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PubMed2005

Patterns of insecticide resistance in larval Culex pipiens populations in Israel: dynamics and trends.

Resistance to insecticides of larval Culex pipiens populations in Israel has been monitored for ten years and the results were used for control planning. The insecticides tested were the organophosphates chlorpyrifos, fenthion, and temephos and the pyrethroids permethrin and cypermethrin. Over the years the relative resistance (R/R) values to chlorpyrifos in most populations tested were between 200-400, with records of up to 700 R/R. Practically no susceptible populations were found and the compound has been withdrawn from use, resulting in a decrease in the relative resistance values. In 1996 when fenthion was reintroduced, no resistant populations were found, but in the following years significant resistance appeared in an increasing number of populations with values lower than recorded for chlorpyrifos but still high (up to 100 R/R). All populations tested were found to be susceptible to temephos and accordingly the compound was reintroduced in 2002. Over the ten years, no significant resistance to cypermethrin was found in the majority of the populations tested, while a trend of increased resistance to permethrin was noted with a few records of >1000 R/R. The results demonstrate the importance of continuous monitoring of insecticide resistance for efficient mosquito control. Alternative insecticides and methods of control are discussed.

Animals↗
PubMed1997

Brief bilateral vocal cord paralysis after insecticide poisoning. A new variant of toxicity syndrome.

We describe a new variant of life-threatening organophosphate toxicity syndrome that produces a brief bilateral vocal cord paralysis. There are 3 recognized types of toxicity syndrome: acute (instantaneous), intermediate (slightly delayed, i.e., hours to days), and delayed (weeks to months). Ingestions of large doses of insecticides lead to a cholinergic crisis and possible death (acute-type syndrome). Exposures to lower doses may cause the intermediate- or delayed-type syndrome. The intermediate-type syndrome is characterized by slightly delayed polyneuropathy and generalized weakness. Transient vocal cord paralysis has also been reported in association with other neurologically profound findings. The delayed-type syndrome can produce muscle weakness for months. Our patient, a 2-year-old boy, was found eating a substance later found to be contaminated with insecticide. Within minutes, fever and somnolence developed, followed by progressive respiratory distress and stridor, without generalized weakness. The child's condition progressed to complete airway obstruction, and intubation was necessary. Emergency laryngoscopy and bronchoscopy were performed to rule out epiglottitis or a foreign body. Instead, a bilateral vocal cord paralysis was found. The paralysis lasted 2 days before completely resolving. Insecticide poisoning was suspected. We theorize that our patient manifested a combination of the acute-type syndrome, because of the immediacy of the onset of the symptoms (i.e., fever and somnolence), and the intermediate-type syndrome, because of the transient vocal cord paralysis. Because of the potential dangers involved, we wish to familiarize physicians concerning organophosphate poisoning; to alert the medical community to this variant of toxicity syndrome, which involves transient bilateral vocal cord paralysis; and to demonstrate the benefit of early otolaryngological consultation for the prevention and treatment of airway obstruction in patients with suspected organophosphate poisoning, be it from insecticides or poison gas.

Child, Preschool↗
PubMed1998

Structural factors contributing to insecticidal and selective actions of neonicotinoids.

Nicotinoids and neonicotinoids are characterized by the presence of the 3-pyridylmethylamine moiety in their structure. In the former, the amino nitrogen atom is ionized, while in the latter the corresponding nitrogen atom is not ionized but bears a partial positive charge. Both types of insecticides interact with nicotinic acetylcholine receptor (nAChR) of insect origin. The poor interaction of neonicotinoids with vertebrate nAChR was shown by its poor binding affinity to the nAChR from Torpedo electric organ and rat brain and poor activation with nAChR expressed in Xenopus oocytes. The full positive charge was essential to interact with the vertebrate nAChR, while the 3-pyridylmethylamine moiety with a partial positive charge was enough to interact with the insect nAChR. For penetration into the insect central nervous system, hydrophobicity seemed to play an important role, as indicated by the binding of the injected compounds to the housefly head nAChR. The ionization reduced hydrophobicity and limited the penetration of nicotinoids, resulting in less insecticidal activity. Among neonicotinoids, nitromethylene type compounds, though far higher in binding affinity, were less hydrophobic than the corresponding nitroimine type, and the net result was better or inferior insecticidal activity. A chlorine atom at the 6 position of the 3-pyridyl group found in commercialized neonicotinoids contributes to increased binding affinity and more importantly hydrophobicity, thus increasing insecticidal activity. N-Me-imidacloprid was found to be a propesticide of imidacloprid.

Animals↗
PubMed2003

Chloride channels as tools for developing selective insecticides.

Ligand-gated chloride channels underlie inhibition in excitable membranes and are proven target sites for insecticides. The gamma-aminobutyric acid (GABA(1)) receptor/chloride ionophore complex is the primary site of action for a number of currently used insecticides, such as lindane, endosulfan, and fipronil. These compounds act as antagonists by stabilizing nonconducting conformations of the chloride channel. Blockage of the GABA-gated chloride channel reduces neuronal inhibition, which leads to hyperexcitation of the central nervous system, convulsions, and death. We recently investigated the mode of action of the silphinenes, plant-derived natural compounds that structurally resemble picrotoxinin. These materials antagonize the action of GABA on insect neurons and block GABA-mediated chloride uptake into mouse brain synaptoneurosomes in a noncompetitive manner. In mammals, avermectins have a blocking action on the GABA-gated chloride channel consistent with a coarse tremor, whereas at longer times and higher concentrations, activation of the channel suppresses neuronal activity. Invertebrates display ataxia, paralysis, and death as the predominant signs of poisoning, with a glutamate-gated chloride channel playing a major role. Additional target sites for the avermectins or other chloride channel-directed compounds might include receptors gated by histamine, serotonin, or acetylcholine.The voltage-sensitive chloride channels form another large gene family of chloride channels. Voltage-dependent chloride channels are involved in a number of physiological processes including: maintenance of electrical excitability, chloride ion secretion and resorption, intravesicular acidification, and cell volume regulation. A subset of these channels is affected by convulsants and insecticides in mammals, although the role they play in acute lethality in insects is unclear. Given the wide range of functions that they mediate, these channels are also potential targets for insecticide development.

Animals↗
PubMed2004

Mechanisms of the insecticidal action of TEL (Talisia esculenta lectin) against Callosobruchus maculatus (Coleoptera: Bruchidae).

Plant lectins have insecticidal activity that is probably mediated through their ability to bind carbohydrates. To examine the influence of sugars on the insecticidal activity of a lectin from Talisia esculenta seeds (TEL), the lectin was mixed with mannose, glucose, or mannose plus glucose. Mannose abolished the insecticidal activity. Affinity chromatography showed that TEL bound to midgut proteins of the insect Callosobruchus maculatus. Immunoblotting showed that TEL recognized some proteins, probably glycoproteins, present in the midgut membrane of this insect. The principal proteases responsible for digestive proteolysis in fourth instar larvae of C. maculatus were purified by chromatography on activated thiol-Sepharose. These purified proteases were unable to digest TEL after a 15-h incubation. These results suggest that the insecticidal activity of TEL involves a specific carbohydrate-lectin interaction with glycoconjugates on the surface of digestive tract epithelial cells, as well as binding to assimilatory glycoproteins present in midgut extracts and resistance to enzymatic digestion by cysteine proteinases.

Animals↗
PubMed1993

Development of recombinant viral insecticides by expression of an insect-specific toxin and insect-specific enzyme in nuclear polyhedrosis viruses.

As supplements to classical chemical insecticides, two approaches to develop recombinant baculovirus insecticides are described. In one approach an insect-specific toxin is expressed leading to a dramatic reduction in time to death. In the second approach an insect juvenile hormone esterase is expressed which leads to a reduction in feeding. Modifications of the wildtype esterase led to viruses which reduced the time to death as effectively as did the toxin-expressing virus. In both cases existing recombinant viruses are viewed as leads, and approaches to further improvement in the engineered viruses are suggested. Many of these approaches are based on analogy with the development of classical synthetic insecticides. Using these viruses as examples, the potential utility and limitations of recombinant viruses and other biological insecticides are discussed.

Amino Acid Sequence↗
PubMed2005

Baculoviral polyhedrin-Bacillus thuringiensis toxin fusion protein: a protein-based bio-insecticide expressed in Escherichia coli.

Previously, we found that baculoviral polyhedrin (Polh) used as a fusion partner for recombinant expression in Escherichia coli showed almost the same characteristics (rapid solubilization under alkaline conditions and specific degradation by specific alkaline proteases in insect midgut) as the native baculoviral Polh, and formed easily isolatable inclusion bodies. Here, Polh derived from the Autographa californica nuclear polyhedrosis virus (AcNPV) was fused with a Bacillus thuringiensis (Bt) toxin protein (truncated Cry1Ac having toxin region as a model Bt toxin) for the novel generation of a new bio-insecticide. The Polh-Cry1Ac fusion protein (approximately 99 kDa) was highly expressed (3.6-fold induction as compared to E. coli-derived single Cry1Ac (approximately 68 kDa)) as an insoluble inclusion body fraction in E. coli. Trypsin and alpha-chymotrypsin, which have similar properties to the insect midgut alkaline proteases, rapidly degraded the Polh portion in vitro, leaving only the toxic Cry1Ac protein behind. In vivo, the Polh-Cry1Ac fusion protein showed high insecticidal activity against the pest, Plutella xylostella. Because this novel bio-insecticide employs E. coli as the host, mass production at a low cost should be possible. Also, since this is a protein-based insecticide, living modified organism (LMO) issues such as environmental and ecological safety can be avoided.

Animals↗
PubMed1978

Field desorption mass spectrometric analysis of organic compound residues in the environment. I--Organochlorine insecticides.

Field desorption mass spectrometry is applied to the positive identification of organochlorine insecticides and their related compounds residing in field soil environment. Additionally, standard field desorption mass spectra of these compounds are presented. Soil samples were collected in lettuce and spinach fields, and insecticides were extracted, cleaned up, and separated with thin-layer chromatography. Residue levels were measured by injecting the extract into a gas chromatography equipped with an electron capture detector. Residues of p,p'-DDT and dieldrin in field soil samples were clearly identified by field desorption mass spectrometry using the emitter dipping method. Moreover, mixed residues of these insecticides were simultaneously confirmed. However, residues of insecticides and their related compounds other than p,p'-DDT and dieldrin could not be characterized. All spectra of standard showed prominent [M].+, [M(35Cl(n-1), 37Cl)].+ and [M(35Cl(n-2, 37Cl2)].+ ions, and the [M(35Cl(n-1), 37Cl)].+ ion was the base peak in all spectra obtained.

Chromatography, Gas↗
PubMed2006

Binding of acetylcholinesterase to multiwall carbon nanotube-cross-linked chitosan composite for flow-injection amperometric detection of an organophosphorous insecticide.

A novel method for immobilization of acetylcholinesterase (AChE) by binding covalently to a cross-linked chitosan-multiwall carbon nanotube (MWNT) composite is described. In addition a sensitive, fast, cheap and automatizable flow injection detection of an organophosphorous insecticide was developed. The MWNTs were homogeneously distributed in the chitosan membrane which showed a homogeneous porous structure. The immobilized AChE could catalyze the hydrolysis of acetylthiocholine with a K(M)app value of 177 microM to form thiocholine, which was then oxidized to produce detectable signal in a linear range of 1.0-500 microM and fast response. MWNTs could catalyze the electrooxidation of thiocholine, thus increasing detection sensitivity. Based on the inhibition of an organophosphorous insecticide on the enzymatic activity of AChE, using Sulfotep as a model compound, the conditions for the flow-injection detection of the insecticide were optimized. Both biocompatibility of chitosan and inherent conductive properties of MWNTs favored the detection of the insecticide from 1.5 to 80 microM along with good stability and reproducibility. 95 % reactivation from inhibited AChE could be regenerated by using 2-pyridinealdoxime methiodide within 15 min for 15 times. The detection of Sulfotep samples exhibited satisfactory results. The proposed flow-injection analysis device can be applied to automated determination and characterization of enzyme inhibitors.

Acetylcholinesterase↗
PubMed2006

Solution structure of the plant defensin VrD1 from mung bean and its possible role in insecticidal activity against bruchids.

Vigna radiata plant defensin 1 (VrD1) is the first reported plant defensin exhibiting insecticidal activity. We report herein the nuclear magnetic resonance solution structure of VrD1 and the implication on its insecticidal activity. The root-mean-square deviation values are 0.51 +/- 0.35 and 1.23 +/- 0.29 A for backbone and all heavy atoms, respectively. The VrD1 structure comprises a triple-stranded antiparallel beta-sheet, an alpha-helix, and a 3(10) helix stabilized by four disulfide bonds, forming a typical cysteine-stabilized alphabeta motif. Among plant defensins of known structure, VrD1 is the first to contain a 3(10) helix. Glu26 is highly conserved among defensins; VrD1 contains an arginine at this position, which may induce a shift in the orientation of Trp10, thereby promoting the formation of this 3(10) helix. Moreover, VrD1 inhibits Tenebrio molitor alpha-amylase. Alpha-amylase has an essential role in the digestion of plant starch in the insect gut, and expression of the common bean alpha-amylase inhibitor 1 in transgenic pea imparts complete resistance against bruchids. These results imply that VrD1 insecticidal activity has its basis in the inhibition of a polysaccharide hydrolase. Sequence and structural comparisons between two groups of plant defensins having different specificity toward insect alpha-amylase reveal that the loop between beta2 and beta3 is the probable binding site for the alpha-amylase. Computational docking experiments were used to study VrD1-alpha-amylase interactions, and these results provide information that may be used to improve the insecticidal activity of VrD1.

Amino Acid Sequence↗
PubMed2006

Insecticide resistance in vector mosquitoes in China.

Because of their special behaviour, physiology and close relationship with humans, mosquitoes act as one of the most important vectors of human diseases, such as filariasis, Japanese encephalitis, dengue and malaria. The major vector mosquitoes are members of the Culex, Aedes and Anopheles genera. Insecticides play important roles in agricultural production and public health, especially in a country with a huge human population, like China. Large quantities of four classes of insecticides, organochlorines, organophosphates, carbamates and pyrethroids, are applied annually to fields or indoors in China, directly or indirectly bringing heavy selection pressure on vector populations. The seven major species of vector mosquito in China are the Culex pipiens L. complex, C. tritaeniorhynchus Giles, Anopheles sinensis Wied., A. minimus Theobald, A. anthropophagus Xu & Feng, Aedes albopictus (Skuse) and Ae. aegypti L., and all have evolved resistance to all the above types of insecticide except the carbamates. The degree of resistance varies among mosquito species, insecticide classes and regions. This review summarizes the resistance status of these important vector mosquitoes, according to data reported since the 1990s, in order to improve resistance management and epidemic disease control, and to communicate this information from China to the wider community.

Animals↗
PubMed2002

Stimulating effects of the insecticide chlorpyrifos on host searching and infestation efficacy of a parasitoid wasp.

Hymenopterous parasitoids play an important role in the control of insect populations. During oviposition, Hymenopterous parasitoids use cues such as odours from their environment to locate their specific host. Leptopilina heterotoma (parasitoid of Drosophila larvae) locate their host by probing the substrate with the ovipositor. This behaviour can be induced by the odour of the host substrate alone. We analysed the sub-lethal effects of chlorpyrifos at LD20 on the probing activity in response to a fruit odour (banana). The insecticide increased the percentage of females spontaneously probing in response to the odour. Parasitoid females were then conditioned to associate banana odour with the oviposition in host larvae. This conditioning enables parasitoids to memorize the odour and to increase their probing response to this odour. During the olfactory conditioning, females exposed to the insecticide found and oviposited in host larvae more quickly than control females. One hour after the olfactory conditioning, females exposed to the insecticide presented a higher increase of their probing response to the odour than controls. Twenty-four hours after conditioning, the stimulation produced by chlorpyrifos was no longer perceptible, but the level of response of conditioned females was still higher than that of non-conditioned females, showing that odour memory was not impaired by the insecticide treatment. These sub-lethal effects, that stimulate host searching by parasitoids without impairing odour memorization, could increase their parasitic efficiency.

Animals↗
PubMed2003

Synthesis and insecticidal activity of benzoheterocyclic analogues of N'-benzoyl-N-(tert-butyl)benzohydrazide: Part 1. Design of benzoheterocyclic analogues.

The N'-benzoyl group of N-tert-butyl-N'-benzoyl-3,5-dimethylbenzohydrazide (1) was converted to a series of benzoheterocyclecarbonyl groups in order to investigate the potential usefulness of superimposing a hydrazine insecticide on 20-hydroxyecdysone. A series of analogues with benzodioxole, benzodioxane, benzodioxapine, indole, benzoxazole, benzoxazine or benzothiazole instead of the phenyl group of (1) were synthesized and tested for their insecticidal activity against the common cutworm (Spodoptera litura F). N-tert-Butyl-N'-(3,5-dimethylbenzoyl)-1,3-benzodioxole-5-carbohydrazide and N-tert-butyl-N'-(3,5-dimethylbenzoyl)-2,3-dihydro-1,4-benzodioxine-6-carbohydrazide showed high insecticidal activities, superior to that of (1) and equal to that of the commercial insecticide tebufenozide (RH-5992).

Animals↗
PubMed2003

Relative effects of the insecticide thiamethoxam on the predator Podisus nigrispinus and the tobacco whitefly Bemisia tabaci in nectaried and nectariless cotton.

The predaceous stinkbug Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) feeds on plants as well as on arthropod prey. The question arises whether feeding on plants might expose the predator to systemic insecticide via ingestion of the active ingredient or its metabolites through plant sap of treated plants. This interaction was investigated with nectaried and nectariless cotton plants cropped in pots and treated with the systemic insecticide thiamethoxam at 0.5, 1.0 and 2.0 mg per plant as a root drench. Development of P. nigrispinus fed on prey and on treated nectaried and nectariless cotton plants and confined at 15, 30 and 45 days after insecticide application, and adult reproduction from nymphs caged 30 days after treatment were determined. Podisus nigrispinus life history traits were unaffected by the type of cotton plant, nectaried or nectariless, but were significantly affected by insecticide dose and time after application. Developmental time was extended and fresh adult body weight was reduced by feeding on prey and treated plants. Nymphs caged on treated plants with the highest thiamethoxam concentration at 15 days after application produced only 13.2% of adults. Females emerged from nymphs caged on both plants and at all thiamethoxam concentrations at day 30 after application presented similar reproductive characteristics, except for age of first oviposition, which was delayed on plants treated with the highest thiamethoxam concentration. Thiamethoxam at 0.5 mg per plant restrained tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) colonization only during the first 15 days after application to either cotton plant, and similar immature densities were sampled at day 35 after application on treated and untreated plants. However, plants treated with 1.0 and 2.0 mg per plant as a drench and cropped in pots were protected from tobacco whitefly for up to 45 days after exposure to a whitefly colony.

Animals↗
PubMed2004

Fate of the insecticide lambda-cyhalothrin in ditch enclosures differing in vegetation density.

Use of the insecticide lambda-cyhalothrin in agriculture may result in the contamination of water bodies, for example by spray drift. Therefore, the possible exposure of aquatic organisms to this insecticide needs to be evaluated. The exposure of the organisms may be reduced by the strong sorption of the insecticide to organic materials and its susceptibility to hydrolysis at the high pH values in the natural range. In experiments done in May and August, formulated lambda-cyhalothrin was mixed with the water body of enclosures in experimental ditches containing a bottom layer and macrophytes (at different densities) or phytoplankton. Concentrations of lambda-cyhalothrin in the water body and in the sediment layer, and contents in the plant compartment, were measured by gas-liquid chromatography at various times up to 1 week after application. Various water quality parameters were also measured. Concentrations of lambda-cyhalothrin decreased rapidly in the water column: 1 day after application, 24-40% of the dose remained in the water, and by 3 days it had declined to 1.8-6.5%. At the highest plant density, lambda-cyhalothrin residue in the plant compartment reached a maximum of 50% of the dose after 1 day; at intermediate and low plant densities, this maximum was only 3-11% of the dose (after 1-2 days). The percentage of the insecticide in the ditch sediment was 12% or less of the dose and tended to be lower at higher plant densities. Alkaline hydrolysis in the water near the surface of macrophytes and phytoplankton is considered to be the main dissipation process for lambda-cyhalothrin.

Chromatography, Gas↗
PubMed1998

Osmotic effects as a factor modifying insecticide toxicity on Aedes and Artemia.

Euryhaline species are more tolerant of various insecticides under isosmotic conditions. Two euryhaline species, Aedes taeniorhynchus (Wiedemann) and Artemia sp., were exposed to four insecticides (aldicarb, dimethoate, imidacloprid, tebufenozide), under isosmotic and hyperosmotic conditions. Mortality under these two osmotic conditions was observed and compared to evaluate salinity as a contributing factor to insecticide toxicity. Artemia was more tolerant of all chemicals tested than A. taeniorhynchus under isosmotic conditions based on the percentage mortality observed. Mortality of Artemia under isosmotic conditions was dependent on the length of exposure; A. taeniorhynchus did not exhibit time dependence. Less mortality was observed in populations of both test species under isosmotic conditions compared with hyperosmotic conditions. However, the variation in mortality due to exposure to test chemicals was of greater magnitude in A. taeniorhynchus than Artemia. This result indicates that higher salinity is a greater stress on A. taeniorhynchus than Artemia when exposed to the test insecticides at the concentration ranges tested in this study.

Aedes↗
PubMed2000

Potential of the insecticides acephate and methamidophos to contaminate groundwater.

The possible contamination of groundwater by the insecticides acephate and methamidophos was assessed using the behavior assessment model (BAM) and the groundwater pollution-potential model (GWP). The dissipation coefficients of the two insecticides in two soils (Annei silt loam and Pingchen silt clay loam) at different moisture contents (50 and 100% field capacity) and soil temperatures (20 and 30 degrees C) were studied by determining the degradation and adsorption of each insecticide in the soil. The movement of acephate and methamidophos was studied by leaching each insecticide in a soil column in the laboratory. The absorption coefficient of methamidophos was much higher than that of acephate in both types of soil. In the leaching test, methamidophos more easily leached out from the Pingchen soil column than from the Annei soil column. Methamidophos was rapidly degraded, with a half-life of 1.11 to 1.61 days in the Annei soil and 7.50 to 13.20 days in the Pingchen soil at different temperatures and soil water contents. Acephate was found to have a longer half-life than methamidophos in soil; however, the mobility of methamidophos in both soils was slower than that of acephate. The mobility of acephate in soil is somewhat faster than that of methamidophos, and thus acephate may lead to the contamination of groundwater much more easily than methamidophos under normal conditions.

Adsorption↗
PubMed2001

Evaluation of chronic exposure of the male rat reproductive system to the insecticide methomyl.

Carbamate insecticides are widely used in industry, agriculture and for public health purposes. Numerous incidents of acute carbamate poisoning have resulted from inhalation of sprays or contamination of crops or food. This work was conducted to study the effect of chronic exposure to methomyl on hormonal, histopathological and histochemical changes in rat testes. The treated group received methomyl orally (17 mg kg(-1)in saline) daily for 2 months, while the control group received saline. A significant decrease in the level of testosterone was observed in the intoxicated animals, while the levels of FSH, LH and prolactin were significantly increased. Histopathological studies of the intoxicated rat testes revealed variable degrees of degenerative changes in the seminiferous tubules up to total cellular destruction. As regards the histochemical results, it was found that both acid phosphatase and alpha esterase enzyme activity was significantly increased compared to the control group. On the other hand succinic dehydrogenase enzyme activity was significantly reduced. No significant change was observed in alkaline phosphatase enzyme activity. The hormonal changes and testicular damage continued for 30 days after withdrawal of the insecticide indicating a persistent effect. From the above-mentioned findings, it has been concluded that chronic exposure to methomyl insecticide has deleterious effects on rat testes. Therefore application of such insecticide should be limited to a designed program with special care in handling to limit or minimize its hazards.

Acid Phosphatase↗