Fatty acid synthase (FAS) is a key enzyme in the lipid synthesis pathway, however, its roles in insects remain largely unknown. Here, we firstly identified two FAS genes from the transcriptome dataset of the general cutworm Spodoptera litura, which is a destructive insect pest of many crops. Both SlFAS1 and SlFAS2 were highly expressed in third instar larvae and in their fat bodies. Then, we successfully silenced SlFAS1 in third instar larvae and the content of α-linolenic acid and triglyceride was significantly decreased. Besides that, the effect of FAS on the metamorphic development in S. litura was evaluated. The results indicate that after silencing SlFAS1, the survival rates of S. litura larvae decreased significantly compared to the control groups. Silencing SlFAS1 in fifth instar larvae resulted in more malformed pupae and adults, and the emergence rates were significantly reduced. Furthermore, the ecdysone content in the haemolymph of fifth instar larvae was significantly decreased after silencing SlFAS1. In addition, knocking down SlFAS1 significantly alters the expression of other key genes in the lipogenesis pathway, implying that FAS has an impact on the lipogenesis pathway. The present study deepens the understanding of FAS in insects and provides novel potential targets for managing insect pests.

Regional soil conditions may affect edible insect nutrients through associated changes in host plants and bacterial communities, but these relationships remain poorly understood. Here, we compared soils, soybean leaves, larval gut bacteria, and nutritional composition of Clanis bilineata tsingtauica across three sites. Soil nutrient parameters were measured before and after larval inoculation, bacterial communities were analyzed in soil, leaves, and larvae, and larval amino acid, protein, and fatty acid profiles were determined. Available potassium increased 1.17-fold in Lianyungang; several nutrients decreased in Huaian, whereas soil pH decreased by 4.0% in Nanjing. Larvae from Lianyungang contained higher levels of several amino acids (Serine, Glycine, etc.), whereas those from Huaian had higher saturated and unsaturated fatty acid contents (Stearic acid, Elaidic acid, etc.). Genus-level overlap analysis showed partial taxonomic overlap among soil, leaves, and larvae, and the number of shared genera generally declined from soil to leaves to larvae, consistent with compartment-specific filtering. Correlation analyses further indicated that soil nutrients, especially available phosphorus and available potassium, were significantly correlated with dominant bacterial genera and with specific larval amino acid and fatty acid traits. Overall, these findings suggest that regional soil background is associated with coordinated variation in soybean-associated bacteria, larval gut bacteria, and the nutritional composition of C. bilineata tsingtauica larvae.

Background/Objectives: Antimicrobial peptides (AMPs) in insect hemolymph are promising alternatives to conventional antibiotics, but their rapid screening from complex biological matrices remains difficult. This study aimed to develop a simple and efficient method for the enrichment and preliminary identification of putative AMPs from the hemolymph of Clanis bilineata tsingtauica larvae. Methods: Phospholipid-coated magnetic nanoparticles (Fe₃O₄@L) were prepared using membrane phospholipids identified from Enterococcus faecium by time-of-flight mass spectrometry. After nanoparticle characterization, enrichment conditions were optimized and the Fe₃O₄@L workflow was compared with a conventional ultrafiltration-electrophoresis-silver staining-mass spectrometry (UESM) method. Peptides were identified by de novo mass spectrometry, followed by sequence filtering, replicate screening, and in silico AMP prediction. Candidate peptides were chemically synthesized and evaluated for antibacterial activity, minimum inhibitory concentration (MIC), growth inhibition, morphological effects, and hemolytic activity. Results: Optimization of the Fe₃O₄@L method resulted in a 1.86-fold increase in peptide concentration in the enriched fraction. Compared with UESM, Fe₃O₄@L reduced the workflow from four steps to three and shortened processing time by 61.2%. De novo analysis generated 724 filtered peptides, of which 58 were reproducibly detected in at least two replicates, yielding five putative AMPs after activity prediction; no putative AMP was identified by UESM under the same conditions. Among the synthesized peptides, CBT-3 showed antibacterial activity against E. faecium and Escherichia coli, with MICs of 32 and 64 mg/L, respectively, and low hemolytic activity toward human erythrocytes. Conclusions: Fe₃O₄@L provides a simple and effective strategy for preliminary AMP screening from insect hemolymph, and CBT-3 represents a promising peptide candidate for further investigation.