Spectroscopic studies of the interactions of the pyrethroid insecticide fenvalerate with gramicidin

Fenvalerate is a pyrethroid insecticide which interacts with ionic channels. Using circular dichroism technique we have studied the interaction of fenvalerate with gramicidin, a model channel peptide which transports ions. In most organic solvents, gramicidin exists as a double helix except in trifluoroethanol where it exists as a channel forming single stranded beta(6.3) helical monomer. In model lipid membranes, under certain experimental conditions, gramicidin exists as a channel forming single stranded beta(6.3) helical dimer. Our results show that fenvalerate interacts more with the single stranded beta(6.3) helical monomer or dimer than with the double helical form of gramicidin. This was further confirmed by an increase in the rate of gramicidin mediated proton transport in liposomes by fenvalerate, using the pH sensitive fluorophore, pyranine.

Identification and preliminary evaluation of viriditoxin, a metabolite of Paecilomyces varioti, as an insecticide for sheep blowfly, Lucilia cuprina (Wied.)

Solvent extracts of cultures of the fungus Paecilomyces varioti are toxic to sheep blowfly, Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae). Different components of the culture extracts were isolated and bioassayed with L. cuprina. The component with most toxicity was purified and identified from its proton magnetic resonance spectrum as viriditoxin, a known antibiotic metabolite of the fungus. The insecticidal properties of viriditoxin were then evaluated. Mean LCso values for first instar larvae of organophosphate susceptible and resistant strains of L. cuprina were 7.5 and 8.4 ppm respectively. Pilot implant trials in sheep demonstrated that the compound provided protection for 9-17 weeks against both strains of L. cuprina. No adverse effects on the trial sheep were detected.

Insecticide resistance and implications for future aphid management in Australian grains and pastures: A review

Aphids can cause substantial damage to cereals, oilseeds and legumes through direct feeding and through the transmission of plant pathogenic viruses. Aphid-resistant varieties are only available for a limited number of crops. In Australia, growers often use prophylactic sprays to control aphids, but this strategy can lead to non-target effects and the development of insecticide resistance. Insecticide resistance is a problem in one aphid pest of Australian grains in Australia, the green peach aphid (Myzus persicae). Molecular analyses of field-collected samples demonstrate that amplified E4 esterase resistance to organophosphate insecticides is widespread in Australian grains across Australia. Knockdown resistance to pyrethroids is less abundant, but has an increased frequency in areas with known frequent use of these insecticides. Modified acetylcholinesterase resistance to dimethyl carbamates, such as pirimicarb, has not been found in Australia, nor has resistance to imidacloprid. Australian grain growers should consider control options that are less likely to promote insecticide resistance, and have reduced impacts on natural enemies. Research is ongoing in Australia and overseas to provide new strategies for aphid management in the future.

Effect of fenvalerate, a pyrethroid insecticide on membrane fluidity

Fenvalerate is a commonly used pyrethroid insecticide, used to control a wide range of pests. We have studied its interaction with the membrane using fluorescence polarization and differential scanning calorimetry (DSC) techniques. Fenvalerate was found to decrease the DPH fluorescence polarization value of synaptosomal and microsomal membrane, implicating that it makes the membrane more fluid. At different concentrations of fenvalerate, the activation energy of the probe molecule in the membrane also changes revealed from the change in slope of the Arrhenius plot. At higher concentrations the insecticide slowly saturates the membrane. The effects of fenvalerate on model membrane were also studied with liposomes reconstituted with dipalmitoylphosphatidylcholine (DPPC). Fenvalerate decreased the phase transition temperature (Tm) of DPPC by 1.5 °C at 40 μM concentration, but there was no effect on the cooperativity of the transition as interpreted from the DSC thermogram. From the change in the thermogram profile with fenvalerate it has been interpreted that it localizes in the acyl chain region of the lipid, possibly between C10 and C16 region and weakens the acyl chain packing. Fenvalerate was also found to interact with DPPC liposomes containing cholesterol to fluidize it.

Effect of the pyrethroid insecticide fenvalerate on sodium current of rat dorsal root ganglion neuron

Fenvalerate is a widely used pyrethroid insecticide. The report presents our findings on the effect of fenvalerate on isolated whole-cell sodium currents in single rat dorsal root ganglionic neurons in culture, studied with patch-clamp technique. Fenvalerate decreased the amplitude of whole-cell sodium current and slowed the inactivation and tail current kinetics.

Application of insecticide in various volumes of waterat stages of Sorghum development for control of fall armyworm (Lepidóptera: Noctuidae)

Una debilidad en las aplicaciones de insecticidas para el control de plagas del sorgo, es el desconocimiento existente acerca del efecto de los volúmenes de agua sobre la efectividad del producto químico aplicado. El objetivo de esta investigación fue determinar el efecto de diferentes volúmenes de agua aplicados en diferentes etapas fonológicas del cultivo sobre la efectividad de clorpirifos sobre el gusano cogollero (Spodoptera frugiperda (J. E. Smith) (lnsecta: Lepidoptera: Noctuidae)) . El ensayo se estableció el 20 de Septiembre de 2001, en terrenos de la es~ación experimental numero 2 del Centro Nacional de Tecnología Agropecuaria y Forestal (CENTA), ubicado en SanAndrés, departamento de la Libertad, El Salvador .. Se efectuaron aplicaciones de chlorpyrifos en dosis de ~ .4 1 ha·, utilizando 285 y ~42 litros de agua, aplicado en dos etapas de crecimiento del cultivo de sorgo (25 y 45 días después de siembra). Los tratamientos incluyeron una aplicación a un determinado volumen y tiempo (25 días después de siembra), y dos a aplicaciones a determinados volúmenes y tiempo, una a los 25 y otra a los 45 días después de siembra. La aplicación de Chlorpyrifos redujo de significativamente la intestación de larvas a las 24 horas después de la primera aplicación, cuando se le compara con el tratamiento control. Sin embargo, no se determinaron diferencias significativas en la eficacia del insecticida, cuando se comparó la infestación de larvas en parcelas tratadas con diferentes cantidades de agua. El volumen mayor de agua pareciera que mejora la distribución del producto qufmico sobre la planta, lo que conduce a una mayor mortalidad de larvas. Una segunda aplicación de insecticida, 20 días después de la primera aplicación, redujo significativamente la infestación de larvas comparada con una sola aplicación. Esta información indica que el incremento en los volúmenes de agua mejora la eficacia del insecticida Chlorpyrifos contra el gusano cogollero en el cultivo de sorgo. Una segunda aplicación del tratamiento insecticida es efectiva contra relnfestaciones de larvas y sugiere que el cogollero que se alimenta de estructuras vegetativas del sorgo, en los ntveles encontrados en este estudio en el Salvador, puede reducir la producción de grano del sorgo.

Frequency of insecticide spray application for control of fall armyworm (Lepidóptera: Noctuidae) on sorghum

Existe desconocimiento del efecto de frecuencias de aplicación de los insecticidas sobre el comportamiento de las poblaciones del gu· sano cogollero ( Spodoptera frugipercta) y la repercusión de estas en los rendimientos del sorgo granifero (Sorghum bicolor l. Moench). El estudio se realizó en la Estación Experimental dos del Centro Nacional de Tecnología Agropecuaria y Forestal (CENTA), ubicado en San Andrés, departamento de La Libertad, El Salvador, durante los meses de septiembre del año 2001 y enero de 2002. El objetivo de la investigación fue determinar el efecto del numero de aplicaciones de clorpirifos sobre las poblaciones de larvas de gusano cogollero en el cultivo del sorgo. Para este ensayo se estableció un diseño de bloques al azar con cinco tratamientos y cuatro repeticiones. Se realizaron aplicaciones de Chlorpyrifos en el cultivo del sorgo, en dosis de 1.4 1 ha·1, en 285 1 de agua durante cuatro fechas (4 estados de desarrollo de la planta), específicamente a los 15, 25, 35 y 45 días después de la siembra. Las parcelas contratamientos recibieron 1 , 2, 3 y 4 aplicaciones de insecticidas y fueron comparadas con una parcela sin aplicación. Cada tratamiento insecticida inicialmente tuvo reducciones significativas en las poblaciones de cogollero, comparados con la parcela sin aplicación. Tratamientos con cada aplicación adicional tuvo reducciones significativas en las poblaciones de larvas vivas, comparados con tratamientos que tuvieron menor numero de aplicaciones. El cogollero, tuvo reinfestaciones, en las parcelas que recibieron ya sea una, dos o tres aplicaciones de insecticidas, durante el periodo de observación después de cada uno de los tres tratamientos. Estos resultados muestran las reinfecciones de las poblaciones de cogollero después de las aplicaciones de insecticidas, y la carencia de efecto residual de los mismos. A pesar de que no se determinaron diferencias significativas en el rendimiento de grano, las diferencias numéricas oscilaron desde 555 a 1 674 kg ha·1 mas allá del rendimiento observado en el tratamiento sin aplicación, lo cual sugiere que el manejo efectivo del daño ocasionado por el cogollero en el cultivo de sorgo, puede resultar en mejora de los rendimientos.

Responses of Cyprinus carpio var. communis to Cyhalothrin, a pyrethroid insecticide

Haematological and biochemical profiles in a freshwater teleost, Cyprinus carpio var. communis, exposed to sub-lethal toxicity of the insecticide cyhalothrin were studied. During the treatment, erythrocyte count, haemoglobin content and protein content decreased, whereas leucocyte count and glucose level increased. The data are discussed in relation to the significance of haematological and biochemical changes as non-specific biomarkers against anthropogenic stress.

Organochlorine insecticide residues in sediments from the coast of Chittagong, Bangladesh

A total of 5 samples of marine sediments were analyzed for residues of organochlorine insecticide from the coast of Chittagong, Bangladesh. The analytical method consisted of 3 phases, extraction, clean-up and, analysis through Gas Chromatography (GC) with Electron Capture Detector (ECD). The concentration ranges were as follows 0.18 - 1.33 ng.g¹ for aldrin, 0.2 - 1.84 ng.g¹ for dielddrin, 0.30 - 1.31 ng.g¹ for endrin, 0.11 - 0.26 ng.g¹ for lindane, 0.56- 3.36 ng.g¹ for heptachlor, 0.2- 1.51 ng.g¹ for P,P' DDE, 0.18- 2.91 ng.g¹ for P,P' DDD, 0.11 - 3.12 ng.g¹ for P,P' DDT. These results reveal that the sediments along coast of Chittagong are slightly contaminated with some of these organochlorine insecticides.

Insecticide resistance in Chinese populations of the Culex pipiens complex through esterase overproduction

In most parts of China, mosquitoes have been subjected to organophosphate (OP) insecticide treatments since the mid-1960s, and resistance gene monitoring in the Culex pipiens complex (Diptera: Culicidae) started in only a few locations from the end of the 1980s. Many resistant alleles at the Ester locus have been found in field populations, including those commonly found around the world (Ester(B1) and Ester(2)), and those endemic to China (Ester(B6), Ester(B7), Ester(8), and Ester(9)). This situation is atypical, and may represent a complex situation for the evolution of insecticide resistance genes in China. To increase our understanding of the Chinese situation and our ability to manage resistance in the C. pipiens complex, a large study was performed. Twenty field populations were sampled from Beijing to Guangzhou. Bioassays with five insecticides (dichlorvos, parathion, chlorpyrifos, 2-sec-butylphenyl methyl carbamate, and propoxur) disclosed resistance levels variable according to the geographic origin, and up to 85-fold for dichlorvos. Six overproduced esterases were identified, including two that have not been previously described. Most of them were found in all samples, although at variable frequencies, suggesting variable selection or a transient situation, e.g., each one was recently restricted to a particular geographic area. The results are discussed in the context of recent alterations to insecticide campaigns, and of the evolution of resistance genes in Chinese C. pipiens populations.

Electrochemical and quantum chemical investigations of the insecticide fipronil.

This work describes an electrochemical and quantum chemical investigation of the fipronil insecticide. Cyclic voltammetry (CV) and square wave voltammetry (SWV) experiments were performed over a graphite-polyurethane (GPU) composite electrode. The fipronil molecule presents an one?electron irreversible oxidation reaction. Profiting the SWV signal a square wave stripping voltammetry (SWSV) procedure to determine the fipronil molecule in a 0.10 mol L-1 Britton-Robinson buffer solution, pH 8.0 was developed with accumulation potential and time of 0.50 V and 120 s, respectively. The limits of detection and quantification were 0.80 and 2.67 ?g L-1, respectively. Recovery tests were performed in three natural waters samples with values ranging from 99.67 to 101.37%. Quantum chemical studies showed that the nitrogen atom of the pyrazole group is the most probable oxidation site of the fipronil molecule.

Studies on the insecticide - nematicide-oxamyl and its quantitative determination by gas chromatographic method

Ox amyl , an insecticide/nematicide with the chemical name; methyl ~'. ~·-dimethyl-~-(methylcarbamoyl)oxy-l-thiooxamimidate, and its major degradation compound; oxime or oximino compound, methyl ~',~'-dimethyl-~-hydroxy-l-thiooxamimidate were studied in this work. NMR and mass spectrometry were utilized in the structural studies. An attempt was made to explain the fragmentation patterns of some major peaks in the mass spectra of oxamyl and oxime. A new gas chromatographic method for the detection and determination of submicrogram levels of intact oxamyl using a electron-capture detector was developed. The principle of this method is to produce a derivative which is highly sensitive to an electron-capture detector. The derivative described is dinitrophenyl methylamine( DNPMA ) • Experimental conditions such as pH , reaction temperature , reaction time, the amount of reagent ( Dinitrofluaro benzene) etc. were thoroughly investigated and optimized. This method was successfully applied to the determination of oxamyl residues in tobacco leaves and soil. Throughout this J9D:oject , thin layer chromatography was also used in the separation:and clean up of oxamyl and oxime samples.