Enzymes In Midgut Research Articles

Ascertaining variations in the activity of larval midgut enzymes of Helicoverpa armigera by dietary emamectin benzoate through biochemical and in silico docking study

Helicoverpa armigera, a ubiquitous polyphagous pest, poses a significant threat to global agriculture, causing substantial economic losses and demonstrating resistance to synthetic pesticides. This study investigates the potential of emamectin benzoate (EMB), an avermectin derivative, as an effective control agent against H. armigera. The larvae of the NBII-MP–NOC–01 strain of H. armigera were reared on an artificial diet. The impact of dietary EMB was examined on four midgut enzymes; alanine aminotransferase (ALT), aspartate aminotransferase (AST), acid phosphatase (ACP), and alkaline phosphatase (ALP). Results showed a dose-dependent and time-dependent reduction in ALT and AST activity, while an initial increase and subsequent decline in ACP and ALP activity at higher EMB concentrations. Computational modelling of enzyme structures and molecular docking studies revealed differential binding of EMB with the midgut enzymes. The strongest interaction was observed between EMB and ALT residues, contrasting with weakest interactions observed with AST. The study also showed that decreased activity of transaminases in H. armigera caused by EMB may be because of stability-activity trade-off, while in phosphatases reverse may be the case. This research provides crucial insights into the biochemical responses and the intricate insecticide-enzyme interactions in H. armigera caused by EMB exposure. This study lays the foundation for further research aimed at developing environmentally friendly approaches for managing H. armigera, addressing the challenges associated with conventional pesticides.

Effect of ivermectin, amitraz and fipronil on midgut epithelium and digestive enzyme profile in Rhipicephalus microplus ticks (Acari: Ixodidae).

Blood feeding and digestion are vital physiological activities essential for the survival and reproduction of ticks. Chemical acaricides viz., ivermectin, amitraz and fipronil, are known to act on the central nervous system, resulting in the mortality of ticks. The present study is focused on the effect of these acaricides on the midgut and gut enzymes ofRhipicephalus microplus.The ultra-thin sections of midgut of ivermectin-treated ticks showed irregular basal membrane and ruptured digestive vesicles. Amitraz treatment resulted in a notable decrease in digestive cells with pleats in the basal membrane, while fipronil-exposed ticks exhibited reduced digestive cells, loss of cellular integrity, and disintegration of the basal membrane and muscle layer.The gut tissue homogenate of ivermectin and fipronil treated ticks showed a significant reduction of cathepsin D level, 76.54 ± 3.20 μg/mL and 92.67 ± 3.72 μg/mL, respectively, as compared to the control group (150.0 ± 3.80 μg/mL). The leucine aminopeptidase level (4.27 ± 0.08 units/mL) was significantly decreased in the ivermectin treated ticks compared to other treatment groups.The acid phosphatase activity (29.16 ± 0.67 μmole/min/L) was reduced in the ivermectin treated group whereas, increased activity was observed in the fipronil and amitraz treated groups. All the treatment groups revealed increased alkaline phosphatase levels (17.47-26.72 μmole/min/L). The present finding suggests that in addition to the established mechanism of action of the tested acaricides on the nervous system, the alterations in the cellular profile of digestive cells and enzymes possibly affect the blood digestion process and thus the synthesis of vital proteins which are essential for vitellogenesis, and egg production in ticks.

Influence of Cry1Ab protein on growth and development of a predatory spider, Pardosa pseudoannulata, from protective perspectives

The expression of Cry proteins in genetically modified rice varieties safeguards the crop from lepidopteran pests. These proteins have the potential to be transferred through the food chain to arthropods like planthoppers and predatory spiders, triggering defensive responses in these unintended organisms. Hence, we hypothesized that Cry protein might influence the growth and development of spiders by altering protective enzyme activities. The results showed that Cry1Ab protein could accumulate in tissues and subcellular organelles of Pardosa pseudoannulata from Nilaparvata lugens. Cry1Ab protein exposure prolonged the developmental duration in the 5th and 7th instar spiderlings but induced no alterations of other growth indicators, such as body length, median ocular area, and survival rate. In addition, Cry1Ab protein exerted no adverse impacts on several detoxifying enzymes (i.e., superoxide dismutase, catalase, glutathione peroxidase, and acetylcholine esterase) in muscle, midgut, ganglia, and hemolymph at subcellular components (i.e., microsome and cytoplasm). To further explore the effects of Cry1Ab protein on the spiderlings, we performed an integrated transcriptome analysis on spiderlings exposed to Cry1Ab protein. The results showed that Cry1Ab protein might prolong the development duration of P. pseudoannulata via the altered cuticle metabolism (e.g., chitin metabolic process and structural constituent of cuticle). In addition, the gene expression profile associated with detoxifying enzymes and three stress-responsive pathways (JAK/STAT, JNK/SAPK, and Hippo pathways) also displayed no significant alterations under Cry1Ab exposure. Collectively, this integrated analysis generates multidimensional insights to assess the effects of Cry1Ab protein on non-target spiders and demonstrates that Cry1Ab protein exerts no toxicity in P. pseudoannulata.

Bio-efficacy of chloroform crude extracts of chick weed Ageratum conyzoides (Linn.) against the tobacco cutworm Spodoptera litura (Linn.) and their non-toxicity against the beneficial earthworm

The current study investigates the phyto-chemical screening of chloroform crude extracts of chickweed Ageratum conyzoides (Linn.) (Cm-Ac) and their target and non-target toxicity against the pest Spodoptera litura and beneficial earthworm. Phyto-chemical characterization of Cm-Ac over GC-MS technique revealed thirty four bio-active compounds with highest peak area% observed in Phenol, 2,4-Bis-(1,1-Dimethylethyl)-(6.340 PA%), followed by n-Hexadecanoic acid (5.95 PA%) and 1- Octadecene (5.94 %) respectively. Larval toxicity was observed maximum at the dosage of 1000 ppm at second instar (98.23 %) as compared to other dosages. Lethal dosage (LC50) obtained on 2.467 log ppm respectively. The sub-lethal toxic dosage of Cm-Ac (100–500 ppm) displayed adverse impact on larval-pupal growth and development in dose dependent manner. Also, the sub-lethal dosage of Cm-Ac also decreased the level of mid-gut enzymes in dose dependent manner. The mid-gut tissues including Gut Lumen-(GL), Epithelial Layer-(EL), and Brush Border Membrane-(BBM) severely affected at the prominent concentration of 500 ppm as paralleled with control. Non-target activity against Eudrilis eugeniae revealed that the Cm-Ac treatment is less toxic at the prominent concentration of 1000 ppm as paralleled to Cypermethrin treatment. Overall, the current results are promising in developing botanical based insecticides which are bio-degradable and importantly harmless or less toxic to the non-target earthworms.

Preservation of Field-Collected Mosquito Blood Meals.

All PCR- and DNA-based blood meal analyses require host DNA from a mosquito blood meal to be effectively preserved between the time when the specimen is collected and the extraction of DNA. As soon as a mosquito ingests blood from a host animal, digestion of host cells and cellular components within the blood meal by enzymes in the mosquito midgut begins to degrade the host DNA templates that are the targets of polymerase chain reaction (PCR) amplification. Without effective preservation, host DNA is typically undetectable by PCR 48 h after feeding, because of digestion. Preservation methods for mosquito blood meals vary in their efficacy, and the logistics of fieldwork can limit the options for preservation of blood meals and maintenance of the integrity of host DNA. This protocol describes a method of blood meal preservation that is effective, convenient, and amenable to fieldwork in remote locations where cryopreservation at -20°C or -80°C may not be feasible. It uses a Flinders Technology Associates (FTA) card, which is a chemically treated card that lyses cells and allows nucleic acids to be preserved. This method is also expected to preserve the DNA or RNA of pathogens present within the engorged mosquito abdomen, including RNA viruses.

Docking-Based Virtual Screening Ascertaining β-Sitosterol-Induced Alterations in the Helicoverpa armigera Hübner Gut Enzymes

Present investigation attempts to study binding of β-sitosterol with Helicoverpa armigera midgut enzymes; alanine aminotransaminase (ALT), aspartate aminotransaminase (AST) and alkaline phosphatase (ALP); through docking-based virtual screening. Extraction of the protein sequence of the enzymes revealed a respective linear chain of 535, 522 and 430 amino acids for ALP, ALT and AST. The binding energy for ALT-ligand complex was lowest as compared to the AST and ALP-docked complexes. The ALT-docked complex had ligand efficiency of (-) 0.32 with an inhibition constant of 104.01, more hydrogen bonds and hydrophobic interactions leading to a more stable complex. However, unfavored bumps in AST and ALP complexes may have led to comparatively unstable complexes. The dietary β-sitosterol exhibits differential binding with midgut enzymes of H. armigera larvae. The strong binding of β-sitosterol with ALT indicates the highest inhibition of ALT activity due to the activity-stability trade-off. The enzymes, AST and ALP exhibited relatively higher activity as a resultant of lesser stabilization of the β-sitosterol-enzyme complex. In silico studies have indicated that β-sitosterol can be used an effective control agent against H. armigera.

Effect of Aspergillus flavus on lipid peroxidation and activity of antioxidant enzymes in midgut tissue of Spodoptera litura larvae

In the present study, effect of Aspergillus flavus was analysed on lipid peroxidation and activities of antioxidant enzymes in midgut of Spodoptera litura. Fungus was administered to the larvae of S. litura using artificial diet method having 1.34 mg/mL (LC50) concentration. The fungus toxicity was observed after 24, 48, 72 and 96 h post treatment in the midgut tissue of insect larvae by examining lipid peroxidation (MDA content) and activities of antioxidant enzymes viz superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APOX) and glutathione-S-transferase (GST) as oxidative stress markers. Additionally, repair of the damage caused due to fungal treatment was also assessed to decipher the longevity of effect by giving control diet to the exposed larvae for two days after particular time exposure using same parameters. In particular, significant (p ≤ 0.05) increased level of lipid peroxidation and antioxidant enzymes activities was observed in all exposure time groups with respect to control which showed that midgut of exposed larvae has oxidative predominance. Repair studies demonstrated the negligible repair in insect larvae. In conclusion, A. flavus contributed to strong oxidative stress and toxicity in S. litura larvae.

Effects of β-sitosterol on growth, development and midgut enzymes of Helicoverpa armigera Hübner

Helicoverpa armigera is a global agricultural pest of serious concern. Continued use of chemical insecticides as control measures has raised grave health and environment concerns, necessitating a search for botanicals as safe alternatives. The current study investigates the effects of ?-sitosterol, a bioactive phytocomponent in Thevetia neriifolia, on the growth and development, as well as on midgut enzymes of H. armigera. Dietary ?-sitosterol produced dose-dependent systemic toxicity and growth inhibitory effects in H. armigera; the most significant effects were obtained with 10 ?g/mL dietary ?-sitosterol. Higher prepupal and pupal mortality in comparison to larval mortality and a comparatively greater reduction in average weight gained by later instars point to cumulative effects of ?-sitosterol. The delayed effects were ascertained by the 82.05%-57.89% reduction in adult emergence in comparison to 95.02% emergence in controls. Dose-dependent effects of ?-sitosterol were observed as significantly decreased enzyme activities of alanine aminotransaminase (ALT), aspartate aminotransaminase (AST) and alkaline phosphatase (ALP) in the larval midgut. Suppression of enzyme activity was obtained in the order ALT>AST>ALP. Impaired activity of gut enzymes possibly lowered the energy reserves and affected nutrient transport through the gut epithelium, affecting the growth and development of H. armigera. Our study points to a promising use of ?-sitosterol against H. armigera, although further examination and field studies are needed to ascertain its possible use in control programs.

The mechanism of damage in the midgut of Bombyx mori after chlorantraniliprole exposure.

Silkworm (Bombyx mori) is an economic insect of the Lepidoptera. Chlorantraniliprole (CAP) exposure results in reduced growth and development of B. mori and failure in cocooning, seriously affecting the development of sericulture. To study the mechanisms underlying the damage to silkworm caused by sublethal doses of CAP, we examined the oxidative damage, the activities of digestive enzymes in midgut, and the expressions of midgut-related genes at the mRNA level. We found that CAP exposure inhibited the growth of silkworm, decreased the body mass and caused the accumulation of reactive oxygen species (ROS) [the levels of O2-, H2O2 and lipid peroxidation (MDA) were increased by 1.62-, 1.87- and 1.46-fold, respectively]. Moreover, we also found that the midgut cells were disintegrated, microvilli disappeared, the stroma became thinner, and the chromatin of nucleus became aggregated after CAP exposure by the analysis of transmission electron microscopy (TEM). In addition, the activities of digestive enzymes were dysregulated in midgut (the activities of α-amylase and trypsin were decreased 0.69- and 0.20-fold, respectively). Furthermore, digital gene expression (DGE) profiling analysis revealed that the expressions of oxidative phosphorylation pathway and antioxidant defense system related genes in midgut were decreased, indicating that it was the oxidative damage in midgut caused by CAP that mainly affected the growth of silkworm, rather than the toxicological effects of CAP. Collectively, this study provided valuable insights into the toxic effects of CAP on insects.

Effects of Chlorella sp. on biological characteristics of the honey bee Apis mellifera

We tested the effect of Chlorella sorokiniana, a green, unicellular, freshwater alga, provided as a food supplement on several biological characteristics of the honey bee Apis mellifera. Chlorella was applied as (1) a moisturized powder, (2) a sugar-water solution, or (3) mixed with honey-sugar candy. All three applications were well accepted by the bees. We observed a positive effect of Chlorella on colony development, and also on basic aspects of metabolism, such as increased fat deposition and vitellogenin transcript levels, and a decrease in TOR and InR2 transcript levels. The effect of Chlorella on other characteristics was lower (protein levels) or even null (total fat body mass, level of adipokinetic hormone). Application of Chlorella modulated the hypopharyngeal gland size, and the activity of basic digestive enzymes in the bee midgut. Our observations suggest that the nutritional composition of Chlorella might be an appropriate dietary supplement for honey bees.

Inhibitory effect of leaf and root bark of Calotropis procera and Parquetina nigrescens on larval midgut enzyme activities of Callosobruchus maculatus

The study evaluated the protein content and effect of leaf and root bark of Calotropis procera and Parquetina nigrescens on midgut enzyme activities of the larvae of Callosobruchus maculatus with a view to solving the problem of cowpea infestation caused by C. maculatus. Evaluation of inhibitory effect of the leaf and root bark of C. procera and P. nigrescens on total protease, trypsin, chymotrypsin, α-amylase and lipase was carried out with 0.5% extract of each plant material as inhibitor source for the enzyme inhibitory assays. Midgut enzyme activities of protease, lipase and alpha amylase and protein content were also quantified. The results showed that the protein content in the midgut of the larvae of C. maculatus were 1.48±0.01, 1.51±0.01, 1.36±0.01 and 1.71±0.01 mg ml-1 in first, second, third, and fourth instar larvae respectively and were significantly (P < 0.05) different. Protease activity was higher than both alpha amylase and lipase activities in the insect midgut while inhibition of the extracts of leaf and root bark of C. procera and P. nigrescens on enzyme activities varied across plant materials and stages of instar larva of C. maculatus.

Purification of fat body glutathione S‐transferase from the desert locust Schistocerca gregaria: investigation of flavonoid inhibitory effects on enzyme activity

AbstractFocus on the development of botanical insecticides such as polyphenols may represent an alternative method to chemical control. In the present study, total glutathione concentration and its related antioxidant enzymes in foregut, midgut, hindgut and fat body homogenates of the desert locust Schistocerca gregaria are examined. Glutathione S‐transferase (GST) activity exhibits a significantly higher value in fat bodies compared with other tissues. A simple and reproducible procedure for the purification of S. gregaria fat body GST is established and the purified enzyme is shown to be homogenous. The purified GST displays a typical Michaelis behaviour with respect to its substrates. Characterization of the GST, including optimum pH, substrate specificity and inhibitor effects, is carried out. The ability of some flavonoids to inhibit S. gregaria fat body GST activity is examined. High‐performance liquid chromatography analysis indicates that the major components in Glycyrrhiza glabra roots are 18α‐glycyrrhetinic acid, quercetin and rutin, and the major components in Hibiscus sabdariffa calyx are cyanidin 3‐O‐glucoside chloride and delphinidin. Quercetin and delphinidin chloride exhibit strong GST inhibition and the inhibition type is determined for both. Rutin shows a smaller inhibitory effect, whereas 18α‐glycyrrhetinic acid and cyanidin have no effect. Inhibition of S. gregaria fat body GST activity would be expected to prevent, or at least delay, the development of resistance to chemical pesticides. Among the examined levels of the antioxidant enzymes, total glutathione concentration and its related enzymes in foregut, midgut, hindgut and fat body crude homogenates of S. gregaria GST activity exhibit a significantly higher value in fat bodies compared with other tissues. Some flavonoids that are detected in H. sabdariffa calyx and G. glabra root extracts are the most effective inhibitors of the purified S. gregaria fat body GST activity. Inhibition of S. gregaria fat body GST activity by quercetin and delphinidin (major compounds detected by HPLC) would be expected to prevent, or at least delay, the development of resistance to chemical pesticides.

Diminished Activity of Larval Midgut Transaminases and Phosphatases in Helicoverpa armigera Hübner (Lepidoptera) Induced by Dietary Stem Extracts of Thevetia neriifolia

Helicoverpa armigera Hubner (Noctuidae) is a common crop pest causing extensive loss of crop yields despite several efforts and diverse measures taken. As utilization of synthetic pesticides in the fields have caused ecological disturbances and lethal effects on humans and organisms; present studies explore Thevetia neriifolia (Apocynaceae), a widely used ornamental plant, against H. armigera as an alternate control measure. The study investigates the dietary effects of hexane and methanol extracts of T. neriifolia stems (HSE, MSE) on the activity of midgut enzymes of H. armigera, the alterations in which could hamper its growth and development. Different concentrations of the stem extracts, ranging from 0.001% to 0.02%, were incorporated in the diet of early IV instars of H. armigera. Effect of each extract was assessed by estimating the activity of four midgut enzymes; alanine aminotransaminase (ALT), aspartate aminotransaminase (AST), acid phosphatase (ACP) and alkaline phosphatase (ALP) of cotton boll worm. Investigations showed that dietary stem extracts resulted in significant and dose-dependent reduced activity of all the enzymes. The percent inhibition of the enzymatic activity was higher with dietary MSE of T. neriifolia as compared to the hexane stem extract. Also, the enzyme inhibition effects of extracts were more pronounced on phosphatases in comparison to transaminases. Larval feeding with T. neriifolia MSE diminished ALT activity by 26.95% to 49.79% and AST activity by 11.02% to 56.53%, whereas the ACP and ALP activity decreased by 44.65% to 87.61% and 21.97% to 85.97%, respectively. On the other hand, HSE inhibited ALT activity by 29.43% to 41.67% and AST activity by just 2.72% to 47.08%. However, a respective reduction of 14.58% to 78.44% and 32.73% to 78.07% was noticed in ACP and ALP activity with dietary HSE. The GC-MS analysis of the stem hexane and methanol extracts of T. neriifolia reveals the presence of 39 and 30 phyto-chemicals, respectively. Investigations showed the possible use of T. neriifolia extracts as a growth regulatory agent against H. armigera. Identification and isolation of bioactive compounds require further investigations.

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 200mg/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.

Effects of Bt cabbage pollen on the honeybee Apis mellifera L

Honeybees may be exposed to insecticidal proteins from transgenic plants via pollen during their foraging activity. Assessing effects of such exposures on honeybees is an essential part of the risk assessment process for transgenic Bacillus thuringiensis (Bt) cabbage. Feeding trials were conducted in a laboratory setting to test for possible effects of Cry1Ba3 cabbage pollen on Italian-derived honeybees Apis mellifera L. Newly emerged A. mellifera were fed transgenic pollen, activated Cry1Ba3 toxin, pure sugar syrup (60% w/v sucrose solution), and non-transgenic cabbage pollen, respectively. Then the effects on survival, pollen consumption, weight, detoxification enzyme activity and midgut enzyme activity of A. mellifera were monitored. The results showed that there were no significant differences in survival, pollen consumption, weight, detoxification enzyme activity among all treatments. No significant differences in the activities of total proteolytic enzyme, active alkaline trypsin-like enzyme and weak alkaline trypsin-like enzyme were observed among all treatments. These results indicate that the side-effects of the Cry1Ba3 cabbage pollen on A. mellifera L. are unlikely.

Comparative transcriptome analysis provides insights of anti-insect molecular mechanism of Cassia obtusifolia trypsin inhibitor against Pieris rapae.

Pieris rapae, a serious Lepidoptera pest of cultivated crucifers, utilizes midgut enzymes to digest food and detoxify secondary metabolites from host plants. A recombinant trypsin inhibitor (COTI) from nonhost plant, Cassia obtusifolia, significantly decreased activities of trypsin-like proteases in the larval midgut on Pieris rapae and could suppress the growth of larvae. In order to know how COTI took effect, transcriptional profiles of P. rapae midgut in response to COTI was studied. A total of 51,544 unigenes were generated and 45.86% of which had homologs in public databases. Most of the regulated genes associated with digestion, detoxification, homeostasis, and resistance were downregulated after ingestion of COTI. Meanwhile, several unigenes in the integrin signaling pathway might be involved in response to COTI. Furthermore, using comparative transcriptome analysis, we detected differently expressing genes and identified a new reference gene, UPF3, by qRT-polymerase chain reaction (PCR). Therefore, it was suggested that not only proteolysis inhibition, but also suppression of expression of genes involved in metabolism, development, signaling, and defense might account for the anti-insect resistance of COTI.

Synergistic activity of Bacillus thuringiensis δ‐endotoxin and TMOF against Culex pipiens and Spodoptera littoralis larvae

AbstractTrypsin Modulating Oostatic Factor (TMOF) is a decapeptide hormone that inhibits the biosynthesis of digestive enzymes in the mosquito midgut. The hormone inhibits food digestion and ultimately leads to starvation and death. It has been used as a biological insecticide to control mosquitoes. In an attempt to increase the insecticidal activity of TMOF, a combination of CryIC (δ‐endotoxin from Bacillus thuringiensis) and TMOF was determined. Eight recombinant proteins fused with GST (glutathione‐S‐transferase) were expressed in Escherichia coli cells. Their insecticidal activities were determined against Culex pipiens and Spodoptera littoralis larvae. Purified GST‐TMOF and its analogue GST‐YDPAS exhibited a moderate toxicity on C. pipiens larvae with LC50 of 145.9 and 339.9 μg/mL, respectively. Unexpectedly, no mortality was observed in first instar larvae of S. littoralis. Puirified GST‐TMOF and GST‐YDPAS together with Bt toxin showed a synergistic toxic effect on both Culex and Spodoptera larvae. In the presence of 100 μg/mL GST‐TMOF and GST‐YDPAS, the median lethal concentration of entomocidus on culex larvae decreased from 52.1 to 16.7 and 31.9 μg/mL, respectively. Likewise, GST‐TMOF and GST‐YDPAS incorporated with 0.07 μg/cm2 of enotmocidus showed insecticidal activity against S. littoralis with LC50 of 16.4 and 21.9 μg/cm2. The E. coli lysates containing GST‐CryIC and its 3′‐truncated version showed low toxicity against the lepidopteran insect (10.8 and 16.6 μg/cm2) compared to 0.15 μg/cm2 of the native crystalline form of CryIC. Similarly, the mosquitocidal activity of the recombinant Bt toxins was low.

Geranium intoxication induces detoxification enzymes in the Japanese beetle, Popillia japonica Newman

Popillia japonica is a generalist herbivore that feeds on >300 host plant species in at least 72 plant families. It is unknown why P. japonica, despite possessing active detoxification enzymes in its gut, is paralyzed when feeding on the petals of one of its preferred host plant, Pelargonium×hortorum, or on artificial diet containing quisqualic acid (QA), the active compound in zonal geranium. We hypothesized that Pelargonium×hortorum or QA do not induce activity of the cytochrome P450, glutathione S transferase (GST), and carboxylesterase (CoE) detoxification enzymes in P. japonica. In this study, P. japonica were fed petals of zonal geranium or agar plugs containing QA, or rose petals, another preferred but non-toxic host. Midgut enzyme activities of P450, GST, and CoE were then assayed after 6, 12, or 24h of feeding. In most cases, P450, GST, and CoE activities were significantly induced in P. japonica midguts by geranium petals and QA, though the induction was slower than with rose petals. Induced enzyme activity reached a peak at 24h after consumption, which coincides with the period of highest recovery from geranium and QA paralysis. This study shows that toxic geranium and QA induce detoxification enzyme activity, but the induced enzymes do not effectively protect P. japonica from paralysis by QA. Further investigation is required through in vitro studies to know if the enzymes induced by geranium are capable of metabolizing QA. This study highlights a rare physiological mismatch between the detoxification tool kit of a generalist and its preferred host.

Sexual differences in destructive capability and midgut enzyme activities in adult variegated grasshoppers Zonocerus variegatus (LINNAEUS, 1758) (Orthoptera: Pyrgomorphidae)

AbstractThe variegated grasshopper Zonocerus variegatus is a polyphagous insect, feeding on numerous food and cash crops. The present study aimed to investigate the sexual variations in the destructive capability of the adult insects and the composition of leaves damaged by them, as well as in the levels of midgut microbial flora and digestive enzymes (cellulase, amylase and α-glucosidase). The results showed that females consumed and caused more damage to cassava leaves than their male congeners. The leaves damaged by males contained more nutrients than those damaged by females. The gut microbial flora and enzyme assay showed that females had significantly larger colony forming units and a non-significant difference in enzyme activities. It can thus be concluded that adult females are more destructive than males.

Circadian variation affects the biology and digestive profiles of a nocturnal insect Spodoptera litura (Insecta: Lepidoptera)

The present study was conducted to decipher the impact of circadian rhythm on digestive enzymes of Spodoptera litura under three photoperiods (12L:12D, 0L:24D, and 24L:0D). Longer life cycle, higher developmental traits and significant food utilizing capability were observed in dark conditions (DD), while there was no effect on survival. The activity of lactate dehydrogenase (LDH), α and β-glucosidase depended on complete absence of light (DD) while LL had a significant effect on protease activity. The presence of polypeptides (35, 60 kDa) and lower protease inhibition by PMSF in 0L:24D, and 24L:0D indicated that serine proteases (trypsin) were the main proteases in larval midgut. Overall, zymography profiles suggested that circadian variation, particularly dark period influenced the S. litura development due to fluctuations in the midgut enzymes via food utilization. Although the effect of photoperiod on digestive processes of insects is still unclear, dark regime may underlie the midgut digestive enzymes in S. litura larvae.