Ascorbic and uric acid responses to xanthotoxin ingestion in a generalist and a specialist caterpillar

Effects of Methyl Jasmonate Fumigation on the Growth and Detoxification Ability of Spodoptera litura to Xanthotoxin

Methyl jasmonate (MeJA) is a volatile substance derived from jasmonic acid (JA), and it responds to interbiotic and abiotic stresses by participating in interplant communication. Despite its function in interplant communication, the specific role of MeJA in insect defense responses is poorly understood. In this study, we found that carboxylesterase (CarE) activities, glutathione-S-transferase (GSTs) activities, and cytochrome mono-oxygenases (P450s) content increased more after the feeding of diets containing xanthotoxin, while larvae exposed to MeJA fumigation also showed higher enzyme activity in a dose-dependent manner: lower and medium concentrations of MeJA induced higher detoxification enzyme activities than higher concentrations of MeJA. Moreover, MeJA improved the growth of larvae fed on the control diet without toxins and diets with lower concentrations of xanthotoxin (0.05%); however, MeJA could not protect the larvae against higher concentrations of xanthotoxin (0.1%, 0.2%). In summary, we demonstrated that MeJA is effective at inducing S. litura defense response, but the enhanced detoxifying ability could not overcome the strong toxins.

Oviposition behaviour and biochemical response of an insect pest, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) to plant phenolic compound phloroglucinol

Phenolic compounds are the secondary metabolites (SMs) present in plants carrying different bioactivities. In the present study, we explored the influence of a phenolic compound namely phloroglucinol on oviposition behaviour and different biochemical entities of an insect pest Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) using artificial diet. Phloroglucinol (IUPAC name: benzene-1,3,5-triol) affected the activity of antioxidant and detoxifying enzymes viz. superoxide dismutases (SOD), catalase (CAT), ascorbate peroxidases (APOX). dehydroascorbate reductase (DHAR), peroxidases (POX), phenol oxidase (PO), glutathione peroxidase (GPOX), glutathione S-transferase peroxidase (GSTpox), glutathione reductase (GR), glutathione S-transferase (GST) and esterases (EST) as well as the biological antioxidants viz. ascorbate content and glutathione. The lipid peroxide content (LP) and hydrogen peroxide content (H₂O₂) were significantly enhanced in the treated larvae indicating oxidative stress in the insect. Significant inhibition in oviposition was observed and effective repellency percentage increased with phloroglucinol treatment as compared to control. The oviposition deterrent activity and toxic effects of phloroglucinol on various biochemical parameters of Z. cucurbitae larvae revealed in the present study clearly confirms its suitability for use in pest management.

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.

THE EFFECTS OF XANTHOTOXIN ON THE BIOLOGY AND BIOCHEMISTRY OF Galleria mellonella L. (LEPIDOPTERA: PYRALIDAE)

The effects of a dietary plant allelochemical, xanthotoxin (XA), on survivorship, development, male and female adult longevity, fecundity, and hatchability of the greater wax moth Galleria mellonella L. were investigated. Oxidative stress indicators, the lipid peroxidation product, malondialdehyde (MDA), and protein oxidation products, protein carbonyl (PCO) contents, and activities of a detoxification enzyme glutathione S-transferase (GST) activity were determined in wax moth adults. The insect was reared from first-instar larvae on an artificial diets containing XA at 0.001, 0.005, or 0.1% to adult stage in laboratory conditions. Relative to the controls, the diets containing XA concentrations led to decreased survivorship in seventh instar, pupal, and adult stages. Compared to control diet (77.7%), the highest dietary XA concentration decreased survivorship to adulthood to 11.0%. The highest XA concentration (0.1%) reduced female longevity from 10.4 to 5.7 days and decreased egg numbers from 95.0 to 33.5 and hatchability from 82.7 to 35.6%. The lowest XA concentration (0.001%) led to about a sixfold increase in MDA content. XA at high concentrations (0.005 and 0.1%) increased MDA (by threefold) and protein carbonyl (by twofold) contents decreased GST activity. The highest dietary XA concentration decreased GST activity from 0.28 ± 0.025 to 0.16 ± 0.005 μmol/mg protein/min. We infer from these findings that XA-induced oxidative stress led to decreased biological fitness.

Adipokinetic hormone-induced antioxidant response in Spodoptera littoralis

The antioxidative potential of the Manduca sexta adipokinetic hormone (Manse-AKH) in the last instar larvae of Spodoptera littoralis (Noctuidae, Lepidoptera) was demonstrated after exposure to oxidative stress (OS) elicited by feeding on artificial diet containing tannic acid (TA). Determination of protein carbonyls (PCs) and reduced glutathione (GSH) levels, monitoring of activity of antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione-S-transferases (GSTs), as well as measuring of the mRNA expression of CAT and SOD were used as markers of the OS. Injection of the Manse-AKH (5 pmol per individual) reversed the OS status by mitigation of PCs formation and by stimulation of glutathione-S-transferases (GSTs) activity. The CAT and SOD mRNA expression was significantly suppressed after the Manse-AKH injection while activity of these enzymes was not affected. These results indicate that diminishing of OS after the AKH injection might be a result of activation of specific enzymatic pathway possibly at the post-translational level rather than a direct effect on regulation of antioxidant marker genes at the transcriptional level.

Glutathione-ascorbic acid redox cycle and thioredoxin reductase activity in the digestive tract of Leptinotarsa decemlineata (Say)

In view of the antioxidant role of glutathione (GSH) and ascorbic acid (AA), we have examined capacity of the GSH-AA redox cycle in relation to oxidative stress effects in the midgut of the Colorado potato beetle Leptinotarsa decemlineata. Adult gut harbors a higher capacity to cope with oxidative stress than the larval gut. Protein carbonylation was pronounced in the wall of anterior larval midgut and was generally lower in the food digest than in the gut wall. Restriction of oxidative stress effects in anterior gut lumen manifested by lipid peroxidation and protein carbonylation is interpreted as a mechanism favoring digestion and absorption in the posterior midgut. Presence of high GSH in the posterior midgut and AA in both posterior and anterior midguts of adults points to higher utility of the GSH-AA redox system in limiting oxidative stress to manageable levels. The presence, gene expression and activity of thioredoxin reductase (TrxR) were demonstrated for the first time in L. decemlineata which was markedly higher in the anterior than in the posterior midgut in both stages. It is probably central to the maintenance of reduced GSH levels in the whole gut, despite a GSSG/2GSH redox potential tending towards oxidizing ranging from -183.5 to -124.4mV. Glutathione-dehydroascorbate reductase (G(DHA)R) activity was markedly augmented in adult gut compared with larva, pointing to a more efficient conversion of dehydroascorbate (DHA) to AA. Also, ascorbate peroxidase (APOX) activity was significantly elevated in all gut compartments of adult except the wall of posterior midgut. The results emphasize the potential importance and role of the GSH-AA redox cycle as a defense strategy against oxidative stress in the gut of L. decemlineata.

Plant phenolics behave as radical scavengers in the context of insect (Manduca sexta) hemolymph and midgut fluid

To evaluate the prooxidant versus antioxidant properties of plant phenolics toward leaf-feeding caterpillars, quenching of the stable ABTS radical by five phenolics was measured in two physiological contexts: hemolymph and midgut fluid. Addition of tannic acid, chlorogenic acid, quercetin, or catechin to Manduca sexta (L.) gut fluid increased its total antioxidant capacity by 12-45%, with tannic acid and quercetin being the most powerful in this regard. The antioxidant contribution of the phenolics increased with longer (30-60 min) incubation time in gut fluid. Chlorogenic acid and caffeic acid exhibited the weakest antioxidant activity in gut fluid. The total antioxidant capacity of hemolymph is considerably less than that of gut fluid, and in hemolymph chlorogenic and caffeic acids sometimes acted as mild prooxidants, particularly after longer incubation periods (30-60 min), although this trend was not statistically significant. Tannic acid, catechin, and quercetin behaved as antioxidants in hemolymph. These results suggest that many phenolics have radical scavenging activity in the digestive tract, but some may have more detrimental effects after absorption into the hemolymph compartment.

Deliberately added and "cryptic" antioxidants in three artificial diets for insects

Characteristics of both deliberately added and "cryptic" antioxidants were assayed from hydrophilic and lipophilic extracts from artificial diets for plant bugs, lepidopteran larvae, and green lacewings. Cryptic antioxidants are defined as substances naturally existing in diet ingredients but not deliberately added because of their antioxidant potential. Diets were tested after 1) being freshly produced, 2) stored for 48 h at 4 degrees C, or 3) held for 48 h under rearing room conditions at 27 degrees C. Tests included 1) a general assay of antioxidant capacity known as the ferric-reducing antioxidant power (FRAP) assay. 2) a cation radical-scavenging assay, 3) an ascorbic acid assay, and 4) an assay of inhibition of lipid peroxidation. In all assays, the lepidopteran diet had the highest values for protection against reactive oxygen species (ROS). The lepidopteran diet (with 0.17-0.23-mg equivalents of gallic acid equals total phenolic compounds per gram of diet) had three- to four-fold higher concentrations of phenolic compounds than did either the plant bug diet or the lacewing diet. Unexpectedly, the plant bug and the lacewing diets caused more lipid peroxidation than did the positive controls. This was attributed to the high concentrations of iron in these diets (mainly from chicken eggs), causing an ascorbate-ferric ion-induced lipid peroxidation. Diet storage, measured after 2 d at 27 or 4-6 degrees C, caused no significant declines in overall antioxidant potential. However, storage did lead to decline in ascorbic acid. The FRAP assay offered the best potential as a general, routine test of the potential of various insect diets to resist the destructive effects of ROS. The importance of addressing issues of protection against ROS in insect diets is discussed.

Antioxidants in the midgut fluids of a tannin-tolerant and a tannin-sensitive caterpillar: effects of seasonal changes in tree leaves

The seasonal decline in foliar nutritional quality in deciduous trees also effects the availability of essential micronutrients, such as ascorbate and alpha-tocopherol, to herbivorous insects. This study first examined whether there are consistent patterns of seasonal change in antioxidant concentrations in deciduous tree leaves. Alpha-tocopherol concentrations increased substantially through time in late summer in sugar maple (Acer saccharum), red oak (Quercus rubra), and trembling aspen (Populus tremuloides). However, seasonal change in the concentrations of other antioxidants differed between each species: P. tremuloides had higher levels of ascorbate and glutathione in the spring, Q. rubra had higher levels of glutathione but lower levels of ascorbate in the spring, and A. saccharum had lower levels of both ascorbate and glutathione in the spring. To test the hypothesis that tannin-tolerant caterpillars maintain higher concentrations of antioxidants in their midgut fluids than do tannin-sensitive species, we measured antioxidants in Orgyia leucostigma (a spring- and summer-feeding, tannin-tolerant species) and Malacosoma disstria (a spring-feeding, tannin-sensitive species) that were fed tree leaves in the spring and summer. The midgut fluids of O. leucostigma larvae generally had higher concentrations of antioxidants in the summer than did those of M. disstria, and were significantly higher overall. The results of this study are consistent with the hypothesis that higher concentrations of antioxidants form an important component of the defenses of herbivores that feed on mature, phenol-rich tree leaves. Some limitations of the interpretation of total antioxidant capacity are also discussed.

Antioxidants in grasshoppers: higher levels defend the midgut tissues of a polyphagous species than a graminivorous species

Polyphagous grasshoppers consume plants that contain markedly greater amounts of potentially prooxidant allelochemicals than the grasses eaten by graminivorous grasshoppers. Therefore, levels of antioxidant defenses maintained by these herbivores might be expected to differ in accordance with host plant ranges. Antioxidant levels were compared in midgut tissues and gut fluids of a polyphagous grasshopper. Melanoplus sanguinipes, and a graminivorous grasshopper, Aulocara ellioti. Glutathione concentrations in midgut tissues of M. sanguinipes (10.6 mM) are among the highest measured in animal tissues and are twice as high as those in A. ellioti. Alpha-tocopherol levels are 126% higher in midgut tissues of M. sanguinipes than in those of A. ellioti, and remain at high levels when M. sanguinipes is reared on plants containing a wide range of alpha-tocopherol concentrations. Ascorbate levels in M. sanguinipes midgut tissues are 27% higher than in those of A. ellioti, but vary depending on the host plant on which they are reared. Midgut fluids of both species contain elevated levels of glutathione, as well as large (millimolar) amounts of undetermined antioxidants that are produced in the insects. The consumption of tannic acid decreases ascorbate concentrations in midgut tisssues and gut fluids of A. ellioti but has no effect on ascorbate levels in M. sanguinipes. The results of this study provide the first measurements of antioxidants in grasshoppers and suggest that the maintenance of high levels of antioxidants in the midgut tissues of polyphagous grasshoppers might effectively protect them from oxidative stress.

Environmental oxidant pollutant effects on biologic systems: a focus on micronutrient antioxidant-oxidant interactions

Oxidative atmospheric pollutants represent a significant source of stress to both terrestrial plants and animals. The biosurfaces of plants and surface-living organisms are directly exposed to these pollutant stresses. These surfaces, including respiratory tract surfaces, contain integrated antioxidant systems that would be expected to provide a primary defense against environmental threats caused by atmospheric reactive oxygen species. When the biosurface antioxidant defenses are overwhelmed, oxidative stress to the cellular components of the exposed biosurfaces can be expected, inducing inflammatory, adaptive, injurious, and reparative processes. Studies of mutants and/or transformed plants and insects, with specific alterations in key components of antioxidant defense systems, offer opportunities to dissect the complex systems that maintain surface defenses against environmental oxidants. In this article, we use a comparative approach to consider interactions of atmospheric oxidant pollutants with selected biosystems, with focus on O3 as the pollutant; plants, flies, skin, and lungs as the exposed biosystems; and nonenzymatic micronutrient antioxidants as significant contributors to overall antioxidant defense strategies of these varied biosystems. Parallelisms among several living organisms, with regard to their protective strategies against environmental atmospheric oxidants, are presented.