Mixed Function Oxidase Activity Research Articles

Biochemical Effects of Petroselinum crispum (Umbellifereae) Essential Oil on the Pyrethroid Resistant Strains of Aedes aegypti (Diptera: Culicidae).

In ongoing screening research for edible plants, Petroselinum crispum essential oil was considered as a potential bioinsecticide with proven antimosquito activity against both the pyrethroid susceptible and resistant strains of Aedes aegypti. Due to the comparative mosquitocidal efficacy on these mosquitoes, this plant essential oil is promoted as an attractive candidate for further study in monitoring resistance of mosquito vectors. Therefore, the aim of this study was to evaluate the impact of P. crispum essential oil on the biochemical characteristics of the target mosquito larvae of Ae. aegypti, by determining quantitative changes of key enzymes responsible for xenobiotic detoxification, including glutathione-S-transferases (GSTs), α- and β-esterases (α-/β-ESTs), acetylcholinesterase (AChE), acid and alkaline phosphatases (ACP and ALP) and mixed-function oxidases (MFO). Three populations of Ae. aegypti, comprising the pyrethroid susceptible Muang Chiang Mai-susceptible (MCM-S) strain and the pyrethroid resistant Pang Mai Dang-resistant (PMD-R) and Upakut-resistant (UPK-R) strains, were used as test organisms. Biochemical study of Ae. aegypti larvae prior to treatment with P. crispum essential oil revealed that apart from AChE, the baseline activity of most defensive enzymes, such as GSTs, α-/β-ESTs, ACP, ALP and MFO, in resistant UPK-R or PMD-R, was higher than that determined in susceptible MCM-S. However, after 24-h exposure to P. crispum essential oil, the pyrethroid susceptible and resistant Ae. aegypti showed similarity in biochemical features, with alterations of enzyme activity in the treated larvae, as compared to the controls. An increase in the activity levels of GSTs, α-/β-ESTs, ACP and ALP was recorded in all strains of P. crispum oil-treated Ae. aegypti larvae, whereas MFO and AChE activity in these mosquitoes was decreased. The recognizable larvicidal capability on pyrethroid resistant Ae. aegypti, and the inhibitory effect on AChE and MFO, emphasized the potential of P. crispum essential oil as an attractive alternative application for management of mosquito resistance in current and future control programs.

Effect of elevated CO2 on the interaction between invasive thrips, Frankliniella occidentalis, and its host kidney bean, Phaseolus vulgaris.

Elevated CO2 can alter the leaf damage caused by insect herbivores. Frankliniella occidentalis (Pergande) is highly destructive invasive pest of crop production worldwide. To investigate how elevated CO2 affects F. occidentalis fed with Phaseolus vulgaris and, in particular, the interaction between plant defense and thrips anti-defense, nutrient content and antioxidant enzyme activity of P. vulgaris were measured, as well as the detoxifying enzyme activity of adult thrips. Elevated CO2 increased the soluble sugar, soluble protein and free amino acid content in non thrip-infested plants, and decreased superoxide dismutase (SOD) and peroxidase (POD) activity in these plants. Feeding thrips reduced the nutrient content in plants, and increased their SOD, catalase and POD activity. Variations in nutrient content and antioxidant enzyme activity in plants showed an opposite tendency over thrip feeding time. After feeding, acetylcholinesterase, carboxylesterase, and mixed-function oxidase activity in thrips increased to counter the plant defenses. Greater thrip densities induced stronger plant defenses and, in turn, detoxifying enzyme levels in thrips increased over thrip numbers. Our study revealed that F. occidentalis can induce not only an antioxidant-associated plant defense, but also detoxifying enzymes in thrips. Elevated CO2 might both enhance plant defense against thrip attack, and increase thrip anti-defense against plant defenses. © 2018 Society of Chemical Industry.

Effect of Relaxation of Deltamethrin Pressure on Metabolic Resistance in a Pyrethroid-Resistant Aedes aegypti (Diptera: Culicidae) Strain Harboring Fixed P989P and G1016G kdr Alleles.

Mutation of the voltage-gated sodium channel genes or knockdown resistance (kdr) and metabolic resistance in Aedes aegypti (L.) (Diptera: Culicidae) are important resistance mechanisms against pyrethroids. The present study investigated the effect of relaxation of deltamethrin selection pressure on the level of mixed-function oxidases (MFO), when the allele frequency of S989P+V1016G mutations is fixed in a resistant Ae. aegypti strain (UPK-R) from Chiang Mai, Thailand. The mosquitoes were divided into two groups, exposure and nonexposure groups, and maintained for 12 generations in an insectary room. Adults of the exposure group (F3 to F12) were treated with 0.05% deltamethrin-impregnated papers. The median lethal concentrations (LC50) of deltamethrin of larvae were determined by World Health Organization (WHO) bioassay. MFO activity was determined in F0 and F12. The results revealed that there was a decreasing trend of adult mortality rates in the exposure group over time. The larval LC50 values of the exposure group were gradually increased, whereas those of the nonexposure group were gradually decreased. The level of MFO activity in the nonexposure group (F12) was lower than the parent and exposure groups (F12) by 1.5 and 4-fold in the larvae, respectively, and 1.5 and 2.5-fold in the adult females, respectively. However, the frequency of P989+G1016 alleles in both groups was 100% up to F12 when the experiment ended. This study indicates that there was a significant but small reduction in the activity levels of MFOs when pyrethroid selection pressure is relaxed in this kdr strain of Ae. aegypti.

The joint toxicity of bifenazate and propargite mixture against Tetranychus urticae Koch

ABSTRACTBifenazate is a new type of hydrazine derivative acaricide which has been registered in China since 2008. In order to prolong the service life of bifenazate, the joint toxicity of bifenazate and propargite against Tetranychus urticae was evaluated in this study. The results showed that, with the mass ratio of 5:1 for bifenazate and propargite, the cotoxicity coefficient was 137.5, which showed synergistic toxicity to T. urticae. Moreover, when T. urticae was treated by the mixture of bifenazate and propargite (5:1) at the serial concentrations of 20.00 mg/L, 14.29 mg/L, 11.11 mg/L, 9.09 mg/L, and 7.69 mg/L for 24 h, the activities of glutathione s-transferase (GST) in T. urticae were 3.37, 3.64, 3.93, 4.04, and 4.08 mmol/min/mgPro, which were significantly (P < 0.05) lower than those in T. urticae being treated by bifenazate (7.25, 6.82, 6.71, 6.44, and 5.81 mmol/min/mgPro) and propargite (10.13, 9.79, 9.14, 8.93, and 8.44 mmol/min/mgPro) individually at the same concentration, indicating that the mixture showed a joint inhibition effect on the activities of GST in T. urticae. However, the activities of mixed-function oxidase, carboxylesterase, and acetylcholinesterase in T. urticae treated by bifenazate and propargite (5:1) were not significantly different from those treated by bifenazate and propargite individually. This study provided theoretical basis for reasonably application of bifenazate and propargite mixture in T. urticae control.

Behavior of detoxifying enzymes of Aedes aegypti exposed to girgensohnine alkaloid analog and Cymbopogon flexuosus essential oil

Because mosquito control depend on the use of commercial insecticides and resistance has been described in some of them, there is a need to explore new molecules no resistant. In vivo effects of girgensohnine analog 2-(3,4-dimethoxyphenyl)-2-(piperidin-1-yl)acetonitrile DPPA and Cymbopogon flexuosus essential oil CFEO, on the detoxifying enzymes acetylcholinesterase (AChE), glutathione-S-transferase (GST), nonspecific esterases (α- and β-), mixed function oxidases (MFO) and p-NPA esterases were evaluated on a Rockefeller (Rock) and wild Aedes aegypti population from Santander, Colombia (WSant). The action was tested after 24h of exposure at concentrations of 20.10, 35.18 and 70.35mgL−1 of DPPA and 18.45, 30.75 and 61.50mgL−1 of CFEO, respectively. It was found that AChE activity of Rock and WSant was not influenced by the evaluated concentration of DPPA and CFEO (p>0.05), while MFO activity was significantly affected by all CFEO concentrations in WSant (p<0.05). GST, α- and β-esterase activities were affected in Rock exposed at the highest CFEO concentration, this concentration also modified β-esterases activity of WSant. DPPA and CFEO sublethal doses induced inhibition of AChE activity on untreated larvae homogenate from 12 to 20% and 18 to 26%, respectively. For untreated adult homogenate, the inhibition activity raised up to 14 to 27% for DPPA and 26 to 34% for CFEO. Elevated levels of detoxifying enzymes, found when CFEO was evaluated, showed a larval sensitivity not observed by the pure compound suggesting that DPPA, contrary to CFEO, was not recognized, transformed or eliminated by the evaluated detoxifying enzymes.

Induction of cytochrome P450-dependent mixed function oxidase activities and peroxisome proliferation by chloramine-T in male rat liver

Chloramine-T is an antimicrobial agent recognized for its disinfectant properties widely used in food industry. As an N-chloro-compound, chloramine-T contains electrophilic chlorine and in water it hydrolyses to hypochlorite. Chlorine as hypochlorous acid or hypochlorite is a very reactive chemical which can function as both an oxidant and halogenating agent. Because chloramine-T could be involved in the metabolic activation of drugs, in the present study the effects of chloramine-T on the activities of some drug metabolizing enzymes in rat liver microsomes and peroxisome proliferation were determined in vivo. Rats were treated orally with chloramine-T at doses of 1.25, 2.50, 5 and 10 mg/kg body weight (bw)/day for 6 days. The activities of CYP2E1, CYP1A1/2 CYP2B1/2, CYP3A4 and CYP4A1/2 enzymes significantly increased after treatment with 2.50, 5 and 10 mg/kg bw/day, in a dose-dependent manner as compared to control. This effect was not observed after chloramine-T treatment at dose of 1.25 mg/kg bw/day. Our results suggest that chloramine-T may potentiate the toxicity of many xenobiotics via metabolic activation and/or accumulation of reactive metabolites.

Activity of carboxylesterases, glutathione-S-transferase and monooxygenase on Rhipicephalus microplus exposed to fluazuron

The objective of this study was to assess the effect of the exposure to fluazuron on the activity of common pesticide detoxification enzyme groups in the cattle tick (Rhipicephalus microplus). Engorged females of a susceptible strain (POA) and a resistant strain (Jaguar) were exposed in vitro to fluazuron and their eggs and larvae were used to compare the activities of the general esterases, mixed-function oxidases (MFO) and glutathione-S-transferase (GST). The results showed significant elevation in MFO contents and esterases activity in the resistant strain when compared with the susceptible strain, in eggs and larvae respectively. In the POA strain, the MFO activity in eggs was down-regulated by fluazuron exposure. Based on these results, it can be concluded that different detoxification enzymes can act in distinct pathways depending on the tick's development stage, and may be related to fluazuron detoxification in resistant strains.

Mechanism of resistance to pirimicarb in the cowpea aphid Aphis craccivora

A resistant strain of Aphis craccivora Koch was selected with pirimicarb for 12 generations. The selected strain exhibited 47-fold resistance compared to the susceptible laboratory strain. The resistant strain also showed cross-resistance to carbosulfan, malathion, chlorpyrifos methyl and thiamethoxam. Low resistance to fenitrothion and acetamiprid was also observed. Bioassays in combination with biochemical synergist studies revealed that the higher inhibition of carboxylesterase using the synergist tributyl phosphorotrithioate (DEF) was associated with increased toxicity of pirimicarb in the resistant strain. On the other hand, piperonyl butoxide (PBO) and diethyl maleate (DEM) had less inhibitory effect on mixed function oxidases (MFO) and glutathione-S-transferase (GST) in the resistant strain. The activity of carboxylesterase was 29-fold greater in the resistant strain, whereas the activity of MFO and GST in the resistant strain was only 5.5 and 1.7- fold greater, respectively. The activity of acetylcholine esterase (AChE) in the resistant strain was 2 fold higher than in the susceptible strain. The I50 (the concentration of pirimicarb that inhibit 50% of the enzyme activity) ratio of R-strain to S-strain was 12.6. Molecular studies using real-time quantitative PCR showed that the transcription level of Ace2 gene in the resistant strain was 3.4-fold higher than that in the susceptible strain. In conclusion, mechanism of resistance in the pirimicarb resistant strain of A. craccivora may include overexpression of Ace2 gene and higher activity of the detoxification enzymes esterases and partly MFO.

Susceptibility profile and metabolic mechanisms involved in Aedes aegypti and Aedes albopictus resistant to DDT and deltamethrin in the Central African Republic.

Background Aedes aegypti and Ae. albopictus are the main epidemic vectors of dengue, chikungunya and Zika viruses worldwide. Their control during epidemics relies mainly on control of larvae and adults with insecticides. Unfortunately, loss of susceptibility of both species to several insecticide classes limits the efficacy of interventions. In Africa, where Aedes-borne viruses are of growing concern, few data are available on resistance to insecticides. To fill this gap, we assessed the susceptibility to insecticides of Ae. aegypti and Ae. albopictus populations in the Central African Republic (CAR) and studied the mechanisms of resistance.MethodsImmature stages were sampled between June and September 2014 in six locations in Bangui (the capital of CAR) for larval and adult bioassays according to WHO standard procedures. We also characterized DDT- and pyrethroid-resistant mosquitoes molecularly and biochemically, including tests for the activities of nonspecific esterases (α and β), mixed-function oxidases, insensitive acetylcholinesterase and glutathione S-transferases.ResultsLarval bioassays, carried out to determine the lethal concentrations (LC50 and LC95) and resistance ratios (RR50 and RR95), suggested that both vector species were susceptible to Bacillus thuringiensis var. israeliensis and to temephos. Bioassays of adults showed susceptibility to propoxur and fenitrothion, except for one Ae. albopictus population that was suspected to be resistant to fenithrothion. None of the Ae. aegypti populations was fully susceptible to DDT. Ae. albopictus presented a similar profile to Ae. aegypti but with a lower mortality rate (41%). Possible resistance to deltamethrin was observed among Ae. aegypti and Ae. albopictus, although some were susceptible. No kdr mutations were detected in either species; however, the activity of detoxifying enzymes was higher in most populations than in the susceptible Ae. aegypti strain, confirming decreased susceptibility to DDT and deltamethrin.ConclusionThese findings suggested that regular, continuous monitoring of resistance is necessary in order to select the most effective adulticides for arbovirus control in Bangui.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1887-5) contains supplementary material, which is available to authorized users.

Cyromazine resistance in a field strain of house flies, Musca domestica L.: Resistance risk assessment and bio-chemical mechanism

Developing resistance management strategies for eco-friendly insecticides is essential for the management of insect pests without harming the environment. Cyromazine is a biorational insecticide with very low mammalian toxicity. Resistance to cyromazine has recently been reported in house flies from Punjab, Pakistan. In order to propose a resistance management strategy for cyromazine, experiments were planned to study risk for resistance development, possibility of cross-resistance and bio-chemical mechanisms. A field strain of house flies with 8.78 fold resistance ratio (RR) to cyromazine was re-selected under laboratory conditions. After seven rounds of selection (G1-G7), the RR values rapidly increased from 8.8 to 211 fold. However, these values declined to 81fold when the cyromazine selected (CYR-SEL) strain was reared without selection pressure, suggesting an unstable nature of resistance. The CYR-SEL strain showed lack of cross-resistance to pyriproxyfen, diflubenzuron, and methoxyfenozide. Synergism bioassays using enzyme inhibitors: piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF), and metabolic enzyme analyses revealed increased activity of carboxylesterase (CarE) and mixed-function oxidase (MFO) in the CYR-SEL strain compared to the laboratory susceptible (Lab-susceptible) strain, suggesting the metabolic resistance mechanism responsible for cyromazine resistance in the CYR-SEL strain. In conclusion, risk of rapid development of cyromazine resistance under consistent selection pressure discourages the sole reliance on cyromazine for controlling house flies in the field. The unstable nature of cyromazine resistance provides window for restoring cyromazine susceptibility by uplifting selection pressure in the field. Moreover, lack of cross-resistance between cyromazine and pyriproxyfen, diflubenzuron, or methoxyfenozide in the CYR-SEL strain suggest that cyromazine could be rotated with these insecticides whenever resistance crisis occur in the field.

Lethal and sublethal effects of the chitin synthesis inhibitor chlorfluazuron on Bradysia odoriphaga Yang and Zhang (Diptera: Sciaridae)

Bradysia odoriphaga Yang and Zhang is the primary insect pest that affects Chinese chive in northern China. Nevertheless, very few studies have been conducted on the use of chitin synthesis inhibitors (CSIs) for the control of B. odoriphaga. Here, lethal and sublethal effects of the CSI chlorfluazuron on B. odoriphaga were studied to explore the use for integrated pest management (IPM) of B. odoriphaga. A contact and ingestion toxicity bioassay showed that chlorfluazuron was more active against B. odoriphaga than three other CSIs, with a 72h LC50 of 0.1593mg/L. Treatment with the LC50 dose of chlorfluazuron decreased both the intrinsic and finite rates of increase of B. odoriphaga, in addition to reproduction rate, survival rate, and fecundity, and the mean generation time, total preovipositional period and larval development duration were shortened, compared with those of the control and LC10 groups. The mean generation time, total preovipositional period and larval development duration were all also markedly decreased by treatment with chlorfluazuron at the LC10. Furthermore, chlorfluazuron inhibited the feeding of the final instar larvae for a short period. Glutathione S-transferase and microsomal mixed function oxidase activities increased after exposure to the chemical. These results showed that chlorfluazuron at the sublethal LC50 treatment inhibited B. odoriphaga population growth, whereas the danger of causing rapid population growth by using a lower sublethal concentration was demonstrated with the sublethal LC10 treatment. Therefore, chlorfluazuron should be used with caution in an IPM program for B. odoriphaga.

The role of detoxifying enzymes in the resistance of the cowpea aphid (Aphis craccivora Koch) to thiamethoxam

Abstract The cowpea aphid (Aphis craccivora Koch) is considered a serious insect pest attacking several crops. We carried out biochemical studies to elucidate the role of the metabolising enzymes in conferring resistance to thiamethoxam, in two strains (resistant and susceptible) of the cowpea aphid. Bioassay experiments showed that the thiamethoxam selected strain developed a 48 fold resistance after consecutive selection with thiamethoxam for 12 generations. This resistant strain also exhibited cross-resistance to the tested carbamates; pirimicarb and carbosulfan, organophosphorus (malathion, fenitrothion, and chlorpyrifos-methyl), and the neonicotinoid (acetamiprid). Synergism studies have indicated that S,S,S-tributyl phosphorotrithioate (DEF), a known inhibitor for esterases, increased thiamethoxam toxicity 5.58 times in the resistant strain compared with the susceptible strain. Moreover, the biochemical determination revealed that carboxylestersae activity was 30 times greater in the resistant strain than in the susceptible strain. In addition, the enzyme activity of glutathione S-transferase (GST) and mixed function oxidases (mfo) increased only in the resistant strain 3.7 and 2.7 times, respectively, in relation to the susceptible (the control). Generally, our results suggest that the higher activity of the detoxifying enzymes, particularly carboxylesterase, in the resistant strain of the cowpea aphid, apparently have a significant role in endowing resistance to thiamethoxam, although additional mechanisms may contribute.

Susceptibility profile of Aedes aegypti from Santiago Island, Cabo Verde, to insecticides

In 2009, Cabo Verde diagnosed the first dengue cases, with 21,137 cases reported and Aedes aegypti was identified as the vector. Since the outbreak, chemical insecticides and source reduction were used to control the mosquito population. This study aimed to assess the susceptibility of A. aegypti populations from Santiago, Cabo Verde to insecticides and identify the mechanisms of resistance. Samples of A. aegypti eggs were obtained at two different time periods (2012 and 2014), using ovitraps in different locations in Santiago Island to establish the parental population. F1 larvae were exposed to different concentrations of insecticides (Bacillus thuringiensis var israelensis (Bti), diflubenzuron and temephos) to estimate the lethal concentrations (LC90) and calculate the respective rate of resistance (RR90). Semi-field tests using temephos-ABATE® were performed to evaluate the persistence of the product. Bottle tests using female mosquitoes were carried out to determine the susceptibility to the adulticides malathion, cypermethrin and deltamethrin. Biochemical and molecular tests were performed to investigate the presence of metabolic resistance mechanisms, associated with the enzymes glutathione S-transferases (GSTs), esterases and mixed-function oxidases (MFO) and to detect mutations or alterations in the sodium channel and acetylcholinesterase genes. A. aegypti mosquitoes from Santiago exhibited resistance to deltamethrin, cypermethrin (mortality<80%) and temephos (RR90=4.4) but susceptibility to malathion (mortality≥98%), Bti and diflubenzuron. The low level of resistance to temephos did not affect the effectiveness of Abate®. The enzymatic analysis conducted in 2012 revealed slight changes in the activities of GST (25%), MFO (18%), α-esterase (19%) and β-esterase (17%), but no significant changes in 2014. Target site resistance mutations were not detected. Our results suggest that the A. aegypti population from Santiago is resistant to two major insecticides used for vector control, deltamethrin and temephos. To our knowledge, this is the first report of temephos resistance in an African A. aegypti population. The low level of temephos resistance was maintained from 2012–2014, which suggested the imposition of selective pressure, although it was not possible to identify the resistance mechanisms involved. These data show that the potential failures in the local mosquito control program are not associated with insecticide resistance.

Thiamethoxam Resistance in the House Fly, Musca domestica L.: Current Status, Resistance Selection, Cross-Resistance Potential and Possible Biochemical Mechanisms.

The house fly, Musca domestica L., is an important ectoparasite with the ability to develop resistance to insecticides used for their control. Thiamethoxam, a neonicotinoid, is a relatively new insecticide and effectively used against house flies with a few reports of resistance around the globe. To understand the status of resistance to thiamethoxam, eight adult house fly strains were evaluated under laboratory conditions. In addition, to assess the risks of resistance development, cross-resistance potential and possible biochemical mechanisms, a field strain of house flies was selected with thiamethoxam in the laboratory. The results revealed that the field strains showed varying level of resistance to thiamethoxam with resistance ratios (RR) at LC50 ranged from 7.66-20.13 folds. Continuous selection of the field strain (Thia-SEL) for five generations increased the RR from initial 7.66 fold to 33.59 fold. However, resistance declined significantly when the Thia-SEL strain reared for the next five generations without exposure to thiamethoxam. Compared to the laboratory susceptible reference strain (Lab-susceptible), the Thia-SEL strain showed cross-resistance to imidacloprid. Synergism tests revealed that S,S,S-tributylphosphorotrithioate (DEF) and piperonyl butoxide (PBO) produced synergism of thiamethoxam effects in the Thia-SEL strain (2.94 and 5.00 fold, respectively). In addition, biochemical analyses revealed that the activities of carboxylesterase (CarE) and mixed function oxidase (MFO) in the Thia-SEL strain were significantly higher than the Lab-susceptible strain. It seems that metabolic detoxification by CarE and MFO was a major mechanism for thiamethoxam resistance in the Thia-SEL strain of house flies. The results could be helpful in the future to develop an improved control strategy against house flies.

Insecticide Resistance and Metabolic Mechanisms Involved in Larval and Adult Stages of Aedes aegypti Insecticide-Resistant Reference Strains from Cuba.

Studies were conducted to compare levels of insecticide resistance and to determine the metabolic resistance mechanisms in larval and adult stages of Aedes aegypti from Cuba. Three insecticide-resistant reference strains of Ae. aegypti from Cuba were examined. These strains were derived from a Santiago de Cuba strain isolated in 1997; it was previously subjected to a strong selection for resistance to temephos (SAN-F6), deltamethrin (SAN-F12), and propoxur (SAN-F13) and routinely maintained in the laboratory under selection pressure up to the present time, when the study was carried out. In addition, an insecticide-susceptible strain was used for comparison. The insecticide resistance in larvae and adults was determined using standard World Health Organization methodologies. Insecticide resistance mechanisms were determined by biochemical assays. The esterases (α EST and β EST) and mixed function oxidase (MFO) activities were significantly higher in adults than in the larvae of the three resistant strains studied. The association of resistance level with the biochemical mechanism for each insecticide was established for each stage. The observed differences between larval and adult stages of Ae. aegypti in their levels of insecticide resistance and the biochemical mechanisms involved should be included as part of monitoring and surveillance activities in Ae. aegypti vector control programs.

Concentrations of DDE in blubber biopsies of free-ranging long-beaked common dolphin (Delphinus capensis) in the Gulf of California.

Long-beaked common dolphins (Delphinus capensis) in the Gulf of California have been exposed to persistent contaminants that originated in large agricultural areas near the coast. Live common dolphins were sampled by remote dart biopsies to determine concentrations of tDDT in blubber. Life stage and initial gender identification was determined by field observations. Gender was confirmed by genetic analysis of the skin. Concentration of tDDT in blubber was analyzed by gas chromatography. The 16 samples collected consisted of: 2 adult males, 6 adult females, and 8 juveniles. 4,4'-DDE was detected in most of the samples with 4,4'-DDD and 4,4'-DDT under detection levels. Concentrations of DDE varied from non-detectable to 87.3 µg/g lipid weight with a median of 16 µg/g lipid weight. The highest concentration was detected in an immature female. No differences were detected between gender or life stage but this could be attributed to small sample size. We recommend continued sampling of D. capensis blubber biopsies from the Gulf of California in order to relate these levels with affected in vitro biomarkers such as mixed function oxidase activity.

Physiological efects of paichongding applied to rice on the Nilaparvata lugens (Stå l), the brown planthopper.

Nilaparvata lugens (Stål) is a major rice pest in Asia. Paichongding is a novel neonicotinoid insecticide developed in 2008. The effects of this insecticide on the activity of detoxification enzymes of N. lugens and on rice resistance to the pest were examined in the laboratory. The results showed that paichongding could significantly decrease the acetylcholinesterase and GSHs transferase activities of N. lugens. The variation tendency of mixed function oxidase (MFO) activity was similar with that of the esterase. After 12 h treatment, there was no significance between the treatment and control. However, the activities of MFO and esterase increased after 24 and 48 h treatment, which suggested that MFO and esterase may play an important role in the detoxification of paichongding for N. lugens. Our results also demonstrated that treated with paichongding, damage levels of rice plants were significantly lower than those of control plants except 15 days after treatment. Compared with the control, injury indices decreased 70.22, 49.12, 34.44, and 23.23% at 3 , 6 , 9, and 12 days after paichongding treatment, respectively. The laboratory results suggested that paichongding may be effective for the control of brown planthopper.

Thiamethoxam resistance selected in the western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae): Cross-resistance patterns, possible biochemical mechanisms and fitness costs analysis

The western flower thrips (WFT) Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), an important pest of various crops in the world, has invaded China since 2003. To understand the risks and to determine possible mechanisms of resistance to thiamethoxam in WFT, a resistant strain was selected under the laboratory conditions. Cross-resistance and the possible biochemical resistance mechanisms were investigated in this study. A 15.1-fold thiamethoxam-resistant WFT strain (TH-R) was established after selection for 55 generations. Compared with the susceptible strain (TH-S), the selected TH-R strain showed extremely high level cross-resistance to imidaclothiz (392.1-fold) and low level cross-resistance to dinotefuran (5.7-fold), acetamiprid (2.9-fold) and emamectin benzoate (2.1-fold), respectively. No cross-resistance to other fourteen insecticides was detected. Synergism tests showed that piperonyl butoxide (PBO) and triphenyl phosphate (TPP) produced a high synergism of thiamethoxam effects in the TH-R strain (2.6- and 2.6-fold respectively). However, diethyl maleate (DEM) did not act synergistically with thiamethoxam. Biochemical assays showed that mixed function oxidase (MFO) activities and carboxylesterase (CarE) activity of the TH-R strain were 2.8- and 1.5-fold higher than that of the TH-S strain, respectively. When compared with the TH-S strain, the TH-R strain had a relative fitness of 0.64. The results show that WFT develops resistance to thiamethoxam after continuous application and thiamethoxam resistance had considerable fitness costs in the WFT. It appears that enhanced metabolism mediated by cytochrome P450 monooxygenases and CarE was a major mechanism for thiamethoxam resistance in the WFT. The use of cross-resistance insecticides, including imidaclothiz and dinotefuran, should be avoided for sustainable resistance management.

Sub-Lethal Effects of Spinetoram on the Activities of Some Detoxifying Enzymes in the Black CutwormAgrotis ipsilon(Hufnagel) (Lepidoptera: Noctuidae)

The present study was designed to investigate the activities of the detoxifying enzymes acetylcholinesterase (AChE), non-specific esterases (α- and β-esterases), glutathione S-transferase (GST) and mixed-function oxidases (MFO) in spinetoram-treated Agrotis ipsilon (Hufnagel). For this purpose, fourth larval instars were exposed to three sub-lethal concentrations (LC10, LC20 and LC50) of spinetoram for 24 h using the leaf dipping technique. The activities of detoxifying enzymes in the survivors after 2, 4 and 6 days of treatment were compared to non-treated larvae (control). AChE activity was significantly increased after 4 and 6 days of treatment with the LC10. In contrast, this activity was significantly decreased after 2 days of treatment with the three sub-lethal concentrations applied, and after 4 and 6 days of treatment with the LC20 and LC50. While both α- and β-esterase activities were significantly enhanced after 2 days of treatment with all the previous sub-lethal concentrations, with no constant pattern after 4 and 6 days of treatment. GST activity was significantly increased on the second day of treatment with the LC10, and on the fourth day of treatment with the LC10 and LC50. Whereas the only significant decrease in GST activity was observed on the sixth day of treatment with the LC10. No significant change was recorded on the second and sixth days of treatment with the LC20 and LC50, and on the fourth day of treatment with the LC20. The activity of MFO was significantly enhanced up to the fourth day of treatment with all the concentrations investigated, whereas this activity was significantly decreased on the sixth day of treatment. Therefore, it appears that higher activities of detoxifying enzymes in A. ipsilon generally occurred in response to the intoxication by the lowest concentration of spinetoram, particularly after a relatively early time of treatment, and MFO may be considered the principal detoxifying enzymes.

Oxidative stress—implications, source and its prevention

Oxidative stress has been a major predicament of present day living. It has been the product of imbalance between the processes involved in free radical generation and their neutralization by enzymatic and non-enzymatic defence mechanisms. The oxidative stress has been contributed by numerous factors including heavy metals, organic compound-rich industrial effluents, air pollutants and changing lifestyle pattern focussing mainly on alcohol consumption, dietary habits, sun exposure, nuclear emissions, etc. The most common outcome of oxidative stress is the increased damage of lipid, DNA and proteins that resulted in the development of different pathologies. Among these pathologies, cancer is the most devastating and linked to multiple mutations arising due to oxidative DNA and protein damage that ultimately affect the integrity of the genome. The chemopreventive agents particularly nutraceuticals are found to be effective in reducing cancer incidences as these components have immense antioxidative, antimutagenic and antiproliferative potentials and are an important part of our dietary components. These secondary metabolites, due to their unique chemical structure, facilitate cell-to-cell communication, repair DNA damage by the downregulation of transcription factors and inhibit the activity of protein kinases and cytochrome P450-dependent mixed function oxidases. These phytochemicals, therefore, are most appropriate in combating oxidative stress-related disorders due to their tendency to exert better protective effect without having any distinct side effect.