Evidence of vitamin D synthesis in insects exposed to UVb light

Vertebrates obtain the prohormone vitamin D primarily by endogenous cutaneous synthesis under ultraviolet b (UVb) exposure. To date, endogenous synthesis of vitamin D in insects has never been investigated. In an initial experiment, we exposed four insect species which differ in ecology and morphology (migratory locusts, house crickets, yellow mealworms and black soldier fly larvae (BSFL)) to a low irradiance UVb source. In a second experiment we exposed these species to a higher UV irradiance, and in a third we tested the effect of exposure duration on vitamin D concentrations in yellow mealworms. Low irradiance UVb tended to increase vitamin D3 levels in house crickets, vitamin D2 levels in BSFL and vitamin D2 and D3 in yellow mealworms. Higher UVb irradiance increased vitamin D3 levels in all species but BSFL. Both BSFL and migratory locusts had increased vitamin D2 levels. Longer UVb exposure of yellow mealworms increased vitamin D2 and increased vitamin D3 until a plateau was reached at 6400 IU/kg. This study shows that insects can synthesize vitamin D de novo and that the amounts depend on UVb irradiance and exposure duration.

RNA-Seq reveals large quantitative differences between the transcriptomes of outbreak and non-outbreak locusts

Outbreaks of locust populations repeatedly devastate economies and ecosystems in large parts of the world. The consequent behavioural shift from solitarious to gregarious and the concomitant changes in the locusts' biology are of relevant scientific interest. Yet, research on the main locust species has not benefitted from recent advances in genomics. In this first RNA-Seq study on Schistocerca gregaria, we report two transcriptomes, including many novel genes, as well as differential gene expression results. In line with the large biological differences between solitarious and gregarious locusts, almost half of the transcripts are differentially expressed between their central nervous systems. Most of these transcripts are over-expressed in the gregarious locusts, suggesting positive correlations between the levels of activity at the population, individual, tissue and gene expression levels. We group these differentially expressed transcripts by gene function and highlight those that are most likely to be associated with locusts' phase change either in a species-specific or general manner. Finally, we discuss our findings in the context of population-level and physiological events leading to gregariousness.

Dopamine signalling in locusts and other insects

Dopamine is an important catecholamine neurotransmitter in invertebrates and vertebrates. It is biochemically derived from tyrosine via L-DOPA. It is most abundant in the central nervous system, but can also be produced in e.g. epidermal cells. Dopamine has conserved roles in the control of movement, pleasure, motivation, arousal and memory between invertebrate and vertebrate animals. It is crucial for melanisation and sclerotisation, important processes for the formation of the exoskeleton of insects and immune function. In this brief review I will discuss some general aspects of insect dopamine biosynthesis and breakdown, dopamine receptors and their pharmacology. In addition, I will provide a glance on the multitude of biological functions of dopamine in insects. More detail is provided concerning the putative roles of dopamine in phase related phenomena in locusts. Finally, molecular and pharmacological adjustments of insect dopamine signalling are discussed in the light of possible approaches towards insect pest management.

A head transcriptome provides insights into odorant binding proteins of the bamboo grasshopper

The bamboo grasshopper Ceracris kiangsu is a famous bamboo pest in China. The identification of genes involved in olfactory behavior of C. kiangsu is necessary for better understanding the molecular basis and expression profiles of behavior ecology. However, necessary genomic and transcriptomic data are lacking in the species, limiting control efficiency. The primary objective of this study was to find and describe odorant binding proteins in the head of the bamboo grasshopper. We performed the paired-end sequencing on an Illumina Hiseq2000 following the vendor's recommended protocol. Functional annotation was performed by comparison with public databases. OBP genes were first identified using BLASTN and BLASTX results from our C. kiangsu datebase, which was established from the date of transcriptome sequencing. The gene-specific primers were used to conduct RT-PCR to detect the tissue distribution of OBPs using a SYBR Premix ExTaq kit following the manufacturer's instructions with a real-time thermal cycler. We obtained more than 133 million clean reads derived from the C. Kiangsu heads using the next-generation sequencing, which were assembled into 260,822 unique sequences (average 814 bp). We have detected eight putative odorant binding protein genes (OBPs) of C. kiangsu for the first time, and analyzed the expression profiles of the OBPs in different tissues (head, antenna, mouthpart, body and leg). Our results reveal that the eight OBPs display a clear divergence, strongly indicating that they possessed diverse functions, and thus provides comprehensive sequence analysis for elucidating the molecular basis of OBPs in C. kiangsu. In addition, we find that the relative expression levels of OBP1, OBP2 and OBP8 are significantly higher in the antennae as compared to the other OBP genes, suggesting that these three OBP genes play crucial roles in the locust's odorant discrimination. In general, this is the first study to characterize the complete head transcriptome of C. kiangsu using high-throughput sequencing. The study opens a window for functional characterization of the OBPs of C. kiangsu, with potential for new or refined applications of semiochemicals for control of this notorious pest.

Respiratory patterns in field collected brown locust, Locustana pardalina, in the gregarious phase

In this paper we report on the metabolic rates and respiratory patterns measured from gregarious brown locusts, Locustana pardalina, collected from the Nama Karoo region in South Africa. All five instar hopper stages and adults were collected over a three year period when significant numbers of locust swarms were seen. Flow-through respirometry was used to measure the CO₂ emission from individual locusts from all the developmental stages and adults within a week of collection. Carbon dioxide emission scaled hypometrically with mass, 0.863 ± 0.026. Except in the 1st and 5th instar stage there was no difference in the mass specific rate of CO₂ emission (V̇_{<ce:small-caps>CO2</ce:small-caps>}). These had significantly higher metabolic rates compared to the other stages which reflects their biology, with the 1st instar undergoing rapid growth and the 5th instar also undergoing rapid growth and development in preparation for becoming an adult. The 1st instars used a form of continuous gas exchange while all the other stages showed discontinuous gas exchange cycles. A clear burst phase and interburst periods could be seen. The 2nd and 3rd instars use mainly diffusion to expel CO₂ and so exhibited an open form of the burst phase. There was an increase in CO₂ volleys seen in the burst phase from the 4th instar stage onwards thus indicating an increased use of convection. There was no change in the duration or frequency of the discontinuous gas exchange cycles through the locust development or with body mass.

De Novo Assembly and Characterization of the Xenocatantops brachycerus Transcriptome

Grasshoppers are common pests but also have high nutritional and commercial potential. Xenocatantops brachycerus Willemse (Orthoptera: Acrididae) is an economically important grasshopper species that is reared in China. Using the IlluminaHiSeqTM 4000 platform, three transcriptomes of the adult male, adult female, and nymph of X. brachycerus were sequenced. A total of 133,194,848 clean reads were obtained and de novo assembled into 43,187 unigenes with an average length of 964 bp (N50 of 1799 bp); of these, 24,717 (57.23%) unigenes matched known proteins. Based on these annotations, many putative transcripts related to X. brachycerus growth, development, environmental adaptability, and metabolism of nutritional components and bioactive components were identified. In addition, the expression profiles of all three transcriptome datasets were analyzed, and many differentially expressed genes were detected using RSEM and PossionDis. Unigenes. Unigenes with functions associated with growth and development exhibited higher transcript levels at the nymph stage, and unigenes associated with environmental adaptability showed increased transcription in the adults. These comprehensive X. brachycerus transcriptomic data will provide a useful molecular resource for gene prediction, molecular marker development, and studies on signaling pathways in this species and will serve as a reference for the efficient use of other grasshoppers.

The roles of mucus-forming mucins, peritrophins and peritrophins with mucin domains in the insect midgut

Most insects have a gut lined with a peritrophic membrane (PM) consisting of chitin and proteins, mainly peritrophins that have chitin-binding domains. The PM is proposed to originate from mucus-forming mucins (Mf-mucins), which acquired a chitin-binding domain that interlocked with chitin, replacing mucus in function. We evaluated the expression of Mf-mucins and peritrophins by RNA-sequencing (RNA-seq) throughout the midgut of four distantly related insects. Mf-mucins were identified as proteins with high o-glycosylation and a series of uninterrupted Pro/Thr/Ser residues. The results demonstrate that the mucus layer is widespread in insects, and suggest that insect Mf-mucins are derived from those found in other animals by the loss of the cysteine knot and von Willebrand domains. The data also support a role of Mf-mucins in protecting the middle midgut of Musca domestica against acidic buffers. Mf-mucins may also produce a jelly-like material associated with the PM that immobilizes digestive enzymes in Spodoptera frugiperda. Peritrophins with a domain similar to Mf-mucins may be close to the ancestor of peritrophins. Expression data of peritrophins and chitin synthase genes throughout the midgut of M. domestica, S. frugiperda and Tenebrio molitor indicated that peritrophins were incorporated along the PM, according to their preferential sites of formation. Finally, the data support the view that mucus has functions distinct from the PM.

Antioxidant and Anti-Inflammatory Activities of Hydrolysates and Peptide Fractions Obtained by Enzymatic Hydrolysis of Selected Heat-Treated Edible Insects

This study investigated the effect of heat treatment of edible insects on antioxidant and anti-inflammatory activities of peptides obtained by in vitro gastrointestinal digestion and absorption process thereof. The antioxidant potential of edible insect hydrolysates was determined as free radical-scavenging activity, ion chelating activity, and reducing power, whereas the anti-inflammatory activity was expressed as lipoxygenase and cyclooxygenase-2 inhibitory activity. The highest antiradical activity against DPPH• (2,2-diphenyl-1-picrylhydrazyl radical) was noted for a peptide fraction from baked cricket Gryllodes sigillatus hydrolysate (IC50 value 10.9 µg/mL) and that against ABTS•+ (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical) was the highest for raw mealworm Tenebrio molitor hydrolysate (inhibitory concentration (IC50 value) 5.3 µg/mL). The peptides obtained from boiled locust Schistocerca gregaria hydrolysate showed the highest Fe2+ chelation ability (IC50 value 2.57 µg/mL); furthermore, the highest reducing power was observed for raw G. sigillatus hydrolysate (0.771). The peptide fraction from a protein preparation from the locust S. gregaria exhibited the most significant lipoxygenase and cyclooxygenase-2 inhibitory activity (IC50 value 3.13 µg/mL and 5.05 µg/mL, respectively).

Overexpression of Mn-superoxide dismutase in Oxya chinensis mediates increased malathion tolerance

Superoxide dismutase (SOD) is the first line of defense against oxidative damage. Malathion is an organophosphate insecticide and can induce the production of reactive oxygen species (ROS) and cause the intracellular oxidative stress. The present study was undertaken to examine the effects of malathion on SODs activity and their transcriptional levels in Oxya chinensis (Thunberg) (Orthoptera: Acrididae). The results showed that total SOD and MnSOD activities increased as a dose-dependent manner while CuZnSOD activity has no significant changes after malathion treatments. Total SOD and MnSOD activities were the highest at the concentration of 0.8 μg μL^-1 malathion treatment and increased significantly about 1.81- and 2.48-fold compared with the control, respectively. Increased mRNA expression of MnSOD, ecCuZnSOD1, and ecCuZnSOD2 were observed after malathion treatments. Moreover, the alteration of MnSOD transcript was similar to the profiles of MnSOD activity. These results suggested that the up-regulation expression of MnSOD transcript led to the increase of MnSOD activity in order to eliminate the excessive ROS caused by malathion. In addition, we evaluated the role of individual SOD gene in malathion stress by using RNAi and recombinant SOD proteins. The results showed that ROS contents increased significantly after the silencing of MnSOD and ecCuZnSOD1 genes. The OD values of the E. coli cells transformed with pET-28a-OcMnSOD plasmid were 1.13-1.31-fold and 1.08-1.33-fold higher than those of cells with pET-28a plasmids under 0.4 and 0.8 μg μL^-1 malathion treatments, respectively. These findings indicated that MnSOD exerted an important role in defense oxidative stress caused by malathion.

Evolution, expression and association of the chemosensory protein genes with the outbreak phase of the two main pest locusts

We analyze the evolutionary relationships and expression patterns of the large set of genes for chemosensory proteins (CSPs) in the two main pest locusts. We used the available transcriptome and genome data to infer the number of genes using BLAST searches and sequence similarity matrices. Maximum likelihood phylogenies revealed the relationships between these CSPs and CSPs from several arthropods. RNAseq and qPCR allowed associating CSPs to locust phases. Crossing the phylogenetic and expression data allowed us to deduce homologies and conservation of the involvement in the phase change. We confirm that Locusta migratoria has at least 58 CSP gene copies, only five of which lack evidence of expression, and we reveal that Schistocerca gregaria has at least 42 expressed CSP genes. Both species share 21 orthologs, whereas 33 L. migratoria and 15 S. gregaria CSPs seem species-specific. Additional six S. gregaria and four L. migratoria CSPs seem duplications. Although the expression profiles are not especially conserved, seven orthologous CSP pairs share a gregarious over-expression pattern in adult locusts. We thus confirm that the number of locusts' CSPs is large, due to gene duplications during the evolution of Orthoptera, we establish sequence and potential functional homologies, and we highlight specific CSPs that appear to be involved in locust gregariousness either in general or in a species-specific manner.

A conserved plan for wiring up the fan-shaped body in the grasshopper and Drosophila

The central complex comprises an elaborate system of modular neuropils which mediate spatial orientation and sensory-motor integration in insects such as the grasshopper and Drosophila. The neuroarchitecture of the largest of these modules, the fan-shaped body, is characterized by its stereotypic set of decussating fiber bundles. These are generated during development by axons from four homologous protocerebral lineages which enter the commissural system and subsequently decussate at stereotypic locations across the brain midline. Since the commissural organization prior to fan-shaped body formation has not been previously analyzed in either species, it was not clear how the decussating bundles relate to individual lineages, or if the projection pattern is conserved across species. In this study, we trace the axonal projections from the homologous central complex lineages into the commissural system of the embryonic and larval brains of both the grasshopper and Drosophila. Projections into the primordial commissures of both species are found to be lineage-specific and allow putatively equivalent fascicles to be identified. Comparison of the projection pattern before and after the commencement of axon decussation in both species reveals that equivalent commissural fascicles are involved in generating the columnar neuroarchitecture of the fan-shaped body. Further, the tract-specific columns in both the grasshopper and Drosophila can be shown to contain axons from identical combinations of central complex lineages, suggesting that this columnar neuroarchitecture is also conserved.

Tracing the fate and transport of secondary plant metabolites in a laboratory mesocosm experiment by employing mass spectrometric imaging

Mass spectrometric imaging (MSI) has received considerable attention in recent years, since it allows the molecular mapping of various compound classes, such as proteins, peptides, glycans, secondary metabolites, lipids, and drugs in animal, human, or plant tissue sections. In the present study, the application of laser-based MSI analysis of secondary plant metabolites to monitor their transport from the grass leaves of Dactylis glomerata, over the crop of the grasshopper Chorthippus dorsatus to its excrements, and finally in the soil solution is described. This plant-herbivore-soil pathway was investigated under controlled conditions by using laboratory mesocosms. From six targeted secondary plant metabolites (dehydroquinic acid, quinic acid, apigenin, luteolin, tricin, and rosmarinic acid), only quinic acid, and dehydroquinic acid, an in-source-decay (ISD) product of quinic acid, could be traced in nearly all compartments. The tentative identification of secondary plant metabolites was performed by MS/MS analysis of methanol extracts prepared from the investigated compartments, in both the positive and negative ion mode, and subsequently compared with the results generated from the reference standards. Except for tricin, all secondary metabolites could be tentatively identified by this approach. Additional liquid-chromatography mass spectrometry (LC-MS) experiments were carried out to verify the MSI results and revealed the presence of quinic acid only in grass and chewed grass, whereas apigenin-hexoside-pentoside and luteolin-hexoisde-pentoside could be traced in the grasshopper body and excrement extracts. In summary, the MSI technique shows a trade-off between sensitivity and spatial resolution. Graphical abstract Monitoring quinic acid in a mesocosm experiment by mass spectrometric imaging (MSI).

Prospective evidence for independent nitrogen and phosphorus limitation of grasshopper (Chorthippus curtipennis) growth in a tallgrass prairie

Insect herbivores play a pivotal role in regulating plant production and community composition, and their role in terrestrial ecosystems is partly determined by their feeding behavior and performance among plants of differing nutritional quality. Historically, nitrogen (N) has been considered the primary limiting nutrient of herbivorous insects, but N is only one of many potential nutrients important to insect performance. Of these nutrients, phosphorus (P) is perhaps the most important because somatic growth depends upon P-rich ribosomal RNA. Yet relatively few studies have assessed the strength of P-limitation for terrestrial insects and even fewer have simultaneously manipulated both N and P to assess the relative strengths of N- and P-limitation. Here, we tested for potential N and P limitation, as well as N:P co-limitation, on Chorthippis curtipennis (Orthoptera, Acrididae), an abundant member of arthropod communities of central US prairies. Our results demonstrate weak evidence for both N and P limitation of C. curtipennis growth rates in laboratory feeding assays. Importantly, P-limitation was just as strong as N-limitation, but we found no evidence for NP co-limitation in our study. Furthermore, nutrient limitation was not apparent in field studies, suggesting that insect growth rates may be predominately controlled by other factors, including temperature and predation. Our results suggest that P should be jointly considered, along with N, as a primary determinant of herbivore feeding behavior under both current and future climate conditions.

Assessment of oxidative stress and activities of antioxidant enzymes depicts the negative systemic effect of iron-containing fertilizers and plant phenolic compounds in the desert locust

For herbivore insects, digesting can be somewhat challenging, as the defense mechanisms evolved by plants, including the release of phenolics like the non-protein amino acid L-3,4-dihydroxyphenylalanine (L-DOPA), can cause fitness costs. In addition, industrial and agricultural activities have elevated the amounts of iron that can be found in nature and more particularly FeSO₄ that is used as fertilizer. Traces of iron can enhance the auto-oxidation of L-DOPA, in turn, generating reactive oxygen species (ROS) and consequently oxidative stress in insects. We examined the effects of the ion Fe²⁺ (as FeSO₄) and L-DOPA on fifth instars of the desert locust Schistocerca gregaria. We measured the level of oxidative damage occurring to macromolecules (proteins and lipids) from midgut and thoracic tissues and assessed the activities of responsive antioxidant enzymes. Injected L-DOPA and redox-active metal iron generated ROS which caused oxidative damages to proteins and lipids to S. gregaria. The protein carbonyls and lipid peroxides present in tissue homogenates were elevated in treated insects. No synergism was observed when L-DOPA was co-injected with Fe²⁺. K _m values of superoxide dismutase (SOD), glutathione reductase (GR), and glutathione peroxidase (GPx) were 4.3, 2.6, and 4.0 mM in thoracic muscles and 5.00, 2.43, and 1.66 mM in whole midgut for SOD, GR, and GPx, respectively, and 8.3 and 3.43 M for catalase (CAT) in the two tissues, respectively. These results suggest higher affinities of GPx and CAT to H₂O₂ in midgut than in muscles. The time-course changes in activities of antioxidant enzymes and amounts of protein carbonyls and lipid peroxides showed fluctuating patterns, suggesting complex interactions among macromolecules, L-DOPA and FeSO₄, and their degradation products. Our results demonstrated the stressful effects of L-DOPA and FeSO₄, proving that iron-containing fertilizers are pollutants that can strongly affect S. gregaria.

Ecdysteroid signalling components in metamorphosis and development of the desert locust, Schistocerca gregaria

The arthropod-specific hormone family of ecdysteroids plays an important role in regulating diverse physiological processes, such as moulting and metamorphosis, reproduction, diapause and innate immunity. Ecdysteroids mediate their response by binding to a heterodimeric complex of two nuclear receptors, the ecdysone receptor (EcR) and the retinoid-X-receptor/ultraspiracle (RXR/USP). In this study we investigated the role of EcR and RXR in metamorphosis and development of the desert locust, Schistocerca gregaria. The desert locust is a voracious, phytophagous, swarming pest that can ruin crops and harvests in some of the world's poorest countries. A profound knowledge of the ecdysteroid signalling pathway can be used in the development of more target-specific insecticides to combat this harmful plague insect. Here we report an in-depth profiling study of the transcript levels of EcR and RXR, as well as its downstream response genes, in different tissues isolated throughout the last larval stage of a hemimetabolous insect, showing a clear correlation with circulating ecdysteroid titres. Using RNA interference (RNAi), the role of SgEcR/SgRXR in moulting and development was investigated. We have proven the importance of the receptor components for successful moulting of locust nymphs into the adult stage. Some SgEcR/SgRXR knockdown females were arrested in the last larval stage, and 65 % of them initiated vitellogenesis and oocyte maturation, which normally only occurs in adults. Furthermore, our results clearly indicate that at the peak of ecdysteroid synthesis, on day six of the last larval stage, knockdown of SgEcR/SgRXR is affecting the transcript levels of the Halloween genes, Spook, Shadow and Shade.

Differential Gene Expression Analysis of the Epacromius coerulipes (Orthoptera: Acrididae) Transcriptome

Epacromius coerulipes (Ivanov) is one of the most widely distributed locusts. To date, the main methods to kill locusts still rely on chemical controls, which can result in the selection of locusts with resistance to chemical pesticides. Butene-fipronil is a new pesticide that was discovered by the structural modification of fipronil. This pesticide has been used to control various agricultural pests and has become an important pesticide product to control pests that exhibit resistance to other pesticides, including locusts. To extend its useful half-life, studies of the initiation and progression of resistance to this pesticide are needed. Herein, two E. coerulipes strains, a pesticide-sensitive (PS) and a pesticide-resistant (PR) strain, were chosen to undergo de novo assembly by paired-end transcriptome Illumina sequencing. Overall, 63,033 unigenes were detected; the average gene length was 772 bp and the N50 was 1,589 bp. Among these unigenes, ∼ 25,132 (39.87% of the total) could be identified as known proteins in bioinformatic databases from national centers. A comparison of the PR and PS strains revealed that 2,568 genes were differentially expressed, including 1,646 and 922 genes that were up- and down-regulated, respectively. According to the Gene Ontology (GO) database, among biological processes the metabolic process group was the largest group (6,900 genes, 22.47%) and contained a high frequency of differentially expressed genes (544 genes, 27.54%). According to the Clusters of Orthologous Groups (COG) categories, 28 genes, representing 2.98% of all genes, belonged to the group of genes involved in the biosynthesis, transportation, and catabolism of secondary metabolites. The differentially expressed genes that we identified are involved in 50 metabolic pathways. Among these pathways, the metabolism pathway was the most represented. After enrichment analysis of differential gene expression pathways, six pathways--ribosome; starch, and sucrose metabolism; ascorbate and aldarate metabolism; drug metabolism-cytochrome P450; metabolism of xenobiotics by cytochrome P450; and glutathione metabolism--showed a high degree of enrichment. Among these pathways, drug metabolism-cytochrome P450, metabolism of xenobiotics by cytochrome P450, and glutathione metabolism have been associated with pesticide metabolism. Furthermore, 316 unigenes in the E. coerulipes transcriptome encode detoxifying enzymes and 76 unigenes encode target proteins of pesticides. Among these genes, 23 genes that encode detoxifying enzymes in the resistance group were found to be up-regulated. The transcriptome sequencing results of E. coerulipes established a genomics database of E. coerulipes for the first time. This study also establishes a molecular basis for gene function analysis of E. coerulipes Moreover, it provides a theoretical resource for mechanistic studies on pesticide resistance through the screening and investigation of resistance genes.

Identification and Characterization of Two "Sensory Neuron Membrane Proteins" (SNMPs) of the Desert Locust, Schistocerca gregaria (Orthoptera: Acrididae)

Pheromone-responsive neurons of insects not only require specific receptors but in addition several auxiliary components, including the "sensory neuron membrane protein," SNMP. Accordingly, SNMP is considered as a marker for neurons responding to pheromones. For the desert locust Schistocerca gregaria, it is known that the behavior, including aggregation behavior and courtship inhibition, is largely controlled by pheromones. However, little is known about pheromones, their receptors, and the pheromone-responsive cells in locusts. In this study, we have identified two SNMP subtypes, SNMP1 and SNMP2, and compared their phylogenetic relationship and primary structure motifs with SNMPs from other species. Both SNMPs were found in chemosensory tissues, especially the antennae. Employing double in situ hybridization, we identified and localized the SNMP-expressing cells in the antennae. Cells expressing SNMP1 were localized to sensilla trichodea but also to sensilla basiconica, which in locust respond to pheromones. One or a few cells express SNMP1 within the multineuron clusters from sensilla basiconica, whereas the SNMP2 subtype was expressed in cells surrounding the neuron clusters, possibly supporting cells. Based on the finding that SNMP1 is expressed in distinct neurons under chemosensory sensilla, it is conceivable that these cells may represent pheromone-responsive neurons of the desert locust.

Molecular Characterization of Six Small Heat Shock Proteins and Their Responses Under Cadmium Stress in Oxya chinensis (Orthoptera: Acridoidea)

Small heat shock proteins (sHSPs) have been implicated in many physiological processes and play important roles in the response to various stresses. In this study, the full-length sequences of six sHSPs: OcHSP19.1, 19.8, 20.4, 20.7, 21.1, and 23.8 were obtained from the rice grasshopper Oxya chinensis transcriptome database. The deduced amino acid sequences of the six OcsHSPs contain a typical α-crystallin domain, which consists of approximately 100 amino acid residues and five β-strands. The phylogenetic analysis suggested that OcHSP23.8 was orthologous to the sHSPs of other species and that OcHSP19.1, 20.4, 20.7, and 21.1 were species specific, whereas OcHSP19.8 did not cluster closely to Orthoptera but was placed on the basal end of the cluster. Developmental stage-dependent and tissue-specific expression patterns were evaluated using quantitative real-time polymerase chain reaction. The six genes were expressed in all developmental stages and showed clear tissue specificity. The cadmium acute experiment indicates that Cd(2+) can induce the six genes. However, various response patterns were observed among these genes under Cd(2+) stress conditions. OcHSP19.1, 19.8, 20.4, and 20.7 were highly induced by 2.61 mM Cd(2+) at 24 h. OcHSP23.8 was significantly upregulated by 2.61 mM Cd(2+) at 6 h. For OcHSP21.1, the highest expression levels were found after treatment with 0.87 mM Cd(2+) for 24 h, 1.74 mM Cd(2+) for 36 h, and 2.61 mM Cd(2+) for 12 h. These differential characteristics will facilitate future investigations into the physiological functions of sHSPs.

Nutrient-dependent control of short neuropeptide F transcript levels via components of the insulin/IGF signaling pathway in the desert locust, Schistocerca gregaria

Peptides of the short neuropeptide F (sNPF) family modulate feeding behavior in a wide variety of insect species, including the desert locust, Schistocerca gregaria. Likewise, the nutritional state of the animal can strongly affect sNPF expression. Although several studies have been published describing these nutrient-dependent effects, it remains largely unclear how they are achieved. In this study, we describe a series of in vivo experiments which indicate that it is not the act of feeding in se, but rather the consequent availability of nutrients in the insect's hemolymph that gives rise to the postprandial modulation of sNPF expression. Furthermore, by performing a series of RNAi-mediated knockdown experiments, we were able to show that components of the evolutionarily conserved insulin/insulin-related growth factor (IGF) signaling pathway form a functional link between nutrient levels and sNPF transcript levels.

Combining RNA-seq and proteomic profiling to identify seminal fluid proteins in the migratory grasshopper Melanoplus sanguinipes (F)

BACKGROUND

Seminal fluid proteins control many aspects of fertilization and in turn, they play a key role in post-mating sexual selection and possibly reproductive isolation. Because effective proteome profiling relies on the availability of high-quality DNA reference databases, our knowledge of these proteins is still largely limited to model organisms with ample genetic resources. New advances in sequencing technology allow for the rapid characterization of transcriptomes at low cost. By combining high throughput RNA-seq and shotgun proteomic profiling, we have characterized the seminal fluid proteins secreted by the primary male accessory gland of the migratory grasshopper (Melanoplus sanguinipes), one of the main agricultural pests in central North America.

RESULTS

Using RNA sequencing, we characterized the transcripts of ~ 8,100 genes expressed in the long hyaline tubules (LHT) of the accessory glands. Proteomic profiling identified 353 proteins expressed in the long hyaline tubules (LHT). Of special interest are seminal fluid proteins (SFPs), such as EJAC-SP, ACE and prostaglandin synthetases, which are known to regulate female oviposition in insects.

CONCLUSIONS

Our study provides new insights into the proteomic components of male ejaculate in Orthopterans, and highlights several important patterns. First, the presence of proteins that lack predicted classical secretory tags in accessory gland proteomes is common in male accessory glands. Second, the products of a few highly expressed genes dominate the accessory gland secretions. Third, accessory gland transcriptomes are enriched for novel transcripts. Fourth, there is conservation of SFPs' functional classes across distantly related taxonomic groups with very different life histories, mating systems and sperm transferring mechanisms. The identified SFPs may serve as targets of future efforts to develop species- specific genetic control strategies.

Change in the Chemical Profile of Mangifera indica Leaves after their Metabolism in the Tropidacris collaris Grasshopper

This present work addresses research on the discovery of new compounds from natural sources. It is based on a study of Mangifera indica leaf metabolism by the Tropidacris collaris grasshopper. We found that the grasshopper hydrolyzed the flavonoid isoquercitrin to quercetin when the O-glycosidic bond was broken and sugar released as a probable energy source for the insect. There was not, however, hydrolysis of the major compound in the leaves, mangiferin, which contains the C-glycosidic bond. All compounds were isolated and their chemical structure determined by UV, IR, MS, 1H and 13C NMR.

Transcriptional response of two metallothionein genes (OcMT1 and OcMT2) and histological changes in Oxya chinensis (Orthoptera: Acridoidea) exposed to three trace metals

This study evaluated the transcriptional responses of two metallothionein (MT) genes (OcMT1 and OcMT2) in various tissues (brain, optic lobe, Malpighian tubules, fat bodies, foregut, gastric caeca, midgut and hindgut) of Oxya chinensis (Thunberg) (Orthoptera: Acridoidea) after exposed to the trace metals cadmium (Cd), copper (Cu) and zinc (Zn) for 48h. The study revealed that the exposure of O. chinensis to each of the three metals at the median lethal concentration (LC50) or lower concentration(s) up-regulated the transcriptions of both OcMT1 and OCMT2 in the eight tissues except for OcMT1 and OcMT2 with Cd in brain and gastric caeca, respectively, and OcMT2 with Cu in gastric caeca. These results suggested that the exposure of O. chinensis to the metals may enhance MT biosynthesis that protects tissues by binding these metals in various tissues. To examine possible histopathological effect of the metals, we examined the histological changes in the fat bodies after O. chinensis was exposed to each of these metals at LC50. The exposure of Cd significantly reduced the size and number of adipocytes as compared with the control. However, such an effect was not observed in O. chinensis exposed to either Cu or Zn. These results suggested that fat bodies might be either significantly affected by Cd or play a crucial role in detoxification of excessive trace metals.

Knockdown of the corazonin gene reveals its critical role in the control of gregarious characteristics in the desert locust

The two plague locusts, Schistocerca gregaria and Locusta migratoria, exhibit density-dependent phase polyphenism. Nymphs occurring at low population densities (solitarious forms) are uniformly colored and match their body color to the background color of their habitat, whereas those occurring at high population densities (gregarious) develop black patterns. An injection of the neuropeptide, corazonin (Crz) has been shown to induce black patterns in locusts and affect the classical morphometric ratio, F/C (F, hind femur length; C, maximum head width). We herein identified and cloned the CRZ genes from S. gregaria (SgCRZ) and L. migratoria. A comparative analysis of prepro-Crz sequences among insects showed that the functional peptide was well conserved; its conservation was limited to the peptide region. Silencing of the identified SgCRZ gene in gregarious S. gregaria nymphs markedly lightened their body color and shifted the adult F/C ratio toward the value typical of solitarious forms. In addition, knockdown of the gene in solitarious nymphs strongly inhibited darkening even after a transfer to crowded conditions; however, these individuals developed black patterns after being injected with the Crz as a rescue treatment. SgCRZ was constitutively expressed in the brains of S. gregaria during nymphal development in both phases. This gene was highly expressed not only in the brain in both phases, but also in the corpora allata in the gregarious phase. This conspicuous phase-dependent difference in SgCRZ gene expression may indicate a functional role in the control of phase polyphenism in this locust.

Non-random expression of ribosomal DNA units in a grasshopper showing high intragenomic variation for the ITS2 region

We analyse intragenomic variation of the ITS2 internal transcribed spacer of ribosomal DNA (rDNA) in the grasshopper Eyprepocnemis plorans, by means of tagged PCR 454 amplicon sequencing performed on both genomic DNA (gDNA) and RNA-derived complementary DNA (cDNA), using part of the ITS2 flanking coding regions (5.8S and 28S rDNA) as an internal control for sequencing errors. Six different ITS2 haplotypes (i.e. variants for at least one nucleotide in the complete ITS2 sequence) were found in a single population, one of them (Hap4) being specific to a supernumerary (B) chromosome. The analysis of both gDNA and cDNA from the same individuals provided an estimate of the expression efficiency of the different haplotypes. We found random expression (i.e. about similar recovery in gDNA and cDNA) for three haplotypes (Hap1, Hap2 and Hap5), but significant underexpression for three others (Hap3, Hap4 and Hap6). Hap4 was the most extremely underexpressed and, remarkably, it showed the lowest sequence conservation for the flanking 5.8-28S coding regions in the gDNA reads but the highest conservation (100%) in the cDNA ones, suggesting the preferential expression of mutation-free rDNA units carrying this ITS2 haplotype. These results indicate that the ITS2 region of rDNA is far from complete homogenization in this species, and that the different rDNA units are not expressed at random, with some of them being severely downregulated.

Drosha, Dicer-1 and Argonaute-1 in the desert locust: phylogenetic analyses, transcript profiling and regulation during phase transition and feeding

In this article, we identify and characterise the miRNA machinery components Drosha, Dicer-1 and Argonaute-1 of the desert locust. By means of phylogenetic analyses, we reveal important insights in the evolutionary context of these components. Our data illustrate that insect Argonaute-1 proteins form a monophyletic group with ALG-1 and ALG-2 of Caenorhabditis elegans and with the four (non-Piwi) Argonaute proteins present in humans. On the other hand, humans apparently lack clear homologues of the insect Argonaute-2 proteins. In addition, we demonstrate that drosha, dicer-1 and argonaute-1 display wide transcript tissue-distribution in adult desert locusts, and that during locust phase transition and feeding of starved locusts the expression levels of the miRNA pathway are regulated at the transcript level.