Insect gut microbes have important roles in host feeding, digestion, immunity, development, and coevolution with pests. The fall armyworm, Spodoptera frugiperda (Smith, 1797), is a major migratory agricultural pest worldwide. The effects of host plant on the pest’s gut bacteria remain to be investigated to better understand their coevolution. In this study, differences in the gut bacterial communities were examined for the fifth and sixth instar larvae of S. frugiperda fed on leaves of different host plants (corn, sorghum, highland barley, and citrus). The 16S rDNA full-length amplification and sequencing method was used to determine the abundance and diversity of gut bacteria in larval intestines. The highest richness and diversity of gut bacteria were in corn-fed fifth instar larvae, whereas in sixth instar larvae, the richness and diversity were higher when larvae were fed by other crops. Firmicutes and Proteobacteria were dominant phyla in gut bacterial communities of fifth and sixth instar larvae. According to the LDA Effect Size (LEfSe) analysis, the host plants had important effects on the structure of gut bacterial communities in S. frugiperda. In the PICRUSt2 analysis, most predicted functional categories were associated with metabolism. Thus, the host plant species attacked by S. frugiperda larvae can affect their gut bacterial communities, and such changes are likely important in the adaptive evolution of S. frugiperda to host plants.

Although Telenomus remus is an important parasitoid of Spodoptera frugiperda, the chemical basis for its host selection behavior remains unclear. To elucidate the chemical basis of this behavior, this study combined behavioral ecology and chemical ecology methods to systematically investigate the host location and recognition behaviors of this wasp, as well as the semiochemicals that regulate these behaviors. In Y-tube olfactometer assays, T. remus exhibited a significantly stronger olfactory preference for eggs of S. frugiperda over those of S. litura (p < 0.05) or the non-host Ostrinia furnacalis. A total of 759 metabolites belonging to 11 categories were identified via metabolomics analysis, and principal component analysis (PCA) clearly distinguished between host eggs and non-host eggs. Analysis of differential metabolites revealed that the significantly upregulated metabolites in host eggs mainly included aldehydes, ketones and esters, followed by hydrocarbons, alcohols and amines. Subsequently, we screened and verified the effects of the significantly upregulated metabolites in host eggs compared with non-host eggs on the host-selection behavior of T. remus, including indole, 2-hexanol, and trans-1,2-dimethylcyclohexane, as well as 2-heptadecanone and n-nonadecane—two alkane compounds which are specifically upregulated on the surface of S. frugiperda eggs. Behavioral validation demonstrated that 2-hexanol exerted a significant repellent effect on T. remus, whereas trans-1,2-dimethylcyclohexane exhibited a significant attractive effect on the parasitoid wasp. Among the metabolites specifically upregulated in S. frugiperda eggs, 2-heptadecanone exhibited significant attractive activity at concentrations ranging from 0.1 to 1.0 mg/mL. This study is the first to report that the cycloalkane compound trans-1,2-dimethylcyclohexane acts as a potential broad-spectrum chemical marker for T. remus to recognize the eggs of host species belonging to the family Noctuidae, while 2-heptadecanone may further enhance its preference for the optimal host S. frugiperda. These findings provide novel candidate molecular targets for the development of behavioral regulators targeting egg parasitoids against S. frugiperda.

Spodoptera frugiperda poses a severe threat to crops, causing substantial economic losses. The increased use of chemical pesticides has led to resistance in S. frugiperda populations. Micro ribonucleic acids (MicroRNAs or miRNAs) are pivotal in insect growth and development. This study aims to identify miRNAs across different developmental stages of S. frugiperda to explore differential expression and predict target gene functions. High-throughput sequencing of miRNAs was conducted on eggs, 3rd instar larvae, pupae, and adults. Bioinformatics analyses identified differentially expressed miRNAs specifically in larvae, with candidate miRNAs screened to predict target genes, particularly those involved in detoxification pathways. A total of 184 known miRNAs and 209 novel miRNAs were identified across stages. Comparative analysis revealed 54, 15, and 18 miRNAs differentially expressed in larvae, compared to egg, pupa, and adult stages, respectively. Eight miRNAs showed significant differential expression across stages, validated by quantitative reverse transcription PCR (qRT-PCR). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses predicted target genes’ functions, identifying eight differentially expressed miRNAs targeting 10 gene families associated with detoxification metabolism, including P450s, glutathione S-transferase (GSTs), ATP-binding cassette (ABC) transporters, and sodium channels. These findings elucidate the species-specific miRNA profiles and regulatory mechanisms of detoxification-related genes in S. frugiperda larvae, offering insights and strategies for effectively managing this pest.

Diaphorina citri Kuwayama (1908), the Asian citrus psyllid (ACP), is a major pest of citrus crops, responsible for transmitting the bacterium that causes Huanglongbing (HLB), a disease devastating to citrus industries worldwide. Despite extensive research on its population genetics in other regions, the genetic structure of D. citri in Sichuan Province, China, remains poorly understood, complicating the development of effective pest management strategies. This study aims to fill this gap by investigating the genetic diversity and population structure of D. citri using genome-wide single nucleotide polymorphisms (SNPs). Three natural populations of D. citri from southeastern Sichuan were sequenced, revealing a total of 7,010,305 SNPs and relatively low genetic differentiation among populations. Phylogenetic analysis identified two primary genetic groups with limited gene flow, supported by principal component analysis (PCA) and Admixture analysis. The populations exhibited high genetic diversity, with notable variations in nucleotide diversity and inbreeding coefficients. Functional enrichment analysis highlighted genes involved in cellular processes and stress response, which may contribute to local adaptation. These findings provide valuable insights into the evolutionary dynamics of D. citri and suggest that genetic diversity and selective pressures play a key role in its adaptability. The results underscore the importance of considering genetic variation in the development of targeted and sustainable pest management strategies in southeastern China.