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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.

Cold storage of host eggs is important for Trichogramma mass rearing, but the fitness of Trichogramma is affected by the refrigerated eggs. Corcyra cephalonica eggs are frequently utilized as factitious hosts of Trichogramma chilonis. In this study, we investigated the physicochemical property of fresh rice moth eggs (U) and sterilized eggs cold-stored at 4 °C for 0 (CK), 15 (N15), 30 (N30), 45 (N45), and 60 (N60) days and evaluated the effect of cold storage of host eggs on the fitness of T. chilonis. The results showed that the moisture content, dry matter and pH of C. cephalonica eggs decreased significantly with increasing cold storage time. The survival rates of T. chilonis embryos, larvae and pupae decreased significantly when C. cephalonica eggs were cold-stored for more than 15 days. The fecundity rate of adult T. chilonis in refrigerated eggs declined markedly, and a similar result was observed in the rate of black parasitized eggs. However, no clear difference was observed in either emergence rate or sex ratio between the CK and N15 treatment. A fitted linear regression model revealed that the survival rates of immature T. chilonis were positively correlated to the moisture content and pH of host eggs. Thus, cold storage changed the internal environment of C. cephalonica eggs and reduced the fitness for T. chilonis. This finding suggests that the storage period of rice moth eggs sterilized by UV at 4 °C should not exceed 15 days for mass-rearing of T. chilonis.

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.

Food utilization and growth of the 5th and 6th instar Spodoptera litura Fabricius larvae, and its effect on reproduction potential was evaluated by feeding larvae diets with different doses of Ni for 3 generations. Dose-dependent relationships between Ni levels and food consumption and growth were variable with different larval developmental period and Ni exposure duration. RCR, AD and RGR of the 6th instar larvae were much more affected by Ni exposure than those of 5th instar larvae, and the effects were strongest in the 3rd generation. It was found that RCR was significantly stimulated after 1 and 20 mg kg(-1) Ni exposure, while AD was significantly inhibited after 1, 5, 10 and 40 mg kg(-1) Ni exposure. However, lower levels of Ni (≤5 mg kg(-1)) significantly increased and higher levels of Ni (≥10 mg kg(-1)) significantly decreased RGR. In 3 successive generations, 10 mg kg(-1) Ni significantly increased the ECI and ECD of the 5th instar larvae, and 5 mg kg(-1) Ni significantly increased the ECD of the 6th instar larvae. However, ECD were all significantly inhibited with 20 mg kg(-1) Ni exposure. Results also revealed that durations of larvae were shortened at low levels of Ni, but extended at high levels of Ni. Fecundity was inhibited by the highest Ni doses in each generation, while improved by low Ni doses in the 3rd generation. Hatching rates in all treatments were significantly decreased in a Ni dose-dependent manner. Study indicated that effects of Ni on these parameters were predominant with the increasing Ni exposure period.

Rice is one of the most important food crops in the world. China has the second largest area of the rice growing in the world and the highest yield of rice produced. Infestation by insect pests, especially rice planthoppers, stem borers and leaf folders, is always a serious challenge to rice production in China. Current methods for controlling insect pests in China mainly include good farming practices, biological control, breeding and growing resistant varieties, and the use of chemical insecticides. However, for farmers, the favorite method for insect pest control is still the application of chemical insecticide, which not only causes severe environmental pollution and the resurgence of herbivores but also reduces populations of the natural enemies of herbivores. To control insect pests safely, effectively and sustainably, strategies encouraging biological control are currently demanded. Here we review the progress that has been made in the development and implementation of biological controls for rice in China since the 1970s. Such progress includes the species identification of the natural enemies of rice insect pests, the characterization of their biology, and the integration of biological controls in integrated pest management. To develop effective ecological engineering programs whose aim is to implement conservation biological controls, further research, including the evaluation of the roles of plants in non-crop habitats in conservation biological controls, volatiles in enhancing efficiency of natural enemies and natural enemies in manipulating insect pests, and education to increase farmers’ knowledge of biological controls, is proposed.

Two new species of the genus Thitarodes, T. sejilaensis sp. nov. and T. jiachaensis sp. nov., from Tibet in China are described and illustrated. All specimens are deposited in the Biological Museum of Sun Yat-sen University, Guangzhou, China.

Two types of Hepialus larvae with different diets were distinguished in the Sejila Mountain, Tibetan Plateau based on the stable carbon isotope data of the host Hepialus larva of Cordyceps sinensis and its closely adjacent tender plant roots and humus fractions. Type I is the larva chiefly fed by soil humus, and characterized by the δ 13C values of −22.6‰ to −23.4‰, and more than −23.4‰ in its heads. Type II is the larva chiefly fed by tender plant roots, and characterized by the δ 13C values of −24.6‰ to −27.6‰, and less than −24.6‰ in its heads. Our result has exceeded the traditional understanding that their food sources only come from the tender plant roots, and may provide evidence for choosing cheap and high-quality foods and further establishing artificial habitats in their large-scale reproduction.

Moulting is an essential process of insect development but little is known about cysteine proteases in the process. Here, we detail a proteolytic activity profile from fifth larval instar to new pupae of the lepidopteran Helicoverpa armigera. At fifth to sixth instar moulting, the activities were significantly higher than those in non-moulting stages, and were inhibited by the cysteine protease inhibitor, 2S, 3S-trans-epoxysuccinyl-L-leucylamido-3-methylbutane ethyl ester (E-64), or by the cathepsin L-selective inhibitor CLIK148. Further, a 1513 bp cathepsin L cDNA (Har-CL) was isolated from the H. armigera larval cuticle and epidermis layer. Har-CL gene expression, which is correlated closely with ecdysone, was higher during larval moulting. Injection of E-64 or CLIK148 resulted in delayed fifth to sixth instar moulting, suggesting an essential role for cathepsin L in larval moulting.

The larvae of Hepialus insects are the host of Ophiocordyceps (Berkeley) Saccardo with extreme cold- tolerance. The fatty acid composition of the whole caterpillar was determined by gas chromatography- mass spectrometer (GC- MS) after the sixth instar larvae of Hepialus jianchuanensis were exposed to low temperatures. The result indicated that the contents of total lipids and unsaturated fatty acids (UFAs) were increased, while the content of saturated fatty acids (SFAs) were decreased. The ratios of UFAs to SFAs were increased from 1.13 to 1.40 with temperature reduction. In addition, the linolenic acid (0.59–0.91%) was induced in the larvae after treatment of low temperatures, −3°C and 0°C. The regular changes in the fatty acid composition may result from their self-adaptation to the low- temperature environment.