Responses of aphid and ladybird to lead transfer through soil and broad beans

The impact of heavy metals on agricultural ecosystems has consistently been a topic of social concern. This study investigated the translocation of lead (Pb) along the soil – Vicia faba L. (Fabales: Fabaceae) – Megoura crassicauda (Hemiptera: Aphidoidea) – Harmonia axyridis (Coleoptera: Coccinellidae) system. Lead in soil could be transferred to broad bean, and the accumulation amount was highest in roots, followed by stems and leaves. Aphids and ladybirds could also accumulate lead through the food chain. Interestingly, the lead content of broad bean roots in the aphid feeding group was significantly higher than that in the non-aphid feeding group. Lead stress significantly reduced the germination rate and seedling height of broad bean, and inhibited root elongation. The expression levels of trehalase (TRE), trehalose-6-phosphate synthase (TPS), and vitellogenin (Vg), TRE activity, and carbohydrate content in aphids changed under lead treatment. The number of offspring produced by the second and fifth generation aphids was significantly reduced under lead treatment. Furthermore, high concentrations of lead treatment can prolong the development time of the 2nd and 3rd instar larvae of the ladybird. Feeding on aphids contaminated with lead can affect the survival of ladybirds. Our results further confirm the biological transfer of lead in the food chain and explore the adaptive mechanisms of aphids and ladybirds. These relevant results provide a theoretical basis for further exploring the molecular mechanism of lead homeostasis in plants and insects under lead stress.