Search

The egg parasitoid, Trichogramma chilonis, has significant control effects on agriculture and forestry pests and is widely employed in southern China for the biological control of lepidopteran pests. In this study, transcriptomic analysis was used to gain a clear understanding of the molecular changes in prepupae and pupae of T. chilonis. A total of 16.88 Gb of clean data were obtained and finally assembled into 43,136 unigenes, 18,880 of which were annotated. After FPKM standardization, 117 and 838 specific expression genes were found in prepupae and pupae, respectively. There were 3129 differentially expressed genes between prepupae and pupae. Compared to pupae, 806 genes were up-regulated and 2323 were down-regulated in prepupae. Background on the T. chilonis transcriptome, the enriched GO function and KEGG pathway analysis of DEGs were considered. As indicated by GO classification, up-regulated genes were mainly involved in chitin metabolism, cell adhesion and endocytic, while most down-regulated genes were involved in synthesis of cell components, ion transport and biological regulation. KEGG enrichment analysis showed that 458 DEGs were enriched in 94 metabolic pathways. DEGs involved in nucleotide replication and transcription, substance metabolism, insect hormone biosynthesis, cell growth and death, reproductive metabolism, circadian rhythms and signal transduction pathways were up-regulated or down-regulated to different degrees, indicating that these genes played important roles during the process of metamorphosis in T. chilonis. This study provides a rich data source for the future study of T. chilonis molecular and biological mechanisms. A large number of genes related to metamorphosis were found based on comparison analysis between prepupae and pupae transcriptomes. This study lays a good foundation for in-depth study of gene transcription and regulation mechanisms during T. chilonis metamorphosis.

Pardosa pseudoannulata, one of the dominant predators in the paddy ecosystem, is a potential resource in the biological control of rice pests. Olfaction is crucial for insect behaviors such as feeding, mating and foraging, and odorant-binding proteins (OBPs) play a vital role in smell sensing, so we suppose that OBPs may be also important in spider behaviors. In this study, we identified two putative OBP genes and obtained their complete cDNA sequences. PpseOBP1 is 842 bp long and encodes a 188 amino acids protein. PpseOBP2 is 996 bp long and encodes a 213 amino acids protein. By our predictions and analysis, both of the PpseOBPs share some similar physicochemical and structural characteristics with insect classic OBP genes, but they do not strictly observe the cysteine pattern of OBPs in insects, in which there are three amino acid residues between the second and the third cysteine residues but 27 amino acid residues in P. pseudoannulata. Phylogenetic analysis showed that two PpseOBPs clustered together at the edge of the tree, indicating their distant relationship with insects. Regarding insects, PpseOBPs were most closely related to the Periplaneta americana OBP1. Both PpseOBPs are mainly expressed in appendages (pedipalps and legs). Expression of PpseOBP1 was significantly higher in female appendages than in male appendages, while PpseOBP2 showed an extreme expression level in male pedipalps. This is the first report of molecular characterization and expression patterns of OBPs in Lycosidae and will establish a foundation for better understanding of molecular mechanisms of P. pseudoannulata olfaction and facilitate its function in biological control.

In insects, the gustatory system has a critical function not only in selecting food and feeding behaviours but also in growth and metabolism. Gustatory receptors play an irreplaceable role in insect gustatory signalling. Trichogramma chilonis is an effective biocontrol agent against agricultural insect pests. However, the molecular mechanism of gustation in T. chilonis remains elusive. In this study, we found that T. chilonis adults had a preference for D-fructose and that D-fructose contributed to prolong longevity and improve fecundity. Then, We also isolated the full-length cDNA encoding candidate gustatory receptor (TchiGR43a) based on the transcriptome data of T. chilonis, and observed that the candidate gustatory receptor gene was expressed from the larval to adult stages. The expression levels of TchiGR43a were similar between female and male. A Xenopus oocyte expression system and two-electrode voltage-clamp recording further verified the function analysis of TchiGR43a. Electrophysiological results showed that TchiGR43a was exclusively tuned to D-fructose. By the studies of behaviour, molecular biology and electrophysiology in T. chilonis, our results lay a basic fundation of further study on the molecular mechanisms of gustatory reception and provide theoretical basis for the nutritional requirement of T. chilonis in biocontrol.

Trichogramma is a kind of egg parasitoid wasp that is widely used to control lepidopterous pests. Temperature is one of the main factors that determines the various life activities of this species, including development, reproduction and parasitism efficiency. Heat shock proteins (HSPs) are highly conserved and ubiquitous proteins that are best known for their responsiveness to temperature and other stresses. To explore the potential role of HSPs in Trichogramma species, we obtained the full-length cDNAs of six HSP genes (Tchsp10, Tchsp21.6, Tchsp60, Tchsp70, Tchsc70-3, and Tchsp90) from T. chilonis and analyzed their expression patterns during development and exposure to temperature stress. The deduced amino acid sequences of these HSP genes contained the typical signatures of their corresponding protein family and showed high homology to their counterparts in other species. The expression levels of Tchsp10, Tchsp21.6 and Tchsp60 decreased during development. However, the expression of Tchsc70-3 increased from the pupal stage to the adult stage. Tchsp70 and Tchsp90 exhibited the highest expression levels in the adult stage. The expression of six Tchsps was dramatically upregulated after 1 h of exposure to 32 and 40°C but did not significantly change after 1 h of exposure to 10 and 17°C. This result indicated that heat stress, rather than cold stress, induced the expression of HSP genes. Furthermore, the expression of these genes was time dependent, and the expression of each gene reached its peak after 1 h of heat exposure (40°C). Tchsp10 and Tchsp70 exhibited a low-intensity cold response after 4 and 8 h of exposure to 10°C, respectively, but the other genes did not respond to cold at any time points. These results suggested that HSPs may play different roles in the development of this organism and in its response to temperature stress.

Chemoreception is critical for the survival of insects. Insects have a variety of behavioral responses, such as mating, host searching and ovipositing, in response to different odor signals detected in their living environment. Trichogramma chilonis, an egg parasitoid, acts as an efficient and effective biocontrol reagent for many agricultural and forestry insect pests in many parts of China. However, little is known about the molecular mechanism of the olfaction-evoked behavior in T. chilonis. In the present study, we conducted transcriptome profiling analysis of T. chilonis based on the Illumina high-throughput sequencing platform in order to explore differences of chemoreception between male and female T. chilonis. In this study, a total of 85 chemosensory genes were identified from transcriptomic data, including 45 odorant receptors (ORs), 22 odorant binding proteins (OBPs), 14 ionotropic receptors (IRs), 2 sensory neuron membrane proteins (SNMPs) and 2 chemosensory proteins (CSPs). From the analysis of the transcriptome, most of the candidate olfactory genes had similar expression levels in males and females, including a few OR and OBP genes (TchiOR38, TchiOR39, TchiOR40, TchiOR41, TchiOR42, TchiOR43, TchiOR44, TchiOR45, TchiOBP1, TchiOBP4, TchiOBP10, TchiOBP12, TchiOBP18 and TchiOBP19) which showed male-biased expression. Some annotated unigenes were chosen randomly to have qRT-PCR, which verified the correctness of analysis of transcriptome in T. chilonis. This is the first study to obtain and identify candidate genes related to chemoreception in T. chilonis. Our work lays a solid foundation for related future research on the chemosensory system of T. chilonis at the molecular level and helps advance the use of T. chilonis as biological control agents.

Vitellogenin (Vg) and vitellogenin receptor (VgR) play important roles in the vitellogenesis of insects. In this study, we cloned and characterized the two corresponding genes (TpVg and TpVgR) in an economically important insect, Thitarodes pui (Lepidoptera: Hepialidae), from the Tibetan plateau. The full length of TpVg is 5566 bp with a 5373 bp open reading frame (ORF) encoding 1,790 amino acids. Sequence alignment revealed that TpVg has three conserved domains: a Vitellogenin_N domain, a DUF1943 domain, and a von Willebrand factor type D domain (VWD). The full length of TpVgR is 5732 bp, with a 5397 bp ORF encoding 1798 amino acids. BLASTP showed that TpVgR belongs to the low-density lipoprotein receptor (LDLR) gene superfamily. Structural analysis revealed that TpVgR has a group of four structural domains: a ligand-binding domain (LBD), an epidermal growth factor (EGF)–precursor homology domain, a transmembrane (TM) domain, and a cytoplasmic domain. In addition, TpVgR has four cysteine-rich LDL repeats in the first ligand-binding site and seven in the second. Quantitative real-time polymerase chain reaction analysis revealed that the expression levels of TpVg and TpVgR are much higher in later pupa than in either the larval or adult stage, implying that the synthesis and uptake of Vg in T. pui occurs in the later pupal stage. These results will help us to understand the molecular mechanism of the reproductive capacity and will provide new insight into the mass rearing and utilization of T. pui.