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.

Root exudates play a pivotal role in belowground interactions in both ecological and agricultural contexts. The metabolic composition of exudates profoundly influences the dynamics of these interactions, thereby shaping the intricate relationships between plants, microbes, and soil environments. Recent advances in mass-spectrometry have facilitated the analysis of root exudate metabolic composition to a greater depth. Previously used methods primarily analyze root exudates in hydroponic systems, or employ hybrid methodologies, which cultivate plants in soil and transitioning them briefly to hydroponic systems for exudate collection. Modern day ecological studies demand that exudates are collected in their natural habitats, because this will provide a more ecologically meaningful exudate metabolic profile. However, collecting exudates from soil grown plants poses several challenges with regard to the collection procedures, amongst others, the need for recovery after excavation of the roots, the collection period, and the solution in which to collect. Here, we present an optimized, cost-effective protocol for root exudate collection from potted plants, which is readily adaptable to field-grown specimens. Using tomato plants grown in pots, we examined and optimized various parameters: the collection medium (water versus nutrient solution), the use of wetted glass beads versus roots submerged in water, the recovery phase post-substrate removal, and the duration of exudation. Employing liquid chromatography-mass spectrometry (LC-MS), we assessed total amount of exudate, the number of features and background noise. Subsequent to data processing and statistical analyses, we assessed the chemical classes within exudates and variations in key metabolites among the different methods. Our results showed that each of the tested parameters can influence the outcome in different ways. Omitting the recovery phase increased the numbers of features and exudate amounts, likely due to adding metabolites from damaged roots, whereas the exudation medium and the duration of exudation had fewer effects. Based on our results, we propose to collect exudates in beakers containing ultrapure water, and to collect exudates for 4 h after a 24 h recovery phase. This is a straightforward and economical approach for collecting root exudates from soil-grown plants which is suitable for LC-MS analysis.