Sex-specific induction of CYP6 cytochrome P450 genes in cadmium and lead tolerant Anopheles gambiae

Evidence for the Participation of Chemosensory Proteins in Response to Insecticide Challenge in Conopomorpha sinensis

Chemosensory proteins (CSPs) are a type of efficient transporters that can bind various hydrophobic compounds. Previous research has shown that the expression levels of some insect CSPs were significantly increased after insecticide treatment. However, the role of CSPs in response to insecticide challenge is unclear. Conopomorpha sinensis is the most destructive borer pest of litchi (Litchi chinensis) and longan (Euphoria longan) in the Asia-Pacific region. Here, we studied the expression patterns and potential functions of 12 CSP genes (CsCSPs) from C. sinensis in response to λ-cyhalothrin exposure. The spatiotemporal distribution of CsCSPs suggested that they were predominantly expressed in the female abdomen, female legs, and male legs. The expression levels of CsCSPs were affected in a time-dependent manner after λ-cyhalothrin treatment in both sexes of C. sinensis adults. Compared to the control group, the expression levels of CsCSP1, CsCSP2, CsCSP9, and CsCSP12 in females were significantly increased by 2-4 times, while only one CsCSP, three CsCSPs, and two CsCSPs were significantly upregulated in males at three time points post-treatment. The sex-biased variance of CSP expression may be related to sex-specific detoxification enzymatic activities and survival rates of C. sinensis in response to insecticide challenge. Homology modeling and molecular docking analyses showed that the binding energy value of CsCSP1-12 to λ-cyhalothrin was negative and the binding energy between CsCSP9 and λ-cyhalothrin was the lowest (-11.35 kJ/mol). Combined with expression alterations of CsCSP1-12, the results indicate that CsCSP1, CsCSP2, CsCSP9, and CsCSP12 were involved in binding and ferrying of λ-cyhalothrin in C. sinensis.

Analysis of Differential Gene Expression of the Aquatic Insect Protohermes costalis (Walker) (Megaloptera: Corydalidae) in Response to Cadmium Exposure

Heavy metal pollution in freshwater ecosystems is a serious threat to aquatic organisms. Species of Megaloptera are important predators of aquatic invertebrates and have been widely used as bioindicators in assessing the quality of freshwater ecosystems. In this study, we determined the differential gene expression profile of Protohermes costalis (Walker) (Megaloptera: Corydalidae) in response to cadmium (Cd) exposure by using transcriptome analysis. A total of 60,627 unigenes were obtained in the transcriptomes of 150 mg/liter (PL), 1,000 mg/liter (PH) CdCl2 treatment, and the no Cd control (PC). Differential expression gene (DEG) analysis by pairwise comparison identified 2,794 DEGs after filtering the noninsect genes and repetitive counts. 606 DEGs were shared in comparisons of PL versus PC and PH versus PC, with 165 DEGs consistently up-regulated and 441 down-regulated by both PL and PH. Six heat shock proteins (HSPs) in the HSP70 family were identified in P. costalis and PcosHSP68 was up-regulated by both PL and PH. Real-time quantitative polymerase chain reaction (RT-qPCR) confirmed that the expression levels of PcosHSP68 in PL and PH were higher than that of PC by 31 and 197%, respectively. These results showed that exposure to Cd altered the gene expression profiles of P. costalis and the transcriptome data presented in this study provide insight into future studying on molecular mechanisms of Cd toxicity to these insects.

Integration of transcriptome and proteome reveals molecular mechanisms underlying stress responses of the cutworm, Spodoptera litura, exposed to different levels of lead (Pb)

Heavy metals are major environmental pollutants that affect organisms across different trophic levels. Herbivorous insects play an important role in the bioaccumulation, and eventually, biomagnification of these metals. Although effects of heavy metal stress on insects have been well-studied, the molecular mechanisms underlying their effects remain poorly understood. Here, we used the RNA-Seq profiling and isobaric tags for relative and absolute quantitation (iTRAQ) approaches to unravel these mechanisms in the polyphagous pest Spodoptera litura exposed to lead (Pb) at two different concentrations (12.5 and 100 mg Pb/kg; PbL and PbH, respectively). Altogether, 1392 and 1630 differentially expressed genes (DEGs) and 58, 114 differentially expressed proteins (DEPs) were identified in larvae exposed to PbL and PbH, respectively. After exposed to PbL, the main up-regulated genes clusters and proteins in S. litura larvae were associated with their metabolic processes, including carbohydrate, protein, and lipid metabolism, but the levels of cytochrome P450 associated with the pathway of xenobiotic biodegradation and metabolism were found to be decreased. In contrast, the main up-regulated genes clusters and proteins in larvae exposed to PbH were enriched in the metabolism of xenobiotic by cytochrome P450, drug metabolism-cytochrome P450, and other drug metabolism enzymes, while the down-regulated genes and proteins were found to be closely related to the lipid (lipase) and protein (serine protease, trypsin) metabolism and growth processes (cuticular protein). These findings indicate that S. litura larvae exposed to PbL could enhance food digestion and absorption to prioritize for growth rather than detoxification, whereas S. litura larvae exposed to PbH reduced food digestion and absorption and channelized the limited energy for detoxification rather than growth. These contrasting results explain the dose-dependent effects of heavy metal stress on insect life-history traits, wherein low levels of heavy metal stress induce stimulation, while high levels of heavy metal stress cause inhibition at the transcriptome and proteome levels.

Energy reserves, oxidative stress and development traits of Spodoptera exigua Hübner individuals from cadmium strain

Cadmium as a common environmental stressor may exert highly toxic effects on herbivorous insects. The question was whether possible elevation of an oxidative stress and imbalance of energetic reserves in insects may depend on developmental stage, sex and insect population's multigenerational history of exposure to cadmium. So, the aim of this study was to compare of the development traits, total antioxidant capacity, lipid peroxidation, RSSR to RSH ratio and the concentration of carbohydrates, glycogen, lipids and proteins in whole individuals (larvae or pupae) of Spodoptera exigua originating from two strains: control and selected over 120 generations with sublethal metal concentration (44 Cd mg per dry weight of diet). Generally, the increase of the protein, carbohydrates, glycogen concentration and lipid peroxidation decrease with age of the larvae were found. Revealed cases of a higher mobilisation of carbohydrates and proteins, and changes in total antioxidant capacity or lipid peroxidation, in individuals being under metal exposure, occurred in strain-depended mode. Short-term Cd exposure effect was connected with possible higher engagement of proteins and glycogen in detoxification processes, but also higher concentration of lipid peroxidation. In turn, for long-term Cd exposure effect lower lipids concentration and higher thiols usage seemed to be more specific.

Differential gene expression profile of male and female copepods in response to cadmium exposure

In this study, the whole transcriptome and sex-specific differential gene expression of the copepod Pseudodiaptomus annandalei exposed to cadmium (Cd) were investigated. P. annandalei were exposed to 40 μg/L Cd from the naupliar stage to male and female adults. High-throughput transcriptome sequencing (RNA-seq) was performed with copepod samples using an Illumina Hiseq™ 2000 platform. TransDecoder analysis found 32,625 putative open reading frame contigs. At p-values of <0.001, a total of 4756 differentially expressed genes (DEGs) (2216 up-regulated and 2540 down-regulated genes) were found in male copepods. Whereas a total of 2879 DEGs (2007 up-regulated and 872 down-regulated genes) were found in female copepods. A few selected cellular stress response genes, involved in xenobiotic metabolism, energy metabolism, growth, and development as a result of Cd exposure in the copepods were discussed. The study showed that most of these processes were changed in a sex-specific manner, accounting for the different sensitivities of male and female copepods. Results suggest and reinforce that sex is an important factor to be considered in ecotoxicogenomics.

Second generation effects of larval metal pollutant exposure on reproduction, longevity and insecticide tolerance in the major malaria vector Anopheles arabiensis (Diptera: Culicidae)

Background

Members of the Anopheles gambiae complex breed in clean, sunlit temporary bodies of water. Anthropogenic pollution is, however, altering the breeding sites of the vectors with numerous biological effects. Although the effects of larval metal pollution have previously been examined, this study aims to assess the transgenerational effects of larval metal pollution on the major malaria vector An. arabiensis.

Methods

Two laboratory strains of An. arabiensis, SENN (insecticide-susceptible) and SENN-DDT (insecticide-resistant), were used in this study. After being bred in water polluted with either cadmium chloride, copper nitrate or lead nitrate, several life history characteristics that can have epidemiological implications (fertility, apoptotic damage to reproductive structures, adult longevity and insecticide tolerance) were examined in the adults and compared to those of adults bred in clean water.

Results

All metal treatments reduced fecundity in SENN, but only lead treatment reduced fertility in SENN-DDT. Cadmium chloride exposure resulted in apoptosis and deformation of the testes in both strains. After breeding generation F0 in polluted water, F1 larvae bred in clean water showed an increase in longevity in SENN-DDT adult females. In contrast, after breeding the F0 generation in polluted water, longevity was reduced after cadmium and copper exposure in the F1 generation. Larval metal exposure resulted in an increase in insecticide tolerance in adults of the SENN strain, with SENN-DDT adults gaining the greatest fold increase in insecticide tolerance.

Conclusions

This study demonstrates that a single exposure to metal pollution can have transgenerational effects that are not negated by subsequent breeding in clean water.

The Roles of Four Novel P450 Genes in Pesticides Resistance in Apis cerana cerana Fabricius: Expression Levels and Detoxification Efficiency

Cytochrome P450 monooxygenases (P450s) are widely distributed multifunctional enzymes that play crucial roles in insecticide detoxification or activation. In this study, to ascertain the molecular mechanisms of P450s in the detoxification of Chinese honeybees, Apis cerana cerana Fabricius (A. c. cerana), we isolated and characterized four new P450 genes (Acc301A1, Acc303A1, Acc306A1, and Acc315A1). The open reading frames of the four genes are 1263 to 1608 bp in length and encode four predicted polypeptides of 499 to 517 amino acids in length. Real-time quantitative PCR (RT-qPCR) results showed that expression of all four genes was observed in all developmental stages. In addition, Western blot assays further indicated the RT-qPCR results that showed that the four genes were induced by pesticide (thiamethoxam, deltamethrin, dichlorovos, and paraquat) treatments. Furthermore, we also used double-stranded RNA-mediated RNA interference to investigate the functions of Acc301A1, Acc303A1,and Acc306A1 in the antioxidant defense of honeybees. RNA interference targeting Acc301A1, Acc303A1, and Acc306A1 significantly increased the mortality rate of A. c. cerana upon pesticide treatment. These results provide important evidence about the role of the four P450 genes involved in detoxification.

Copper exposure enhances Spodoptera litura larval tolerance to β-cypermethrin

Environmental xenobiotics can influence the tolerance of insects to chemical insecticides. Heavy metals are widespread distributed, can be easily bio-accumulated in plants and subsequently within phytophagous insects via the food chains. However, less attention has been paid to the effect of heavy metal exposure on their insecticide tolerance. In this study, pre-exposure of copper (Cu, 25-100 mg kg^-1) significantly enhanced the subsequent tolerance of Spodoptera litura to β-cypermethrin, a widely used pyrethroid insecticide in crop field. Cytochrome P450 monooxygenases (CYPs) activities were cross-induced in larvae exposed to Cu and β-cypermethrin, while the activities of glutathione S-transferase (GST) and carboxylesterase (CarE) were not affected. Application of piperonyl butoxide (PBO), a P450 synergist, effectively impaired the tolerance to β-cypermethrin in Cu-exposed S. litura larvae with a synergistic ratio of 1.72, indicating that P450s contribute to larval tolerance to β-cypermethrin induced by Cu exposure. Among the four CYP6AB family genes examined, only larval midgut-specific CYP6AB12 was found to be cross-induced by Cu and β-cypermethrin. RNA interference (RNAi)-mediated silencing of CYP6AB12 effectively decreased the mRNA levels of the target gene, and significantly reduced the larval tolerance to β-cypermethrin following exposure to Cu. These results showed that pre-exposure of heavy metal Cu enhanced larval tolerance to β-cypermethrin in S. litura, possibly through the cross-induction of P450s. Our findings provide new insights on the relationship between heavy metals and chemical insecticides that may benefit both the risk evaluation of heavy metal contamination and development of pest management strategies.

Copper-induced H2O2 accumulation confers larval tolerance to xanthotoxin by modulating CYP6B50 expression in Spodoptera litura

In the plant-insect arms race, plants synthesize toxic compounds to defend against herbivorous insects, whereas insects employ cytochrome P450 monooxygenases (P450s) to detoxify these phytotoxins. As ubiquitous environmental contaminants, heavy metals can be easily absorbed by plants and further accumulated in herbivorous insects through the food chains, resulting in tangible consequences for plant-insect interactions. However, whether heavy metals can influence P450 activities and thereby cause further effects on larval tolerance to phytotoxins remains unknown. In this study, we shown that prior exposure to copper (Cu) enhanced larval tolerance to xanthotoxin in Spodoptera litura, a major polyphagous pest of agriculture. P450 activities were induced in larvae exposed to Cu or xanthotoxin, and a midgut specific expressed P450 gene, CYP6B50 was cross-induced after exposure to these two toxic xenobiotics. Knocking down CYP6B50 by RNA interference (RNAi) rendered the larvae more sensitive to xanthotoxin. As defense against oxidative stress following metal exposure has been demonstrated to affect insecticide resistance, the reactive oxygen species (ROS) generation and antioxidant enzyme activities were assessed. Cu exposure caused the accumulation of hydrogen peroxide (H₂O₂) and enhanced the activities of superoxide dismutase (SOD) and peroxidase (POD) in larval midgut. In addition, two antioxidant response elements (AREs) were identified from the CYP6B50 promoter, indicating that Cu-induced CYP6B50 expression may be related to the ROS burst. Application of ROS scavenger N-acetylcysteine (NAC) effectively suppressed CYP6B50 expression, inhibited P450 activities and impaired larval tolerance to xanthotoxin that had been induced by Cu. These results indicate that the increase in CYP6B50 expression regulated by Cu-induced H₂O₂ generation contributed to the enhancement of larval tolerance to xanthotoxin in S. litura. Ingestion of heavy metals from their host plants can inadvertently boost the counter-defense system of herbivorous insects to protect themselves against plant defensive toxins.

Differential Expression of Cytochrome P450 CYP6 Genes in the Brown Marmorated Stink Bug, Halyomorpha halys (Hemiptera: Pentatomidae)

Cytochrome (CYP) P450s are a superfamily of enzymes that detoxify xenobiotics and regulate numerous physiological processes in insects. The genomes of phytophagous insects usually contain large numbers of P450s, especially within the CYP3 clan. Within this clan, CYP6 subfamily members help detoxify plant host secondary metabolites. In this study, we analyzed three CYP6 genes in the highly polyphagous invasive pest, Halyomorpha halys (Stål), commonly known as brown marmorated stink bug. We characterized and validated the expression of HhCYP6BQ27, HhCYP6BK13, and HhCYP6BK24 among sexes, tissues (gut, fat body, and Malpighian tubules) and hosts (apple, corn, soybean). Sequence characterization by amino acid alignments confirmed the presence of conserved motifs typical of the P450 superfamily. No significant differences existed in gene expression among sexes or when fed different hosts, suggesting that these transcripts might have broad substrate specificities. However, significant differences in gene expression were observed among the tissues studied and were gene-dependent. Collectively, the results show that H. halys differentially expressed CYP6 genes among tissues, which may be related to important and specific physiological functions. This study has increased our understanding of H. halys biology that can be useful for functional studies and can potentially be exploited in developing sustainable pest management strategies.

Differential biological effects in two pedigrees of clam Ruditapes philippinarum exposed to cadmium using iTRAQ-based proteomics

Due to the industrial discharges, cadmium (Cd) has been one of typical heavy metal pollutants in the Bohai Sea. Manila clam Ruditapes philippinarum is frequently used for pollution biomonitoring and consists of several pedigrees, of which White and Zebra clams are the dominant pedigrees along the Bohai Sea coast. However, limited attention has been paid on the differential biological effects in different pedigrees of clam to heavy metals. In this work, the proteome profiling analysis was performed to reveal the differential proteomic responses in White and Zebra clams to Cd exposure (200 μg/L) for 48 h, followed by bioinformatical analysis. The proteomic investigations showed that Cd treatment induced more differentially expressed proteins (DEPs) in White clam samples than in Zebra clam samples. Based on the DEPs, we found that some key biological processes consisting of immune response and metabolism were commonly induced in both two pedigrees of clam. Uniquely, some processes related to cellular signaling, proteolysis and energy production were enhanced in Cd-treated White clam samples. Comparatively, the depletion in some unique processes on proteolysis and energy production was elicited in Cd-treated Zebra clam samples, as well as disorder in gene expression. Moreover, Cd exposure caused increases in CAT and POD activities in White clam samples and decreases in SOD and CAT activities in Zebra clams samples, which were consistent with the proteomic responses. Overall, these findings confirmed the differential biological effects of White and Zebra clams to Cd treatment, suggesting that the pedigree of animal should be taken into consideration in ecotoxicology studies.

Identification and Characterization of Three New Cytochrome P450 Genes and the Use of RNA Interference to Evaluate Their Roles in Antioxidant Defense in Apis cerana cerana Fabricius

Cytochrome P450s play critical roles in maintaining redox homeostasis and protecting organisms from the accumulation of toxic reactive oxygen species (ROS). The biochemical functions of the P450 family have essentially been associated with the metabolism of xenobiotics. Here, we sequenced and characterized three P450 genes, AccCYP314A1, AccCYP4AZ1, and AccCYP6AS5, from Apis cerana cerana Fabricius; these genes play a critical role in maintaining biodiversity. Quantitative PCR (qPCR) analysis indicated that the three genes were all predominantly expressed in the epidermis (EP), followed by the brain (BR) and midgut (MG). In addition, the highest expression levels were detected in the dark-eyed pupae and adult stages. The three genes were induced by temperature (4°C and 44°C), heavy metals (CdCl₂ and HgCl₂), pesticides (DDV, deltamethrin, and paraquat) and UV treatments. Furthermore, Western blot analysis indicated that the protein expression levels could be induced by some abiotic stressors, a result that complements the qPCR results. We analyzed the silencing of these three genes and found that silencing these genes enhanced the enzymatic activities of peroxidase (POD) and catalase (CAT). Additionally, we investigated the expression of other antioxidant genes and found that some were upregulated, while others were downregulated, suggesting that the upregulated genes may be involved in compensating for the silencing of AccCYP314A1, AccCYP4AZ1, and AccCYP6AS5. Our findings suggest that AccCYP314A1, AccCYP4AZ1, and AccCYP6AS5 may play very significant roles in the antioxidant defense against damage caused by ROS.

Cytochrome P450 CYP6EV11 in Chironomus kiiensis Larvae Involved in Phenol Stress

Phenol is one of the organic pollutants which can cause water environment pollution. It is not only enriched in aquatic organisms but is also a serious threat to human health. Chironomus kiiensis is very sensitive to the contaminants in water and its cytochrome P450s are usually chosen as biomarkers for water pollution. To examine whether CYP6EV11 plays a role in the oxidative metabolism of phenol, we measured the silencing efficiency of CYP6EV11 and evaluated larval susceptibility to sublethal phenol levels by RNA interference (RNAi) technology. The results showed that the transcription of CYP6EV11 was found significantly up-regulated when the 4th instar C.kiiensis larvae were exposed to three doses of phenol. However, the transcriptional levels of CYP6EV11 were significantly suppressed by 92.7% in the 4th instar C. kiiensis larvae soaked in dsCYP6EV11 compared with those soaked in dsGFP for 6 h. The CYP6EV11 expression and mortality of the 4th instar C. kiiensis larvae with CYP6EV11 silencing were mostly decreased under phenol stress. Therefore, the CYP6EV11 gene may be used as a molecular biomarker for earlier warning and monitoring for water pollution.

The effect of metal pollution on the life history and insecticide resistance phenotype of the major malaria vector Anopheles arabiensis (Diptera: Culicidae)

Metal exposure is one of the commonest anthropogenic pollutants mosquito larvae are exposed to, both in agricultural and urban settings. As members of the Anopheles gambiae complex, which contains several major malaria vector species including An. arabiensis, are increasingly adapting to polluted environments, this study examined the effects of larval metal exposure on various life history traits of epidemiological importance. Two laboratory strains of An. arabiensis, SENN (insecticide susceptible) and SENN DDT (insecticide resistant), were reared in maximum acceptable toxicity concentrations, (MATC-the highest legally accepted concentration) of cadmium chloride, lead nitrate and copper nitrate. Following these exposures, time to pupation, adult size and longevity were determined. Larvae reared in double the MATC were assessed for changes in malathion and deltamethrin tolerance, measured by lethal time bottle bioassay, as well as changes in detoxification enzyme activity. As defence against oxidative stress has previously been demonstrated to affect the expression of insecticide resistance, catalase, glutathione peroxidase and superoxide dismutase activity was assessed. The relative metal toxicity to metal naïve larvae was also assessed. SENN DDT larvae were more tolerant of metal pollution than SENN larvae. Pupation in SENN larvae was significantly reduced by metal exposure, while adult longevity was not affected. SENN DDT showed decreased adult size after larval metal exposure. Adult insecticide tolerance was increased after larval metal exposure, and this effect appeared to be mediated by increased β-esterase, cytochrome P450 and superoxide dismutase activity. These data suggest an enzyme-mediated positive link between tolerance to metal pollutants and insecticide resistance in adult mosquitoes. Furthermore, exposure of larvae to metal pollutants may have operational consequences under an insecticide-based vector control scenario by increasing the expression of insecticide resistance in adults.

Molecular changes in vitellogenin gene of Spodoptera exigua after long-time exposure to cadmium - Toxic side effect or microevolution?

The reproduction of pest insects is a continuously ongoing issue, especially in the environmental pollution context. Natural or artificial stressing factors enforce a kind of trade-off, most often between growth/survival and reproduction, which improves fitness of the organism. Harmful factors, such as cadmium, can affect the vitellogenesis leading to reduction of yolk synthesis and egg production. The aim of this study was to assess whether 130-generational selection to cadmium in food might have induced change in vitellogenesis of Spodoptera exigua. We analyzed the level of Vg gene expression in S. exigua from the control and the cadmium strain at regular time intervals within 48h after eclosion. The full sequence of Vg gene was also compared between strains. The vitellogenin gene expression in both strains was time-dependent. This dependence was more visible in the control strain. In the cadmium strain the vitellogenin expression was significantly lower, comparing with the control strain in the first day after eclosion but increased significantly in the second day. The sequenced CDS (5286bp long) of the control and the cadmium strains were translated into protein sequences containing both 1761 aa. The protein sequences comparison revealed that there is one amino acid change at aa position 1282. Multiple alignments of six orthologous proteins from different species showed that amino acid change is located in the conserved position. Long-lasting exposure to cadmium resulted in permanent mutation in vitellogenin gene. We do not know yet if the mutation can improve fitness of the cadmium-selected insects. However, we can suppose that the mutation is neutral or even beneficial. The mutation and most probably additional effects of cadmium exposure have an influence on the vitellogenin expression. Some modification in the expression of the vitellogenin receptor are also likely to be important.

Genetic Diversity in Insect Metal Tolerance

Insects encounter a variety of metals in their environment, many of which are required at some concentration for normal organismal homeostasis, but essentially all of which are toxic at higher concentrations. Insects have evolved a variety of genetic, and likely epigenetic, mechanisms to deal with metal stress. A recurring theme in all these systems is complexity and diversity; even simple, single gene, cases are complex. Of the known gene families, the metallothioneins are perhaps the best understood and provide good examples of how diverse metal response is. Interestingly, there is considerable diversity across taxa in these metal-responsive systems, including duplications to form small gene families and complex expression of single loci. Strikingly, different species have evolved different mechanisms to cope with the same, or similar, stress suggesting both independent derivation of, and plasticity in, the pathways involved. It is likely that some metal-response systems evolved early in evolutionary time and have been conserved, while others have diverged, and still others evolved more recently and convergently. In addition to conventional genetics, insects likely respond to environmental metal through a variety of epigenetic systems, but direct tests are lacking. Ultimately, it is likely that classical genetic and epigenetic factors interact in regulating insect metal responses. In light of this diversity across species, future studies including a broad-based examination of gene expression in non-model species in complex environments will likely uncover additional genes and genetic and epigenetic mechanisms.

Effects of phenol on metabolic activities and transcription profiles of cytochrome P450 enzymes in Chironomus kiinensis larvae

Phenol, also known as carbolic acid or phenic acid, is a priority pollutant in aquatic ecosystems. The present study has investigated metabolic activities and transcription profiles of cytochrome P450 enzymes in Chironomus kiinensis under phenol stress. Exposure of C. kiinensis larvae to three sublethal doses of phenol (1, 10 and 100 µM) inhibited cytochrome P450 enzyme activity during the 96 h exposure period. The P450 activity measured after the 24 h exposure to phenol stress could be used to assess the level (low or high) of phenol contamination in the environment. To investigate the potential of cytochrome P450 genes as molecular biomarkers to monitor phenol contamination, the cDNA of ten CYP6 genes from the transcriptome of C. kiinensis were identified and sequenced. The open reading frames of the CYP6 genes ranged from 1266 to 1587 bp, encoding deduced polypeptides composed of between 421 and 528 amino acids, with predicted molecular masses from 49.01 to 61.94 kDa and isoelectric points (PI) from 6.01 to 8.89. Among the CYP6 genes, the mRNA expression levels of the CYP6EW3, CYP6EV9, CYP6FV1 and CYP6FV2 genes significantly altered in response to phenol exposure; therefore, these genes could potentially serve as biomarkers in the environment. This study shows that P450 activity combined with one or multiple CYP6 genes could be used to monitor phenol pollution.

Response of the common cutworm Spodoptera litura to lead stress: changes in sex ratio, Pb accumulations, midgut cell ultrastructure

When cutworm Spodoptera litura larvae were fed on the diets with different lead (Pb) concentrations for one or five generations, changes in growth and food utilization were recorded; Pb accumulations were detected by Atomic Absorption Spectrophotometer; changes in midgut cell ultrastructure were observed by Transmission Electron Microscopy (TEM). The effects of Pb stress on S. litura growth and food utilization differed significantly between insects of the 1st and 5th generation. The male-female rate of 200mgkg(-1) Pb treatment from the 1st generation and 50mgkg(-1) Pb treatment from the 5th generation was significantly higher than control. No significant difference of Pb accumulations was found in larvae, pupae and adults between the 1st and 5th generation. No significant difference of Pb accumulations in corresponding tissues of larvae was found between male and female. Compared to fat body, hemolymph, head, foregut and hindgut, the highest Pb accumulation was found in migut of larvae exposed to 200mgkg(-1) Pb. TEM showed that expanded intercellular spaces were observed in Pb-treated midgut cells. The nuclei were strongly destroyed by Pb stress, evidenced by chromatin condensation and destroyed nuclear envelope. Mitochondria became swollen with some broken cristae after exposure to Pb. Therefore, neither gender nor progeny difference was present in Pb accumulations of S. litura, although effects of Pb stress on S. litura growth and food utilization differed from different generations and genders. Pb accumulations in midgut caused pathological changes in cells ultrastructure, possibly reflected the growth and food utilization of S. litura.

Exposure to disinfectants (soap or hydrogen peroxide) increases tolerance to permethrin in Anopheles gambiae populations from the city of Yaoundé, Cameroon

Background

The rapid expansion of insecticide resistance is limiting the efficiency of malaria vector control interventions. However, current knowledge of factors inducing pyrethroid resistance remains incomplete. In the present study, the role of selection at the larval stage by disinfectants, such as soap and hydrogen peroxide (H₂O₂), on adult mosquito resistance to permethrin was investigated.

Methods

Field Anopheles gambiae sensu lato larvae, were exposed to variable concentrations of soap and H₂O₂. Larvae surviving to acute toxicity assays after 24 hours were reared to the adult stage and exposed to permethrin. The susceptibility level of adults was compared to the untreated control group. The effect of soap or hydrogen peroxide selection on the length of larval development and emergence rate was assessed.

Result

Larval bioassays analysis showed a more acute effect of hydrogen peroxide on mosquito larvae compared to soap. The regression lines describing the dose mortality profile showed higher mean and variance to hydrogen peroxide than to soap. The duration of larval development (<5 days) and adults emergence rates (1 to 77%) were shorter and lower compare to control. Anopheles gambiae s.l. larvae surviving to selection with either soap or hydrogen peroxide or both, produced adults who were up to eight-times more resistant to permethrin than mosquitoes from the untreated control group.

Conclusion

The present study shows that selective pressure exerted by non-insecticidal compounds such as soap and hydrogen peroxide affect An. gambiae s.l. tolerance to pyrethroids. This requires further studies with regard to the adaptation of An. gambiae s.l. to polluted habitats across sub-Saharan Africa cities.