Transcriptome response to pollutants and insecticides in the dengue vector Aedes aegypti using next-generation sequencing technology

<p>Abstract</p> <p>Background</p> <p>The control of mosquitoes transmitting infectious diseases relies mainly on the use of chemical insecticides. However, mosquito control programs are now threatened by the emergence of insecticide resistance. Hitherto, most research efforts have been focused on elucidating the molecular basis of inherited resistance. Less attention has been paid to the short-term response of mosquitoes to insecticides and pollutants which could have a significant impact on insecticide efficacy. Here, a combination of LongSAGE and Solexa sequencing was used to perform a deep transcriptome analysis of larvae of the dengue vector <it>Aedes aegypti </it>exposed for 48 h to sub-lethal doses of three chemical insecticides and three anthropogenic pollutants.</p> <p>Results</p> <p>Thirty millions 20 bp cDNA tags were sequenced, mapped to the mosquito genome and clustered, representing 6850 known genes and 4868 additional clusters not located within predicted genes. Mosquitoes exposed to insecticides or anthropogenic pollutants showed considerable modifications of their transcriptome. Genes encoding cuticular proteins, transporters, and enzymes involved in the mitochondrial respiratory chain and detoxification processes were particularly affected. Genes and molecular mechanisms potentially involved in xenobiotic response and insecticide tolerance were identified.</p> <p>Conclusions</p> <p>The method used in the present study appears as a powerful approach for investigating fine transcriptome variations in genome-sequenced organisms and can provide useful informations for the detection of novel transcripts. At the biological level, despite low concentrations and no apparent phenotypic effects, the significant impact of these xenobiotics on mosquito transcriptomes raise important questions about the 'hidden impact' of anthropogenic pollutants on ecosystems and consequences on vector control.</p

Hygroscopic properties following drying affects wood consumption by Odontotermes obesus

The relationship between drying and hygroscopic ability of Crateva adansonii and Populus deltoides woods to resist feeding by Odontotermes obesus was studied. Woods were dried under the sun and in the oven for a range of 5-25 days and then these were exposed to termites for 25 days in underground pits in Randomized Complete Block Design pattern with five replications. Results showed that lowest moisture gain was observed at a short time for drying with each method. Weight loss after termites’ exposure was more in less dried sap and heartwood of either plant species. The practical implication of these results is discussed

Hygroscopic properties following drying affects wood consumption by Odontotermes obesus

The relationship between drying and hygroscopic ability of Crateva adansonii and Populus deltoides woods to resist feeding by Odontotermes obesus was studied. Woods were dried under the sun and in the oven for a range of 5-25 days and then these were exposed to termites for 25 days in underground pits in Randomized Complete Block Design pattern with five replications. Results showed that lowest moisture gain was observed at a short time for drying with each method. Weight loss after termites’ exposure was more in less dried sap and heartwood of either plant species. The practical implication of these results is discussed

Sublethal and transgenerational effects of synthetic insecticides on the biological parameters and functional response of Coccinella septempunctata (Coleoptera: Coccinellidae) under laboratory conditions

Synthetic insecticides have been an inevitable part of plant protection throughout the world. Sublethal effects of these chemicals on beneficial insect species are one of the contemporary issues these days. Using the age-stage, two-sex life table model, this study evaluated the sublethal and transgenerational effects of six synthetic insecticides (imidacloprid, thiamethoxam, lambda-cyhalothrin, cypermethrin, chlorpyrifos and profenofos) commonly applied to winter vegetables, on the fitness and predation of the seven-spotted ladybeetle, Coccinella septempunctata, which is an efficient predator of aphids worldwide. According to results, all insecticides at their sublethal doses (LC30) significantly suppressed the emergence of adults, adult weight, fertility and fecundity of the parental generation compared to control treatment. The larval stage was prolonged and oviposition, fecundity and total longevity of the adult beetles were decreased in unexposed progeny whose parents were exposed to sublethal doses of all insecticides. Moreover, the biological parameters of adults, including the intrinsic rate of increase (r), finite rate of increase (λ) and net reproductive rate (R0) were significantly reduced when exposed to sublethal doses of insecticides. The predation rate of the F1 generation adults was also decreased after exposure to the sublethal doses of insecticides. However, chlorpyrifos, profenofos, lambda-cyhalothrin and cypermethrin exhibited more deleterious effects on the fitness and population parameters of beetles than imidacloprid and thiamethoxam

Molecular basis of metabolic resistance to the neonicotinoid imidacloprid in Aedes aegypti.

Résumé trop longMosquitoes transmit several human and animal diseases and their control represents a public health challenge worldwide. In most tropical countries, efficient control of mosquitoes relies on the use of chemical insecticides targeting adults or larvae. However, resistance to the four main classes of chemical insecticides has been reported worldwide and threatens vector control programs. In this context, there is an urgent need to find alternatives to conventional insecticides used in vector control. In this thesis, I explored the potential use of the neonicotinoid insecticide imidacloprid for mosquito control, focusing on the identification of metabolic resistance mechanisms, cross-resistance with other insecticides and the impact of environmental pollutants on imidacloprid tolerance. The mosquito Aedes aegypti was used as a model species for this research work. Basal tolerance of Ae. aegypti to imidacloprid was first evaluated at the larval and adult stages. Effects of a larval exposure across a single generation to a sub-lethal dose of imidacloprid were then investigated at the toxicological and molecular levels using transcriptome profiling. Short sub-lethal exposures were also used to identify potential cross-responses between imidacloprid, other chemical insecticides and anthropogenic pollutants. Long-term adaptive response of Ae. aegypti to imidacloprid was then investigated across several generations by selecting an insecticide-susceptible strain (Bora-Bora strain) with imidacloprid at the larval stage for 14 generations in the laboratory. Such artificial selection allowed obtaining the Imida-R strain. This strain showed an increased resistance to imidacloprid in larvae while no significant resistance was measured in adults. Resistance mechanisms were then investigated using various approaches including the use of detoxification enzyme inhibitors, biochemical assays and transcriptome profiling with DNA microarray and massive mRNA sequencing. Several protein families potentially involved in resistance were identified including detoxifications enzymes and cuticle proteins. Among the formers, 8 cytochrome P450s and 1 glutathione S-transferase appears as good candidates for a role in imidacloprid metabolism. The role of P450s in the elevated resistance of the Imida-R strain was confirmed by comparative P450-dependent in vitro metabolism assays conducted on microsomal fractions of the susceptible and Imida-R strains. At the gene level, substrate binding modeling allowed restricting the panel of P450 candidates. Meantime, heterologous expression of one P450 was performed and its ability to metabolize imidacloprid confirmed. Bioassay with other insecticides revealed potential cross-resistance of the Imida-R at the larval stage to other neonicotinoids but also to an insect growth inhibitor and in a lesser extent to DDT, confirming the probable role of detoxification enzymes. Relaxing the selection pressure of the Imida-R strain for few generations led to a rapid decrease of resistance, suggesting a cost of resistance mechanisms. Comparing the inducibility of candidate detoxification genes by imidacloprid in susceptible and resistant strains revealed a higher induction of these genes in the resistant strain, suggesting the selection of both a higher constitutive expression but also a greater phenotypic plasticity of these enzymes in the Imida-R strain. Finally, the potential role of cuticle protein in resistance was preliminary investigated by exposing larvae to a chitin synthesis inhibitor before bioassays. Overall, although this research work requires additional functional validation experiments, these data provide a better understanding of imidacloprid resistance mechanisms in mosquitoes and its potential use as an alternative to conventional insecticides in vector control

Bases moléculaires de la résistance métabolique au néonicotinoïde imidaclopride chez le moustique Aedes aegypti

Mosquitoes transmit several human and animal diseases and their control represents a public health challenge worldwide. In most tropical countries, efficient control of mosquitoes relies on the use of chemical insecticides targeting adults or larvae. However, resistance to the four main classes of chemical insecticides has been reported worldwide and threatens vector control programs. In this context, there is an urgent need to find alternatives to conventional insecticides used in vector control. In this thesis, I explored the potential use of the neonicotinoid insecticide imidacloprid for mosquito control, focusing on the identification of metabolic resistance mechanisms, cross-resistance with other insecticides and the impact of environmental pollutants on imidacloprid tolerance. The mosquito Aedes aegypti was used as a model species for this research work. Basal tolerance of Ae. aegypti to imidacloprid was first evaluated at the larval and adult stages. Effects of a larval exposure across a single generation to a sub-lethal dose of imidacloprid were then investigated at the toxicological and molecular levels using transcriptome profiling. Short sub-lethal exposures were also used to identify potential cross-responses between imidacloprid, other chemical insecticides and anthropogenic pollutants. Long-term adaptive response of Ae. aegypti to imidacloprid was then investigated across several generations by selecting an insecticide-susceptible strain (Bora-Bora strain) with imidacloprid at the larval stage for 14 generations in the laboratory. Such artificial selection allowed obtaining the Imida-R strain. This strain showed an increased resistance to imidacloprid in larvae while no significant resistance was measured in adults. Resistance mechanisms were then investigated using various approaches including the use of detoxification enzyme inhibitors, biochemical assays and transcriptome profiling with DNA microarray and massive mRNA sequencing. Several protein families potentially involved in resistance were identified including detoxifications enzymes and cuticle proteins. Among the formers, 8 cytochrome P450s and 1 glutathione S-transferase appears as good candidates for a role in imidacloprid metabolism. The role of P450s in the elevated resistance of the Imida-R strain was confirmed by comparative P450-dependent in vitro metabolism assays conducted on microsomal fractions of the susceptible and Imida-R strains. At the gene level, substrate binding modeling allowed restricting the panel of P450 candidates. Meantime, heterologous expression of one P450 was performed and its ability to metabolize imidacloprid confirmed. Bioassay with other insecticides revealed potential cross-resistance of the Imida-R at the larval stage to other neonicotinoids but also to an insect growth inhibitor and in a lesser extent to DDT, confirming the probable role of detoxification enzymes. Relaxing the selection pressure of the Imida-R strain for few generations led to a rapid decrease of resistance, suggesting a cost of resistance mechanisms. Comparing the inducibility of candidate detoxification genes by imidacloprid in susceptible and resistant strains revealed a higher induction of these genes in the resistant strain, suggesting the selection of both a higher constitutive expression but also a greater phenotypic plasticity of these enzymes in the Imida-R strain. Finally, the potential role of cuticle protein in resistance was preliminary investigated by exposing larvae to a chitin synthesis inhibitor before bioassays. Overall, although this research work requires additional functional validation experiments, these data provide a better understanding of imidacloprid resistance mechanisms in mosquitoes and its potential use as an alternative to conventional insecticides in vector control.Résumé trop lon

INTERNATIONAL JOURNAL OF AGRICULTURE &amp; BIOLOGY Full Length Article Pathogenicity of Isolates of Metarhizium anisopliae from Gujranwala (Pakistan) against Coptotermes heimi (Wasmann) (Isoptera: Rhinotermitidae)

) of conidial suspension. LT 50 for three strains of M anisopliae on C. heimi were comparatively more (65-106 h) in soil than on filter paper (50-83 h). There was significant difference in different concentrations of all strains of M. anisolpliae (p&lt;0.05)

Bases moléculaires de la résistance métabolique au néonicotinoïde imidaclopride chez le moustique Aedes aegypti

Les moustiques sont vecteurs de nombreuses maladies humaines et animales. Leur contrôle représente donc un enjeu de santé publique au niveau mondial. Dans la plupart des pays tropicaux, le contrôle efficace des populations de moustiques dépend de l'utilisation d'insecticides chimiques ciblant les adultes ou les larves. Cependant, des phénomènes de résistance aux quatre principales classes d'insecticides chimiques couramment utilisées, menacent aujourd'hui les programmes de lutte anti-vectorielle. Dans ce contexte, il est urgent de trouver des alternatives aux insecticides conventionnellement utilisés.-moustiques. Durant cette thèse, j'ai étudié l'utilisation potentielle du néonicotinoïde imidaclopride dans le contrôle des populations de moustiques. Je me suis plus particulièrement intéressé à l'identification des mécanismes de résistance métabolique, à la mise en évidence de résistances croisées avec d'autres insecticides ainsi qu'à l'étude de l'impact des polluants environnementaux sur la tolérance à l'imidaclopride. Pour ce travail, le moustique Aedes aegypti a été utilisé comme une espèce modèle. La tolérance basale d'Ae. aegypti à l'imidaclopride a d'abord été évalué chez les larves et adultes. L'effet d'une exposition larvaire à une dose sub-létale d'imidaclopride sur une seule génération a ensuite été étudié au niveau toxicologique et moléculaire à l'aide de profils transcriptomiques. Les expositions larvaires à des doses sub-létales ont également été utilisées pour identifier les interactions potentielles entre l'imidaclopride, les insecticides chimiques et des polluants environnementaux. A long terme, la réponse adaptative du moustique Ae. aegypti à l'imidaclopride a été étudiée sur plusieurs générations en sélectionnant au laboratoire une souche sensible aux insecticides (souche Bora-Bora) avec de l'imidaclopride durant le stade larvaire pendant 14 générations. Cette sélection artificielle a permis d'obtenir la souche Imida-R. Cette souche présente une résistance accrue à l'imidaclopride chez les larves alors qu'aucune résistance significative n'a été détectée chez les adultes. Les mécanismes de résistance ont ensuite été étudiés en utilisant diverses approches, y compris l'utilisation d'inhibiteurs d'enzymes de détoxication, la mesure des activités de biotransformation et l'étude des profils transcriptomiques par puces à ADN et séquençage massif des ARNm. Plusieurs familles de protéines potentiellement impliquées dans la résistance ont été identifiées, notamment les enzymes de détoxification et les protéines cuticulaires. Parmi les gènes de détoxication, 8 cytochromes P450 et 1 glutathion S-transférase apparaissent comme des candidats pouvant jouer un rôle dans le métabolisme de l'imidaclopride. Le rôle des cytochromes P450 dans la résistance élevée de la souche Imida-R a été confirmée in vitro par des études comparatives du métabolisme de l'imidaclopride par des fractions microsomales des souches sensibles et Imida-R. Au niveau génique, la modélisation de liaison du substrat a permis de restreindre le panel des cytochromes P450 candidats. De façon concomitante, l'expression hétérologue d'un P450 a été effectuée et sa capacité à métaboliser l'imidaclopride a été confirmée. Des bioessais avec d'autres insecticides ont révélé une résistance croisée aux autres néonicotinoïdes chez la souche Imida-R au stade larvaire, ainsi qu'à un inhibiteur de croissance des insectes et dans une moindre mesure au DDT confirmant le rôle probable des enzymes de détoxication. Le relâchement de la pression de sélection sur la souche Imida-R durant quelques générations a entraîné une diminution rapide de la résistance, suggérant un coût métabolique. L'étude comparative de l'inductibilité des gènes de détoxication par l'imidaclopride dans les souches sensible et résistante a révélé une plus grande induction de ces gènes dans la souche résistante, suggérant à la fois la sélection d'une expression constitutive élevée mais également une plus grande plasticité phénotypique de ces enzymes dans la souche Imida-R. Enfin, le rôle potentiel des protéines cuticulaires dans la résistance a été étudié de manière préliminaire en exposant les larves à un inhibiteur de synthèse de la chitine, avant d'effectuer des bioessais. Dans l'ensemble, bien que ce travail de recherche nécessite d'autres expériences de validation fonctionnelle, les données obtenues fournissent une meilleure compréhension des mécanismes de résistance à l'imidaclopride chez les moustiques et permettent de discuter de son utilisation potentielle comme une alternative aux insecticides conventionnellement utilisés en lutte anti-vectorielle.Mosquitoes transmit several human and animal diseases and their control represents a public health challenge worldwide. In most tropical countries, efficient control of mosquitoes relies on the use of chemical insecticides targeting adults or larvae. However, resistance to the four main classes of chemical insecticides has been reported worldwide and threatens vector control programs. In this context, there is an urgent need to find alternatives to conventional insecticides used in vector control. In this thesis, I explored the potential use of the neonicotinoid insecticide imidacloprid for mosquito control, focusing on the identification of metabolic resistance mechanisms, cross-resistance with other insecticides and the impact of environmental pollutants on imidacloprid tolerance. The mosquito Aedes aegypti was used as a model species for this research work. Basal tolerance of Ae. aegypti to imidacloprid was first evaluated at the larval and adult stages. Effects of a larval exposure across a single generation to a sub-lethal dose of imidacloprid were then investigated at the toxicological and molecular levels using transcriptome profiling. Short sub-lethal exposures were also used to identify potential cross-responses between imidacloprid, other chemical insecticides and anthropogenic pollutants. Long-term adaptive response of Ae. aegypti to imidacloprid was then investigated across several generations by selecting an insecticide-susceptible strain (Bora-Bora strain) with imidacloprid at the larval stage for 14 generations in the laboratory. Such artificial selection allowed obtaining the Imida-R strain. This strain showed an increased resistance to imidacloprid in larvae while no significant resistance was measured in adults. Resistance mechanisms were then investigated using various approaches including the use of detoxification enzyme inhibitors, biochemical assays and transcriptome profiling with DNA microarray and massive mRNA sequencing. Several protein families potentially involved in resistance were identified including detoxifications enzymes and cuticle proteins. Among the formers, 8 cytochrome P450s and 1 glutathione S-transferase appears as good candidates for a role in imidacloprid metabolism. The role of P450s in the elevated resistance of the Imida-R strain was confirmed by comparative P450-dependent in vitro metabolism assays conducted on microsomal fractions of the susceptible and Imida-R strains. At the gene level, substrate binding modeling allowed restricting the panel of P450 candidates. Meantime, heterologous expression of one P450 was performed and its ability to metabolize imidacloprid confirmed. Bioassay with other insecticides revealed potential cross-resistance of the Imida-R at the larval stage to other neonicotinoids but also to an insect growth inhibitor and in a lesser extent to DDT, confirming the probable role of detoxification enzymes. Relaxing the selection pressure of the Imida-R strain for few generations led to a rapid decrease of resistance, suggesting a cost of resistance mechanisms. Comparing the inducibility of candidate detoxification genes by imidacloprid in susceptible and resistant strains revealed a higher induction of these genes in the resistant strain, suggesting the selection of both a higher constitutive expression but also a greater phenotypic plasticity of these enzymes in the Imida-R strain. Finally, the potential role of cuticle protein in resistance was preliminary investigated by exposing larvae to a chitin synthesis inhibitor before bioassays. Overall, although this research work requires additional functional validation experiments, these data provide a better understanding of imidacloprid resistance mechanisms in mosquitoes and its potential use as an alternative to conventional insecticides in vector control.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Associative interplay of plant growth promoting rhizobacteria (Pseudomonas aeruginosa QS40) with nitrogen fertilizers improves sunflower (Helianthus annuus L.) productivity and fertility of aridisol

The environmental and economic impacts of chemical fertilizer have encouraged farmers to integrate them with organic materials, an important nutrient management strategy for sustainable agriculture production. In the present study, we conducted field experiments to study the effects of nitrogen enriched compost (NEC) and mineral nitrogen (MN) fertilizer with a selected plant growth promoting rhizobacterial (PGPR) strain, Pseudomonas aeruginosa QS40, on productivity of sunflower and soil fertility. The results demonstrated that integrated application of PGPR with organic-inorganic N significantly increased shoot and root length, leaf area, total chlorophyll, head diameter, fresh biomass, straw-achene yield and N uptake in sunflower compared to unamended control and PGPR alone. The results also showed that integrated N biofertilizer regime enhanced soil microbial biomass, enzymatic activities and soil nitrogen contents. We also observed significant changes in rhizosphere soil pH, abundance of cultivable bacteria and arbuscular mycorrhizae fungi (AMF) root colonization. Treatment and year interaction was significant for dissolved organic carbon (DOC) and microbial biomass carbon (MBC) only. These results suggest that the efficiency of PGPR could be improved with increased availability of labile C substrate resource in NEC amended aridisol. We conclude that the application of NEC fertilizer with efficient PGPR biofertilizer may improve sunflower productivity and soil chemical and biological fertility in nutrient-poor agroecosystems of arid and semi-arid regions