Insect herbivores employ many adaptive mechanisms to successfully colonize host plants. Transcriptional plasticity is one mechanism that enables broad host use in polyphagous insect herbivores; however, whether specialist herbivores use transcriptional plasticity or undergo epigenome modifications to cope with host shifts remains largely unexplored. We measured the transcriptome and DNA methylome of the specialist aphid herbivore, Daktulosphaira vitifoliae, after transfer to new hosts using RNA-seq and whole-genome bisulfite sequencing. We found the transcriptome of D. vitifoliae is highly plastic and responsive to host genotype – 3706 genes (28% of expressed genes) are significantly differentially expressed in at least one contrast comparing host genotypes. Most host-responsive genes (2667 genes) were upregulated when feeding on the non-native host Vitis vinifera and enriched for genes encoding predicted secretory effectors, detoxification enzymes, and cuticle- and chitin-associated proteins. We found gene co-expression modules that correlated with variation in fitness suggesting plasticity in transcriptional networks contributes to D. vitifoliae adaptation to host plants. We also identified a previously undescribed family of proline-rich secretory proteins conserved across the Aphidomorpha infraorder of insects. Our analysis of DNA methylation revealed a negative correlation between gene-level CpG methylation and host-induced transcriptional plasticity, suggesting a lack of gene body methylation may enable transcriptional plasticity when insects move to new host environments. Together, these results provide new insight into the molecular mechanisms of host use in insect herbivores.
Triacylglycerol (TAG) is the main lipid reserve in insect eggs and represents a critical energy source for embryonic development. In the hematophagous vector Rhodnius prolixus, oocyte growth relies heavily on lipids transported from the fat body through the hemolymph, which are delivered mainly as diacylglycerol and free fatty acids. Therefore, the ovary must catalyze the final esterification step converting these substrates into TAG to ensure proper lipid storage in developing oocytes. This reaction is mediated by diacylglycerol acyltransferases (DGATs), yet the specific roles of DGAT1 and DGAT2 in insect reproduction remain poorly understood. Here, we investigated the functions of RpDGAT1 and RpDGAT2 in ovarian physiology and reproduction in R. prolixus. RNAi gene knockdown efficiently reduced transcript levels of both enzymes without affecting blood digestion, survival, or oviposition rates. However, RpDGAT1 knockdown caused pronounced reproductive defects. Females produced morphologically abnormal eggs with collapsed appearance and reduced size, leading to an approximately 70% reduction in hatching rates. Ultrastructural analyses revealed alterations in eggshell organization as seen by SEM, but no changes in the hydrocarbon contents of the eggshell were detected. Lipid analyses showed that RpDGAT1 knockdown reduced ovarian TAG levels at day 10 after blood feeding, but not at day 5, while increasing ovarian phosphatidylethanolamine at day 10. Ovarian free fatty acid levels remained unchanged at both time points. In phenotypic eggs, TAG levels were reduced and free fatty acids were increased. Consistently, oocytes from RpDGAT1-knocked down females exhibited smaller lipid droplets, reflecting impaired neutral lipid storage. Hemolymph lipid composition and ovarian incorporation of radiolabeled palmitate were unchanged, indicating that reduced ovarian TAG was not associated with detectable changes in circulating lipid availability or overall ovarian fatty acid uptake. In contrast, RpDGAT2 knockdown produced no detectable reproductive phenotype. Together, our findings demonstrate that RpDGAT1, but not RpDGAT2, is essential for TAG accumulation, proper oocyte development, and egg hatchability in R. prolixus, highlighting the importance of lipid metabolism in insect reproductive physiology.
The olfactory system is essential for insect survival and behavior, with odorant-binding proteins (OBPs) playing a key role by binding and transporting chemical signals to olfactory receptors. Although MaltOBP9 from Monochamus alternatus, a primary vector of pine wilt disease, has been linked to olfactory functions in M. alternatus, its regulatory mechanisms and specific roles are not well understood. In this study, we show that MaltOBP9 is highly expressed in the antennae of both male and female adults after sexual maturation. Using fluorescence spectroscopy, molecular docking, and site-directed mutagenesis, we identified the amino acid Phe54 as essential for MaltOBP9's ability to bind 18 different volatile compounds. RNA interference (RNAi) and behavioral tests revealed that MaltOBP9 is necessary for sexually mature adults to detect the pheromone 2-methoxy-4-vinylphenol (2M4VP). Additionally, dual-luciferase reporter assays, electrophoretic mobility shift assays, and RNAi experiments demonstrated that the transcription factor MaltEms positively regulates MaltOBP9 expression, thereby influencing the detection of 2M4VP. By combining insights into transcriptional regulation and protein-ligand interactions, this study clarifies the MaltEms-MaltOBP9-2M4VP axis as a mediator of sex-specific olfactory behavior—where females avoid and males are attracted to the pheromone—in sexually mature M. alternatus. These findings provide a theoretical basis for developing pest control methods that target MaltOBP9 and its critical residue Phe54 through behavior-based strategies.
Moths rely on sex pheromones for long-distance mate attraction and recognition. The biosynthesis of moth sex pheromones involves multiple enzymatic steps, among which desaturases play a pivotal role in introducing carbon-chain unsaturation. However, the specific desaturases involved in sex pheromone biosynthesis in the diamondback moth, Plutella xylostella, remain largely unexplored. In this study, we identified a Δ11-desaturase gene, PxylDES3, from the pheromone gland transcriptome and generated a homozygous mutant line using the CRISPR/Cas9 system. Gas chromatography–mass spectrometry (GC-MS) analysis revealed that the three major sex pheromone components (Z11-16:Ald, Z11-16:OH, and Z11-16:Ac) were significantly reduced, but not completely abolished, in homozygous mutant females compared with wild-type females. Behavioral assays demonstrated that the loss of PxylDES3 led to a significant reduction in female mating success, impaired male orientation preference, and attenuated male wing-fanning and hair-pencil responses. Notably, the residual pheromone components detected in mutant females suggest potential functional redundancy within the desaturase gene family. Collectively, these findings establish PxylDES3 as an important contributor to sex pheromone biosynthesis and courtship behavior in P. xylostella, and provide a potential target for pheromone-based pest management strategies.
