Synergy between Repellents and Organophosphates on Bed Nets: Efficacy and Behavioural Response of Natural Free-Flying An. gambiae Mosquitoes

Background: Chemicals are used on bed nets in order to prevent infected bites and to kill aggressive malaria vectors. Because pyrethroid resistance has become widespread in the main malaria vectors, research for alternative active ingredients becomes urgent. Mixing a repellent and a non-pyrethroid insecticide seemed to be a promising tool as mixtures in the laboratory showed the same features as pyrethroids. Methodology/Principal Findings: We present here the results of two trials run against free-flying Anopheles gambiae populations comparing the effects of two insect repellents (either DEET or KBR 3023, also known as icaridin) and an organophosphate insecticide at low-doses (pirimiphos-methyl, PM) used alone and in combination on bed nets. We showed that mixtures of PM and the repellents induced higher exophily, blood feeding inhibition and mortality among wild susceptible and resistant malaria vectors than compounds used alone. Nevertheless the synergistic interactions are only involved in the high mortality induced by the two mixtures. Conclusion: These field trials argue in favour of the strategy of mixing repellent and organophosphate on bed nets to better control resistant malaria vectors

Reduced efficacy of insecticide-treated nets and indoor residual spraying for malaria control in pyrethroid resistance area, Benin

The pyrethroid knockdown resistance gene (kdr) has become widespread in Anopheles gambiae in West Africa. A trial to test the continuing efficacy of insecticide-treated nets (ITN) and indoor residual spraying (IRS) was undertaken in experimental huts at 2 sites in Benin, the first where kdr is present at high frequency (Ladji), the second-where An. gambiae is susceptible (Malanville). Holes were made in the nets to mimic worn nets. At Malanville, 96% of susceptible An. gambiae were inhibited from blood-feeding, whereas at Ladji feeding was uninhibited by ITNs. The mortality rate of An. gambiae in ITN huts was 98% in Malanville but only 30% at Ladji. The efficacy of IRS was equally compromised. Mosquitoes at Ladji had higher oxidase and esterase activity than in a laboratory-susceptible strain, but this fact did not seem to contribute to resistance. Pyrethroid resistance in An. gambiae appears to threaten the future of ITN and IRS in Benin

DEET microencapsulation : a slow-release formulation enhancing the residual efficacy of bed nets against malaria vectors

Textile materials treated with synthetic repellents have the potential to provide protection against insect disease vectors but lack the residual activity necessary to achieve a prolonged effect or to be cost-effective. DEET MC is a formulation of DEET (N,N diethyl-m-toluamide) in which the repellent is gradually released from a capsule that binds the repellent. An experiment carried out on DEET-treated mosquito netting showed that the formulation repels, inhibits blood-feeding and kilts mosquitoes for a period of at least 6 months under laboratory conditions. Such formulations may have the potential for use on nets against pyrethroid-resistant mosquitoes or on clothing or bedding materials distributed in disasters, emergencies or refugee camp situations

Experimental and Theoretical Investigation into the Formation and Reactivity of M(Cp)(CO)₂(CO₂) (M = Mn or Re) in Liquid and Supercritical CO₂ and the Effect of Different CO₂ Coordination Modes on Reaction Rates with CO, H₂, and N₂

Nanosecond time-resolved infrared spectroscopy (TRIR) has been used to study the coordination of CO₂ to the metal centers by UV photolysis of M(Cp)(CO)₃ (M = Mn or Re) in liquid or supercritical CO₂ (scCO₂) solution, which led to the formation of the CO₂ complexes M(Cp)(CO)₂(CO₂). Differences between the positions of the ν(C−O) IR bands of the CO ligands in Mn(Cp)(CO)₂(CO₂) and Re(Cp)(CO)₂(CO₂) suggest that the CO₂ ligand has different coordination modes to the metal centers in these complexes. The kinetic data and the IR spectra of the CO₂, Xe, and heptane complexes provided evidence that the CO₂ coordination mode is η¹-O end-on bound in Mn(Cp)(CO)₂(CO₂), and η²-C,O side-on bound in Re(Cp)(CO)₂(CO₂). These different coordination modes lead to dramatic differences in reactivity with CO, H₂, and N₂, with the Re complexes being significantly less reactive. To provide more evidence for the nature of the CO₂ binding modes, a series of DFT calculations were performed at the B3LYP/SDD-6-311G** level. The calculations supported the experimentally proposed CO₂ coordination modes. A significant charge transfer from Re to CO₂ occurs, resulting in partial oxidation of Re

Experimental and Theoretical Investigation into the Formation and Reactivity of M(Cp)(CO)₂(CO₂) (M = Mn or Re) in Liquid and Supercritical CO₂ and the Effect of Different CO₂ Coordination Modes on Reaction Rates with CO, H₂, and N₂

Nanosecond time-resolved infrared spectroscopy (TRIR) has been used to study the coordination of CO₂ to the metal centers by UV photolysis of M(Cp)(CO)₃ (M = Mn or Re) in liquid or supercritical CO₂ (scCO₂) solution, which led to the formation of the CO₂ complexes M(Cp)(CO)₂(CO₂). Differences between the positions of the ν(C−O) IR bands of the CO ligands in Mn(Cp)(CO)₂(CO₂) and Re(Cp)(CO)₂(CO₂) suggest that the CO₂ ligand has different coordination modes to the metal centers in these complexes. The kinetic data and the IR spectra of the CO₂, Xe, and heptane complexes provided evidence that the CO₂ coordination mode is η¹-O end-on bound in Mn(Cp)(CO)₂(CO₂), and η²-C,O side-on bound in Re(Cp)(CO)₂(CO₂). These different coordination modes lead to dramatic differences in reactivity with CO, H₂, and N₂, with the Re complexes being significantly less reactive. To provide more evidence for the nature of the CO₂ binding modes, a series of DFT calculations were performed at the B3LYP/SDD-6-311G** level. The calculations supported the experimentally proposed CO₂ coordination modes. A significant charge transfer from Re to CO₂ occurs, resulting in partial oxidation of Re

Insecticide resistance in mosquito vectors

Resistance to insecticides among mosquitoes that act as vectors for malaria (Anopheles gambiae) and West Nile virus (Culex pipiens) emerged more than 25 years ago in Africa, America and Europe; this resistance is frequently due to a loss of sensitivity of the insect's acetylcholinesterase enzyme to organophosphates and carbamates1. Here we show that this insensitivity results from a single amino-acid substitution in the enzyme, which we found in ten highly resistant strains of C. pipiens from tropical (Africa and Caribbean) and temperate (Europe) areas, as well as in one resistant African strain of A. gambiae. Our identification of this mutation may pave the way for designing new insecticides

Proteogenomic Monitoring of Geobacter Physiology during Stimulated Uranium Bioremediation▿ †

Implementation of uranium bioremediation requires methods for monitoring the membership and activities of the subsurface microbial communities that are responsible for reduction of soluble U(VI) to insoluble U(IV). Here, we report a proteomics-based approach for simultaneously documenting the strain membership and microbial physiology of the dominant Geobacter community members during in situ acetate amendment of the U-contaminated Rifle, CO, aquifer. Three planktonic Geobacter-dominated samples were obtained from two wells down-gradient of acetate addition. Over 2,500 proteins from each of these samples were identified by matching liquid chromatography-tandem mass spectrometry spectra to peptides predicted from seven isolate Geobacter genomes. Genome-specific peptides indicate early proliferation of multiple M21 and Geobacter bemidjiensis-like strains and later possible emergence of M21 and G. bemidjiensis-like strains more closely related to Geobacter lovleyi. Throughout biostimulation, the proteome is dominated by enzymes that convert acetate to acetyl-coenzyme A and pyruvate for central metabolism, while abundant peptides matching tricarboxylic acid cycle proteins and ATP synthase subunits were also detected, indicating the importance of energy generation during the period of rapid growth following the start of biostimulation. Evolving Geobacter strain composition may be linked to changes in protein abundance over the course of biostimulation and may reflect changes in metabolic functioning. Thus, metagenomics-independent community proteogenomics can be used to diagnose the status of the subsurface consortia upon which remediation biotechnology relies