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Liverpool, United Kingdom

Christian R.N.,South African National Institute for Communicable Diseases | Christian R.N.,University of Witwatersrand | Strode C.,Vector Research Group | Ranson H.,Vector Research Group | And 5 more authors.
Pesticide Biochemistry and Physiology

Anopheles funestus is one of the major malaria vectors in southern Africa and several populations in this region are resistant to pyrethroids. The current study uses a microarray based approach to identify genes up-regulated in the pyrethroid resistant population, FUMOZ, from Mozambique. As the full set of detoxification genes in A. funestus are unknown, this study investigated the utility of the Anopheles gambiae 'detox chip' to screen for differentially expressed detoxification genes in A. funestus. Differential expression of detoxification genes in 3 day old adult females and males from the FUMOZ resistant strain and the FANG susceptible strain was identified using the A. gambiae 'detox chip'. After optimization of the hybridization conditions, over 90% of the probes showed a positive signal. Only three genes were significantly (p<. 0.001) differentially expressed in the females, CYP6P9 (5.4-fold), COI (2.7-fold) and CYP6M7 (1.8-fold). The same genes were also significantly differentially expressed in the adult males, CYP6P9 (6.0-fold), COI (2.9-fold) and CYP6M3 (3.6-fold) together with an additional 21 transcripts. Quantitative PCR (qPCR) analysis was conducted to validate the microarray results. This study demonstrated that heterologous hybridization is a helpful tool in identifying detoxification genes differentially expressed in A. funestus strains. © 2011. Source

Nardini L.,South African National Institute for Communicable Diseases | Nardini L.,University of Witwatersrand | Christian R.N.,South African National Institute for Communicable Diseases | Christian R.N.,University of Witwatersrand | And 6 more authors.
Parasites and Vectors

Background: The use of insecticides to control malaria vectors is essential to reduce the prevalence of malaria and as a result, the development of insecticide resistance in vector populations is of major concern. Anopheles arabiensis is one of the main African malaria vectors and insecticide resistance in this species has been reported in a number of countries. The aim of this study was to investigate the detoxification enzymes that are involved in An. arabiensis resistance to DDT and pyrethroids. Methods: The detoxification enzyme profiles were compared between two DDT selected, insecticide resistant strains of An. arabiensis, one from South Africa and one from Sudan, using the An. gambiae detoxification chip, a boutique microarray based on the major classes of enzymes associated with metabolism and detoxification of insecticides. Synergist assays were performed in order to clarify the roles of over-transcribed detoxification genes in the observed resistance phenotypes. In addition, the presence of kdr mutations in the colonies under investigation was determined. Results: The microarray data identifies several genes over-transcribed in the insecticide selected South African strain, while in the Sudanese population, only one gene, CYP9L1, was found to be over-transcribed. The outcome of the synergist experiments indicate that the over-transcription of detoxification enzymes is linked to deltamethrin resistance, while DDT and permethrin resistance are mainly associated with the presence of the L1014F kdr mutation. Conclusions: These data emphasise the complexity associated with resistance phenotypes and suggest that specific insecticide resistance mechanisms cannot be extrapolated to different vector populations of the same species. © 2012 Nardini et al.; licensee Biomed Central Ltd. Source

Riaz M.A.,CNRS Alpine Ecology Laboratory | Riaz M.A.,University of Sargodha | Chandor-Proust A.,CNRS Alpine Ecology Laboratory | Dauphin-Villemant C.,CNRS Alpine Ecology Laboratory | And 8 more authors.
Aquatic Toxicology

Mosquitoes are vectors of several major human diseases and their control is mainly based on the use of chemical insecticides. Resistance of mosquitoes to organochlorines, organophosphates, carbamates and pyrethroids led to a regain of interest for the use of neonicotinoid insecticides in vector control. The present study investigated the molecular basis of neonicotinoid resistance in the mosquito Aedes aegypti. A strain susceptible to insecticides was selected at the larval stage with imidacloprid. After eight generations of selection, larvae of the selected strain (Imida-R) showed a 5.4-fold increased tolerance to imidacloprid while adult tolerance level remained low. Imida-R larvae showed significant cross-tolerance to other neonicotinoids but not to pyrethroids, organophosphates and carbamates. Transcriptome profiling identified 344 and 108 genes differentially transcribed in larvae and adults of the Imida-R strain compared to the parental strain. Most of these genes encode detoxification enzymes, cuticle proteins, hexamerins as well as other proteins involved in cell metabolism. Among detoxification enzymes, cytochrome P450 monooxygenases (CYPs) and glucosyl/glucuronosyl transferases (UDPGTs) were over-represented. Bioassays with enzyme inhibitors and biochemical assays confirmed the contribution of P450s with an increased capacity of the Imida-R microsomes to metabolize imidacloprid in presence of NADPH. Comparison of substrate recognition sites and imidacloprid docking models of six CYP6s over-transcribed in the Imida-R strain together with Bemisia tabaci CYP6CM1vQ and Drosophila melanogaster CYP6G1, both able to metabolize imidacloprid, suggested that CYP6BB2 and CYP6N12 are good candidates for imidacloprid metabolism in Ae. aegypti. The present study revealed that imidacloprid tolerance in mosquitoes can arise after few generations of selection at the larval stage but does not lead to a significant tolerance of adults. As in other insects, P450-mediated insecticide metabolism appears to play a major role in imidacloprid tolerance in mosquitoes. © 2012 Elsevier B.V. Source

Poupardin R.,CNRS Alpine Ecology Laboratory | Poupardin R.,Vector Research Group | Riaz M.A.,CNRS Alpine Ecology Laboratory | Jones C.M.,Vector Research Group | And 3 more authors.
Aquatic Toxicology

The control of mosquitoes transmitting infectious diseases relies mainly on the use of chemical insecticides. However, the emergence of insecticide resistance threatens mosquito control programs. Until now, most research efforts have been focused on elucidating resistance mechanisms caused by insecticide treatments. Less attention has been paid to the impact of the mosquito chemical environment on insecticide-driven selection mechanisms. Here the mosquito Aedes aegypti was used as a model species to conduct laboratory experiments combining the exposure of mosquito larvae to a sub-lethal concentration of xenobiotics and their selection with the insecticide permethrin. After 10 generations, bioassays and a transcriptome profiling with a 15k microarray were performed comparatively on all strains. The three selected strains showed a small but significant increase of permethrin resistance compared to the susceptible parental strain. Microarray analysis revealed that the transcription of many genes was altered by insecticide selection. Exposing larvae to sub-lethal concentrations of the pollutant fluoranthene or the insecticide permethrin prior to selection at each generation affected the selection of several genes, including those involved in detoxification, transport and cell metabolism. Genes potentially involved in permethrin resistance and cross-responses between xenobiotics and insecticide were identified. The present study investigated for the first time the impact of the presence of pollutants in mosquito environment on insecticide-driven selection mechanisms. Our results revealed that mosquitoes exposed to xenobiotics show a different adaptive response to insecticide selection pressure. This suggests that insect chemical environment can shape the long-term selection of metabolic mechanisms leading to insecticide resistance. © 2012 Elsevier B.V. Source

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