutathione S-transferase (GST) activity. The observed changes in enzyme activities suggest that heavy metals may affect detoxification pathways. Our results highlight the importance of considering environmental contaminants when designing pest management strategies, as combined exposure to heavy metals and pesticides can either enhance or reduce the efficacy of control measures.