Oedaleus Asiaticus Research Articles

High-carb diet gives migrating locusts a head start

Some feats of migration are truly astounding. Arctic terns journey pole to pole each year, the great-great-great-grandchildren of the monarch butterflies that embarked initially in autumn return to their northern homes after their ∼5000 km odyssey and some desert locusts have even crossed the Atlantic, reaching the Caribbean and South America from North Africa. Stav Talal and colleagues from Arizona State University (ASU) explain that most creatures fuel these epic voyages with carbohydrate and energy-rich lipids, often obtained directly from an animal's diet. However, locusts, which tend to feast on vegetation, have to supply their own lipid fuels created from the carbohydrates in their diet and little was known about the impact that a locust's diet might have on its ability to sustain a long flight. In 2017, Arianne Cease, Jon Harrison and ASU colleagues discovered that Mongolian locusts (Oedaleus asiaticus) raised on a high-carb diet flew longer than locusts fed a low-carb diet. But how well would the true champions of the locust world, the migratory locust (Locusta migratoria), fly when they too were provided with a high-carb diet?‘We reared the locusts in crowded cages from hatchlings, sometimes with more than 1000 locusts in one cage, to produce the migratory form of the insects’, says Talal, who, with Geoffrey Osgood (ASU), fed the locusts one of three separate diets – a high-carb, low-protein diet; a medium-carb, medium-protein diet; and a low-carb, high-protein diet – before building locust-sized flight tunnels to measure the insects’ flight endurance. Filming more than 100 locusts, the team recorded that the locusts on the high-carb diet had the most stamina, while the locusts that had been reared on the low-carb diet were much weaker. ‘Six out of 34 locusts fed the high-carb diet flew continuously for 12 h, whereas only one locust out of 35 from the medium-carb diet flew for 12 h’ says Shivam Parmar (ASU), adding that none of the locusts on the low-carb diet managed to fly for the full 12 h. But how had the diets affected the locusts’ body composition and how did that change after their epic flights?Sure enough, when Parmar and Talal compared the locusts, the insects that had dined on the high-carb food were carrying the most lipid, accounting for up to 37% of their body mass, before embarking on their day-long flights. But by the time they had completed their marathons, all of the insects, regardless of diet, had used up a significant proportion of their lipid stores. However, even though the low-carb diet locusts were still carrying 75 mg of lipid – which is sufficient to keep a locust airborne for a full 12 h – they stopped flying after just 5.5 h. So why were they giving up so soon?The team suspects that several factors could be responsible for the low-carb locusts giving up early. They suggest that the locusts may simply be guarding their carbohydrate reserves, terminating a flight when their carb levels fall too low, or a high-carb diet might somehow protect flying insects from the damaging effects of oxygen that they use to power their flight. Another possibility is that the locusts fed a low-carb diet dry out faster when flying, or their muscle composition might be subtly different, limiting their endurance.Whatever the reason, it is clear that a high-carb diet is essential for locusts intent on a high endurance flight, unless they get some tailwind assistance, which probably accounts for the intrepid transatlantic voyage of the locusts that made it all the way to South America.

Phenotypic and Differential Gene Expression Analyses of Phase Transition in Oedaleus asiaticus under High-Density Population Stress.

The high-density-dependent phase change from solitary to gregarious individuals in locusts is a typical example of phenotypic plasticity. However, the underlying molecular mechanism is not clear. In this study, first, Oedaleus asiaticus were treated with high-density population stress and then analyzed by Illumina sequencing on days 1, 3, 5, and 7 of the body color change to identify the stage-specific differentially expressed genes (DEGs). The KEGG pathway enrichment analysis of the identified DEGs revealed their role in metabolic pathways. Furthermore, the expression patterns of the nine key DEGs were studied in detail; this showed that the material change in locusts began on the third day of the high-density treatment, with the number of DEGs being the largest, indicating the importance of this period in the phase transition. In addition, the phenotypic change involved several key genes of important regulatory pathways, possibly working in a complex network. Phenotypic plasticity in locusts is multifactorial, involving multilevel material network interactions. This study improves the mechanistic understanding of phenotypic variation in insects at the genetic level.

Resistance to Beta-cypermethrin, Azadirachtin, and Matrine, and Biochemical Characterization of Field Populations of Oedaleus asiaticus (Bey-Bienko) in Inner Mongolia, Northern China.

Oedaleus asiaticus (Bey-Bienko) is an economically devastating locust species found in grassland and pastoral areas of the Inner Mongolia region of northern China. In this study, resistance to three frequently used insecticides (beta-cypermethrin, matrine, and azadirachtin) was investigated in six field populations of O. asiaticus using the leaf-dip bioassay method. The inhibitory effects of synergists and the activities of detoxification enzyme activities in the different populations were determined to explore potential biochemical resistance mechanisms. The results showed that the field populations SB (resistance ratio [RR] = 7.85), ZB (RR = 5.64), and DB (RR = 6.75) had developed low levels of resistance to beta-cypermethrin compared with a susceptible control strain. Both the SB (RR = 5.92) and XC (RR = 6.38) populations had also developed low levels of resistance against matrine, with the other populations remaining susceptible to both beta-cypermethrin and matrine. All field populations were susceptible to azadirachtin. Synergism analysis showed that triphenyl phosphate (TPP) and diethyl-maleate (DEM) increased the toxicity of beta-cypermethrin significantly in the SB population, while the synergistic effects of TPP, piperonyl butoxide (PBO), and DEM on the toxicity of matrine were higher in SB (SR 3.86, 4.18, and 3.07, respectively) than in SS (SR 2.24, 2.86, and 2.29, respectively), but no synergistic effects of TPP, PBO, and DEM on azadirachtin were found. Biochemical assays showed that the activities of carboxylesterases (CarEs) and glutathione-S-transferases (GSTs) were significantly raised in all field populations of O. asiaticus, with a significant positive correlation observed between beta-cypermethrin resistance and CarE activity. The activities of cytochrome P450 monooxygenases (P450) and multi-function oxidases (MFO) were elevated in all six field populations, and P450 activity displayed strong positive correlations with the three insecticides. Our findings suggest that resistance to beta-cypermethrin in O. asiaticus may be mainly attributed to elevated CarE and GST activities, while P450 plays an important role in metabolizing matrine and azadirachtin. Our study provides insights that will help improve insecticide resistance management strategies.

Effects of Soil Temperature and Moisture on the Development and Survival of Grasshopper Eggs in Inner Mongolian Grasslands

Grasshopper eggs overwinter in soil for almost half a year. Changes in soil temperature and moisture have a substantial effect on grasshopper eggs, especially temperature and moisture extremes. However, the combinatorial effect of temperature and moisture on the development and survival of grasshopper eggs has not been well studied. Here, we examined the effects of different soil moistures (2, 5, 8, 11, 14% water content) at 26°C and combinations of extreme soil moisture and soil temperature on the egg development and survival of three dominant species of grasshopper (Dasyhippus barbipes, Oedaleus asiaticus, and Chorthippus fallax) in Inner Mongolian grasslands. Our data indicated that the egg water content of the three grasshopper species was positively correlated with soil moisture but negatively correlated with hatching time. The relationship between hatching rate and soil moisture was unimodal. Averaged across 2 and 11% soil moisture, a soil temperature of 35oCsignificantly advanced the egg hatching time of D. barbipes, O. asiaticus, and C. fallax by 5.63, 4.75, and 2.63 days and reduced the egg hatching rate of D. barbipes by 18%. Averaged across 26 and 35°C, 2% soil moisture significantly delayed the egg hatching time of D. barbipes, O. asiaticus, and C. fallax by 0.69, 11.01, and 0.31 days, respectively, and decreased the egg hatching rate of D. barbipes by 10%. The hatching time was prolonged as drought exposure duration increased, and the egg hatching rate was negatively correlated with drought exposure duration, except for O. asiaticus. Overall, the combination of high soil temperature and low soil moisture had a significantly negative effect on egg development, survival, and egg hatching. Generally, the response of grasshopper eggs to soil temperature and moisture provides important information on the population dynamics of grasshoppers and their ability to respond to future climate change.

Synergy in Efficacy of Artemisia sieversiana Crude Extract and Metarhizium anisopliae on Resistant Oedaleus asiaticus.

In order to explore the synergistic control effect of crude extracts of Artemisia sieversiana and Metarhizium anisopliae on Oedaleus asiaticus, we used different doses of M. anisopliae and crude extracts of A. sieversiana singly and in combination, to determine their toxicities to fourth instar O. asiaticus. The results showed that the combination of 10% crude extract of A. sieversiana with 107 and 108 spores/g M. anisopliae concentrations and the combination of 20% crude extract of A. sieversiana with 107 and 108 spores/g M. anisopliae concentrations had significant effects on the mortality, body weight gain, body length gain, growth rate, and overall performance of O. asiaticus than those of the crude extract of A. sieversiana and M. anisopliae alone. Among them, the 20% A. sieversiana crude extract mixed with 108 spores/g M. anisopliae and 10% A. sieversiana crude extract combined with 107 spores/g M. anisopliae, had the best control efficacy. In order to clarify the biochemical mechanism underlying the immune responses of O. asiaticus to the pesticide treatments, we monitored the activities of four enzymes: superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT), and polyphenol oxidase (PPO). The results showed that the activities of three enzymes (SOD, CAT, and PPO) were significantly increased from the treatment with the combination of M. anisopliae mixed with crude extract of A. sieversiana. Interestingly, compared to the crude extract, the combination treatment did not significantly induce the expression of POD enzyme activity, which may be a biochemical factor for increasing the control effect of the combination treatment. Our results showed that the combination treatment had synergistic and antagonistic effects on host mortality, growth, development, and enzyme activities in O. asiaticus.

The survival, growth, and detoxifying enzyme activities of grasshoppers Oedaleus asiaticus (Orthoptera: Acrididae) exposed to toxic rutin

Secondary compounds from plants are often insecticidal. Rutin, a plant bioflavonoid, has demonstrated insect control activity. We studied the survival, growth, and detoxifying enzyme activities of grasshopper Oedaleus asiaticus Bey-Bienko (Orthoptera: Acrididae) exposed to rutin using an artificial indoor feeding trial and field cage study for three years. O. asiaticus had reduced growth rate and decreased survival when exposed to rutin. The 7-day LC50 was 763.7 mg/L. Rutin induced an elevated level of reactive oxygen species (ROS) representing oxygen damage. Activities of antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD); and the detoxifying enzymes, cytochrome P450s (CYP450s), UDP-glucuronosyltransferase (UGTs), carboxylesterase (CarEs), and glutathione-S-transferase (GSTs) were all significantly increased when Oedaleus asiaticus exposed to rutin. Rutin was toxic to O. asiaticus and suppressed grasshopper growth. The detrimental effects of rutin to O. asiaticus offer a new option for the development of biological pesticides and potential application to grasshopper biological control.

Migratory Take-Off Behaviour of the Mongolian Grasshopper Oedaleus asiaticus.

Oedaleus asiaticus is one of the dominant species of grasshoppers in the rangeland on the Mongolian plateau, and a serious pest, but its migratory behavior is poorly known. We investigated the take-off behavior of migratory O. asiaticus in field cages in the inner Mongolia region of northern China. The species shows a degree of density-dependent phase polyphenism, with high-density swarming populations characterized by a brown morph, while low-density populations are more likely to comprise a green morph. We found that only 12.4% of brown morphs engaged in migratory take-off, and 2.0% of green morphs. Migratory grasshoppers took off at dusk, especially in the half hour after sunset (20:00–20:30 h). Most emigrating individuals did not have any food in their digestive tract, and the females were mated but with immature ovaries. In contrast, non-emigrating individuals rarely had empty digestive tracts, and most females were mated and sexually mature. Therefore, it seems clear that individuals prepare for migration in the afternoon by eliminating food residue from the body, and migration is largely restricted to sexually immature stages (at least in females). Furthermore, it was found that weather conditions (particularly temperature and wind speed at 15:00 h) in the afternoon had a significant effect on take-off that evening, with O. asiaticus preferring to take off in warm, dry and calm weather. The findings of this study will contribute to a reliable basis for forecasting migratory movements of this pest.

Inhibitory effect of genistein and PTP1B on grasshopper Oedaleus asiaticus development

Protein tyrosine kinase (PTKs) and protein tyrosine phosphatase (PTPs) collectively regulate the insect insulin-signaling pathway (ISP), cell growth, metabolism, proliferation, differentiation, cell communication and monitoring of immune responses. We studied the inhibitory response of the grasshopper Oedaleus asiaticus Bey-Bienko to treat with the flavonoid genistein (PTK inhibitor), the enzyme PTP1B-IN-1 (PTP1B inhibitor) and control (dimethyl sulfoxide (DMSO)). Mean survival rates were not significantly different amongst the three treatments, but growth rate, body mass, and overall biological performance were reduced significantly following treatment with genistein. On comparison, treatment with PTP1B-IN-1 was not significantly different from the control. Relative gene expression of INSR, IRS, PI3K, PDK, and Akt was substantially lower (P < 0.05) following treatment with genistein compared to PTP1B-IN-1 and control. Similarly, gene expression and protein phosphorylation levels of the PTK5, PTP1B → FOXO cascade, indicators of stress response in the ISP, were also reduced in response to genistein treatments. The activity of the protective enzymes (POD and CAT) was upregulated by FOXO in response to PTP1B-IN-1. Our results demonstrated that genistein negatively regulates the ISP pathway, with a consequent effect on growth and development of O. asiaticus, as higher energy was required for detoxification. Given the negative effect of genistein on O. asiaticus physiology and development, the compound could be used in a biopesticide formulation for insect pest control in grasslands and other crop plants as a potential application to grasshopper biological control.

Phenotypic and Transcriptomic Response of the Grasshopper Oedaleus asiaticus (Orthoptera: Acrididae) to Toxic Rutin.

Rutin, a widely distributed phytochemical flavonoid, can be used to control insect pests. In this study, we studied the growth performance of the grasshopper Oedaleus asiaticus Bey-Bienko given xenobiotic rutin using feeding experiments and transcriptomic analysis. O. asiaticus had reduced body size, lower survival rate, and reduced growth performance when fed with xenobiotic rutin. Rutin-fed nymphs had large variation in gene expression profiles, with a total of 308 genes significantly upregulated and 287 genes downregulated. The upregulated genes were significantly enriched in stress resistance-, immune-, and detoxification-related biological processes and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Downregulated genes mainly involved cuticle biosynthesis and nutrition metabolism-related pathways. The quantitative real-time PCR (qRT-PCR) analysis of 15 candidate genes also produced results consistent with the transcriptome data. These results suggested that grasshoppers’ capacity for biosynthesis and nutrition metabolism decreased, and stress resistance and metabolized capacity to toxic substances were significantly induced when O. asiaticus was fed on xenobiotic rutin. Rutin, as a phytotoxin, had detrimental effects and induced changes in gene expression profiles for O. asiaticus. This study can provide a molecular basis and offer future opportunities for the development of rutin-related insecticides and their application to grasshopper control.

Three Chemosensory Proteins Involved in Chemoreception of Oedaleus asiaticus (Orthopera: Acridoidea).

Chemosensory proteins (CSPs) are thought to play roles in the insect olfactory system by binding and carrying hydrophobic odorants across the aqueous sensillar lymph. The band-winged grasshopper, Oedaleus asiaticus Bei-Bienko, is one of the most important grasshopper pests in northern China, but there is little information about its olfactory system. In order to investigate the olfactory functions of CSPs in this pest, three CSP genes (OasiCSP4, OasiCSP11 and OasiCSP12) were expressed in Escherichia coli, and the binding affinities of the three recombinant CSP proteins were measured for 16 volatiles from the host plant (Stipa krylovii), fecal material and body of live adult O. asiaticus using fluorescence competitive binding assays. To further verify their olfactory functions, RNA interference (RNAi) and electrophysiological recording were conducted. The three recombinant proteins displayed different degrees of binding to various volatiles in ligand-binding assays, with OasiCSP12 having higher binding affinities for more volatiles than OasiCSP4 and OasiCSP11. OasiCSP12 exhibited strong binding affinities (Ki < 20 μΜ) for five host plant volatiles and one volatile from the live body of adult O. asiaticus. The transcript levels of the three OasiCSP genes were significantly lower after silencing the individual genes by RNAi, which in turn reduced the EAG responses in adults of both sexes to most tested compounds. Our study indicates that these three OasiCSPs are involved in the detection of volatile semiochemicals, and may play important roles in finding host plants and in aggregation in O. asiaticus.

Plant composition changes in a small-scale community have a large effect on the performance of an economically important grassland pest

BackgroundThe grasshopper Oedaleus asiaticus Bey-Bienko (Acrididae: Oedipodinae) is a dominant and economically important pest that is widely distributed across the Mongolian plateau. This herbivore pest causes major damage to the grassland of the Inner Mongolian steppe in China. The population dynamics of herbivore pests is affected by grassland management practices (e.g., mowing and heavy livestock grazing) that alter plant community structures and stoichiometric characteristics. For example, O. asiaticus outbreak is closely associated with plant preference changes caused by nitrogen loss from heavy livestock grazing. However, the manner by which small-scale variation in vegetation affects grasshopper performance and promotes outbreak is poorly characterized. To address this question, we investigated the relationship between small-scale (1 m2) vegetation variability and measures of O. asiaticus performance associated with plant stoichiometric characteristics.ResultsWe found that food preferences of O. asiaticus varied significantly, but maintained a specific dietary structure for different plant compositions. Notably, small-scale changes in plant community composition significantly affected grasshopper food preference and body size. Partial least-square modeling indicated that plant proportion and biomass affected grasshopper body size and density. We found that this effect differed between sexes. Specifically, female body mass positively correlated with the proportion of Stipa krylovii grass, whereas male mass positively correlated with the proportion of Artemisia frigida grass. Further analyses indicated that grasshopper performance is closely associated with plant stoichiometric traits that might be responsible for the pest’s plague.ConclusionsThis study provides valuable information for managing grasshoppers using rational grassland management practices.

Dietary Stress From Plant Secondary Metabolites Contributes to Grasshopper (Oedaleus asiaticus) Migration or Plague by Regulating Insect Insulin-Like Signaling Pathway.

Diets essentially affect the ecological distribution of insects, and may contribute to or even accelerate pest plague outbreaks. The grasshopper, Oedaleus asiaticus B-Bienko (OA), is a persistent pest occurring in northern Asian grasslands. Migration and plague of this grasshopper is tightly related to two specific food plants, Stipa krylovii Roshev and Leymus chinensis (Trin.) Tzvel. However, how these diets regulate and contribute to plague is not clearly understood. Ecological studies have shown that L. chinensis is detrimental to OA growth due to the presence of high secondary metabolites, and that S. krylovii is beneficial because of the low levels of secondary metabolites. Moreover, in field habitats consisting mainly of these two grasses, OA density has negative correlation to high secondary metabolites and a positive correlation to nutrition content for high energy demand. These two grasses act as a ‘push-pull,’ thus enabling the grasshopper plague. Molecular analysis showed that gene expression and protein phosphorylation level of the IGF → FOXO cascade in the insulin-like signaling pathway (ILP) of OA negatively correlated to dietary secondary metabolites. High secondary metabolites in L. chinensis down-regulates the ILP pathway that generally is detrimental to insect survival and growth, and benefits insect detoxification with high energy cost. The changed ILP could explain the poor growth of grasshoppers and fewer distributions in the presence of L. chinensis. Plants can substantially affect grasshopper gene expression, protein function, growth, and ecological distribution. Down-regulation of grasshopper ILP due to diet stress caused by high secondary metabolites containing plants, such as L. chinensis, results in poor grasshopper growth and consequently drives grasshopper migration to preferable diet, such as S. krylovii, thus contributing to grasshopper plague outbreaks.

Quercetin Affects the Growth and Development of the Grasshopper Oedaleus asiaticus (Orthoptera: Acrididae).

Flavonoids are secondary metabolites that help plants resist insect attack, but pest insects have evolved enzymes that reduce the toxicity of these secondary metabolites. We studied the response of the grasshopper Oedaleus asiaticus Bey-Bienko fed different concentrations of quercetin, a representative flavonoid. Oedaleus asiaticus growth (survival rate and growth rate) was significantly reduced at high quercetin concentrations. Reactive oxygen species (ROS) increased significantly in response to the diet stress associated with high quercetin concentrations. Gene expression and protein phosphorylation level of the IGF→FOXO cascade related to the stress response in the O. asiaticus insulin-like signaling pathway (ILP) were also reduced. Multiple protective enzyme activities were regulated by FOXO. Mixed-function oxidase (MFO), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), were all significantly increased with exposure to high quercetin concentrations. Quercetin negatively regulated the ILP pathway, and was detrimental to O. asiaticus growth and survival, as more energy was required for detoxification. This study showed how flavonoids impact on O. asiaticus biochemical pathways, physiology, and development. Flavonoids offer a new option for the development of biological pesticides for application to grasshopper biological control.

Identification and expression profiling of candidate chemosensory membrane proteins in the band-winged grasshopper, Oedaleus asiaticus

The band-winged grasshopper Oedaleus asiaticus (Orthoptera: Acridoidea) is an important insect pest in north China. Chemosensory membrane proteins are believed to be crucial factors in direct interactions with odorants in the chemosensory process. However, there is much limited information on the chemosensory system in this pest. In this study, a total of 69 candidate chemosensory membrane protein genes, including 60 olfactory receptors (ORs), 6 ionotropic receptors (IRs) and 3 sensory neuron membrane proteins (SNMPs), were identified for the first time from the antennal transcriptomes of O. asiaticus. Blastp match and phylogenetic analysis demonstrated that these chemosensory membrane proteins were the closest to their orthologous species, Locusta migratoria. The qRT-PCR analysis revealed that all tested 14 OR and two SNMP genes (OasiSNMP1 and OasiSNMP2a) were strongly expressed in adult antennae, and nearly all tested genes (15/16) displayed significant differences in the expression levels between both sexes. Moreover, two IR genes (OasiIR25a and OasiIR76b) had uniquely high expression levels in the antennae, labial palps and maxillary palps, while three IR genes (OasiIR1, OasiIR2 and OasiIR3) were highly expressed in most tested tissues (heads without antennae and mouthparts, labial palps, maxillary palps, labia without labial palps, thoraxes, tarsi, and abdomens) except for antennae, labra, and wings but OasiIR5a was just faintly expressed in the antennae, labia without labial palps, labial palps, maxillary palps and abdomen. Our results provide important molecular information for further investigation on the chemoreception mechanisms in O. asiaticus.

Role of PTP/PTK trans activated insulin-like signalling pathway in regulation of grasshopper (Oedaleus asiaticus) development.

Protein tyrosine phosphatase (PTPs) and protein tyrosine kinase (PTKs) genes are responsible for the regulation of insect insulin-like pathway (ILP), cells growth, metabolism initiation, gene transcription and observing immune response. Signal transduction in insect cell is also associated with PTPs and PTKs. The grasshopper (Oedaleus asiaticus) 'Bey-Bienko' were treated withdsRNA of protein tyrosine non-receptor type 4 (PTPN4) and protein tyrosine kinase 5 (PTK5) along with control (water). Applying dsPTK5 treatments in 5th instar of Oedaleus asiaticus, significant reduction was recorded in body dry mass, growth rate and overall performance except survival rate. Whereas with PTPN4, no such significant impact on all of these growth parameters was recorded. Expression of genes in ILP 5th instar of Oedaleus asiaticus by the application of dsPTPN4 and dsPTK5 revealed that PTK, INSR (insulin receptor), IRS (insulin receptor substrate), PI3K (phosphoinositide 3-kinase), PDK (3-phosphoinositide-dependent protein kinase), Akt (protein kinase B) and FOXO (forkhead transcription factor) significantly expressed with downregulation except PTPN4, which remained non-significant. On the other hand, the phosphorylation level of ILP four proteins in O. asiaticus with the treatment of dsPTPN4 and dsPTK5 significantly affected P-IRS and P-FOXO, while P-INSR and P-AKT remained stable at the probability level of 5%. This indicated that the stress response in the O. asiaticus insulin-like signalling pathway (ILP) reduced. Regarding association of protective enzymatic activities, ROS (relative oxygen species), CAT (catalase) and PO (phenol oxidase) increased significantly with exposure to dsPTK5 as compared to dsPTPN4 and control, while exposure of 5th instar of O. asiaticus to dsPTPN4 treatment slightly raised CAT and PO activities with but significant contribution. No such significant effect on MFO and POD was seen using dsPTPN4 and dsPTK5. This showed that in the ILP of O. asiaticus, PTK5 was detrimental to growth, body mass and overall performance, which ultimately benefited insect detoxification with high-energy cost.

Diet alters performance and transcription patterns in Oedaleus asiaticus (Orthoptera: Acrididae) grasshoppers.

We reared Oedaleus asiaticus grasshoppers under four different single-plant diets to examine the relationships among diet, performance, stress, and transcription patterns. Grasshoppers fed only Artemisia frigida (Asteraceae) were stressed, as indicated by their lower growth, size, development, and survival, in comparison to grasshoppers fed on any of three grasses, Cleistogenes squarrosa, Leymus chinensis, or Stipa krylovii (all Poaceae). We then used transcriptome analysis to examine how gene expression levels in O. asiaticus were altered by feeding on these diets. Nymphs fed A. frigida had the largest variation in gene expression profiles with a total of 299 genes significantly up- or down-regulated compared to those feeding on the three grasses: down-regulated genes included those involved in cuticle biosynthesis, DNA replication, biosynthesis and metabolism of nutrition. The up-regulated genes included stress-resistant and detoxifying enzymes. GO and KEGG enrichment analysis also showed that feeding on A. frigida could down-regulate biosynthesis and metabolism related pathways, and up-regulate stress-resistant and detoxification terms and pathways. Our results show that diet significantly altered gene-expression, and that unfavorable, stressful diets induce more transcriptional changes than favorable diets. Altered gene-expression represents phenotypic plasticity, and many such changes appear to be evolved, adaptive responses. The ease and regularity by which individuals shift phenotypes via altered transcription suggests that populations consist not of similar, fixed phenotypes, but of a collection of ever-changing, divergent phenotypes.

Molecular Ecological Basis of Grasshopper (Oedaleus asiaticus) Phenotypic Plasticity under Environmental Selection.

While ecological adaptation in insects can be reflected by plasticity of phenotype, determining the causes and molecular mechanisms for phenotypic plasticity (PP) remains a crucial and still difficult question in ecology, especially where control of insect pests is involved. Oedaleus asiaticus is one of the most dominant pests in the Inner Mongolia steppe and represents an excellent system to study phenotypic plasticity. To better understand ecological factors affecting grasshopper phenotypic plasticity and its molecular control, we conducted a full transcriptional screening of O. asiaticus grasshoppers reared in four different grassland patches in Inner Mongolia. Grasshoppers showed different degrees of PP associated with unique gene expressions and different habitat plant community compositions. Grasshopper performance variables were susceptible to habitat environment conditions and closely associated with plant architectures. Intriguingly, eco-transcriptome analysis revealed five potential candidate genes playing important roles in grasshopper performance, with gene expression closely relating to PP and plant community factors. By linking the grasshopper performances to gene profiles and ecological factors using canonical regression, we first demonstrated the eco-transcriptomic architecture (ETA) of grasshopper phenotypic traits (ETAGPTs). ETAGPTs revealed plant food type, plant density, coverage, and height were the main ecological factors influencing PP, while insect cuticle protein (ICP), negative elongation factor A (NELFA), and lactase-phlorizin hydrolase (LCT) were the key genes associated with PP. Our study gives a clear picture of gene-environment interaction in the formation and maintenance of PP and enriches our understanding of the transcriptional events underlying molecular control of rapid phenotypic plasticity associated with environmental variability. The findings of this study may also provide new targets for pest control and highlight the significance of ecological management practice on grassland conservation.

Biology, physiology and gene expression of grasshopper Oedaleus asiaticus exposed to diet stress from plant secondary compounds

We studied the role of plant primary and secondary metabolites in mediating plant-insect interactions by conducting a no-choice single-plant species field experiment to compare the suitability, enzyme activities, and gene expression of Oedaleus asiaticus grasshoppers feeding on four host and non-host plants with different chemical traits. O. asiaticus growth showed a positive relationship to food nutrition content and a negative relationship to secondary compounds content. Grasshopper amylase, chymotrypsin, and lipase activities were positively related to food starch, crude protein, and lipid content, respectively. Activity of cytochrome P450s, glutathione-S-transferase, and carboxylesterase were positively related to levels of secondary plant compounds. Gene expression of UDP-glucuronosyltransferase 2C1, cytochrome P450 6K1 were also positively related to secondary compounds content in the diet. Grasshoppers feeding on Artemisia frigida, a species with low nutrient content and a high level of secondary compounds, had reduced growth and digestive enzyme activity. They also had higher detoxification enzyme activity and gene expression compared to grasshoppers feeding on the grasses Cleistogenes squarrosa, Leymus chinensis, or Stipa krylovii. These results illustrated Oedaleus asiaticus adaptive responses to diet stress resulting from toxic chemicals, and support the hypothesis that nutritious food benefits insect growth, but plant secondary compounds are detrimental for insect growth.

Nutritional imbalance suppresses migratory phenotypes of the Mongolian locust (Oedaleus asiaticus).

For many species, migration evolves to allow organisms to access better resources. However, the proximate factors that trigger these developmental changes, and how and why these vary across species, remain poorly understood. One prominent hypothesis is that poor-quality food promotes development of migratory phenotypes and this has been clearly shown for some polyphenic insects. In other animals, particularly long-distance bird migrants, it is clear that high-quality food is required to prepare animals for a successful migration. We tested the effect of diet quality on the flight behaviour and morphology of the Mongolian locust, Oedaleus asiaticus. Locusts reared at high population density and fed low-N grass (performance-enhancing for this species) had enhanced migratory morphology relative to locusts fed high-N grass. Furthermore, locusts fed synthetic diets with an optimal 1 : 2 protein : carbohydrate ratio flew for longer times than locusts fed diets with lower or higher protein : carbohydrate ratios. In contrast to the hypothesis that performance-degrading food should enhance migration, our results support the more nuanced hypothesis that high-quality diets promote development of migratory characteristics when migration is physiologically challenging.

Gut Transcriptome Analysis Shows Different Food Utilization Efficiency by the Grasshopper Oedaleous asiaticus (Orthoptera: Acrididae).

Oedaleus asiaticus B. Bienko is a persistent pest occurring in north Asian grasslands. We found that O. asiaticus feeding on Stipa krylovii Roshev. had higher approximate digestibility (AD), efficiency of conversion of ingested food (ECI), and efficiency of conversion of digested food (ECD), compared with cohorts feeding on Leymus chinensis (Trin.) Tzvel, Artemisia frigida Willd., or Cleistogenes squarrosa (Trin.) Keng. Although this indicated high food utilization efficiency for S. krylovii, the physiological processes and molecular mechanisms underlying these biological observations are not well understood. Transcriptome analysis was used to examine how gene expression levels in O. asiaticus gut are altered by feeding on the four plant species. Nymphs (fifth-instar female) that fed on S. krylovii had the largest variation in gene expression profiles, with a total of 88 genes significantly upregulated compared with those feeding on the other three plants, mainly including nutrition digestive genes of protein, carbohydrate, and lipid digestion. GO and KEGG enrichment also showed that feeding S.krylovii could upregulate the nutrition digestion-related molecular function, biological process, and pathways. These changes in transcripts levels indicate that the physiological processes of activating nutrition digestive enzymes and metabolism pathways can well explain the high food utilization of S. krylovii by O. asiaticus.