The growth of different grafted guava was different as affected by grafting on different rootstock varieties, which also influenced the damage degree of Spodoptera litura larvae. The co-regulation of the pest gut by rhizosphere microorganisms and root exudates may contribute to this differential damage. In this study, the microorganisms of soil, plants, S. litura larvae and root exudates of guava grafted on different rootstock varieties were analysed and compared. The activities of superoxide dismutase, peroxidase and catalase in the midgut of S. litura larvae feeding on heterograft leaves of guava (where rootstock and scion are of the different variety) were significantly higher than those in the midgut of S. litura larvae feeding on homograft leaves of guava (where rootstock and scion are of the same variety), and glutathione s-transferase activity showed an opposite result. Enterococcus spp. and Escherichia spp. were the two bacterial genera with the greatest difference in abundance in the midgut of S. litura larvae and exhibited a negative correlation with each other. The root system of guava influenced the root structure, soil nutrients and the population structure and diversity of rhizosphere microorganisms by regulating the type and amount of root exudates. Root exudates also influenced the physiological and biochemical status of S. litura larvae by regulating the rhizosphere microorganisms driving the tritrophic interaction of plant-microbes-insects. Based on our results and the observed differences in pest occurrence among different grafted plants, improving varieties through grafting may become an effective strategy to reduce the impact of insect pests on guava.

The current study aimed to isolate Beauveria brongniartii conidia from forest soils, identify the fungus, and evaluate its effectiveness on the eggs, larvae, pupae, and adults of Spodoptera litura. Insect mortality rates were recorded every 3, 6, 9, and 12 days. The identification of entomopathogenic fungi was carried out using molecular techniques, including PCR, DNA sequencing, and molecular markers, to detect species-specific 18 S rDNA genetic sequences, all performed under aseptic conditions. The results indicated that higher conidia concentrations (2.7 x 109 conidia/mL) exhibited greater virulence, with eggs showing a mortality rate of 98.66%, followed by larvae 96%, adults 90.66%, and pupae 77.33% after 12 days. Probit analysis revealed minimal LC50 and LC90 values: eggs (5.5 x 102; 1.0 x 106 spores/mL), larvae (8.2 x 102; 1.2 x 107 spores/mL), pupae (9.6 x 104; 7.3 x 1010 spores/mL), and adults (1.0 x 103; 2.0 x 108 spores/mL). The total hemocyte counts and detailed observational results revealed that B. brongniartii induces cellular breakdown and cell lysis in S. litura larvae by producing enzymes that degrade the cuticle and cell membranes. Earthworm bioindicator studies showed minimal effects from B. brongniartii conidia compared to controls, while chemical treatments resulted in 96% mortality at 100 ppm. Histopathological examinations revealed no significant differences in gut tissue between earthworms treated with fungal conidia and those in the control group, unlike the substantial damage caused by chemical treatments. Biochemical analysis revealed significant alterations in enzyme activity, including reduced levels of phosphatase and catalase, as well as increased levels of lipid peroxides and superoxide dismutase. This study highlights the effectiveness of B. brongniartii in controlling S. litura, demonstrating its potential as a viable biocontrol agent and promoting eco-friendly alternatives to chemical pesticides, with no risk to non-target species or the environment.

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.

BACKGROUND: Spodoptera litura is one of the most harmful lepidoptera pests in China, and is difficult to control due to its strong resistance to the current frequently used insecticide species. The requirement to develop pesticides with novel toxicology mechanisms to control S. litura is urgent. The quassinoid of bruceine D display outstanding systemic properties and strong insecticidal activity against S. litura, which possess notable application potential for integrative management of S. litura, but the mechanism of toxicity remains unclear. RESULTS: In this study, we found that bruceine D exerts potent growth inhibitory activity against S. litura, disrupting the ecdysone and juvenile hormone titers, and causing long-term adverse effects. Association analysis between transcriptomics and metabolomics suggested that bruceine D affected the digestion and absorption capacity of S. litura larvae by inducing a strong oxidative stress response and cell apoptosis in the intestine. Further analysis demonstrated that bruceine D can inhibit the activities of digestive and antioxidant enzymes and induce malondialdehyde (MDA) and reactive oxygen species (ROS) overaccumulation in the midgut. Moreover, the protein level of Bax, cleavage caspase 3, and cytochrome c expressed in cytoplasm (cyto) were up-regulated by bruceine D, while Bcl-2 and cytochrome c expressed in mitochondria (mito) were down-regulated. In addition, there was a noticeable increase in caspase-3 protease activity. Histopathological observations revealed that bruceine D damages the structure of midgut epithelial cells and activates lysosomes, which subsequently disrupts the midgut tissue. CONCLUSION: Overall, our findings suggested that bruceine D induced excessive ROS accumulation in midgut epithelial cells. The resulting cell apoptosis disrupted midgut tissue, leading ultimately to reduced nutrient digestion and absorption in the midgut and the inhibition of larval growth. (c) 2024 Society of Chemical Industry.