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Simple Summary: Zinc is a vital nutrient required by all living organisms; however, its impact varies based on Zn concentration and chemical form. This study examined the effect of zinc chloride (ZnCl2) and zinc sulfate (ZnSO4) on the life history performance and hemolymph metabolism of the common moth, Spodoptera litura, which is known to damage many crops. We found that, while low levels of ZnCl2 benefit the reproduction of Spodoptera litura, higher levels of ZnCl2 prolong the preadult developmental period and decrease the preadult survival rate. Additionally, dietary ZnSO4 exerts a devastating effect on the survival of S. litura larvae, even at the lowest concentration. This helps us better understand the effect of the chemical forms and concentrations of zinc on the biological processes and toxicological impacts on insects. Zinc is an essential micronutrient crucial in various biological processes of an organism. However, the effects of zinc vary depending on its chemical form. Therefore, the aim of this study was to conduct a comparative analysis of the life history performances and hemolymph metabolism of Spodoptera litura exposed to different concentrations of dietary zinc chloride (ZnCl2) and zinc sulfate (ZnSO4), utilizing two-sex life tables and untargeted metabolomics. The preadult survival rate of S. litura significantly decreased, while the preadult developmental period of S. litura was prolonged as the dietary ZnCl2 concentration increased. However, the fecundity of S. litura at 50 mg/kg dietary ZnCl2 was significantly increased. The intrinsic rate of increase (r) and the finite rate of increase (lambda) in S. litura in the control group (CK, no exogenous ZnCl2 or ZnSO4 added) and with 50 mg/kg dietary ZnCl2 were significantly higher than those at 100 mg/kg, 200 mg/kg, and 300 mg/kg. Dietary ZnSO4 exerts a devastating effect on the survival of S. litura. Even at the lowest concentration of 50 mg/kg dietary ZnSO4, only 1% of S. litura could complete the entire life cycle. Furthermore, as the dietary ZnSO4 concentration increased, the developmental stage achievable by the S. litura larvae declined. High-throughput untargeted metabolomics demonstrated that both 100 mg/kg dietary ZnCl2 and ZnSO4 decreased the hemolymph vitamins levels and increased the vitamin C content, thereby helping S. litura larvae to counteract the stress induced by ZnCl2 and ZnSO4. Simultaneously, dietary ZnCl2 obstructed the chitin synthesis pathway in the hemolymph of S. litura, thus extending the developmental period of S. litura larvae. These results indicate that low concentrations of Zn2+ positively impact populations of S. litura, but the effectiveness and toxicity of Zn depend on its chemical form and concentration.

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