Biochemical defence of pro-oxidant plant allelochemicals by herbivorous insects

Singlet Oxygen Produced by Aspalathin and Ascorbic Acid Leads to Fragmentation of Dihydrochalcones and Adduct Formation

Singlet oxygen-mediated fragmentation of various dihydrochalcones and chalcones was reported. (Dihydro)cinnamic acids formed in the fragmentation showed a B-ring substitution pattern of the precursor (dihydro)chalcone. For the first time, the intrinsic generation of singlet oxygen by aspalathin and ascorbic acid under mild aqueous conditions (37 °C, pH 7.0) and exclusion of light was verified using HPLC-(+)-APCI-MS2 experiments. If a 4 molar excess of aspalathin or ascorbic acid was used, fragmentation of dihydrochalcones with monohydroxy and o-hydroxymethoxy B-ring substitution was induced up to 2 mol %, respectively. Incubations of the dihydrochalcone phloretin with ascorbic acid not only led to p-dihydrocoumaric acid but also to a novel ascorbyl adduct, which was isolated and identified as 2,4,6-trihydroxy-5-[3-(4-hydroxyphenyl)propanoyl]-2-[(1R, 2S)-1,2,3-trihydroxypropyl]-1-benzofuran-3(2H)-one. The impact of different structural elements on adduct formation was evaluated and verified to be a phloroglucinol structure linked to an acyl moiety. Formation of the ascorbyl adduct was shown to occur in apple puree when both ascorbic acid and phloretin were present at the same time.

Intraspecific Variation in the Alkaloids of Adalia decempunctata (Coleoptera, Coccinellidae): Sex, Reproduction and Colour Pattern Polymorphism

In this paper, we examine intraspecific variation in the quantity of alkaloid chemical defence in field collected individuals of the polymorphic ladybird beetle Adalia decempunctata (10-spot ladybird). Like its more widely studied relative Adalia bipunctata (2-spot ladybird), A. decempunctata possesses the alkaloids adaline and adalinine, which are, respectively, the major and minor alkaloids of A. bipunctata. We focused especially on alkaloid concentration in relation to colour pattern morph, sex, and the relationship between female and egg parameters. There was a marked sexual dimorphism in the balance of the two alkaloids, with adaline predominating in females and adalinine predominating in males: in males, on average, over 70% of total alkaloid was adalinine. Females had a lower proportion of adalinine (< 10%) than their eggs (> 15%) and relationships between egg alkaloid and female alkaloid or fecundity were weak or non-existent. Colour pattern morph had a borderline (although not) significant relationship with adaline concentration and total alkaloid concentration, which could be further explored with laboratory reared individuals. The sexual dimorphism in alkaloid content, which seems likely due to differences in synthesis, might be related to their relative costs to the two sexes and might provide insight into the evolution of alkaloid diversity in ladybirds.

Spermidine supplementation influence on protective enzymes of Apis mellifera (Hymenoptera: Apidae)

Dietary supplementation has been proposed as a sustainable way to improve the health and resilience of honey bees (Apis mellifera, L.), as the decline in their numbers in recent decades has raised scientific, environmental, and economic concerns. Spermidine, a natural polyamine, has been shown to be a promising substance for honey bee supplementation, as its health-promoting effects have been demonstrated in numerous studies and in different organisms. As already shown, supplementation with spermidine at a certain concentration prolonged lifespan, reduced oxidative stress, and increased antioxidative capacity in honey bees. The aim of the present study was to investigate whether spermidine supplementation affects gene expression and/or enzyme activity of antioxidative and detoxification enzymes and immune response markers in honey bee workers. The different gene expression and enzyme activity patterns observed in abdominal and head tissues in response to spermidine supplementation suggest tissue-specific and concentration-dependent effects. In addition, the immune response markers suggest that spermidine has the ability to boost honey bee immunity. The observed changes make a valuable contribution to understanding the molecular mechanisms by which spermidine may exert its beneficial effects on the bee's health and lifespan. These results support the idea of the use of spermidine supplementation to promote bee health and resilience to environmental stressors, emphasizing that the dose must be carefully chosen to achieve a balance between the pro- and antioxidant effects of spermidine.

Impacts of Combining Steinernema carpocapsae and Bracon hebetor Parasitism on Galleria mellonella Larvae

The greater wax moth, Galleria mellonella, is a significant pest in apiculture and a well-established model organism for immunological and ecotoxicological studies. This investigation explores the individual and combined effects of the ectoparasite Bracon hebetor (B.h.) and the entomopathogenic nematode Steinernema carpocapsae (S.c.) on G. mellonella larvae. We evaluated the activity of oxidative stress enzymes, including superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST), malondialdehyde (MDA) levels, cytochrome P450 activity, cell viability using Annexin V-FITC, DNA damage via comet assay, and larval morphology through scanning electron microscopy (SEM). Control larvae exhibited higher GPx and GST activities compared to those treated with B.h., S.c., or the B.h. + S.c. combination. Conversely, MDA levels displayed the opposite trend. SOD activity was reduced in the B.h. and S.c. groups but significantly higher in the combined treatment. Cytochrome P450 activity increased in response to parasitism by B. hebetor. The Annexin V-FITC assay revealed decreased cell viability in parasitized groups (B.h. 79.4%, S.c. 77.3%, B.h. + S.c. 70.1%) compared to controls. DNA damage analysis demonstrated significant differences between groups, and SEM observations confirmed severe cuticle abnormalities or malformations in G. mellonella larvae. These findings highlight the complex interactions between B. hebetor, S. carpocapsae, and their host, G. mellonella. Additionally, they illuminate the intricate physiological responses triggered within the host larvae.

Growth inhibitory, immunosuppressive, cytotoxic, and genotoxic effects of γ-terpinene on Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae)

γ-Terpinene, a monoterpene widely present in essential oils of many medicinal and aromatic plants with numerous biological properties, was evaluated for its insecticidal activity against melon fruit fly, Zeugodacus cucurbitae (Coquillett). Different concentrations (5, 25, 125, 625, and 3125 ppm) of γ-terpinene along with control were fed to larvae of melon fly. The number of pupae formed and adults emerged declined significantly after treatment. Morphologically deformed adults and pupae were also observed. The developmental duration too prolonged in treated larvae. Food assimilated, mean relative growth rate, larval weight gain, and pupal weight also declined. In the larvae treated with LC30 and LC50 concentrations, there was a decline in the titers of phenoloxidase and total hemocyte count, and variations were observed in the differential hemocyte count, suggesting an immunosuppressive effect of γ-terpinene on melon fly. Both concentrations also led to an increase in the apoptotic and necrotic cells as well as decrease in the viable hemocytes in the circulating hemolymph of treated larvae. Comet parameters (tail length, % tail DNA, tail moment, and olive tail moment) of γ-terpinene fed larvae increased significantly. Given the observed effects of γ-terpinene on normal developmental and nutritional physiology, its immunosuppressive properties, and its potential for genome damage, it can be considered for incorporation into integrated pest management strategies for controlling Z. cucurbitae.

Hormetic effects of neonicotinoid insecticides on Rhizoglyphus robini (Acari: Acaridae)

The stimulation of biological processes by sublethal doses of insecticides or other stressors is known as hormesis. Here, we have evaluated whether exposure to field-relevant or low concentrations of neonicotinoids induce changes in the reproductive capacity of the bulb mite Rhizoglyphus robini (Acari: Acaridae). Among the tested neonicotinoids imidacloprid, thiamethoxam, and dinotefuran, the highest hormetic effect on the reproduction of R. robini occurred 24 h after the 48 h exposure period to imidacloprid at concentrations of 70 and 140 mg a.i./L. Despite the stimulating effects of imidacloprid on mite reproduction, no significant differences were observed in the offspring (F₁) for biological aspects including egg hatch rate, embryonic period and sex ratio, while an increase was found in the duration of development time from egg to adult. Evaluation of the detoxification enzyme activities of treated adults showed that the highest activity of carboxyl/cholinesterases, cytochrome P450s, and glutathione S-transferases was obtained when exposed to 70, 140 and 70 mg a.i./L imidacloprid, immediately after the exposure period, respectively. Also, an increase in the activity of the antioxidant enzyme catalase was observed compared to that of the control. After imidacloprid pretreatment (140 mg a.i./L), the tolerance of adult mites to diazinon was increased about two-fold. This study shows that exposure to imidacloprid can induce hormetic effects on R. robini and could severely complicate its control due to a higher reproduction, enhanced detoxification enzyme activities, and increased tolerance against other pesticides.

Elucidating the Effect of Temperature Stress on the Protein Content, Total Antioxidant Capacity, and Antioxidant Enzyme Activities in Tetranychus urticae (Acari: Tetranychidae)

Tetranychus urticae Koch is a worldwide agricultural pest mite that feeds on more than 1100 kinds of crops. The mite has developed a high level of tolerance to high temperatures, but the physiological mechanism underlying the outstanding adaptability of this pest to high temperatures remains unclear. To clarify the physiological mechanisms of T. urticae in response to short-term heat stress, four temperatures (36, 39, 42, and 45 °C) and three short-term heat durations (2, 4, and 6 h) were conducted to test the effects on protein content, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and the total antioxidant capacity (T-AOC). The results showed that protein content, antioxidant enzyme activity, and T-AOC in T. urticae were significantly induced by heat stress. These results suggest that heat stress induces oxidative stress and that antioxidant enzymes play an important role in reducing oxidative damage in T. urticae. The data of this study will provide a basis for further research on the molecular mechanisms of thermostability and ecological adaptability of T. urticae.

Antioxidant availability trades off with warning signals and toxin sequestration in the large milkweed bug (Oncopeltus fasciatus)

In some aposematic species the conspicuousness of an individual's warning signal and the concentration of its chemical defense are positively correlated. Several mechanisms have been proposed to explain this phenomenon, including resource allocation trade-offs where the same limiting resource is needed to produce both the warning signal and chemical defense. Here, the large milkweed bug (Oncopeltus fasciatus: Heteroptera, Lygaeinae) was used to test whether allocation of antioxidants, that can impart color, trade against their availability to prevent self-damage caused by toxin sequestration. We investigated if (i) the sequestration of cardenolides is associated with costs in the form of changes in oxidative state; and (ii) oxidative state can affect the capacity of individuals to produce warning signals. We reared milkweed bugs on artificial diets with increasing quantities of cardenolides and examined how this affected signal quality (brightness and chroma) across different instars. We then related the expression of warning colors to the quantity of sequestered cardenolides and indicators of oxidative state-oxidative lipid damage (malondialdehyde), and two antioxidants: total superoxide dismutase and total glutathione. Bugs that sequestered more cardenolides had significantly lower levels of the antioxidant glutathione, and bugs with less total glutathione had less luminant orange warning signals and reduced chroma of their black patches compared to bugs with more glutathione. Bugs that sequestered more cardenolides also had reduced red-green chroma of their black patches that was unrelated to oxidative state. Our results give tentative support for a physiological cost of sequestration in milkweed bugs and a mechanistic link between antioxidant availability, sequestration, and warning signals.

Impact of caffeic acid on growth, development and biochemical physiology of insect pest, Spodoptera litura (Fabricius)

The tobacco cutworm, Spodoptera litura (Fabricius) is a serious cosmopolitan pest that attacks several economically important crops such as maize, sorghum, chickpea, pigeon pea, cotton, tobacco and sunflower. It has developed resistance to most pesticides resulting in its continual outbreak. The effect of caffeic acid on second instar larvae of S. litura was evaluated by carrying out bioassays, nutritional assays, immune assays and biochemical assays with phenolic acids. Bioassays carried out with second instar larvae of S. litura showed growth inhibiting effects of various concentrations (5 ppm, 25 ppm, 125 ppm, 625 ppm and 3125 ppm) of caffeic acid on S. litura in comparison to control. A significant increase in mortality as well as an increased development time was observed with increase in the concentration of caffeic acid. A decrease in nutritional indices, including relative growth rate (RGR), relative consumption rate (RCR), efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD), and approximate digestibility (AD), indicated that dietary caffeic acid also negatively impacted the nutritional physiology of S. litura larvae. Caffeic acid has a significant impact on the immunological response of S. litura larvae. As the concentration of caffeic acid increased, the overall number of hemocytes decreased. Enzymatic assays revealed a significant increase in antioxidant enzymes when S. litura larvae were given an artificial diet containing LC₅₀ concentration of phenolic acid for an interval of 24, 48, 72 and 96 h. The levels of oxidative stress markers (hydrogen peroxide, protein carbonyl and lipid peroxide) were also significantly enhanced in S. litura larvae after treatment with phenolic acid. According to our study, caffeic acid can be employed as a substitute for traditional insecticides to reduce the population of S. litura.

The price of defence: toxins, visual signals and oxidative state in an aposematic butterfly

In a variety of aposematic species, the conspicuousness of an individual's warning signal and the quantity of its chemical defence are positively correlated. This apparent honest signalling is predicted by resource competition models which assume that the production and maintenance of aposematic defences compete for access to antioxidant molecules that have dual functions as pigments and in protecting against oxidative damage. To test for such trade-offs, we raised monarch butterflies (Danaus plexippus) on different species of their milkweed host plants (Apocynaceae) that vary in quantities of cardenolides to test whether (i) the sequestration of cardenolides as a secondary defence is associated with costs in the form of oxidative lipid damage and reduced antioxidant defences; and (ii) lower oxidative state is associated with a reduced capacity to produce aposematic displays. In male monarchs conspicuousness was explained by an interaction between oxidative damage and sequestration: males with high levels of oxidative damage became less conspicuous with increased sequestration of cardenolides, whereas those with low oxidative damage became more conspicuous with increased levels of cardenolides. There was no significant effect of oxidative damage or concentration of sequestered cardenolides on female conspicuousness. Our results demonstrate a physiological linkage between the production of coloration and oxidative state, and differential costs of sequestration and signalling in monarch butterflies.

Analysis of antioxidants in water striders (Hemiptera: Gerridae) as bioindicator of water pollution

The antioxidant enzyme system is an important defense mechanism to cope with Reactive Oxygen Species (ROS) produced due to exposure to heavy metals. In the present study lead (Pb), chromium (Cr), arsenic (As), cadmium (Cd) and nickel (Ni) in water and the antioxidant activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) was investigated in three species (Metrocoris communis, Limnogonus fossarum fossarum, and Aquarius adelaidis) of water striders collected from the industrial triangle of Punjab, Pakistan. The results of present study revealed that Pb, Cr, As, Cd and Ni were according to the permissible amount of WHO. The antioxidant activity of SOD, CAT and POD was found significantly different among species against oxidative stress, but found the highest activity of determining parameters in A. adelaidis. This is one of the pioneer studies in Pakistan reporting the role of water striders as a bioindicator of heavy metals present in the water through antioxidants enzyme variations. The current results supported that variant level of antioxidant enzyme activities in different species of water strider were reflective of heavy metal pollution in the Industrial triangle of Punjab, Pakistan and will be a useful ecotoxicological tools to evaluate the detrimental effects of heavy metal pollutants in aquatic organisms.

Identification and Characterization of Antioxidant Enzyme Genes in Parasitoid Aphelinus asychis (Hymenoptera: Aphelinidae) and Expression Profiling Analysis under Temperature Stress

Simple Summary

High temperature affects the control efficiency of Aphelinus asychis, an important parasitic natural enemy of aphids. Antioxidative enzymes can protect organisms against oxidative damage by eliminating excess reactive oxygen species (ROS). This study identified 14 genes belonging to four classes of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidases (POD), and glutathione-S-transferase (GST). The results showed that the expression levels and enzymatic activities of most antioxidant enzyme genes are significantly induced by high temperature, which indicates that antioxidant enzymes increase the resistance of A. asychis to lethal high temperature. Taken together, this study enriches the understanding of the molecular mechanisms of resistance of A. asychis to environmental high temperatures.

Abstract

It is well known that high temperature, a typically negative environmental factor, reduces the parasitism of a parasitoid. Generally, high temperature causes the rapid overproduction of reactive oxygen species (ROS) in organisms, and antioxidative enzymes participate in the process of resisting environmental stress by eliminating excess ROS. In the present study, we identify two superoxide dismutase (SOD), one catalase (CAT), six peroxidases (POD), and five glutathione-S-transferase (GST) genes; and the survival rate and antioxidative enzyme patterns under short-term high temperature exposure of the parasitoid wasp, A.asychis, are examined. Survival results of A.asychis reveal that females show higher thermal tolerance than males. Under short-term high-temperature exposure, in females, the expression levels of most antioxidant enzyme genes decreased first and then increased to a peak at 41 °C, while only the expression of AasyGST4 showed a continuous increase. In males, the expression patterns of most antioxidant enzyme genes fluctuated and reached a maximum at 41 °C. Moreover, the expression levels of the majority of antioxidant enzyme genes were higher in females than in males. In addition, at temperatures of and above 35 °C, the activities of these four antioxidant enzymes were induced. The results show that the antioxidant enzymes confer thermo-tolerance to A. asychis against lethal thermal stress. Our observations enrich the understanding of the response mechanism to high-temperature assaults of A. asychis.

Inception of redox cycling and its impact in biology and medicine

This commentary discusses how the idea of employing redox cycling compounds to generate partially reduced oxygen species (O₂^-, H₂O₂, HO^.) to cause oxidative stress in the model organism, Escherichia coli, was born. The concept was materialized during our studies on the induction and regulation of the Mn-superoxide dismutase in this unicellular organism. I described how the findings revolutionized the field of oxygen free radicals and oxidative stress and demonstrated its continued relevance and impact to the field today and most probably in the future.

Lethal and sublethal effects of emamectin benzoate on life-table and physiological parameters of citrus red mite, Panonychus citri

The citrus red mite (Panonychus citri) is a challenge to manage in citrus orchards due to resistance against several pesticides. There is a necessity therefore to find new pesticides for effective control of P. citri. This study was designed to evaluate the lethal and sublethal effects of emamectin benzoate against P. citri. The results showed that the LC50 of emamectin benzoate to adults of P. citri was 0.35 (0.26-0.43) mg a.i. L-1 and the LC90 was 1.44 (1.16-1.96) mg a.i. L-1. The sublethal concentration exposures (LC10 and LC30) had a significant negative impact on the larval, protonymph, and deutonymph developmental periods. Male longevity was much lower in LC30 treatments than in the controls. Although female longevity was unaffected, the fecundity (eggs per female) was decreased in the sublethal concentration treatments. Results revealed that the adult pre-oviposition period (APOP) and total pre-oviposition period (TPOP) were increased. Other growth parameters r, λ, and R0 decreased, whereas mean generation time (T) increased due to pesticide exposure. The survival rate (Sxj), age-specific fecundity and net maternity, life expectancy (Exj), and reproduction (Vxj) was reduced by LC10 and LC30 exposure. An increase in malondialdehyde (MDA) contents with increasing emamectin benzoate concentration demonstrates that emamectin benzoate induces oxidative stress in P. citri. The activity of antioxidant enzymes (superoxide dismutase, SOD and catalase, CAT) was decreased due to LC30 and LC10 treatments compared to the control. Detoxification enzyme activity (cytochrome P450, glutathione-S-transferases, GST and acetylcholinesterase, AChE) was increased in treated mites compared to the control. This study demonstrates that emamectin benzoate has both a lethal effect on citrus red mite and sublethal effects on its biology and physiology. It is, therefore, potentially an effective pesticide for management of P. citri.

ROS Metabolism Perturbation as an Element of Mode of Action of Allelochemicals

The allelopathic interaction between plants is one of the elements that influences plant communities. It has been commonly studied by applying tissue extracts onto the acceptors or by treating them with isolated allelotoxins. Despite descriptive observations useful for agricultural practice, data describing the molecular mode of action of allelotoxins cannot be found. Due to the development of -omic techniques, we have an opportunity to investigate specific reactive oxygen species (ROS)-dependent changes in proteome or transcriptome that are induced by allelochemicals. The aim of our review is to summarize data on the ROS-induced modification in acceptor plants in response to allelopathic plants or isolated allelochemicals. We present the idea of how ROS are involved in the hormesis and plant autotoxicity phenomena. As an example of an -omic approach in studies of the mode of action of allelopatic compounds, we describe the influence of meta-tyrosine, an allelochemical exudated from roots of fescues, on nitration-one of nitro-oxidative posttranslational protein modification in the roots of tomato plants. We conclude that ROS overproduction and an induction of oxidative stress are general plants' responses to various allelochemicals, thus modification in ROS metabolisms is regarded as an indirect mode of action of allelochemicals.

Fitness Costs of Two Maize Lepidopteran Pests Fed on Bacillus thuringiensis (Bt) Diets Enriched with Vitamins A and C

Simple Summary

Biotechnologists are designing new transgenic plants enriched with micronutrients and vitamins that are resistant to insects. These new plants could favor the development of some pest insects. This work aims to discover the effect of adding two vitamins, A and C, to insect diets prepared with Bt and no-Bt maize in two maize insect pests. M. unipuncta was less sensitive to the toxin, although ingestion of the Bt diet resulted in longer larval development and lower pupal weight, which were not mitigated by any of the vitamins. However, the two vitamins reduced the mortality of H. armigera larvae fed on the Bt diet. In addition, we found evidence of the antioxidant function of vitamin A. The results obtained here indicate that crops enriched with these vitamins will hardly favor the development of H. armigera and suggest that they do not affect M. unipuncta’s development at all.

Abstract

Serious malnutrition problems occur in developing countries where people’s diets are mainly based on staple crops. To alleviate this, high-production crops are being developed that are better adapted to climate change, enriched in micronutrients and vitamins, or resistant to pests. In some cases, new varieties have been developed with several of the characteristics mentioned above, such as biofortified and pest-resistant crops. The development of biofortified Bacillus thuringiensis (Bt) crops raises the question of whether vitamin enrichment of Bt crops can in any way favor those pests that are not very susceptible to the Bt toxin that feed on these crops, such as Helicoverpa armigera (Hübner) or Mythimna unipuncta (Haworth) (Lepidoptera: Noctuidae). In this study, the response to a Bt diet enriched with vitamins A (β-carotene) and C (ascorbic acid) was somewhat different between the two species. M. unipuncta was less sensitive to the toxin than H. armigera, although the ingestion of the Bt diet resulted in oxidative stress (longer larval development and lower pupal weight) which was not mitigated by the vitamins. However, the two vitamins reduced the mortality of H. armigera larvae fed on a Bt-enriched diet; in addition, ß-carotene reduced the activity of the antioxidant glutathione S-transferase (GST) of both species, suggesting it has an antioxidant role. The results obtained here indicate that biofortified Bt crops will not favor the development of H. armigera very much and will not affect M. unipuncta’s development at all, although the effect of the increase in vitamins may be very variable and should be studied for each specific phytophagous.

Tissue-specific responses of Lymantria dispar L. (Lepidoptera: Erebidae) larvae from unpolluted and polluted forests to thermal stress

In this paper the effects of increased environmental temperature on the relative growth rate (RGR) and developmental time in 5th instar L. dispar larvae originating from unpolluted and polluted forests were analyzed. As indicators of the level of generated reactive oxygen species in thermal stress, we estimated midgut and hemolymph activity of the antioxidative enzymes, superoxide dismutase (SOD) and catalase (CAT), as well as the detoxifying enzymes glutathione S-transferase (GST), carboxylesterase (CaE) and acetylcholinesterase (AChE) from the midgut and brain tissue. We also examined the influence of induced thermotolerance as a species' ability to overcome the negative effects of this stressor. In larvae originating from the unpolluted forest, the midgut is the primary location of increased SOD and CAT activity and induced thermotolerance did not modified their activity in either tissue. In larvae from the polluted forest, in both tissues SOD activity was more sensitive to an increased temperature and induced thermotolerance than CAT. Carboxylesterase responded diversely to thermal stress depending on the analyzed tissue regardless the origin of larvae, while the activity of GST and AChE in tissue depended on the origin of larvae. Induced thermotolerance modified the activity of detoxifying enzymes in larvae originating from the polluted forest. Combining the selected parameters into an integrated biomarker response (IBR) the GST, CaE and AChE battery emerged as a potential biomarker for thermal stress in L. dispar larvae.

Glucosinolate induces transcriptomic and metabolic reprogramming in Helicoverpa armigera

Glucosinolates protect plants from herbivory. Lepidopteran insects have developed resistance to glucosinolates which is well studied. However, the molecular effects of glucosinolate intake on insects are unexplored. To elucidate this, we performed transcriptomics and metabolomics of sinigrin-fed Helicoverpa armigera. Transcriptomics exhibits significant dysregulation of 2375 transcripts, of which 1575 are upregulated and 800 downregulated. Gene Ontology analysis of differentially expressed genes reveals that key hydrolases, oxidoreductases, and transferases are majorly affected. The negative impact of sinigrin is significant and localized in the endomembrane system and mitochondria. It also disturbs various biological processes such as regulation of protein metabolism and cytoskeletal organization. Furthermore, H. armigera putative myrosinase-like enzymes may catalyze the breakdown of sinigrin to allyl isothiocyanate (AITC). AITC targets the electron transport chain causing oxidative stress. KEGG pathway enrichment shows significant upregulation of oxidative phosphorylation, glutathione metabolism and amino acid metabolism. Activation of these pathways induces glutathione synthesis for sinigrin detoxification. Differential gene expression indicates upregulation of glutathione S-transferase and succinate dehydrogenase suggesting mitochondrial impact. Transcriptomics data correlated with metabolomics show changes in serine, methionine, ornithine, and other metabolite levels. It corroborates well with the transcript alterations supporting the increased glutathione production. Thus, our data suggest that sinigrin generates oxidative stress in H. armigera and insects alter their metabolic wiring to overcome sinigrin-mediated deleterious effects.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02596-5.

Detoxification Strategies of Two Types of Spiders Revealed by Cypermethrin Application

In order to compare the detoxification capacities of two species of spiders, Linyphia triangularis and Pardosa prativaga were exposed to a commonly used pesticide, cypermethrin (a chlorinated pyrethroid). Two detoxification enzyme systems — glutathione S-transferase (GST) and glutathione peroxidase (GSH-Px) — were assayed as biomarkers. The two species of spiders have different life-styles and eat different food, and in our experiment were at different stages of their life-cycle. Therefore, differences in detoxification strategies could be expected. From our results, we suggest two different strategies. L. triangularis had a generally high basal level of GST, which could be further induced by exposure to cypermethrin. The basal activity of GSH-Px was relatively low, and no response to toxic exposure could be traced. Thus, this enzyme plays only a minor role in the detoxification process of cypermethrin in L. triangularis. In P. prativaga, a low basal GST activity was found. However, the basal level of GSH-Px was comparable to that of L. triangularis. A significant rise in GSH-Px activity (with t-butyl-hydroxyperoxide as substrate) was apparent 12 hours after exposure. This may indicate that P450 enzyme systems are involved in the cypermethrin metabolising process in P. prativaga. In addition, GSH-Px activity (with H2O2as substrate) could be traced in P. prativaga but not in L. triangularis, indicating that a true peroxidase system is active in P. prativaga.

Conidiobolus coronatus induces oxidative stress and autophagy response in Galleria mellonella larvae

Cell homeostasis requires the correct levels of reactive oxygen species (ROS) to be maintained as these regulate the proliferation and differentiation of cells, and control the immune response and inflammation. High levels of ROS can cause oxidative stress, leading to protein, lipid and DNA damage, or even cell death. Under physiological conditions, the rate of autophagy remains stable; however, it can be accelerated by a number of exogenous stimuli such as oxidative stress, starvation or hypoxia, leading to cell death. The present paper examines the effect of Conidiobolus coronatus infection on the immune response, oxidative stress processes and autophagy in the greater wax moth, Galleria mellonella. Fungal infection was found to result in the disorganization of the cytoskeleton of the larval immune cells and the enhancement of oxidative defense processes. Lipid peroxidation and autophagy were also induced in the hemocytes. Our findings show that G. mellonella is an ideal model for exploring immune mechanisms.

A Role for Zinc in Plant Defense Against Pathogens and Herbivores

Pests and diseases pose a threat to food security, which is nowadays aggravated by climate change and globalization. In this context, agricultural policies demand innovative approaches to more effectively manage resources and overcome the ecological issues raised by intensive farming. Optimization of plant mineral nutrition is a sustainable approach to ameliorate crop health and yield. Zinc is a micronutrient essential for all living organisms with a key role in growth, development, and defense. Competition for Zn affects the outcome of the host-attacker interaction in both plant and animal systems. In this review, we provide a clear framework of the different strategies involving low and high Zn concentrations launched by plants to fight their enemies. After briefly introducing the most relevant macro- and micronutrients for plant defense, the functions of Zn in plant protection are summarized with special emphasis on superoxide dismutases (SODs) and zinc finger proteins. Following, we cover recent meaningful studies identifying Zn-related passive and active mechanisms for plant protection. Finally, Zn-based strategies evolved by pathogens and pests to counteract plant defenses are discussed.

Effect of fluoranthene on antioxidative defense in different tissues of Lymantria dispar and Euproctis chrysorrhoea larvae

This study examined the effect of long-term exposure to environmentally relevant concentrations of dietary fluoranthene (6.7 and 67 ng / g dry food weight) on defense mechanisms of the polyphagous forest insects Lymantria dispar L. and Euproctis chrysorrhoea L. The activities and expression of isoforms of superoxide dismutase (SOD) and catalase (CAT), the activities of glutathione S-transferase (GST) and glutathione reductase (GR), and total glutathione content (GSH) were determined in the whole midgut and midgut tissue, while SOD and CAT activities were assessed in hemolymph of the larvae. The results showed significant changes of enzyme activities, with more pronounced responses in larval midgut tissues, and between-species differences in patterns of response. Significantly increased activity of SOD was recorded in the whole midgut and midgut tissue of L. dispar larvae, as well as in midgut tissue of E. chrysorrhoea larvae. Fluoranthene increased CAT activity in midgut tissue of L. dispar larvae, and in the whole midgut and midgut tissue of E. chrysorrhoea larvae. Different expression patterns were detected for enzyme isoforms in tissues of larvae exposed to dietary fluoranthene. Total GSH content and GST activity increased in E. chrysorrhoea larval midgut tissue. Significantly decreased SOD activity in hemolymph of L. dispar larvae, and opposite changes in CAT activity were recorded in the hemolymph of larvae of two insect species. The tissue-specific responses of enzymes to dietary fluoranthene, recorded in each species, enabled the larvae to overcome the pollutant induced oxidative stress, and suggest further assessment of their possible use as early-warning signals of environmental pollution.

Parameters of oxidative stress, cholinesterase activity, Cd bioaccumulation in the brain and midgut of Lymantria dispar (Lepidoptera: Lymantriidae) caterpillars from unpolluted and polluted forests

Cadmium (Cd) can display a variety of different effects on living organisms. The objectives of the present study were to investigate Cd bioaccumulation and differences in parameters of oxidative stress (activities of the enzymes: superoxide dismutase, catalase, glutathione reductase, ascorbate peroxidase, glutathione S-transferase, and amounts of non-enzymatic free sulfhydryl groups and total glutathione) and cholinesterase activity in larval brain and midgut tissues of the polyphagous forest insect Lymantria dispar collected from unpolluted and polluted oak forests. Fourth instar L. dispar caterpillars from the unpolluted forest had higher body mass but accumulated more Cd in comparison to caterpillars from the polluted forest. In both populations the midgut was more sensitive than the brain to the prooxidative effects of Cd. Enzyme activities and amounts of non-enzymatic parameters tended to be greater in midgut tissues than in the brain, except for cholinesterase activity. Parameters of oxidative stress had higher values in caterpillar tissues from the polluted than from the unpolluted oak forest. The observed differences between the two natural populations point to the importance of knowing the history of population exposure to environmental pollution when monitoring forest ecosystems.

Antioxidant enzyme activity in responses to environmentally induced oxidative stress in the 5th instar nymphs of Aiolopus thalassinus (Orthoptera: Acrididae)

The response of antioxidant enzymes to oxidative environmental stress was determined in 5th instar nymphs of Aiolopus thalassinus (Orthoptera: Acrididae) collected from sites with different level of pollution with heavy metals, PO₄^3-, and SO₄^2-. The high polluted site induced higher DNA damage to individuals compared to the control site. The highest values of tail length (TL), tail moment (TM), and percent of DNA in tail (TDNA) were found in the gut of 5th instar nymphs from a high polluted site. Also, protein carbonyls and lipid peroxide levels were significantly higher in insects collected from polluted sites compared to those from the control site. A strong positive correlation between both protein carbonyl and lipid peroxide concentration and the pollution level of the sites was found in all tissues of the insects. The activity of superoxide dismutase (SOD) in the brain of insects collected from the high polluted site was significantly higher than that in the thoracic muscles and gut. We observed strong inhibition of catalase (CAT) activity. This effect was apparently caused by pollutants present at the high polluted site. The level of pollution significantly influenced polyphenol oxidase (PPO) activity in A. thalassinus nymphs in all examined tissues. The highest values were observed in the brain. The relationship between pollution and ascorbate peroxidase (APOX) activity in the examined tissues had no clear tendency. However, the lowest APOX activity was observed in individuals from the low polluted site. Level of pollution of sampling sites, oxidative stress biomarkers, and enzymatic response in A. thalanthsis 5th instar were negatively or positively correlated. Oxidative damage parameters, especially the percent of severed cells, lipid peroxides, and the activity of APOX, can be perceived as good markers of environmental multistress.

Green light and light stress in moth: influence on antioxidant enzymes in the oriental armyworm, Mythimna separata (Lepidoptera: Noctuidae)

Recently, light traps equipped with light-emitting diodes (LEDs) have been widely applied for controlling nocturnal pest moths. The oriental armyworm, known as Mythimna separata Walker, is an important insect pest in eastern Asia. The present study aimed to evaluate an influence of green light irradiation on antioxidant enzymes and light stress in M. separata adults. We determined total antioxidant capacity (T-AOC) and an activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione-S-transferase (GST) in the moth bodies according to an exposure time (0 to 180 min) of a green LED light. By our results, we suggested that the green (520 nm) LED light irradiation could induce a weak oxidative stress in M. separata adult moths, and the moths under the green light could restore the damage caused by this light stress. Additionally, we proposed that the adaptive ability to the light stress varied between the moths of different sexes. Our results may provide a theoretical and scientific basis for elucidating a reason of the phototactic behavior of nocturnal moths, including M. separata adults.

Preventive effects of N-acetyl-l-cysteine against imidacloprid intoxication on Bombyx mori larvae

Imidacloprid, a widely used neonicotinoid insecticide, is toxic to silkworm (Bombyx mori). To explore whether N-acetyl-l-cysteine (NAC) has an effect on preventing silkworm (B. mori) from toxification caused by imidacloprid, we fed the fifth-instar larvae with mulberry leaves dipped in 200 mg/L NAC solution before exposing in imidacloprid, and investigated the silkworm growth, survival rate, feed efficiency, cocoon quality, and the activities of antioxidant enzymes in midgut. The results showed that addition of NAC could significantly increase body weight, survival rate, and feed efficiency of imidacloprid poisoned silkworm larvae (P < 0.05), as well as cocoon mass, cocoon shell mass, and the ratio of cocoon shell (P < 0.05). Furthermore, it could significantly promote the activities of the antioxidant enzymes including superoxide dismutase, catalase, and glutathione peroxide in the midgut of fifth-instar larvae under imidacloprid exposure at the late stage of treatment. In addition, it also could downregulate the malondialdehyde content. The results of our findings proved that the added NAC may have some beneficial effects on protection or restoration of antioxidant balance in imidacloprid exposed larvae.

Origanum vulgare Terpenoids Induce Oxidative Stress and Reduce the Feeding Activity of Spodoptera littoralis

Terpenoids are toxic compounds produced by plants as a defense strategy against insect herbivores. We tested the effect of Origanum vulgare terpenoids on the generalist herbivore Spodoptera littoralis and the response of the plant to herbivory. Terpenoids were analyzed by GC-FID and GC-MS and quantitative gene expression (qPCR) was evaluated on selected plant genes involved in both terpene biosynthesis. The insect detoxification response to terpenes was evaluated by monitoring antioxidant enzymes activity and expression of insect genes involved in terpene detoxification. O. vulgare terpenoid biosynthesis and gene expression was modulated by S. littoralis feeding. The herbivore-induced increased level of terpenoids (particularly carvacrol and p-cymene) interacted with the herbivore by decreasing larval survival and growth rate. The assimilation by S. littoralis of more than 50% of ingested terpenes correlated with the possible toxic effects of O. vulgare terpenoids. In choice test experiments, carvacrol and γ-terpinene mediated the larval feeding preferences, wherease the prolonged feeding on O. vulgare terpenoids (particularly on γ-terpinene) exerted relevant antinutritional effects on larvae. S. littoralis was found to react to O. vulgare terpenoids by increasing its antioxidant enzymes activities and gene expression, although this was not sufficient to sustain the toxicity of O. vulgare terpenoids.

Biological responses to environmental contamination. How can metal pollution impact signal honesty in avian species?

Environmental pollution, for example with metals, can significantly affect the ecosystem balance leading to severe changes. Biologically active pigments are relevant for the appearance and condition of birds. Melanin and carotenoid particles are the most frequently deposited pigments in avian integument. They are responsible for the majority of colors of bird plumage. The phenotypic expression can be affected by metal contamination. It can be manifested as color bleaching or differences in the size of plumage badges. In this study, we performed a comprehensive review of related studies in order to estimate the underlying population effect of this potential dependency. The study is based on the review of the literature regarding several avian species. It was designed to identify an area where the effect of the exposure is still poorly known. The analysis was specifically conducted to investigate the correlation between trace element concentration and eumelanin deposition. Moreover, we searched for factors that could affect spectral properties of feathers with carotenoid-based pigmentation. As a result, we found carotenoid-based pigmentation to be of a good use in terms of visual condition assessment. Changes in melanin-based pattern should be analyzed separately for eu- and pheomelanin as well as for a range of essential and toxic elements. Comprehensive studies on the subject are still scarce. Therefore, the issue requires further investigation.

Effect of Polygonum persicaria (Polygonales: Polygonaceae) Extracted Agglutinin on Life Table and Antioxidant Responses in Helicoverpa armigera (Lepidoptera: Noctuidae) Larvae

Plant lectins could reduce insect populations by imposing imbalances in biology and physiology. Here, an agglutinin was extracted from Polygonum persicaria L. (PPA; Polygonales: Polygonaceae) and its effects were investigated on life table parameters and antioxidant system of Helicoverpa armigera Hübner (Lepidoptera: Noctuidae). PPA significantly changed demographic parameters showing adverse effects on age-stage survival rate (Sxj), age-specific survival rate (lx), age-specific fecundity rate (mx), age stage specific fecundity (fxj), and life expectancy (exj). Also, life table parameters including net reproduction rate (R0) (Offspring/female), intrinsic rate of population increase (rm) (days-1), finite rate of increase (λ) (days-1), gross reproduction rate (GRR) (Offspring/female) significantly decreased in the PPA-treated H. armigera compared to control except for mean generation time (T) (days). Activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CA), peroxidase (POX), glutathione S-transferase (GST) and glucose 6-phosphate dehydrogenase (GPDH) increased statistically in the PPA-treated larvae compared to control while no significant difference was observed in the activity of ascorbate peroxidase (APOX) activity. Moreover, ratio of RSSR/RSH and concentration of malondialdehyde (MDA) were found to be statistically higher in PPA-treated larvae than control. The current results clearly showed that PPA not only had a negative impact on demography of H. armigera but also induced antioxidant raise by releasing free radicals. These released radicals, together with impaired digestion and absorption observed in our previous report, could be considered as a reason for reducing biological fitness of H. armigera.

Bidirectional interactions between beet armyworm and its host in response to different fertilization conditions

Fertilizer with different ratios of nitrogen (N) to phosphorus (P) can influence crop plant performance and defense against herbivores. Spodoptera exigua is an important agricultural pest that has caused serious economic loss, especially in recent decades. In the present study, we explored effects of different intensities and durations of S. exigua herbivory on host plant biomass and on S. exigua enzyme activities in response to five fertilizer treatments with different N: P ratios of 1: 5, 1: 3, 1: 1, 3: 1 and 5: 1. The results showed that fertilizer type can significantly influence interactions between caterpillars and its hosts. Compensatory growth of leaf biomass was detected under fertilizer with N: P = 3: 1. Fertilizer with a higher proportion of N appears to maintain stem biomass in defoliated seedlings similar to controls that are not exposed to herbivory. There was no significant difference in root biomass under most conditions. High proportion of N also enhanced the activity of two antioxidant enzymes, catalase (CAT) and superoxide dismutase (SOD) in low density of beet armyworm. However, with increased herbivorous intensity, a higher proportion of P played a more important role in increasing the activities of CAT and SOD. Higher P likely enhanced acetylcholine esterase (AChE) activity at lower degrees of defoliation, but a higher N proportion resulted in higher AChE activity at higher degrees of defoliation. Higher N proportion contributed to reduced carboxylesterase (CarE) activity at high intensity, short-term defoliation. However, when defoliation intensity increased, the difference in CarE activity between fertilizer categories was little. The study explored the interaction between the damage of S. exigua and the biomass accumulation of its host plant Brassica rapa, and the influence of the N/P ratio in plant fertilizer on this interaction. Systematic analysis was provided on the biomass of B. rapa and the activity of metabolic enzymes of S. exigua under different treatments.

Bioassay-guided isolation of potent aphicidal Erythrina alkaloids against Aphis gossypii from the seed of Erythrina crista-galli L

BACKGROUND

The cotton aphid (Aphis gossypii Glover) is one of the most invasive pests of cotton. Many botanical phytochemicals have a long history as a source of insecticides, and as templates for new insecticides. This study was undertaken to isolate aphicidal compounds from the seeds of Erythrina crista-galli L. using the bioassay-guided isolation method.

RESULTS

Three novel and 11 known Erythrina alkaloids were isolated. Erysodine (9), erysovine (10), erysotrine (8) and erythraline (11) showed moderate to excellent aphicidal activity with LD₅₀ values of 7.48, 6.68, 5.13 and 4.67 ng aphid^-1 , respectively. The Potter spray tower bioassay gave corresponding LC₅₀ values of 186.81, 165.35, 163.74 and 112.78 µg ml^-1 . A unique substructure, which presents an sp³ methylene at C-8, a non-oxygenated site at N-9 and a conjugated dienes group (Δ^1,2 and Δ^6,7 ), plays a crucial role in the aphicidal activity. Application of erythraline (11) led to different increases in the activities of superoxide dismutase, catalase and glutathione S-transferase.

CONCLUSION

The study demonstrated that the Erythrina alkaloids erysodine (9), erysovine (10), erysotrine (8) and erythraline (11) have potential use as botanical aphicides for commercial application, or as templates for the development of new insecticides. © 2017 Society of Chemical Industry.

Comparison of the trapping effect and antioxidant enzymatic activities using three different light sources in cockchafers

Light traps have been widely used for controlling underground pests. However, very little is known regarding the relationship between trapping effect and antioxidant enzymatic activities using light irradiation in underground pests. Thus, we determined the trapping effect of three light sources of the frequoscillation pest-killing lamp on two species of cockchafers, Serica orientalis Motschulsky (Coleoptera: Melolonthidae) and Anomala corpulenta Motschulsky (Coleoptera: Rutelidae), and evaluated the effect of the same three light sources on the activities of their antioxidant enzymes. The catches of S. orientalis were significantly higher compared to A. corpulenta using light source A in peanut fields in China. After irradiation by light source A, the malondialdehyde (MDA) contents and activities of superoxide dismutase (SOD) and glutathione S-transferases (GST) in S. orientalis were significantly and marginally significantly lower compared to A. corpulenta. Taken together, these results indicated a weaker antioxidant enzyme activity response to light stress and a larger quantity of trapping catches using light irradiation in cockchafers. Thus, we proposed a potential negative relationship between trapping effect and antioxidant enzymatic activities in response to light irradiation in cockchafers.

NMR-based untargeted metabolomic study of hydrogen peroxide-induced development and diapause termination in brine shrimp

Artemia diapause has been extensively studied in embryonic biology for a long time. It has been demonstrated that hydrogen peroxide (H₂O₂) can increase the hatching rate in the development and diapause termination of Artemia cysts. This study used an untargeted ¹H NMR-based metabolomic approach to explore the physiological regulation of H₂O₂ in initiating the development and terminating the diapause of Artemia cysts. This experiment was divided into two parts. In the first part, we analyzed three groups with or without H₂O₂ as control-0h, control-5h and H₂O₂ (180μM)-5h; in the second part, after 7-d incubation, the non-hatching cysts were treated with different H₂O₂ concentrations as low as 180μM and as high 1800μM. The results showed that arginine and proline metabolism were up-regulated after 5h, and H₂O₂ up-regulated valine, leucine and isoleucine biosynthesis in the development of cysts. In the second part, low H₂O₂ (180μM) showed alanine, aspartate and glutamate metabolism, but high H₂O₂ (1800μM) also up-regulated arginine and proline metabolism, as in the control group without H₂O₂ stimulus. These results suggest that enough H₂O₂ can catalyze cell transcription and translation in Artemia cysts, and it improves the cell growth rate, thus allowing embryo cells to grow again.

Plant growth regulator-mediated anti-herbivore responses of cabbage (Brassica oleracea) against cabbage looper Trichoplusia ni Hübner (Lepidoptera: Noctuidae)

Plant elicitors can be biological or chemical-derived stimulators of jasmonic acid (JA) or salicylic acid (SA) pathways shown to prime the defenses in many crops. Examples of chemical elicitors of the JA and SA pathways include methyl-jasmonate and 1,2,3-benzothiadiazole-7-carbothioate (BTH or the commercial plant activator Actigard 50WG, respectively). The use of specific elicitors has been observed to affect the normal interaction between JA and SA pathways causing one to be upregulated and the other to be suppressed, often, but not always, at the expense of the plant's herbivore or pathogen defenses. The objective of this study was to determine whether insects feeding on Brassica crops might be negatively affected by SA inducible defenses combined with an inhibitor of detoxification and anti-oxidant enzymes that regulate the insect response to the plant's defenses. The relative growth rate of cabbage looper Trichoplusia ni Hübner (Lepidoptera: Noctuidae) fed induced cabbage Brassica oleraceae leaves with the inhibitor, quercetin, was significantly less than those fed control cabbage with and without the inhibitor. The reduced growth was related to the reduction of glutathione S-transferases (GSTs) by the combination of quercetin and increased levels of indole glucosinolates in the cabbage treated with BTH at 2.6× the recommended application rate. These findings may offer a novel combination of elicitor and synergist that can provide protection from plant disease and herbivores in cabbage and other Brassica crops.

Host plant driven transcriptome plasticity in the salivary glands of the cabbage looper (Trichoplusia ni)

Generalist herbivores feed on a wide array of plants and need to adapt to varying host qualities and defenses. One of the first insect derived secretions to come in contact with the plant is the saliva. Insect saliva is potentially involved in both the pre-digestion of the host plant as well as induction/suppression of plant defenses, yet how the salivary glands respond to changes in host plant at the transcriptional level is largely unknown. The objective of this study was to determine how the labial salivary gland transcriptome varies according to the host plant on which the insect is feeding. In order to determine this, cabbage looper (Trichoplusia ni) larvae were reared on cabbage, tomato, and pinto bean artificial diet. Labial glands were dissected from fifth instar larvae and used to extract RNA for RNASeq analysis. Assembly of the resulting sequencing reads resulted in a transcriptome library for T. ni salivary glands consisting of 14,037 expressed genes. Feeding on different host plant diets resulted in substantial remodeling of the gland transcriptomes, with 4,501 transcripts significantly differentially expressed across the three treatment groups. Gene expression profiles were most similar between cabbage and artificial diet, which corresponded to the two diets on which larvae perform best. Expression of several transcripts involved in detoxification processes were differentially expressed, and transcripts involved in the spliceosome pathway were significantly downregulated in tomato-reared larvae. Overall, this study demonstrates that the transcriptomes of the salivary glands of the cabbage looper are strongly responsive to diet. It also provides a foundation for future functional studies that can help us understand the role of saliva of chewing insects in plant-herbivore interactions.

Feeding-induced phenol production in Capsicum annuum L. influences Spodoptera litura F. larval growth and physiology

We studied the role of induced plant phenols as a defense response to insect herbivory. Phenolic compounds were induced in Capsicum annuum L., the source of many culinary peppers, after feeding by different stages of the insect pest, Spodoptera litura F. The phenols were identified and quantified using high performance liquid chromatography (HPLC) and effects produced by these phenols on larval development were studied. Vanillic acid was identified in plants challenged by second, fourth, and fifth instar larvae, but not in plants challenged by third instar nor unchallenged plants. Syringic acid production was induced in chili plants infested with second (0.429 ± 0.003 μg/g fresh weight, fourth (0.396 ± 0.01 μg/g fresh weight), and fifth instar (5.5 ± 0.06 μg/g fresh weight) larvae, compared to untreated plants (0.303 ± 0.01 μg/g fresh weight) plants. Leaves surface treated with the rutin deterred oviposition. Dietary exposure to chlorogenic acid, vanillic acid, syringic acid, sinapic acid, and rutin led to enhanced activities of detoxifying enzymes, β-glucosidase, carboxyl esterase, glutathione S-transferase, and glutathione reductase in the midgut tissues of all the larval instars, indicating the toxic nature of these compounds. Protein carbonyl content and acetylcholinesterase activity was analyzed to appreciate the role of induced plant phenols in insect protein oxidation and terminating nerve impulses.

Evaluation of oxidative stress biomarkers in Aiolopus thalassinus (Orthoptera: Acrididae) collected from areas polluted by the fertilizer industry

The waste products of the fertilizer industry such as heavy metals, but especially phosphates and sulphates, are a serious problem that influences the structure and functioning of ecosystems. The levels of Cd, Pb, Zn, Cu, sulphates and phosphates were measured in soil samples from four sites: a control and sites that were 1, 3 and 6 km (sites A-C) away from the Abu-Zaabal Fertilizer Company. Oxidative stress markers (protein carbonyls, lipid peroxides), antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), polyphenoloxidase (PPO) and ascorbate peroxidase (APOX)) were evaluated in the tissues of Aiolopus thalassinus, collected from the corresponding sites. The highest concentrations of Cu and Zn were found in the soil from site A. The level of protein carbonyls in the brain, thoracic muscles and gut of the males and females from sites A, B and C were 11.82, 4.38, 5.97 (males) and 19.04, 16.65, 7.79 (females) times higher, respectively, compared to the individuals from the control site. Lipid peroxides levels in both sexes were significantly correlated with the distance from the source of the contamination. In the brain, thoracic muscles and gut of the males and females collected from site A, the level of lipid peroxides were 15.41, 23.49, 11.50 (males) and 25.36, 11.34, 15.37 (females) times higher compared to the values of the control animals. The activities of SOD, PPO, CAT and APOX were significantly affected by the environmental pollutants. The enzymatic and non-enzymatic oxidative markers in the Aiolopus thalassinus, a common insect species that inhabits various ecosystems, can also be used as a relevant biomarker of the pollution that is caused by the fertilizer industry.

Assessment of the effects of orally administered ferrous sulfate on Oncopeltus fasciatus (Heteroptera: Lygaeidae)

Iron is an essential nutrient needed for multiple biological processes, but it is also an effective pro-oxidant in its reduced form. Environmental sources of iron toxic species include reduced soils from rice plantations, polluted natural areas from metal industry waste, or iron oxides used in soil bioremediation. Few studies have been conducted to assess the toxicity of iron species in insects. The present work aims to assess the oxidative stress effects of ferrous sulfate administered in drinking water after acute exposure (96 h) to adults of the insect model Oncopeltus fasciatus (Dallas). Mortality was higher in exposed groups and significantly associated with iron treatment (OR [95% CI]; 11.8 [6.1-22.7]). Higher levels of body iron content were found in insects exposed to ferrous sulfate, with an increase of 5-6 times with respect to controls. Catalase activity and lipid peroxidation (TBARS content), but not glutathione S-transferase activity, were significantly higher in exposed insects and significantly correlated with body iron content (Pearson coefficient of 0.68 and 0.74, respectively) and between them (0.78). The present work demonstrates that, despite the disruption in water and food intake caused by iron administration, this metal is accumulated by insect causing lipid peroxidation and eliciting an antioxidant response mediated by catalase.

Biochemical and histological biomarkers in the midgut of Apis mellifera from polluted environment at Beheira Governorate, Egypt

The aim of this study was to analyze the impact of organophosphorus (OP) pollutants on oxidative stress and ultrastructural biomarkers in the midgut of the honeybee Apis mellifera collected from three locations that differ in their extent of spraying load with OP insecticides: a weakly anthropised rural site, Bolin which is considered as a reference site; moderately spraying site, El Kaza; and a strongly anthropised urban site, Tiba with a long history of pesticide use. Results showed that high concentrations of chlorpyrifos, malathion, diazinon, chlorpyrifos-methyl, and pirimiphos-methyl were detected in midgut at locations with extensive pesticide spraying. Reduced glutathione content, superoxide dismutase, catalase, and glutathione peroxidase displayed lowest activities in the heavily sprayed location (Tiba). Lipid peroxidation level in the midgut of honeybees in the sprayed locations was found to be significantly higher compared to the reference values. Meanwhile, various ultrastructural abnormalities were observed in the epithelial cells of midgut of honeybees collected from El Kaza and Tiba, included confluent and disorganized microvilli and destruction of their brush border, the cytoplasm with large vacuoles and alteration of cytoplasmic organelles including the presence of swollen mitochondria with lysis of matrices, disruption of limiting membranes, and disintegration of cristae. The nuclei with indented nuclear envelope and disorganized chromatin were observed. These investigated biomarkers indicated that the surveyed honeybees are being under stressful environmental conditions. So, we suggest using those biomarkers in the assessment of environmental quality using honeybees in future monitoring of ecotoxicological studies.

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

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

Low Temperature Storage of Eggs Improve the Development and Reproduction of Locusta migratoria (Orthoptera: Acrididae)

Locusta migratoria L. is an insect with significant economic value. Improving the long-term storage of L. migratoria eggs will help promote the large-scale rearing of this insect. We assessed multiple fitness parameters and enzyme activities of locusts emerged from eggs exposed to 4 °C for 1-4 wk. Locusts emerged from eggs stored at 4 °C for 2 wk showed significantly improved development and reproduction compared with locusts emerged from eggs stored for other time periods. The preimaginal survival rate increased significantly after 2-wk storage while it decreased significantly after 4-wk storage compared with other storage times. The fecundity, hatching rate, and growth rate increased significantly after 2-wk storage, but decreased significantly after 1, 3, and 4 wk compared with the control. However, the preimaginal developmental duration decreased significantly after 2-wk storage but increased significantly after storage for 1, 3, and 4 wk compared with the control. The activities of esterase, glutathione-S-transferases, phenol oxidase, and chitinase were obviously fluctuated with changes in intrinsic rate of increase (rm). These results showed that eggs stored at 4 °C for 2 wk could improve the development and reproduction of locust emerged from eggs, and four enzymes activities in above could reflect the health of locust. Our results could be useful in developing large-scale rearing protocols for L. migratoria.

Activity changes of antioxidant and detoxifying enzymes in Tenebrio molitor (Coleoptera: Tenebrionidae) larvae infected by the entomopathogenic nematode Heterorhabditis beicherriana (Rhabditida: Heterorhabditidae)

Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis are lethal parasites of many insect species. To investigate defensive mechanisms towards EPNs in relation to antioxidative and detoxifying enzymes, we chose Tenebrio molitor (Coleoptera: Tenebrionidae) as experimental insect. We studied the activity changes of superoxide dismutases (SODs), peroxidases (PODs), and catalases (CATs), as well as tyrosinase (TYR), acetylcholinesterase (AChE), carboxylesterase (CarE), and glutathione S-transferase (GSTs) for 40 h in T. molitor larvae infected with Heterorhabditis beicherriana infective juveniles (IJs) at 5 rates (0, 20, 40, 80, and 160 IJs/larva). We found that when T. molitor larvae infected with H. beicherriana at higher rates (80 and 160 IJs/larva), SOD activity quickly increased to more than 70 % higher than that control levels. The activities of POD and CAT increased after 24 h. TYR activity increased slowly at lower rates of infection for 16 h, followed by a slight decrease, and then increasing from 32 to 40 h. The other detoxifying enzymes (GST, CarE, and AChE) were enhanced at lower infection rates, but were inhibited at higher rates. Our results suggested that host antioxidative response and detoxification reactions played a central role in the defensive reaction to EPNs, and that this stress which was reflected by the higher level enzymes activity contributed to the death of hosts. Further study should explore the exact function of these enzymes using different species of EPNs and investigate the links between enzyme activity and host susceptibility to EPNs.

Influence of plant resistance traits in selectiveness and species strength in a tropical plant-herbivore network

PREMISE OF THE STUDY

Plant-herbivore networks are highly specialized in their interactions, yet they are highly variable with regard to the relative importance of specific host species for herbivores. How host species traits determine specialization and species strength in this antagonistic network is still an unanswered question that we addressed in this study.

METHODS

We assessed plant cover and antiherbivore resistance traits to assess the extent to which they accounted for the variation in specialization and strength of interactions among species in a plant-herbivore network. We studied a tropical antagonistic network including a diverse herbivore-host plant assemblages in different habitat types and climatic seasons, including host plants with different life histories.

KEY RESULTS

Particular combinations of leaf toughness, trichome density, and phenolic compounds influenced herbivore specialization and host species strength, but with a significant spatiotemporal variation among plant life histories. Conversely, plant-herbivore network parameters were not influenced by plant cover.

CONCLUSIONS

Our study highlights the importance of species-specific resistance traits of plants to understand the ecological and evolutionary consequences of plant-herbivore interaction networks. The novelty of our research lies in the use of a trait-based approach to understand the variation observed in diverse plant-herbivore networks.

Effects of resistant and susceptible rubber germplasms on development, reproduction and protective enzyme activities of Eotetranychus sexmaculatus (Acari: Tetranychidae)

Systematic research or technical support regarding rubber germplasm resistance against mites was not performed yet. To develop a preliminary understanding of the mite-resistance mechanisms of rubber germplasms, stably resistant rubber germplasms were obtained, the development and reproduction of Eotetranychus sexmaculatus that fed on leaves of resistant and susceptible rubber germplasms were examined in the laboratory, and the activities of protective enzymes in this mite species were also compared. The results indicated that: (1) among the 23 rubber core germplasms identified, five (IRCI12, Reyan87-6-5, IAN717, RRIM600 and RRIC52) steadily developed resistance to E. sexmaculatus; (2) E. sexmaculatus that fed on the highly resistant germplasm IRCI12 did not complete development and reproduction-the female adults laid only 4.90 eggs on average, and none of these eggs hatched; (3) the resistant germplasms extended the duration of each developmental stage, reduced the fecundity, egg hatchability, and female offspring percentage, and significantly decreased the offspring survival rate compared with the susceptible germplasms; and (4) during each developmental stage of the mites that fed on resistant rubber germplasms, decreased activities (by 0.25-fold to 0.63-fold times) of the protective enzymes peroxidase, ascorbate peroxidase, polyphenol oxidase, superoxide dismutase and catalase were observed compared with those in the mites that fed on susceptible rubber germplasms (P < 0.05). These findings may explain why E. sexmaculatus did not complete their development and reproduction on the resistant rubber germplasms. This study lays a foundation for elucidation of the mechanism of rubber resistance to mites and provides experimental material and technical support for the breeding of mite-resistant rubber plants.

Biochemical basis of synergism between pathogenic fungus Metarhizium anisopliae and insecticide chlorantraniliprole in Locusta migratoria (Meyen)

We challenged Locusta migratoria (Meyen) grasshoppers with simultaneous doses of both the insecticide chlorantraniliprole and the fungal pathogen, Metarhizium anisopliae. Our results showed synergistic and antagonistic effects on host mortality and enzyme activities. To elucidate the biochemical mechanisms that underlie detoxification and pathogen-immune responses in insects, we monitored the activities of 10 enzymes. After administration of insecticide and fungus, activities of glutathione-S-transferase (GST), general esterases (ESTs) and phenol oxidase (PO) decreased in the insect during the initial time period, whereas those of aryl acylamidase (AA) and chitinase (CHI) increased during the initial period and that of acetylcholinesterase (AChE) increased during a later time period. Activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) decreased at a later time period post treatment. Interestingly, treatment with chlorantraniliprole and M. anisopliae relieved the convulsions that normally accompany M. anisopliae infection. We speculate that locust mortality increased as a result of synergism via a mechanism related to Ca²⁺ disruption in the host. Our study illuminates the biochemical mechanisms involved in insect immunity to xenobiotics and pathogens as well as the mechanisms by which these factors disrupt host homeostasis and induce death. We expect this knowledge to lead to more effective pest control.

Different Effects of Metarhizium anisopliae Strains IMI330189 and IBC200614 on Enzymes Activities and Hemocytes of Locusta migratoria L

BACKGROUND

Metarhizium is an important class of entomopathogenic fungi in the biocontrol of insects, but its virulence is affected by insect immunity. To clarify the mechanism in virulence of Metarhizium, we compared the immunological differences in Locusta migratoria L. when exposed to two strains of Metarhizium anisopliae (Ma).

RESULTS

The virulence of Ma IMI330189 was significantly higher than that of Ma IBC200614 to locust, and IMI330189 overcame the hemocytes and began destroying the hemocytes of locust at 72 h after spray, while locust is immune to IBC200614. IMI330189 could overcome the humoral immunity of locust by inhibiting the activities of phenol oxidase (PO), esterases, multi-function oxidases (MFOs) and acetylcholinesterases in locust while increasing the activities of glutathione-S-transferases (GSTs), catalase and aryl-acylamidase (AA). However IBC200614 inhibit the activities of GSTs and AA in locust and increase the activities of MFOs, PO, superoxide dismutase, peroxidase and chitinase in locust. The changes of enzymes activities in period of infection showed that the time period between the 2nd and the 5th day after spray is critical in the pathogenic process.

CONCLUSION

These results found the phenomenon that Ma initiatively broke host hemocytes, revealed the correlation between the virulence of Ma and the changes of enzymes activities in host induced by Ma, and clarified the critical period in the infection of Ma. So, these results should provide guidance for the construction of efficient biocontrol Ma strains.