Antioxidant defense response in a galling insect

Involvement of a catalase gene in lignin catalysis and immune defense against pathogenic fungus in Coptotermes formosanus: a potential new target for termite control

BACKGROUND

Detoxifying enzymes are likely involved in lignin feeding and immune defense mechanisms within termites, rendering them potential targets for biological control. However, investigations into the dual functionality of termite detoxification enzymes in vivo have not been documented.

RESULTS

In this study, the complete cDNA of the catalase gene (Cfcat) derived from Coptotermes formosanus Shiraki was amplified. CFCAT comprises an open reading frame spanning 1527 bp, encoding a 508-amino acid sequence. The highest expression was observed in the epidermal tissues (including the fat body and hemolymph) followed by the foregut/salivary gland. Furthermore, we confirmed the catalase activity of the recombinant Cfcat protein. Using RNA interference (RNAi) technology, the importance of Cfcat in the lignin-feeding of C. formosanus was demonstrated, and the role of Cfcat in innate immunity was investigated. Survival assays showed that Cfcat RNAi significantly increased the susceptibility of C. formosanus to Metarhizium anisopliae. Irrespective of the infection status, Cfcat inhibition had a significant impact on multiple factors of humoral and intestinal immunity in C. formosanus. Notably, Cfcat RNAi exhibited a more pronounced immunosuppressive effect on humoral immunity than on intestinal immunity.

CONCLUSION

Cfcat plays an important role in the regulation of innate immunity and lignin feeding in C. formosanus. Cfcat RNAi can weaken the immune response of termites against M. anisopliae, which may aid the biocontrol efficiency of M. anisopliae against C. formosanus. This study provides a theoretical basis and technical reference for the development of a novel biocontrol strategy targeting detoxifying enzymes of termites. © 2024 Society of Chemical Industry.

Antioxidant Defence in Labeo rohita to Biotic and Abiotic Stress: Insight from mRNA Expression, Molecular Characterization and Recombinant Protein-Based ELISA of Catalase, Glutathione Peroxidase, CuZn Superoxide Dismutase, and Glutathione S-Transferase

Fish possess numerous enzymatic antioxidant systems as part of their innate immunity. These systems have been poorly studied in Labeo rohita (rohu). The present study characterized and investigated the role of antioxidant genes in the defence mechanisms against two types of stressors, including infection and ammonia stress. Four key genes associated with antioxidant activity-catalase, glutathione peroxidase, glutathione S-transferase, and CuZn superoxide dismutase were successfully cloned and sequenced. These genes were found to be expressed in different tissues and developmental stages of rohu. The expression levels of these antioxidant genes in the liver and anterior kidney tissues of rohu juveniles were modulated in response to bacterial infection (Aeromonas hydrophila), parasite infection (Argulus siamensis), poly I:C stimulation and ammonia stress. Additionally, the recombinant proteins derived from these genes exhibited significant antioxidant and antibacterial activities. These proteins also demonstrated a protective effect against A. hydrophila infection in rohu and had an immunomodulatory role. Furthermore, indirect ELISA assay systems were developed to measure these protein levels in healthy as well as A. hydrophila and ammonia-induced rohu serum. Overall, this study characterized and emphasised the importance of the antioxidant mechanism in rohu's defence against oxidative damage and microbial diseases.

Midgut Cell Damage and Oxidative Stress in Partamona helleri (Hymenoptera: Apidae) Workers Caused by the Insecticide Lambda-Cyhalothrin

The stingless bee Partamona helleri plays a role in pollinating both native and cultivated plants in the Neotropics. However, its populations can be reduced by the pyrethroid insecticide lambda-cyhalothrin. This compound may cross the intestinal barrier and circulate through the hemolymph, affecting various non-target bee organs. The aim of the present study was to assess the extent of cellular damage in the midgut and the resulting oxidative stress caused by lambda-cyhalothrin in P. helleri workers. Bees were orally exposed to lambda-cyhalothrin. The lethal concentration at which 50% of the bees died (LC50) was 0.043 mg a.i. L-1. The P. helleri workers were fed this concentration of lambda-cyhalothrin and their midguts were evaluated. The results revealed signs of damage in the midgut epithelium, including pyknotic nuclei, cytoplasm vacuolization, changes in the striated border, and the release of cell fragments, indicating that the midgut was compromised. Furthermore, the ingestion of lambda-cyhalothrin led to an increase in the activity of the detoxification enzyme superoxide dismutase and the levels of the NO2/NO3 markers, indicating oxidative stress. Conversely, the activities of the catalase and glutathione S-transferase enzymes decreased, supporting the occurrence of oxidative stress. In conclusion, the ingestion of lambda-cyhalothrin by P. helleri workers resulted in damage to their midguts and induced oxidative stress.

Insight into the regulation of the Nrf2 pathway in response to ascovirus infection in Spodoptera exigua

BACKGROUND

Ascoviruses are a type of entomopathogenic microorganism with high biological pest control potential and are expected to contribute to the natural control of lepidopteran pests. However, knowledge of the molecular mechanism underlying the biocidal activity of ascovirus on its host insects remains limited.

RESULTS

In this study, the relative enzyme activity of superoxide dismutase and peroxidase, as well as the expression level of Spodoptera exigua peroxidase (SePOD), were found to be significantly increased at 6 h post infection with Heliothis virescens ascovirus 3h (HvAV-3h). H₂ O₂ accumulation and enhanced expression of NADPH Oxidase (SeNOX) were also observed. In addition, Nuclear Factor erythroid 2-Related Factor 2 (SeNrf2) and muscle aponeurosis fibromatosis (SeMaf) were overexpressed following infection with HvAV-3h. Silencing of SeNrf2 decreased the expression of SePOD, whereas the mortality of SeNrf2-silenced larvae and viral genome copy number also increased. Further RNA interference of SeNOX significantly decreased expression of SeNrf2 and SePOD and therefore increased the mortality and viral genome copy number of the ascovirus-infected host.

CONCLUSION

The HvAV-3h activated Nrf2/ARE pathway of S. exigua and reactive oxygen species were found to respond to ascovirus infection by regulating alterations in antioxidant enzyme genes mediated by the host Nrf2/ARE pathway. These findings enhance our knowledge of ascovirus-host interactions and lay the foundation for the application of ascoviruses in biological pest control. © 2022 Society of Chemical Industry.

Increased survival of honey bees consuming pollen and beebread is associated with elevated biomarkers of oxidative stress

Introduction

Significant losses of honey bee colonies have been observed worldwide in recent decades. Inadequate nutrition is considered to be one of the factors that can reduce honey bee resistance to abiotic and biotic environmental stresses. Accordingly, we assessed the impact of food composition on worker bee survival.

Methods

Bees in cages were fed six different diets, and then their survival, levels of thiobarbituric acid reactive substances and protein carbonyl groups, catalase and lysozyme activities were evaluated.

Results and Discussion

After 17 days of feeding, the lowest mortality was observed in the group of bees that received sucrose solution with the addition of willow pollen or artificial rapeseed beebread or artificial willow beebread (diets 4–6). The highest mortality was found in bees that consumed only sucrose solution (diet 1) or the sucrose solution supplemented with a mixture of amino acids (diet 2), which can be explained by the lack of vitamins and microelements in these diets. In the group of bees that received the sucrose solution with rapeseed pollen (diet 3), mortality was intermediate. To check whether the decrease in insect survival could be related to oxidative damage, we evaluated biomarkers of oxidative stress. Consumption of pollen (diets 3 and 5) and artificial beebread (diets 4 and 6) enhances protein carbonylation in worker bees. Feeding bees artificial beebread also resulted in increase in lipid peroxidation and catalase activity, which is probably due to the presence of hydrogen peroxide in the honey contained in beebread. Remarkably, the increase in biomarkers of oxidative stress was not accompanied by adverse but positive effects on insect survival. A lack of amino acids and proteins in the diet 1 did not cause oxidative stress, but led to an increase in lysozyme activity in hemolymph, a biomarker of immune system status. In conclusion, we believe that the increase in oxidative stress biomarkers we found do not indicate oxidative damage, but rather reflect the changes in redox balance due to consumption of certain dietary options.

Cannabidiol (CBD) Supports the Honeybee Worker Organism by Activating the Antioxidant System

In the experiment, we tested the effect of 30% CBD oil on the activity of the antioxidant system (superoxide dismutase, catalase, glutathione peroxidase, glutathione), the level of total antioxidant capacity, and the concentrations of ions (calcium, magnesium, and phosphorus) in honeybee workers in the hive test. For this purpose, we prepared hives containing all stages of the development of honey bees and started the experiment by adding 200 marked, one-day old bees to each colony (intended for hemolymph collection). In the test, we created three groups (two colonies per group): (1) Experimental with CBD oil mixed with sugar syrup (CSy); (2) experimental with CBD oil on textile strips (CSt); and (3) control with pure sugar syrup only (C). Every week, we collected hemolymph from the marked bees. In the experiment, all antioxidant enzyme activities were higher for the experimental groups CSy and CSt compared to group C. The highest concentrations/levels were obtained for the CSy group. Concentrations of calcium, magnesium, and phosphorus ions were also higher for the experimental groups compared to the C group (the highest concentration for the CSy group). We conclude that CBD oil positively contributes to stimulating the antioxidant system of honeybees.

Effects of multigenerational imidacloprid and thiamethoxam stress on metabolism and physiology of Aphis glycines Matsumura (Hemiptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), a primary pest of soybean, poses a severe threat to soybean production. In this study, the 4th instar nymphs were exposed to the LC50 and LC30 of imidacloprid and thiamethoxam from F0 to F4 generations to evaluate the activities of peroxidase, pyruvate kinase, and trehalase using microassay. We found that peroxidase and pyruvate kinase activities in soybean aphids increased rapidly, first to peak and then decreased slowly generation by generation under imidacloprid and thiamethoxam stress. In contrast, the trehalase activity was significantly decreased in F1 to F5 generations when treated with the LC50 and LC30 and imidacloprid and thiamethoxam compared to control. In addition, the Enzyme-Linked Immunosorbent Assay (ELISA) was used to monitor the changes in molting and juvenile hormone expressions of the soybean aphids in each generation (F1-F5). The expression of juvenile hormone in soybean aphids was increased significantly in each generation under continuous stress of imidacloprid and thiamethoxam LC50 imidacloprid and LC50 thiamethoxam inhibited the expression of molting hormones in soybean aphids of each generation. LC30 imidacloprid or LC30 thiamethoxam significantly stimulated the expression of molting hormone in the 1st and 2nd instar nymphs in each generation. In this paper, the differences in antioxidant regulation, energy metabolism intensity, and hormone expression of multi-generation soybean aphids were monitored under continuous stress of imidacloprid and thiamethoxam. Our results revealed the effects of continuous insecticide stress on the main endogenous substances. Further, they clarified the regulation rules of resistance in soybean aphids, providing a reference for efficient control with imidacloprid and thiamethoxam.

Role of Genes in Regulating Host Plants Expansion in Tephritid Fruit Flies (Diptera) and Potential for RNAi-Based Control

Host plant expansion is an important survival strategy for tephritids as they expand their range. Successful host expansion requires tephritids to adapt to the chemical and nonchemical properties of a novel host fruit, such as fruit color, phenology, and phytochemicals. These plant properties trigger a series of processes in tephritids, with each process having its own genetic basis, which means that various genes are involved in regulating host plant expansion by tephritids. This review summarizes current knowledge on the categories and roles of genes involved in host plant expansion in several important tephritid species, including genes related to chemoreception (olfactory and gustation), vision, digestion, detoxification, development, ribosomal and energy metabolism. Chemoreception- and detoxification- and digestion-related genes are stimulated by volatile chemicals and secondary chemicals of different hosts, respectively, which are involved in the regulation of nervous signal transduction that triggers behavioral, physical, and chemical responses to the novel host fruit. Vision-, nerve-, and development-related genes and metabolism-associated genes are activated in response to nonchemical stimuli from different hosts, such as color and phenology, to regulate a comprehensive adaptation of the extending host for tephritids. The chemical and nonchemical signals of hosts activate ribosomal and energy-related genes that result in the basic regulation of many processes of host expansion, including detoxification and development. These genes do not regulate novel host use individually, but multiple genes regulate multilevel adaptation to novel host fruits via multiple mechanisms. These genes may also be potential target genes for RNAi-based control of tephritid pests.

Anthropogenic Zinc Exposure Increases Mortality and Antioxidant Gene Expression in Monarch Butterflies with Low Access to Dietary Macronutrients

Biologists seek to understand why organisms vary in their abilities to tolerate anthropogenic contaminants, such as heavy metals. However, few studies have considered how tolerance may be affected by condition-moderating factors such as dietary resource availability. For instance, the availability of crucial limiting macronutrients, such as nitrogen and phosphorous, can vary across space and time either naturally or due to anthropogenic nutrient inputs (e.g., agricultural fertilizers or vehicle emissions). Organisms developing in more macronutrient-rich environments should be of higher overall condition, displaying a greater ability to tolerate metal contaminants. In monarch butterflies (Danaus plexippus), we factorially manipulated dietary macronutrient availability and exposure to zinc, a common metal contaminant in urban habitats that can be toxic but also has nutritional properties. We tested whether (1) the ability to survive zinc exposure depends on dietary macronutrient availability and (2) whether individuals exposed to elevated zinc levels display higher expression of antioxidant genes, given the roles of antioxidants in combatting metal-induced oxidative stress. Exposure to elevated zinc reduced survival only for monarchs developing on a low-macronutrient diet. However, for monarchs developing on a high-macronutrient diet, elevated zinc exposure tended to increase survival. In addition, monarchs exposed to elevated zinc displayed higher expression of antioxidant genes when developing on the low-macronutrient diet but lower expression when developing on the high-macronutrient diet. Altogether, our study shows that organismal survival and oxidative stress responses to anthropogenic zinc contamination depend on the availability of macronutrient resources in the developmental environment. In addition, our results suggest the hypothesis that whether zinc acts as a toxicant or a nutrient may depend on macronutrient supply. Environ Toxicol Chem 2022;41:1286-1296. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Impressive Impact of Hemp Extract on Antioxidant System in Honey Bee (Apis mellifera) Organism

We examined the effect of hemp extract on the activity of the antioxidant system (catalase, peroxidase, glutathione, superoxide dismutase, and total antioxidant capacity) in the hemolymph of adult honey bees (Apis mellifera). The bees were divided into three groups: (1) an experimental group fed with pure sugar syrup with cotton strips soaked with hemp extract put inside the cage; (2) an experimental group fed with a mixture of sugar syrup with hemp extract; and (3) a control group fed with a mixture of sugar and a water–glycerine solution. Hemolymph samples were collected on the 1st day of this study and then every week, until all bees in the group died. The activities of all antioxidant enzymes were higher for the experimental groups, compared to those for the control group. The highest antioxidant activities were noted in the group supplemented with cannabis with the use of syringes. Supplementation with hemp also increased the lifespan of bees in this group compared to that of the bees consuming only sugar syrup (control: 35 days), with 49 and 52 days for groups of cannabis on strips and in syrup, respectively. Hemp extract, thanks to its antioxidant properties, increased the activities of key antioxidant enzymes that protect the bee’s organisms against free radicals and thus delay the aging processes.

Transcriptional expression analysis reveals multiple effects of nonylphenol exposure on scallop immune system

Nonylphenol (NP) is an endocrine disruptor and environmental hormone representing alkylphenol compounds. Marine mollusks are an important source of protein for people worldwide. Many researchers have begun to study the effect of NP on marine mollusks immune system in view of its toxicity; however, the underlying molecular mechanisms require in-depth analysis. In this study, we focused on the transcriptional expression change of immune-related genes and antioxidant enzymes activities variation after NP exposure in a marine bivalve mollusk, Chlamys farreri, to explore the immunomodulatory capacity of NP in marine mollusks. We identified MAVS (Mitochondrial antiviral signaling protein), a key adaptor molecule in the RLR (RIG-I like receptor) pathway, and studied the expression of multiple immune-related genes in response to different concentrations of NP. The key genes involved in RLR/TLR (Toll like receptor) innate immune pathway, apoptosis, and cellular antioxidation mechanism were investigated. Changes in the enzymatic activities of scallop antioxidant enzymes after NP exposure were also examined. The results revealed that the genes expression and the antioxidant enzymes activities show significant changes, thus proving that NP stimulation affects the scallop immune system. Our research results demonstrate the immunomodulatory capacity of NP in marine bivalve mollusks and lay the foundation for further in-depth analysis of the molecular mechanism of NP toxicity.

Synergistic effects of Zn, Cu, and Ni and Bacillus thuringiensis on the hemocyte count and the antioxidant activities of Hyphantria cunea Drury (Lepidoptera: Arctiidae) larvae

In nature, insects are constantly exposed to various environmental stressors. Heavy metals are one of the important factors of environmental pollution. Heavy metals can cause adverse effects on the growth rate and the survival of herbivores, as well as immune function. In addition to heavy metals, another factor that insects are exposed to in nature is entomopathogens. The cellular and the antioxidant enzyme responses of insects are major bioindicators against the stressors. In this study, the differences in the hemocyte counts and the antioxidant enzyme activities of Hyphantria cunea larvae exposed to the different amounts of zinc, copper, and nickel and Bacillus thuringiensis infection were determined. With metal exposure, the superoxide dismutase, catalase, and glutathione peroxidase activities increased, but the hemocyte counts decreased. Additionally, both the hemocyte counts and the enzyme activities increased with Bacillus thuringiensis infection. Although heavy metal exposure decreased the hemocyte counts and increased the antioxidant enzyme activities, the increase in the hemocyte counts with bacterial infection and the increased antioxidant enzyme activities demonstrated that the response to infection in the insect was stronger and the synergistic effect was occurred. As a result of this study, we found that the activities of superoxide dismutase, catalase, and glutathione peroxidase and the hemocyte counts varied in response to both metal exposure and bacterial infection.

Comparative Hessian Fly Larval Transcriptomics Provides Novel Insight into Host and Nonhost Resistance

The Hessian fly is a destructive pest of wheat. Employing additional molecular strategies can complement wheat's native insect resistance. However, this requires functional characterization of Hessian-fly-responsive genes, which is challenging because of wheat genome complexity. The diploid Brachypodium distachyon (Bd) exhibits nonhost resistance to Hessian fly and displays phenotypic/molecular responses intermediate between resistant and susceptible host wheat, offering a surrogate genome for gene characterization. Here, we compared the transcriptomes of Biotype L larvae residing on resistant/susceptible wheat, and nonhost Bd plants. Larvae from susceptible wheat and nonhost Bd plants revealed similar molecular responses that were distinct from avirulent larval responses on resistant wheat. Secreted salivary gland proteins were strongly up-regulated in all larvae. Genes from various biological pathways and molecular processes were up-regulated in larvae from both susceptible wheat and nonhost Bd plants. However, Bd larval expression levels were intermediate between larvae from susceptible and resistant wheat. Most genes were down-regulated or unchanged in avirulent larvae, correlating with their inability to establish feeding sites and dying within 4-5 days after egg-hatch. Decreased gene expression in Bd larvae, compared to ones on susceptible wheat, potentially led to developmentally delayed 2nd-instars, followed by eventually succumbing to nonhost resistance defense mechanisms.

Acute exposure to fipronil induces oxidative stress, apoptosis and impairs epithelial homeostasis in the midgut of the stingless bee Partamona helleri Friese (Hymenoptera: Apidae)

Partamona helleri is an important pollinator in natural and agricultural ecosystems in the neotropics. However, the foraging activity of this bee increases its risk of exposure to pesticides, which may affect both the individuals and the colony. Thus, this study aims to evaluate the side effects of LC₅₀ of fipronil (0.28 ng a.i. μL^-1) on the midgut morphology, antioxidant activity and some pathways of cell death, proliferation and differentiation in workers of P. helleri, after 24 h of oral exposure. Fipronil caused morphological alterations in the midgut of the bees. The activities of the detoxification enzymes superoxide dismutase, catalase and glutathione S-transferase increased after exposure, which suggests the occurrence of a detoxification mechanism. Furthermore, exposure to fipronil changed the number of positive cells for signaling-pathway proteins in the midgut of bees, which indicates the induction of cell death by the apoptotic pathway and impairment of the midgut epithelial regeneration. These results demonstrate that fipronil may negatively affect the morphology and physiology of the midgut of the stingless bee P. helleri and impose a threat to the survival of non-target organisms.

Comparative transcriptome analysis of the newly discovered insect vector of the pine wood nematode in China, revealing putative genes related to host plant adaptation

BACKGROUND

In many insect species, the larvae/nymphs are unable to disperse far from the oviposition site selected by adults. The Sakhalin pine sawyer Monochamus saltuarius (Gebler) is the newly discovered insect vector of the pine wood nematode (Bursaphelenchus xylophilus) in China. Adult M. saltuarius prefers to oviposit on the host plant Pinus koraiensis, rather than P. tabuliformis. However, the genetic basis of adaptation of the larvae of M. saltuarius with weaken dispersal ability to host environments selected by the adult is not well understood.

RESULTS

In this study, the free amino and fatty acid composition and content of the host plants of M. saltuarius larvae, i.e., P. koraiensis and P. tabuliformis were investigated. Compared with P. koraiensis, P. tabuliformis had a substantially higher content of various free amino acids, while the opposite trend was detected for fatty acid content. The transcriptional profiles of larval populations feeding on P. koraiensis and P. tabuliformis were compared using PacBio Sequel II sequencing combined with Illumina sequencing. The results showed that genes relating to digestion, fatty acid synthesis, detoxification, oxidation-reduction, and stress response, as well as nutrients and energy sensing ability, were differentially expressed, possibly reflecting adaptive changes of M. saltuarius in response to different host diets. Additionally, genes coding for cuticle structure were differentially expressed, indicating that cuticle may be a potential target for plant defense. Differential regulation of genes related to the antibacterial and immune response were also observed, suggesting that larvae of M. saltuarius may have evolved adaptations to cope with bacterial challenges in their host environments.

CONCLUSIONS

The present study provides comprehensive transcriptome resource of M. saltuarius relating to host plant adaptation. Results from this study help to illustrate the fundamental relationship between transcriptional plasticity and adaptation mechanisms of insect herbivores to host plants.

Transcriptome sequencing reveals Cnaphalocrocis medinalis against baculovirus infection by oxidative stress

Cnaphalocrocis medinalis granulovirus (CnmeGV) is a potential microbial agent against the rice leaffolder. Innate immunity is essential for insects to survive pathogenic infection. Therefore, to clarify the immune response of Cnaphalocrocis medinalis to the viral colonization, the gene expression profile of C. medinalis infected with CnmeGV was constructed by RNA-seq. A total of 8,503 differentially expressed genes (DEGs) were found including 5,304 up-regulated and 3,199 down-regulated unigenes. Gene enrichment analysis indicated that these DEGs were mainly linked to protein synthesis and metabolic process as well as ribosome and virus-infection pathways. Specifically, a significantly up-regulated PiggyBac-like transposon gene was identified suggested that the enhancement of transposon activity is related to host immunity. Further, the DEGs encoding oxidative stress related genes were identified and validated by RT-qPCR. Overall, 9 antioxidant enzyme genes and 4 antioxidant protein genes were up-regulated, and the extensive glutathione S-transferase genes were down-regulated. Our results provide a basis for understanding the molecular mechanisms of baculovirus action and oxidative stress response in C. medinalis and other insects.

Response of Protective Enzymes in Western Flower Thrips (Thysanoptera: Thripidae) to Two Leguminous Plants

The western flower thrips, Frankliniella occidentalis, is a major invasive pest of commercially important crops worldwide. We compared the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) and the expressions of two putative SOD and two putative POD sequences in second instar larvae and adults after three generations of adaptation to kidney bean and broad bean plants. The results showed that the SOD, POD, and CAT activities in adults were significantly higher than those in the second instar larvae. The SOD activities were significantly higher in both the second instar larvae and the adults fed on kidney bean (Phaseolus vulgaris) plants versus broad bean (Vicia faba) plants, whereas the POD and CAT activities showed the opposite trend. The gene expression data showed that the FoPOD-2 expression levels were lower in the second instar larvae after three generations of feeding on broad bean plants versus kidney bean plants. The expression levels of FoSOD-1 and FoSOD-2, and FoPOD-1 under broad bean plant treatment were higher than those under kidney bean plant treatment. Additionally, gene expression fluctuated among the different generations. Our results indicated that western flower thrips demonstrated plasticity in gene expression and activity of protective enzymes, which is related to their adaptability to the host plants. Western flower thrips can change the expression of protective enzyme genes and enzyme activity in vivo to better adapt to kidney bean and broad bean plants.

Transcriptome Analysis of Ophraella communa Male Reproductive Tract in Indirect Response to Elevated CO2 and Heat Wave

Increase in atmospheric CO₂ directly affects the insect physiology and behavior, and indirectly affects the herbivorous insects by affecting their hosts. The increase in atmospheric CO₂ is accompanied by an increase in temperature and heat waves. Ophraella communa LeSage is a natural enemy of Ambrosia artemisiifolia (common ragweed). The development and reproduction of this beetle is weakened upon eating common ragweed grown under stress conditions. As female behavior and physiology alter after mating, the reproductive tract of males is likely to modulate reproduction and development in this species. Herein, the transcriptional profiles of testes and accessory glands from male O. communa individuals feeding on common ragweed under conditions of high CO₂ concentration and heat waves and that grown under ambient CO₂ concentration were compared. Differentially expressed genes (DEGs) were identified between the same tissues from beetles fed on common ragweed grown under different stress conditions. There were 3, 2, 3, 1and 5 genes related to decomposition and transport of macromolecular substances, host location, stress response, reproduction, and poisonous food-utilization. No expected response was observed in the male reproductive tract, but some of the identified DEGs might control the development of the population. The results presented here should be helpful in guiding future studies on deciphering the indirect response of other organs to high CO₂ concentration and heat waves, as well as the functions of seminal fluid proteins in O. communa.

Growth Performance and Enzymatic Response of the Grasshopper, Calliptamus abbreviatus (Orthoptera: Acrididae), to Six Plant-Derived Compounds

Plant-derived compounds are sources of biopesticides for the control of insect pests. We compared the growth performance and enzymatic response of the grasshopper Calliptamus abbreviatus Ikonn to six plant-derived compounds (rutin, quercetin, nicotine, matrine, azadirachtin, and rotenone) in laboratory and field trials. When exposed to the six compounds, C. abbreviatus had significantly reduced growth and survival. All the compounds significantly induced an elevated level of reactive oxygen species, indicating oxidative damage. The activity of detoxifying enzymes, including cytochrome P450s, carboxylesterase, glutathione-S-transferase, and UDP-glucuronosyltransferase, and the antioxidant enzymes, including superoxide dismutase, catalase, and peroxidase, all significantly increased after exposure to the six compounds. These data suggest that the six plant-derived compounds had negative effects on C. abbreviatus. Of the six compounds, matrine, azadirachtin, and rotenone were more toxic to C. abbreviatus, followed by nicotine, quercetin, and rutin. These results show the potential of these compounds as botanical pesticides, which can be applied for the biological control of the grasshopper C. abbreviatus.

Exploring integument transcriptomes, cuticle ultrastructure, and cuticular hydrocarbons profiles in eusocial and solitary bee species displaying heterochronic adult cuticle maturation

Differences in the timing of exoskeleton melanization and sclerotization are evident when comparing eusocial and solitary bees. This cuticular maturation heterochrony may be associated with life style, considering that eusocial bees remain protected inside the nest for many days after emergence, while the solitary bees immediately start outside activities. To address this issue, we characterized gene expression using large-scale RNA sequencing (RNA-seq), and quantified cuticular hydrocarbon (CHC) through gas chromatography-mass spectrometry in comparative studies of the integument (cuticle plus its underlying epidermis) of two eusocial and a solitary bee species. In addition, we used transmission electron microscopy (TEM) for studying the developing cuticle of these and other three bee species also differing in life style. We found 13,200, 55,209 and 30,161 transcript types in the integument of the eusocial Apis mellifera and Frieseomelitta varia, and the solitary Centris analis, respectively. In general, structural cuticle proteins and chitin-related genes were upregulated in pharate-adults and newly-emerged bees whereas transcripts for odorant binding proteins, cytochrome P450 and antioxidant proteins were overrepresented in foragers. Consistent with our hypothesis, a distance correlation analysis based on the differentially expressed genes suggested delayed cuticle maturation in A. mellifera in comparison to the solitary bee. However, this was not confirmed in the comparison with F. varia. The expression profiles of 27 of 119 genes displaying functional attributes related to cuticle formation/differentiation were positively correlated between A. mellifera and F. varia, and negatively or non-correlated with C. analis, suggesting roles in cuticular maturation heterochrony. However, we also found transcript profiles positively correlated between each one of the eusocial species and C. analis. Gene co-expression networks greatly differed between the bee species, but we identified common gene interactions exclusively between the eusocial species. Except for F. varia, the TEM analysis is consistent with cuticle development timing adapted to the social or solitary life style. In support to our hypothesis, the absolute quantities of n-alkanes and unsaturated CHCs were significantly higher in foragers than in the earlier developmental phases of the eusocial bees, but did not discriminate newly-emerged from foragers in C. analis. By highlighting differences in integument gene expression, cuticle ultrastructure, and CHC profiles between eusocial and solitary bees, our data provided insights into the process of heterochronic cuticle maturation associated to the way of life.

De novo comparative transcriptome analysis of a rare cicada, with identification of candidate genes related to adaptation to a novel host plant and drier habitats

Background

Although the importance of host plant chemistry in plant–insect interactions is widely recognized, our understanding about the genetic basis underlying the relationship between changes in midgut proteins and adaptation of plant-feeding insects to novel host plants and habitats is very limited. To address this knowledge gap, the transcriptional profiles of midguts among three populations of the cicada Subpsaltria yangi Chen were compared. Among which, the Hancheng (HC) and Fengxiang (FX) populations occurring in the Loess Plateau feed on Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chow, while the population occurring in a much drier habitat in the Helan (HL) Mountains is locally specialized on a chemically divergent plant, Ephedra lepidosperma C. Y. Cheng.

Results

Based on comparative analysis, 1826 (HL vs HC) differentially expressed genes (DEGs) and 723 DEGs (HL vs FX) were identified between the populations utilizing different host plants, including 20, 36, 2, 5 and 2 genes related to digestion, detoxification, oxidation-reduction, stress response and water-deprivation response, respectively, and 35 genes presumably associated with osmoregulation. However, only 183 DEGs were identified between the HC and FX populations, including two genes related to detoxification, two genes related to stress response, and one gene presumably associated with osmoregulation. These results suggest that the weakest expression differences were between the populations utilizing the same host plant and occurring in the closest habitats, which may help explain the metabolic mechanism of adaptation in S. yangi populations to novel host plants and new niches.

Conclusions

The observed differences in gene expression among S. yangi populations are consistent with the hypothesis that the host plant shift and habitat adaptation in the HL population was facilitated by differential regulation of genes related to digestion, detoxification, oxidation-reduction, stress response, water-deprivation response and osmoregulation. The results may inform future studies on the molecular mechanisms underlying the relationship between changes in midgut proteins and adaptation of herbivorous insects to novel host plants and new niches.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5547-y) contains supplementary material, which is available to authorized users.

Fitness Costs of the Glutathione S-Transferase Epsilon 2 (L119F-GSTe2) Mediated Metabolic Resistance to Insecticides in the Major African Malaria Vector Anopheles Funestus

Metabolic resistance to insecticides threatens malaria control. However, little is known about its fitness cost in field populations of malaria vectors, thus limiting the design of suitable resistance management strategies. Here, we assessed the association between the glutathione S-transferase GSTe2-mediated metabolic resistance and life-traits of natural populations of Anopheles funestus. A total of 1200 indoor resting blood-fed female An. funestus (F₀) were collected in Mibellon, Cameroon (2016/2017), and allowed to lay eggs individually. Genotyping of F1 mosquitoes for the L119F-GSTE2 mutation revealed that L/L119-homozygote susceptible (SS) mosquitoes significantly laid more eggs than heterozygotes L119F-RS (odds ratio (OR) = 2.06; p < 0.0001) and homozygote resistant 119F/F-RR (OR = 2.93; p < 0.0001). L/L119-SS susceptible mosquitoes also showed the higher ability for oviposition than 119F/F-RR resistant (OR = 2.68; p = 0.0002) indicating a reduced fecundity in resistant mosquitoes. Furthermore, L119F-RS larvae developed faster (nine days) than L119F-RR and L119F-SS (11 days) (X² = 11.052; degree of freedom (df) = 4; p = 0.02) suggesting a heterozygote advantage effect for larval development. Interestingly, L/L119-SS developed faster than 119F/F-RR (OR = 5.3; p < 0.0001) revealing an increased developmental time in resistant mosquitoes. However, genotyping and sequencing revealed that L119F-RR mosquitoes exhibited a higher adult longevity compared to RS (OR > 2.2; p < 0.05) and SS (OR > 2.1; p < 0.05) with an increased frequency of GSTe2-resistant haplotypes in mosquitoes of D30 after adult emergence. Additionally, comparison of the expression of GSTe2 revealed a significantly increased expression from D1-D30 after emergence of adults (Anova test (F) = 8; df= 3; p = 0.008). The negative association between GSTe2 and some life traits of An. funestus could facilitate new resistance management strategies. However, the increased longevity of GSTe2-resistant mosquitoes suggests that an increase in resistance could exacerbate malaria transmission.

Molecular Characterization of a Mitochondrial Manganese Superoxide Dismutase From Chilo suppressalis (Lepidoptera: Crambidae)

In insects, superoxide dismutases (SODs) play a critical role in the scavenging of harmful reactive oxygen species (ROS) and protecting against oxidative stress induced by various environmental stresses. The Asiatic rice borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), is an economically important insect pest of rice crops. In this study, a mitochondrial manganese SOD (Cs-mMnSOD) gene was characterized in C. suppressalis. The deduced Cs-mMnSOD protein has typical highly conserved features of mitochondrial manganese SODs, including four manganese binding residues, the signature DVWEHAYY peptide, and a mitochondrial-targeting sequence at the N-terminus. Transcription of Cs-mMnSOD was detectable at all developmental stages, but highest in pupae. Furthermore, the mRNA level of Cs-mMnSOD was strongly upregulated (more than twofold increase) following exposure to low and high temperatures (4, 30 and 35°C), insecticides (chlorpyrifos and chlorantraniliprole), and chemical reagents (cumene hydroperoxide, paraquat, H2O2 and CdCl2), but slightly elevated (less than twofold increase) in response to 8°C, abamectin and CuSO4. Additionally, the Cs-mMnSOD transcription results were consistent with the enzymatic activity data of the protein product. Purified recombinant Cs-mMnSOD protein expressed in Escherichia coli displayed SOD activity and thermostability. Furthermore, E. coli cells overexpressing Cs-mMnSOD exhibited long-term resistance to the oxidative inducers cumene hydroperoxide and paraquat. Our findings indicate that Cs-mMnSOD plays an important role in protecting C. suppressalis against oxidative damage.

Spatial response of Medicago truncatula plants to drought and spider mite attack

Plant response to imposition of biotic and abiotic stresses by inducing their defense mechanisms, with the production of reactive oxygen species (ROS) representing a major defense response. The present work examined the simultaneous impact of two key stress factors, drought and spider mite attack (Tetranychus urticae) in Medicago truncatula plants. Hydrogen peroxide (H₂O₂), lipid peroxidation (MDA content) and proline content in well-watered and drought-stressed leaves infested by spider mites along with neighboring leaves were examined in order to investigate the local and systemic effect of the two stresses on the antioxidant and osmoprotective response. High levels of lipid peroxidation were recorded in plants under drought stress and plants under combined drought stress and spider mite feeding compared with control plants. Hydrogen peroxide biosynthesis was significantly induced in plants under drought and spider mite attack, with highest levels detected in the feeding leaf (local response). Proline was accumulated in drought stressed-plants, with the highest levels observed in plants exposed to a combination of drought stress and mite feeding. RT-qPCR expression analysis of key genes implicated in ROS metabolism (PAO, DAO, AOX, CuZnSOD, FeSOD, MnSOD) and proline biosynthesis (P5CR, P5CS) pointed to different patterns of regulation between abiotic and biotic stress, as well as their combination. Exposure of plants to both drought stress and attack by spider mites mainly affected the local antioxidant and osmoprotective response of Medicago truncatula, highlighting the relative significance of drought-induced phenomena in combined drought/mite infestation stress responses.

A novel biomarker for marine environmental pollution of CAT from Mytilus coruscus

Bivalves use anti-oxidative enzyme systems to defend themselves against excessive reactive oxygen species, which are often catalyzed by environmental pollution. As a key member of anti-oxidative enzyme family, catalase plays a crucial role in scavenging the high level of reactive oxygen species to protect organisms against various oxidative stresses. In this study, a catalase homologue was identified from Mytilus coruscus (named McCAT, KX957929). The open reading frame of McCAT was 1844bp with a 5' untranslated region of 341bp and a 3' untranslated region of 927bp. The deduced amino acid sequence was 512 residues in length with theoretical pI/MW 8.02/57.91kDa. BLASTn and phylogenetic analyses strongly suggested that it was a member of catalase, also known as CAT family for its conserved catalytic site motif and proximal heme-ligand signature motif. Real-time fluorescence quantitative PCR showed that constitutive expression of McCAT was occurred, with increasing order in mantle, adductor, gill, hemocyte, gonad and hepatopancreas. It was observed that bacterial infection and heavy metals stimulation up-regulated McCAT mRNA expression in hepatopancreas with time-dependent manners. The maximum expression appeared at 8h after pathogenic bacteria injecting, with 15-fold in Vibrio parahemolyticus and 60-fold in Aeromonas hydrophila than that of 0h. The highest point of McCAT mRNA appeared at different times for exposure to heavy metals with copper at day 5 (0.1mg/L 30-fold, 0.5mg/L 15-fold, 1.5mg/L 6-fold) and plumbum at day 3 (3.0mg/L 20-fold). The enzymatic activity analysis found that McCAT activity in the gill of M. coruscus was affected by heavy metals concentration. The results suggested that McCAT plays a significant role in antioxidation and the expression of McCAT can be used as a biomarker for detection of marine environmental pollution.

Termiticidal lectins from Myracrodruon urundeuva (Anacardiaceae) cause midgut damage when ingested by Nasutitermes corniger (Isoptera: Termitidae) workers

BACKGROUND

Myracrodruon urundeuva is a hardwood tree, and its bark, heartwood and leaf contain lectins (MuBL, MuHL and MuLL respectively) with termiticidal activity against Nasutitermes corniger. In this work, the effects of these lectins on the midgut of N. corniger workers were evaluated.

RESULTS

The insects were supplied with an artificial diet containing the lectins at their respective LC₅₀ (previously determined). At 48 h after treatment, the midguts were dissected and fixed for histopathology analyses. Toluidine-blue-stained midguts from lectin-treated workers showed disorganisation, with the presence of debris in the lumen and the absence of brush border. Fluorescence microscopy revealed that the numbers of digestive and proliferating cells were lower in lectin-treated individuals than in the control, and caspase-3 staining confirmed the occurrence of cell apoptosis. Enteroendocrine cells were not seen in the treated individuals. The midguts from treated insects showed greater staining for peroxidase than the control, suggesting that the lectins caused oxidative stress. Staining with wheat germ agglutinin conjugated to FITC revealed that the lectins interfered with the integrity of the peritrophic matrix.

CONCLUSION

This study showed that termiticidal lectins from M. urundeuva cause severe injuries, oxidative stress and cell death in the midgut of N. corniger workers. © 2016 Society of Chemical Industry.

Metagenomic Sequencing of Diamondback Moth Gut Microbiome Unveils Key Holobiont Adaptations for Herbivory

Herbivore specialists adapt to feed on a specific group of host plants by evolving various mechanisms to respond to plant defenses. Insects also possess complex gut microbiotas but their potential role in adaptation is poorly understood. Our previous study of the genome of diamondback moth, Plutella xylostella, revealed an intrinsic capacity to detoxify plant defense compounds, which is an important factor in its success as a pest. Here we expand on that work with a complete taxonomic and functional profile of the P. xylostella gut microbiota obtained by metagenomic sequencing. Gene enrichment in the metagenome, accompanied by functional identification, revealed an important role of specific gut bacteria in the breakdown of plant cell walls, detoxification of plant phenolics, and synthesis of amino acids. Microbes participating in these pathways mainly belonged to three highly abundant bacteria: Enterobacter cloacae, Enterobacter asburiae, and Carnobacterium maltaromaticum. Results show that while the gut microbial community may be complex, a small number of functionally active species can be disproportionally important. The presence of specific enzymes in the microbiota community, such as supporting amino acid synthesis, digestion and detoxification functions, demonstrates the beneficial interactions between P. xylostella and its gut microbiota. These interactions can be potential targets for manipulation to provide novel pest management approaches.

Increased activities of peroxidase and polyphenol oxidase enhance cassava resistance to Tetranychus urticae

In order to study the function of peroxidase (POD) and polyphenol oxidase (PPO) in cassava resistance to spider mites, we tested the changes of transcription levels and activities of these two protective enzymes in both cassava and Tetranychus urticae (=T. cinnabarinus) during the interaction. The results showed that after damage of the mite-susceptible cassava cultivar BRA900 by T. urticae for 1 and 8 days, the transcription levels of MePOD and MePPO and the activities of POD and PPO showed no significant difference compared with those in undamaged leaves. However, the corresponding transcription levels and activities in 1- and 8-day-damaged leaves of mite-resistant cassava cultivar C1115 increased to a significant level of approximately twofold. When T. urticae fed on BRA900 for 1 and 8 days, the transcription levels of TcPPO and TcPOD and the activities of PPO and POD showed no significant difference compared with those before feeding. However, the corresponding transcription levels and activities of these two protective enzymes in T. urticae feeding on C1115 significantly decreased by about half. This study preliminarily validates the function of POD and PPO in cassava resistance to T. urticae, and provides candidate gene resource for molecular breeding of spider mite-resistant cassava.

Reacquisition of New Meristematic Sites Determines the Development of a New Organ, the Cecidomyiidae Gall on Copaifera langsdorffii Desf. (Fabaceae)

The development of gall shapes has been attributed to the feeding behavior of the galling insects and how the host tissues react to galling stimuli, which ultimately culminate in a variable set of structural responses. A superhost of galling herbivores, Copaifera langsdorffii, hosts a bizarre "horn-shaped" leaflet gall morphotype induced by an unidentified species of Diptera: Cecidomyiidae. By studying the development of this gall morphotype under the anatomical and physiological perspectives, we demonstrate the symptoms of the Cecidomyiidae manipulation over plant tissues, toward the cell redifferentiation and tissue neoformation. The most prominent feature of this gall is the shifting in shape from growth and development phase toward maturation, which imply in metabolites accumulation detected by histochemical tests in meristem-like group of cells within gall structure. We hypothesize that the development of complex galls, such as the horn-shaped demands the reacquisition of cell meristematic competence. Also, as mature galls are green, their photosynthetic activity should be sufficient for their oxygenation, thus compensating the low gas diffusion through the compacted gall parenchyma. We currently conclude that the galling Cecidomyiidae triggers the establishment of new sites of meristematic tissues, which are ultimately responsible for shifting from the young conical to the mature horn-shaped gall morphotype. Accordingly, the conservative photosynthesis activity in gall site maintains tissue homeostasis by avoiding hypoxia and hipercarbia in the highly compacted gall tissues.

Pseudomonas syringae enhances herbivory by suppressing the reactive oxygen burst in Arabidopsis

Plant-herbivore interactions have evolved in the presence of plant-colonizing microbes. These microbes can have important third-party effects on herbivore ecology, as exemplified by drosophilid flies that evolved from ancestors feeding on plant-associated microbes. Leaf-mining flies in the genus Scaptomyza, which is nested within the paraphyletic genus Drosophila, show strong associations with bacteria in the genus Pseudomonas, including Pseudomonas syringae. Adult females are capable of vectoring these bacteria between plants and larvae show a preference for feeding on P. syringae-infected leaves. Here we show that Scaptomyza flava larvae can also vector P. syringae to and from feeding sites, and that they not only feed more, but also develop faster on plants previously infected with P. syringae. Our genetic and physiological data show that P. syringae enhances S. flava feeding on infected plants at least in part by suppressing anti-herbivore defenses mediated by reactive oxygen species.

Feeding on resistant rice leads to enhanced expression of defender against apoptotic cell death (OoDAD1) in the Asian rice gall midge

BACKGROUND

The Asian rice gall midge (Orseolia oryzae) is a destructive insect pest of rice. Gall midge infestation in rice triggers either compatible or incompatible interactions leading to survival or mortality of the feeding maggots, respectively. In incompatible interactions, generation of plant allelochemicals/defense molecules and/or inability of the maggots to continue feeding on the host initiate(s) apoptosis within the maggots. Unraveling these molecular events, triggered within the maggots as a response to feeding on resistant hosts, will enable us to obtain a better understanding of host resistance. The present study points towards the likely involvement of a defender against apoptotic cell death gene (DAD1) in the insect in response to the host defense.

RESULTS

The cDNA coding for the DAD1 orthologue in the rice gall midge (OoDAD1) consisted of 339 nucleotides with one intron of 85 bp and two exons of 208 and 131 nucleotides. The deduced amino acid sequence of OoDAD1 showed a high degree of homology (94.6%) with DAD1 orthologue from the Hessian fly (Mayetiola destructor)--a major dipteran pest of wheat. Southern hybridization analysis indicated that OoDAD1 was present as a single copy in the genomes of the Asian rice gall midge biotypes (GMB) 1, 4 and 4 M. In the interactions involving GMB4 with Jaya (susceptible rice host) the expression level of OoDAD1 in feeding maggots gradually increased to 3-fold at 96 hai (hours after infestation) and peaked to 3.5-fold at 96 hai when compared to that at 24 hai. In contrast, expression in maggots feeding on RP2068 (resistant host) showed a steep increase of more than 8-fold at 24 hai and this level was sustained at 48, 72 and 96 hai when compared with the level in maggots feeding on Jaya at 24 hai. Recombinant OoDAD1, expressed in E. coli cells, when injected into rice seedlings induced a hypersensitive response (HR) in the resistant rice host, RP2068, but not in the susceptible rice variety, Jaya.

CONCLUSIONS

The results indicate that the expression of OoDAD1 is triggered in the feeding maggots probably due to the host resistance response and therefore, is likely an important molecule in the initial stages of the interaction between the midge and its rice host.

Alteration in the expression of antioxidant and detoxification genes in Chironomus riparius exposed to zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnONPs) are widely used in several commercial products due to their unique physicochemical properties. However, their release into the aquatic environments through various anthropogenic activities will lead to toxic effect in aquatic organisms. Although several investigations have been reported on the effect of ZnONPs in aquatic organisms using traditional end points such as survival, growth, and reproduction, the molecular level end points are faster and sensitive. In this study, the expression of different genes involved in oxidative stress response, detoxification, and cellular defense was studied in an ecotoxicologically important bio-monitoring organism Chironomus riparius in order to understand the subcellular effects of ZnONPs. The fourth instar larvae were exposed to 0, 0.2, 2, 10, and 20 mg/L of ZnONPs and Zn ions (in the form of ZnSO4.7H2O) for 24 and 48 h period. The expression of CuZn superoxide dismutase, manganese superoxide dismutase, catalase, phospholipid hydroperoxide glutathione peroxidase, thioredoxin reductase 1 and delta-3, sigma-4 and epsilon-1 classes of glutathione S-transferases, cytochrome p4509AT2, and heat shock protein 70 were studied using real-time polymerase chain reaction method. Gene expression results showed that the expression of genes related to oxidative stress response was more pronounced as a result of ZnONPs exposure as compared to Zn ions. The mRNA expression of genes involved in detoxification and cellular protection was also modulated. Significantly higher expression levels of oxidative stress-related genes shows that oxidative stress is an important mechanism of toxicity as a result of ZnONPs exposure in C. riparius.

Genome-wide characterization and expression profiling of immune genes in the diamondback moth, Plutella xylostella (L.)

The diamondback moth, Plutella xylostella (L.), is a destructive pest that attacks cruciferous crops worldwide. Immune responses are important for interactions between insects and pathogens and information on these underpins the development of strategies for biocontrol-based pest management. Little, however, is known about immune genes and their regulation patterns in P. xylostella. A total of 149 immune-related genes in 20 gene families were identified through comparison of P. xylostella genome with the genomes of other insects. Complete and conserved Toll, IMD and JAK-STAT signaling pathways were found in P. xylostella. Genes involved in pathogen recognition were expanded and more diversified than genes associated with intracellular signal transduction. Gene expression profiles showed that the IMD pathway may regulate expression of antimicrobial peptide (AMP) genes in the midgut, and be related to an observed down-regulation of AMPs in experimental lines of insecticide-resistant P. xylostella. A bacterial feeding study demonstrated that P. xylostella could activate different AMPs in response to bacterial infection. This study has established a framework of comprehensive expression profiles that highlight cues for immune regulation in a major pest. Our work provides a foundation for further studies on the functions of P. xylostella immune genes and mechanisms of innate immunity.

Identification and characterization of two phospholipid hydroperoxide glutathione peroxidase genes from the Mediterranean species of the whitefly Bemisia tabaci complex

Phospholipid hydroperoxide glutathione peroxidases (PHGPXs) are essential enzymes of the cellular antioxidant defense system during insect-plant interactions. However, little attention has been devoted to the functional characterization of PHGXPs in the whitefly Bemisia tabaci. Here, we report the identification and characterization of two PHGPX genes, designated as BtQ-PHGPX1 and BtQ-PHGPX2 from the Mediterranean species of the B. tabaci complex. Sequence analysis indicated that the length of BtQ-PHGPX1 is of 942 bp with a 729 bp open-reading frame (ORF) encoding 242 amino acids, and BtQ-PHGPX2 is of 699 bp with a 567 bp ORF encoding 188 amino acids. Sequence alignment analysis showed that BtQ-PHGPX1 and BtQ-PHGPX2 shared high similarity with other known PHGPXs. The NVASXCGXT, FPCNQFXXQEPG, and IKWNFXKFLV surrounded the reactive cysteine, glutamine, and tryptophan residues, respectively. Recombinant BtQ-PHGPX1 and BtQ-PHGPX2 were overexpressed in Escherichia coli and purified. quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis with whiteflies of different development stages showed that the mRNA levels of BtQ-PHGPX2 were significantly higher in larvae than in other stages. The mRNA levels of BtQ-PHGPX2 were significantly higher than BtQ-PHGPX1 during all the developmental stages. The mRNA levels of BtQ-PHGPX1 and BtQ-PHGPX2 in female adults were relatively higher than in male adults. The expression of BtQ-PHGPX1 and BtQ-PHGPX2 was induced by the insecticide imidacloprid. These results suggest that BtQ-PHGPX1 and BtQ-PHGPX2 may participate in detoxification of oxidative hazards in B. tabaci.

Variation in the salivary proteomes of differentially virulent greenbug (Schizaphis graminum Rondani) biotypes

Greenbug (Schizaphis graminum Rondani) biotypes are classified by their differential virulence to wheat, barley, and sorghum varieties possessing greenbug resistance genes. Virulent greenbug biotypes exert phytotoxic effects upon their hosts during feeding, directly inducing physiological and metabolic alterations and accompanying foliar damage. Comparative analyses of the salivary proteomes of four differentially virulent greenbug biotypes C, E, G, and H showed significant proteomic divergence between biotypes. Thirty-two proteins were identified by LC-MS/MS; the most prevalent of which were three glucose dehydrogenase paralogs (GDH), lipophorin, complementary sex determiner, three proteins of unknown function, carbonic anhydrase, fibroblast growth factor receptor, and abnormal oocyte (ABO). Seven nucleotide-binding proteins were identified, including ABO which is involved in mRNA splicing. Quantitative variation among greenbug biotypes was detected in six proteins; two GDH paralogs, carbonic anhydrase, ABO, and two proteins of unknown function. Our findings reveal that the greenbug salivary proteome differs according to biotype and diverges substantially from those reported for other aphids. The proteomic profiles of greenbug biotypes suggest that interactions between aphid salivary proteins and the plant host result in suppression of plant defenses and cellular transport, and may manipulate transcriptional regulation in the plant host, ultimately allowing the aphid to maintain phloem ingestion.

BIOLOGICAL SIGNIFICANCE

Greenbug (Schizaphis graminum Rondani, GB) is a major phytotoxic aphid pest of wheat, sorghum, and barley. Unlike non-phytotoxic aphids, GB directly damages its host, causing uniformly characteristic symptoms leading to host death. As saliva is the primary interface between the aphid and its plant host, saliva is also the primary aphid biotypic determinant, and differences in biotypic virulence are the result of biotypic variations in salivary content. This study analyzed the exuded saliva of four distinct Greenbug biotypes with a range of virulence to crop lines containing greenbug resistance traits in order to identify differences between salivary proteins of the examined biotypes. Our analyses confirmed that the salivary proteomes of the examined greenbug biotypes differ widely, identified 32 proteins of the greenbug salivary proteome, and found significant proteomic variation between six identified salivary proteins. The proteomic variation identified herein is likely the basis of biotypic virulence, and the proteins identified can serve as the basis for functional studies into both greenbug-induced phytotoxic damage and into the molecular basis of virulence in specific GB biotypes. This article is part of a Special Issue entitled: SI: Proteomics of non-model organisms.

Detoxification activity and energy cost is attenuated in whiteflies feeding on tomato yellow leaf curl China virus-infected tobacco plants

The begomovirus Tomato yellow leaf curl China virus (TYLCCNV) can benefit its vector, the whitefly Bemisia tabaci, through suppressing the defences of their shared host plants. However, the mechanisms of this vector-virus mutualism remain largely unknown on the insect side of the interaction. Here, we compared the transcriptional profiles of female adult whiteflies of B. tabaci Middle East-Asia Minor 1 feeding on TYLCCNV-free and TYLCCNV-infected tobacco plants using the next-generation sequencing technique and quantitative real-time PCR. Interestingly, the genes involved in the oxidative phosphorylation (OXPHOS) pathway and detoxification enzyme were down-regulated in whiteflies feeding on virus-infected plants. Decreased detoxification activity costs less energy, which may reduce OXPHOS activity. Moreover, the genes involved in redox activity were also down-regulated, which may indicate that the reduced OXPHOS activity decreased reactive oxygen species production. Reduced detoxification activity is likely to attenuate energy costs, thereby enhancing the performance of whiteflies on virus-infected plants. These results provide further insight into the mechanisms of the plant-mediated whitefly-virus mutualism. Moreover, our study suggests that investigating the transcriptional profiles on the insect side of the interaction can advance our understanding of the tripartite interactions.

Expression of Orseolia oryzae nucleoside diphosphate kinase (OoNDPK) is enhanced in rice gall midge feeding on susceptible rice hosts and its over-expression leads to salt tolerance in Escherichia coli

The Asian rice gall midge, Orseolia oryzae, is a major dipteran pest of rice, with many known biotypes. The present investigation was initiated to understand the molecular mechanisms of infestation for developing novel integrated pest management strategies. We isolated and characterized a gene, nucleoside diphosphate kinase (OoNDPK), from the rice gall midge, encoding a protein with 169 amino acid residues and with a secretory signal sequence - an observation that assumes significance as salivary gland secretions have been implicated to play a major role in insect-plant interactions. Furthermore, up-regulation (> 18 folds) of OoNDPK was observed in the salivary glands of maggots feeding on susceptible host in contrast to those feeding on resistant host. Phylogenetic analysis revealed similarity of OoNDPK with its dipteran orthologues. 3DLigandSite analysis, of the predicted OoNDPK and its orthologues, revealed phenylalanine and tyrosine residues to be specifically present in NDPK proteins from the plant feeders. Results suggest secretion of OoNDPK into the host plant and its probable involvement in gall midge-rice interaction. Using the coleoptile cell elongation assay, we demonstrated that the recombinant OoNDPK is capable of causing elongation of rice coleoptile cells. Additionally, heterologous expression of OoNDPK in Escherichia coli increased the tolerance of these cells to salt (NaCl; up to 1 mM), hinting at the involvement of this gene in abiotic stress response as well.

Pyrosequencing-based transcriptome analysis of the asian rice gall midge reveals differential response during compatible and incompatible interaction

The Asian rice gall midge (Orseolia oryzae) is a major pest responsible for immense loss in rice productivity. Currently, very little knowledge exists with regard to this insect at the molecular level. The present study was initiated with the aim of developing molecular resources as well as identifying alterations at the transcriptome level in the gall midge maggots that are in a compatible (SH) or in an incompatible interaction (RH) with their rice host. Roche 454 pyrosequencing strategy was used to develop both transcriptomics and genomics resources that led to the identification of 79,028 and 85,395 EST sequences from gall midge biotype 4 (GMB4) maggots feeding on a susceptible and resistant rice variety, TN1 (SH) and Suraksha (RH), respectively. Comparative transcriptome analysis of the maggots in SH and RH revealed over-representation of transcripts from proteolysis and protein phosphorylation in maggots from RH. In contrast, over-representation of transcripts for translation, regulation of transcription and transcripts involved in electron transport chain were observed in maggots from SH. This investigation, besides unveiling various mechanisms underlying insect-plant interactions, will also lead to a better understanding of strategies adopted by insects in general, and the Asian rice gall midge in particular, to overcome host defense.

The molecular characterization of antioxidant enzyme genes in Helicoverpa armigera adults and their involvement in response to ultraviolet-A stress

Ultraviolet (UV) radiation can cause oxidative stress in insects. To gain insight into the roles of different antioxidant enzymes of Helicoverpa armigera adults in response to oxidative stress caused by UV-A at a molecular level, three antioxidant enzyme genes [encoding copper zinc superoxide dismutase (Cu/ZnSOD), catalase (CAT) and glutathione peroxidase (GPX)] were cloned. The deduced amino acid sequences of these genes are similar to that of other insects. In addition, the expression profiles of genes from a classic antioxidant defense system, comprising Cu/ZnSOD, manganese superoxide dismutase (MnSOD), CAT, thioredoxin peroxidase, GPX and glutathione-S-transferase, were also determined. The results indicated that all antioxidant enzyme genes (except MnSOD in females) were significantly upregulated at certain time points (from 30 to 90min) in both male and female adults of H. armigera following UV-A radiation. We also found that longer periods of radiation exposure did not yield higher levels of mRNA expression. Furthermore, changes of determined physiological parameters (glutathione, Cu/ZnSOD and MnSOD activity) were basically consistent with the gene expression profiles. We therefore infer that the different antioxidant enzymes of H. armigera act in a coordinated manner at the transcriptional level against oxidative stress caused by UV-A radiation.

Identification of plasmalogen in the gut of silkworm (Bombyx mori)

Herbivorous insect species are constantly challenged with endogenous and exogenous oxidative stress. Consequently, they possess an array of antioxidant enzymes and small molecular weight antioxidants. Lipid-soluble small molecular antioxidants, such as tocopherols, have not been well studied in insects but may play important antioxidant roles. In this study, we identified plasmalogen phosphatidylethanolamines (pPEs) as well as α-, β/γ-, δ-tocopherol in the larvae of the silkworm Bombyx mori by LCMS analyses and examined their distribution. Plasmalogen are reported to inhibit the metal ion induced oxidation. The composition of tocopherols was the same among gut contents, gut tissues, and the other tissues. However, plasmalogens, a unique class of glycerophospholipids rich in polyunsaturated fatty acids and containing a vinyl ether bond at the sn-1 position, were mainly distributed in gut tissues. Plasmalogens might protect gut tissues from oxidation stress.

The proximal costs of case construction in caddisflies: antioxidant and life history responses

Animal construction allows organisms to cope with environmental variations but the physiological costs of such behaviour are still poorly understood. The aim of the present study was to measure the physiological cost of construction behaviour through the oxidative balance that is known to affect the ability of organs to function, stimulates senescence processes and ultimately impacts the fitness of the organism. We used larvae of caddisfly, Limnephilus rhombicus, by experimentally modifying the effort associated with case building. Larvae that were forced to build a new case showed a significant increase in both total antioxidant capacity and the specific activity of superoxide dismutase 48 and 72 h, respectively, after the initiation of the reconstruction. These results strongly suggest that the larval construction behaviour triggered the production of reactive oxygen species, but their effects were reversed 7 days after the reconstruction. In the animals that were forced to build a new case, oxidative stress appeared to be mitigated by a network of antioxidant defences because no oxidative damage was observed in proteins compared with the control larvae. At the adult stage, while longevity was not sex dependent and was not affected by the treatment, body mass and body size of adult males from the reconstruction treatment were significantly lower than the control values. This unexpected sex effect together with data on oxidative stress highlights the difficulty of determining the physiological cost associated with energy-demanding behaviours, implying a consideration of both their energetic and non-energetic components is required.

RNA-Seq and molecular docking reveal multi-level pesticide resistance in the bed bug

BACKGROUND

Bed bugs (Cimex lectularius) are hematophagous nocturnal parasites of humans that have attained high impact status due to their worldwide resurgence. The sudden and rampant resurgence of C. lectularius has been attributed to numerous factors including frequent international travel, narrower pest management practices, and insecticide resistance.

RESULTS

We performed a next-generation RNA sequencing (RNA-Seq) experiment to find differentially expressed genes between pesticide-resistant (PR) and pesticide-susceptible (PS) strains of C. lectularius. A reference transcriptome database of 51,492 expressed sequence tags (ESTs) was created by combining the databases derived from de novo assembled mRNA-Seq tags (30,404 ESTs) and our previous 454 pyrosequenced database (21,088 ESTs). The two-way GLMseq analysis revealed ~15,000 highly significant differentially expressed ESTs between the PR and PS strains. Among the top 5,000 differentially expressed ESTs, 109 putative defense genes (cuticular proteins, cytochrome P450s, antioxidant genes, ABC transporters, glutathione S-transferases, carboxylesterases and acetyl cholinesterase) involved in penetration resistance and metabolic resistance were identified. Tissue and development-specific expression of P450 CYP3 clan members showed high mRNA levels in the cuticle, Malpighian tubules, and midgut; and in early instar nymphs, respectively. Lastly, molecular modeling and docking of a candidate cytochrome P450 (CYP397A1V2) revealed the flexibility of the deduced protein to metabolize a broad range of insecticide substrates including DDT, deltamethrin, permethrin, and imidacloprid.

CONCLUSIONS

We developed significant molecular resources for C. lectularius putatively involved in metabolic resistance as well as those participating in other modes of insecticide resistance. RNA-Seq profiles of PR strains combined with tissue-specific profiles and molecular docking revealed multi-level insecticide resistance in C. lectularius. Future research that is targeted towards RNA interference (RNAi) on the identified metabolic targets such as cytochrome P450s and cuticular proteins could lay the foundation for a better understanding of the genetic basis of insecticide resistance in C. lectularius.

Effects of antinutrient proteins on Hessian fly (Diptera: Cecidomyiidae) larvae

One strategy to enhance the durability of Hessian fly resistance (R) genes in wheat is to combine them with transgenes for resistance. To identify potential transgenes for resistance a protocol for rapidly screening the proteins they encode for efficacy toward resistance is required. However, the Hessian fly is an obligate parasite of wheat and related grasses. Consequently, no protocol for in vitro delivery of antinutrient or toxic proteins to feeding larvae is available. We report here the development of a Hessian fly in plantatranslocation (HIT) feeding assay and the evaluation of eight lectins and the Bowman-Birk serine proteinase inhibitor for potential in transgenic resistance. Of the antinutrient proteins evaluated, Galanthus nivalis L. agglutinin (GNA), commonly termed snowdrop lectin, was the most efficacious. Ingestion of GNA caused a significant reduction in growth of Hessian fly larvae, disruption of midgut microvilli, and changes in transcript level of genes involved in carbohydrate metabolism, digestion, detoxification, and stress response. These effects of GNA are discussed from the perspective of larval Hessian fly physiology.

Cadmium exposure route affects antioxidant responses in the mayfly Centroptilum triangulifer

Aquatic organisms accumulate metals directly from water and from their diets. Exposure to metals is known to generate oxidative stress in living organisms and this stress may be ameliorated via activation of antioxidant enzymes and non-enzymatic antioxidants. To determine if antioxidant physiology is dependent on Cd exposure route in the mayfly Centroptilum triangulifer, we exposed larvae to environmentally relevant concentrations of Cd from isolated dissolved or dietary exposure routes to achieve comparable tissue concentrations. Dissolved Cd had no effect on the antioxidant enzymes examined. However, dietary Cd significantly suppressed catalase and superoxide dismutase activities, and decreased concentrations of the reduced (active) form of glutathione in C. triangulifer larvae. These findings suggest that dietary Cd is potentially more toxic than aqueously derived Cd in this mayfly. We further examined the effect of dietary Cd tissue loading rates on antioxidant enzyme suppression and found that absolute tissue load appeared more important than loading rate. These results may help explain why insects are routinely unresponsive to dissolved metal exposures in the laboratory, yet highly responsive to metal pollution in nature.

Compatible interaction with its rice host leads to enhanced expression of the gamma subunit of oligosaccharyl transferase in the Asian rice gall midge, Orseolia oryzae

The Asian rice gall midge, Orseolia oryzae, is a fast evolving, damaging pest of rice. Understanding the underlying molecular mechanism of interaction between the gall midge and rice will help in devising strategies to control and manage the pest. The present study aims to identify rice-responsive genes in the gall midge that aid pest survival. The abundance of transcripts coding for enzymes related to glycosylation, in a cDNA library prepared from maggots of the rice gall midge feeding on susceptible hosts, indicated their probable involvement in the gall midge-rice interaction. Hence, a full-length transcript for a gamma subunit of the oligosaccharyl transferase gene (OoOST) from the gall midge was cloned and characterized. It has 72% similarity to its orthologue cloned from Aedes aegypti. Tissue-specific analysis of the expression of OoOST revealed an increase (> sevenfold) in the transcripts of the gene in the salivary glands of maggots in susceptible plants when compared with the transcript level in the salivary glands of maggots feeding on resistant hosts. Using quantitative PCR, performed on different developmental stages of the maggots in two susceptible and two resistant hosts, we observed similar expression patterns (i.e. overexpression in the compatible interaction). These results indicate the involvement of OoOST in maggot survival and establishment in the susceptible host. In order to identify polymorphism in the gene, OoOST was cloned from three gall midge biotypes GMB1, GMB4 and GMB4M.

Effect of magnetic fields on antioxidative defense and fitness-related traits of Baculum extradentatum (insecta, phasmatodea)

This study aimed to determine the effect of magnetic fields on the antioxidative defense and fitness-related traits of Baculum extradentatum. Following exposure to magnetic fields, antioxidative defense (superoxide dismutase (SOD), catalase (CAT) activities, and total glutathione (GSH) content) and fitness-related traits (egg mortality, development dynamics, and mass of nymphs) were monitored in nymphs. The experimental groups were: control (kept out of influence of the magnets), a group exposed to a constant magnetic field (CMF) of 50 mT, and a group exposed to an alternating magnetic field (AMF) of 50 Hz, 6 mT. We found increased SOD and CAT activities in animals exposed to constant and AMFs, whereas GSH activity was not influenced by experimental magnetic fields. No differences were found in egg mortality between control and experimental groups. Significant differences in the time of development between the control and the CMF group were observed, as well as between the CMF and the AMF group. No differences were found in the mass of the nymphs between the three experimental groups. In conclusion, CMF and AMF have the possibility to modulate the antioxidative defense and some of the fitness-related traits in B. extradentatum.