Expression and Enzyme Activity of Catalase in Chilo suppressalis (Lepidoptera: Crambidae) Is Responsive to Environmental Stresses

Catalase promotes whitefly adaptation to high temperature by eliminating reactive oxygen species

Thermal stress usually leads to excessive production of reactive oxygen species (ROS) in all aerobic organisms. Catalases (CAT) are the key antioxidant enzymes, which act as the first line of defense against ROS in the antioxidant pathway. The highly invasive and widely distributed whitefly Bemisia tabaci MED damages plants by feeding as well as by transmitting many plant viruses. Previous studies have shown that strong adaptability to high temperature helps explain the spread of MED around the world. However, the mechanism underlying high temperature adaptation of this pest is not well understood. In this study, 6 CAT genes were identified from the MED genome and transcriptome dataset, among which BtCAT1, BtCAT2, and BtCAT3 were found to be highly expressed in adults. The expression of BtCAT1, BtCAT2, or BtCAT3 increased with induction temperature and induction time. The MED was exposed with mean high temperature (30 °C or 35 °C) and a short-term extremely high temperature (39 °C or 41 °C) after the silencing of BtCAT1, BtCAT2, or BtCAT3 to significantly increased ROS levels by at least 0.5 times and significantly decreased survival rate and fecundity of MED adults. The ROS level in the treated specimens gradually returned to a normal level after 24 h at 25 °C, but the survival rate still declined significantly. Taken together, our results demonstrate that CAT could help B. tabaci adapt to long-term mean high temperatures and short-term extremely high temperatures by eliminating excessive ROS.

Identification and characterization of Prx5 and Prx6 in Chilo suppressalis in response to environmental stress

The antioxidant proteins, peroxiredoxins (Prxs), function to protect insects from reactive oxygen species-induced toxicity. In this study, two Prx genes, CsPrx5, and CsPrx6, were cloned and characterized from the paddy field pest, Chilo suppressalis, containing open reading frames of 570 and 672 bp encoding 189 and 223 amino acid polypeptides, respectively. Then, we investigated the influence of various stresses on their expression levels using quantitative real-time PCR (qRT-PCR). The results showed expression of CsPrx5 and CsPrx6 in all developmental stages, with eggs having the highest level. CsPrx5 and CsPrx6 showed higher expression in the epidermis and fat body, and CsPrx6 also showed higher expression in midgut, fat body, and epidermis. Increasing concentrations of insecticides (chlorantraniliprole and spinetoram) and hydrogen peroxide (H2 O2 ) increased the expression levels of CsPrx5 and CsPrx6. In addition, the expression levels of CsPrx5 and CsPrx6 were almost markedly upregulated in larvae under temperature stress or fed by vetiver. Thus, CsPrx5 and CsPrx6 upregulation might increase the C. suppressalis defense response by reducing the impact of environmental stress, providing a better understanding of the relationship between environmental stresses and insect defense systems.

Cloak Scavenges the Reactive Oxygen Species around the Larvae of Drino inconspicuoides (Diptera: Tachinidae)

Drino inconspicuoides (Diptera: Tachinidae) is an endoparasitoid that develops inside the lepidopteran host. When the larva of D. inconspicuoides penetrates into the host, Mythimna separata (Lepidoptera: Noctuidae), the larva creates a cap-like structure, called the funnel, by using host hemocytes, forming a respiratory attachment to permit efficient respiration. A newly described cloudy and cottony structure, called the "cloak", is formed outside the funnel within 24 h of parasitism. The cloak contains the host fat body and hemocytes. In this study, we aimed to clarify the function of the cloak, which has to date remained unknown. We hypothesized that the funnel generates reactive oxygen species (ROS) through melanization, and that the cloak detoxifies them. We confirmed that the black pigments of the funnel were caused by melanization, which inevitably generates ROS that are potentially harmful to the D. inconspicuoides larva inside the funnel. The cloak showed high activities of antioxidant enzymes, including superoxide dismutase, glutathione peroxidase, and catalase. These results suggest that the cloak scavenged the ROS from the melanized funnel through the diversion of antioxidant enzymes in the fat body, thereby protecting the D. inconspicuoides larva from oxidative damage.

Failure of methanol detoxification in pests confers broad spectrum insect resistance in PME overexpressing transgenic cotton

Methanol is noxious to insect pests, but most plants do not make enough of it to shield themselves from encroaching insects. Methanol emission is known to increase in the instance of herbivory. In the current study, we showed that Aspergillus niger pectin methylesterase over-expression increases methanol emission and confers resistance to polyphagous insect pests on transgenic cotton plants by impeding the possible methanol detoxification pathways. Transgenic plants emitted ~11 fold higher methanol displaying insect mortality of 96% and 93% in Helicoverpa armigera and Spodoptera litura, respectively. The larvae were unable to survive and finish their life cycle and the surviving larvae exhibited severe growth retardation. Insects try to detoxify methanol via catalase, carboxylesterase and cytochrome P450 monooxygenase enzymes, amongst which cytochrome P450 plays a major role in oxidizing methanol to formaldehyde and formaldehyde to formic acid, which is broken down into carbon dioxide and water. In our study, catalase and esterase enzymes were found to be upregulated, but cytochrome P450 monooxygenase levels were not much affected. Leaf disc assays and In-planta bioassays also showed 50-60% population reduction in the sap sucking pests, such as Bemisia tabaci and Phenacoccus solenopsis. These findings imply that elevated methanol emissions confer resistance in plants against chewing and sap-sucking pests by tampering the methanol detoxification pathways. Such mechanism will be useful in imparting expansive resistance against pests in plants.

Sublethal effects of chlorantraniliprole on growth, biochemical and molecular parameters in two chironomids, Chironomus kiiensis and Chironomus javanus

Pesticide residues have serious environmental impacts on rice-based ecosystems. In rice fields, Chironomus kiiensis and Chironomus javanus provide alternative food sources to predatory natural enemies of rice insect pests, especially when pests are low. Chlorantraniliprole is a substitute for older classes of insecticides and has been used extensively to control rice pests. To determine the ecological risks of chlorantraniliprole in rice fields, we evaluated its toxic effects on certain growth, biochemical and molecular parameters in these two chironomids. The toxicity tests were performed by exposing third-instar larvae to a range of concentrations of chlorantraniliprole. LC₅₀ values at 24 h, 48 h, and 10 days showed that chlorantraniliprole was more toxic to C. javanus than to C. kiiensis. Chlorantraniliprole significantly prolonged the larval growth duration, inhibited pupation and emergence, and decreased egg numbers of C. kiiensis and C. javanus at sublethal dosages (LC₁₀ = 1.50 mg/L and LC₂₅ = 3.00 mg/L for C. kiiensis; LC₁₀ = 0.25 mg/L and LC₂₅ = 0.50 mg/L for C. javanus). Sublethal exposure to chlorantraniliprole significantly decreased the activity of the detoxification enzymes carboxylesterase (CarE) and glutathione S-transferases (GSTs) in both C. kiiensis and C. javanus. Sublethal exposure to chlorantraniliprole also markedly inhibited the activity of the antioxidant enzyme peroxidase (POD) in C. kiiensis and POD and catalase (CAT) in C. javanus. Expression levels of 12 genes revealed that detoxification and antioxidant abilities were affected by sublethal exposures to chlorantraniliprole. There were significant changes in the expression levels of seven genes (CarE6, CYP9AU1, CYP6FV2, GSTo1, GSTs1, GSTd2, and POD) in C. kiiensis and ten genes (CarE6, CYP9AU1, CYP6FV2, GSTo1, GSTs1, GSTd2, GSTu1, GSTu2, CAT, and POD) in C. javanus. These results provide a comprehensive overview of the differences in chlorantraniliprole toxicity to chironomids, indicating that C. javanus is more susceptible and suitable as an indicator for ecological risk assessment in rice ecosystems.

Two P450 genes, CYP6SN3 and CYP306A1, involved in the growth and development of Chilo suppressalis and the lethal effect caused by vetiver grass

Chilo suppressalis is a widely distributed pest occurring in nearly all paddy fields, which has developed high level resistance to different classes of insecticides. Vetiver grass has been identified as a dead-end trap plant for the alternative control of C. suppressalis. In this study, two cytochrome P450 monooxygenase (P450) genes, CsCYP6SN3 and CsCYP306A1, were identified and characterized, which are expressed at all developmental stages, with the highest expression in the midguts and fat bodies of 3rd instar larvae. Vetiver significantly inhibited the expression levels of CsCYP6SN3 and CsCYP306A1 in 3rd larvae after feeding. RNA interference showed that silencing CsCYP6SN3 and CsCYP306A1 genes dramatically reduced the pupation rate and pupa weight. Feeding on vetiver after silencing CsCYP6SN3 and CsCYP306A1 led to higher mortality compared with feeding on rice. In conclusion, these findings indicated that the expression levels of CsCYP6SN3 and CsCYP306A1 were associated with the lethal effect of vetiver against C. suppressalis larvae and functional knowledge about these two detoxification genes could provide new targets for agricultural pest control.

Insecticidal Activity of a Component, (-)-4-Terpineol, Isolated from the Essential Oil of Artemisia lavandulaefolia DC. against Plutella xylostella (L.)

Plutella xylostella (L.) is one of the most serious pests of cruciferous vegetables. Our previous work demonstrated that the essential oil of Artemisia lavandulaefolia DC. exhibits promising insecticidal activities against P. xylostella. This study further characterizes the key components that are responsible for the insecticidal effect. In total, 47 compounds (96.52% of the total compounds) were identified from the total oil using GC-MS, and the major compounds were eucalyptol (21.57%), D(+)-camphor (17.33%), (-)-4-terpineol (9.96%) and caryophyllene oxide (10.96%). Among them, (-)-4-terpineol showed significantly larvicidal and fumigant activities against P. xylostella. The LD₅₀ of (-)-4-terpineol was 43.15 mg/mL at 12 h and 31.22 mg/mL at 24 h for 3rd instar larvae, and the LC₅₀ for adults was 8.34 mg/mL at 12 h and 7.35 mg/mL at 24 h. In addition, the adults treated with (-)-4-terpineol showed varying degrees of inhibitory activity toward glutathione S-transferase, catalase, acetylcholinesterase and Na⁺/K⁺-ATPase at different post-treatment intervals and concentrations. The results indicate that (-)-4-terpineol has promising insecticidal activities against P. xylostella, and it has good inhibitory effects on the four enzymes of P. xylostella adults.

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.

Molecular characterization of a catalase gene from the green peach aphid (Myzus persicae)

The green peach aphid, Myzus persicae (Sulzer), is a serious agricultural pest with a worldwide distribution. Catalase (CAT), which is encoded by the catalase (Cat) gene, is an extremely important antioxidant enzyme that plays a pivotal role in protecting cells against the toxic effects of hydrogen peroxide. The Cat gene has not been characterized in M. persicae; therefore, this study describes the identification of the Cat (MpCat) gene from M. persicae. MpCat contains an open reading frame of 1515 bp and encodes a MpCAT protein consisting of 504 amino-acid residues. MpCAT possesses features typical of other insect catalases, including 7 conserved amino acids involved in binding heme and 15 involved in binding nicotinamide adenine dinucleotide phosphate. Phylogenetic analysis showed that MpCAT was closely related to orthologs from other aphid species. MpCat consisted of nine exons and eight introns, and the number and insertion sites of introns are consistent with those of Cat genes from Acyrthosiphon pisum (Harris) and Aphis gossypii Glover. The mRNA transcripts of MpCat were detected at all tested developmental stages, with the highest mRNA level in alate adults. The expression of MpCat was significantly upregulated when M. persicae was exposed to low and high temperatures, ultraviolet radiation, Beauveria bassiana, and permethrin. The transcription of MpCat and the activity of catalase were suppressed by RNA interference, and knockdown of MpCat significantly reduced the survival rate in M. persicae under heat stress. The results provide valuable information for further study on the physiological functions of MpCat.

Differential regulation of antioxidant enzymes in Frankliniella occidentalis (Thysanoptera: Thripidae) exposed to thermal stress

Frankliniella occidentalis is an invasive insect pest that incites damage to ornamental and agronomic crops on a global scale. In this study, the effects of temperature on gene expression and enzyme activity were studied for superoxide dismutase (SOD), peroxidase (POD), and glutathione-S-transferase (GST) in F. occidentalis. SOD, POD and GST enzyme activity increased significantly at 35–37 °C but declined as the temperature increased to 41 °C. In a time course study at 35 °C, SOD, POD and GST activities were significantly elevated at 0.5, 1 and 2 h in comparison to the control at 26 °C. Expression patterns were evaluated for the three antioxidant genes under high and low temperature stress. In a time course study at –4 °C, SOD, POD and GST expression peaked at 1 h and declined at 2 h of exposure. In contrast, when transcription was monitored at 35 °C, expression was lowest at 1 h and increased at 2 h. The results provide data that will be useful in deciphering the role of antioxidant enzymes in the adaptation of F. occidentalis to climate change.

Changes in Antioxidative, Oxidoreductive and Detoxification Enzymes during Development of Aphids and Temperature Increase

Temperature, being the main factor that has an influence on insects, causes changes in their development, reproduction, winter survival, life cycles, migration timing, and population dynamics. The effects of stress caused by a temperature increase on insects may depend on many factors, such as the frequency, amplitude, duration of the stress, sex, or the developmental stage of the insect. The aim of the study was to determine the differences in the enzymatic activity of nymphs and adult aphids Aphis pomi, Macrosiphum rosae and Cinara cupressi, and changes in their response to a temperature increase from 20 to 28 °C. The activity of enzymatic markers (superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), β-glucosidase, polyphenol oxidase (PPO) and peroxidase (POD)) in aphid tissues was analysed for three constant temperatures. The results of our research showed that the enzymatic activity of aphids (measured as the activity of antioxidant, detoxifying and oxidoreductive enzymes) was mainly determined by the type of morph. We observed a strong positive correlation between the activity of the detoxifying and oxidoreductive enzymes and aphids' development, and a negative correlation between the activity of the antioxidant enzymes and aphids' development. Moreover, the study showed that an increase in temperature caused changes in enzyme activity (especially SOD, CAT and β-glucosidase), which was highest at 28 °C, in both nymphs and adults. Additionally, a strong positive correlation between metabolic activity (heat flow measured by microcalorimeter) and longevity was observed, which confirmed the relationship between these characteristics of aphids. The antioxidant enzyme system is more efficient in aphid nymphs, and during aphid development the activity of antioxidant enzymes decreases. The antioxidant enzyme system in aphids appears to deliver effective protection for nymphs and adults under stressful conditions, such as high temperatures.

Characterisation of a copper/zinc superoxide dismutase from Pieris rapae and its role in protecting against oxidative stress induced by chlorantraniliprole

Insecticide exposure typically leads to abnormally high levels of reactive oxygen species (ROS) and oxidative damage in insects. Superoxide dismutases (SODs) are potent antioxidant enzymes for ROS scavenging that are essential to protect insects against insecticide-induced oxidative injury. The small white butterfly, Pieris rapae, is an economically important lepidopteran pest of cruciferous crops, and the anthranilic diamide insecticide chlorantraniliprole is widely used to control this organism. However, whether chlorantraniliprole causes oxidative stress, and whether SODs are involved in ROS scavenging, remains unclear in P. rapae. In this study, an intracellular copper/zinc SOD (designated PrSOD1) gene was identified and characterised in P. rapae. The gene consists of four exons and three introns, and the PrSOD1 protein encoded by the gene has typical highly conserved features of CuZnSODs, including two signature motifs and seven Cu/Zn-interacting residues. Transcription of PrSOD1 was highest in the larval fat body and at the fifth-instar larval stage. Recombinant PrSOD1 protein expressed in Escherichia coli displayed antioxidant activity and high thermal and pH stability, confirming that PrSOD1 encodes a functional enzyme. Exposure to three sublethal doses of chlorantraniliprole for 6, 12 or 24 h resulted in significantly increased malondialdehyde concentration in P. rapae larvae, indicating insecticide-induced oxidative stress. Furthermore, both PrSOD1 transcription levels and CuZnSOD activity were quickly (6 and 12 h, respectively) upregulated in larvae subjected to chlorantraniliprole, strongly suggesting that PrSOD1 plays an important role in protecting against oxidative damage and possibly chlorantraniliprole tolerance in P. rapae.

Increase in longevity and amelioration of pesticide toxicity by natural levels of dietary phytochemicals in the honey bee, Apis mellifera

For the past decade, migratory beekeepers who provide honey bees for pollination services have experienced substantial colony losses on a recurring basis that have been attributed in part to exposure to insecticides, fungicides, or their combinations applied to crops. The phytochemicals p-coumaric acid and quercetin, which occur naturally in a wide variety of bee foods, including beebread and many types of honey, can enhance adult bee longevity and reduce the toxicity of certain pesticides. How variation in concentrations of natural dietary constituents affects interactions with xenobiotics, including synthetic pesticides, encountered in agroecosystems remains an open question. We tested the effects of these two phytochemicals at a range of natural concentrations on impacts of consuming propiconazole and chlorantraniliprole, a triazole fungicide and an insecticide frequently applied as a tank mix to almond trees during bloom in California's Central Valley. Propiconazole, even at low field concentrations, significantly reduced survival and longevity when consumed by adult bees in a sugar-based diet. The effects of propiconazole in combination with chlorantraniliprole enhanced mortality risk. The detrimental effects of the two pesticides were for the most part reduced when either or both of the phytochemicals were present in the diet. These findings suggest that honey bees may depend on non-nutritive but physiologically active phytochemical components of their natural foods for ameliorating xenobiotic stress, although only over a certain range of concentrations; particularly at the high end of the natural range, certain combinations can incur additive toxicity. Thus, efforts to develop nectar or pollen substitutes with phytochemicals to boost insecticide tolerance or immunity or to evaluate toxicity of pesticides to pollinators should take concentration-dependent effects of phytochemicals into consideration.

A transcriptional and functional analysis of heat hardening in two invasive fruit fly species, Bactrocera dorsalis and Bactrocera correcta

Many insects have the capacity to increase their resistance to high temperatures by undergoing heat hardening at nonlethal temperatures. Although this response is well established, its molecular underpinnings have only been investigated in a few species where it seems to relate at least partly to the expression of heat shock protein (Hsp) genes. Here, we studied the mechanism of hardening and associated transcription responses in larvae of two invasive fruit fly species in China, Bactrocera dorsalis and Bactrocera correcta. Both species showed hardening which increased resistance to 45°C, although the more widespread B. dorsalis hardened better at higher temperatures compared to B. correcta which hardened better at lower temperatures. Transcriptional analyses highlighted expression changes in a number of genes representing different biochemical pathways, but these changes and pathways were inconsistent between the two species. Overall B. dorsalis showed expression changes in more genes than B. correcta. Hsp genes tended to be upregulated at a hardening temperature of 38°C in both species, while at 35°C many Hsp genes tended to be upregulated in B. correcta but not B. dorsalis. One candidate gene (the small heat shock protein gene, Hsp23) with a particularly high level of upregulation was investigated functionally using RNA interference (RNAi). We found that RNAi may be more efficient in B. dorsalis, in which suppression of the expression of this gene removed the hardening response, whereas in B. correcta RNAi did not decrease the hardening response. The different patterns of gene expression in these two species at the two hardening temperatures highlight the diverse mechanisms underlying hardening even in closely related species. These results may provide target genes for future control efforts against such pest species.

Molecular cloning, characterization, expression and enzyme activity of catalase from planarian Dugesia japonica in response to environmental pollutants

Catalase (CAT) is an important antioxidant enzyme that protects aerobic organisms against oxidative damage by degrading hydrogen peroxide to oxygen and water. CAT mRNAs have been cloned from many species and employed as useful biomarkers of oxidative stress. In the present study, we cloned the cDNA sequence of CAT gene from freshwater planarian Dugesia japonica (designated as DjCAT) by means of RACE method. Sequence analysis and multiple alignment jointly showed that the full-length cDNA sequence consists of 1734 nucleotides, encoding 506 amino acids. Three catalytic amino acid residues of His71, Asn144 and Tyr354, two CAT family signature sequences of a proximal active site signature (60FDRERIPERVVHAKGGGA77) and a heme-ligand signature motif (350RLFSYRDTQ358) are highly conserved, suggesting that the DjCAT belongs to the NADPH and heme-binding CAT family and has similar functions. In addition, the transcriptional level of CAT gene and activity of CAT enzyme upon acute exposure of environmental pollutants glyphosate and 1-decyl-3-methylimidazolium bromide ([C10mim]Br) were investigated systematically. The variation of CAT mRNA expression in D. japonica was quantified by real-time PCR and the results indicated that it was up-regulated after exposure to glyphosate or [C10mim]Br with a dose-dependent manner but not linearly. Even though the variation trend of CAT activity upon glyphosate stress was not monotonously increased and inconsistent with that after [C10mim]Br exposure on day 1 and 3 sampling time, with the duration prolonged to day 5 they both presented a dose-dependent increase and the differences achieved extreme significance in all treated groups compared to the control. These findings suggested that DjCAT plays an important role in antioxidant defense in D. japonica, and the mRNA expression of CAT would also be used as an effective biomarker to monitor the pollution in aquatic environment just like its corresponding enzyme.

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

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

Antioxidant Responses of Ragweed Leaf Beetle Ophraella communa (Coleoptera: Chrysomelidae) Exposed to Thermal Stress

Ophraellacommuna LeSage is an effective biological control agent of common ragweed, Ambrosia artemisiifolia L., which competes with crops and causes allergic rhinitis and asthma. However, thermal stress negatively affects the developmental fitness and body size of this beetle. High temperatures cause a variety of physiological stress responses in insects, which can cause oxidative damage. We investigated the total protein content and activity of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and peroxidases (PODs) in O. communa adults when its different developmental stages were exposed to high temperatures (40, 42, and 44°C) for 3 h each day for 3, 5, 5, and 5 days, respectively (by stage), and a whole generation to high temperatures (40, 42, and 44°C) for 3 h each day. A control group was reared at 28 ± 2°C. Under short-term daily phasic high-temperature stress, total protein contents were close to the control as a whole; overall, SOD activities increased significantly, CAT activities were closer to or even higher than the control, POD activities increased at 40°C, decreased at 42 or 44°C; stage-specific response was also observed. Under long-term daily phasic high-temperature stress, total protein content increased significantly at 44°C, SOD activities increased at higher temperatures, decreased at 44°C; CAT activities of females increased at ≤42°C, and decreased at 44°C, CAT activities of males decreased significantly; POD activities of females increased at 40°C, decreased at ≥42°C, POD activities of males decreased at 44°C; and antioxidant enzymes activities in females were significantly higher than those in males. Antioxidative enzymes protect O. communa from oxidative damage caused by thermal stress.