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PubMed1993

Cocaine as a naturally occurring insecticide.

Although cocaine has a fascinating and complex medicinal history in man, its natural function in plants is unknown. The present studies demonstrate that cocaine exerts insecticidal effects at concentrations which occur naturally in coca leaves. Unlike its known action on dopamine reuptake in mammals, cocaine's pesticidal effects are shown to result from a potentiation of insect octopaminergic neurotransmission. Amine-reuptake blockers of other structural classes also exert pesticidal activity with a rank order of potency distinct from that known to affect vertebrate amine transporters. These findings suggest that cocaine functions in plants as a natural insecticide and that octopamine transporters may be useful sites for targeting pesticides with selectivity toward invertebrates.

Animals↗

PubMed1994

Tight genetic linkage between the kdr insecticide resistance trait and a voltage-sensitive sodium channel gene in the house fly.

The kdr insecticide resistance trait in the house fly, Musca domestica, confers resistance to the rapid paralysis (knockdown) and lethal effects of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and pyrethroids. Flies with the kdr trait exhibit reduced neuronal sensitivity to these compounds, which are known to act at voltage-sensitive sodium channels of nerve membranes. To test the hypothesis that a mutation in a voltage-sensitive sodium channel gene confers the kdr phenotype, we have cloned genomic DNA corresponding to a segment of the house fly homologue of the para sodium channel gene of Drosophila melanogaster, identified restriction-site polymorphisms within this segment between the kdr strain 538ge and an inbred insecticide-susceptible lab stain, and developed a sensitive polymerase chain reaction-based diagnostic procedure to determine the sodium channel genotype of individual flies. A genetic linkage analysis performed with these molecular markers shows that the kdr trait is tightly linked (within about 1 map unit) to the voltage-sensitive sodium channel gene segment exhibiting the DNA sequence polymorphism. These findings provide genetic evidence for a mutation at or near a voltage-sensitive sodium channel gene as the basis for kdr resistance.

Amino Acid Sequence↗

PubMed1996

Fipronil insecticide: novel photochemical desulfinylation with retention of neurotoxicity.

Fipronil is an outstanding new insecticide for crop protection with good selectivity between insects and mammals. The insecticidal action involves blocking the lambda-aminobutyric acid-gated chloride channel with much greater sensitivity of this target in insects than in mammals. Fipronil contains a trifluoromethylsulfinyl moiety that is unique among the agrochemicals and therefore presumably important in its outstanding performance. We find that this substituent unexpectedly undergoes a novel and facile photoextrusion reaction on plants upon exposure to sunlight, yielding the corresponding trifluoromethylpyrazole, i.e., the desulfinyl derivative. The persistence of this photoproduct and its high neuroactivity, resulting from blocking the lambda-aminobutyric acid-gated chloride channel, suggest that it may be a significant contributor to the effectiveness of fipronil. In addition, desulfinylfipronil is not a metabolite in mammals, so the safety evaluations must take into account not only the parent compound but also this completely new environmental product.

Animals↗

PubMed1997

Disruption of lysosomal targeting is associated with insecticidal potency of juvenile hormone esterase.

Juvenile hormone esterase (JHE; EC 3.1.1.1), which is intrinsically involved in regulation of development of some insect larvae, is rapidly removed from the hemolymph by the pericardial cells. Lys-29 and Lys-524, which are implicated in the degradation of JHE, were mutated to Arg. Neither the half-life of the modified JHE in the hemolymph nor the catalytic parameters were changed significantly, but when combined, these mutations resulted in apparent failure of lysosomal targeting in the pericardial cell complex. A hypothesis for the mechanism of reduced efficiency of lysosomal targeting is presented. Infection of larvae with a recombinant baculovirus expressing the modified JHE resulted in a 50% reduction in feeding damage compared with larvae infected with the wild-type virus, thus demonstrating improved properties as a biological insecticide. These data demonstrate that alteration of specific residues of JHE that disrupted lysosomal targeting, dramatically increased the insecticidal activity of this protein.

Animals↗

PubMed2001

Functional significance of the beta hairpin in the insecticidal neurotoxin omega-atracotoxin-Hv1a.

omega-Atracotoxin-Hv1a is an insect-specific neurotoxin whose phylogenetic specificity derives from its ability to antagonize insect, but not vertebrate, voltage-gated calcium channels. In order to help understand its mechanism of action and to enhance its utility as a lead compound for insecticide development, we used a combination of protein engineering and site-directed mutagenesis to probe the toxin for key functional regions. First, we constructed a Hairpinless mutant in which the C-terminal beta-hairpin, which is highly conserved in this family of neurotoxins, was excised without affecting the fold of the residual disulfide-rich core of the toxin. The Hairpinless mutant was devoid of insecticidal activity, indicating the functional importance of the hairpin. We subsequently developed a highly efficient system for production of recombinant toxin and then probed the hairpin for key functional residues using alanine-scanning mutagenesis followed by a second round of mutagenesis based on initial "hits" from the alanine scan. This revealed that two spatially proximal residues, Asn(27) and Arg(35), form a contiguous molecular surface that is essential for toxin activity. We propose that this surface of the beta-hairpin is a key site for interaction of the toxin with insect calcium channels.

Amino Acid Sequence↗

PubMed2002

Oxyopinins, large amphipathic peptides isolated from the venom of the wolf spider Oxyopes kitabensis with cytolytic properties and positive insecticidal cooperativity with spider neurotoxins.

Five amphipathic peptides with antimicrobial, hemolytic, and insecticidal activity were isolated from the crude venom of the wolf spider Oxyopes kitabensis. The peptides, named oxyopinins, are the largest linear cationic amphipathic peptides from the venom of a spider that have been chemically characterized at present. According to their primary structure Oxyopinin 1 is composed of 48 amino acid residues showing extended sequence similarity to the ant insecticidal peptide ponericinL2 and to the frog antimicrobial peptide dermaseptin. Oxyopinins 2a, 2b, 2c, and 2d have highly similar sequences. At least 27 out of 37 amino acid residues are conserved. They also show a segment of sequence similar to ponericinL2. Circular dichroism analyses showed that the secondary structure of the five peptides is essentially alpha-helical. Oxyopinins showed disrupting activities toward both biological membranes and artificial vesicles, particularly to those rich in phosphatidylcholine. Electrophysiological recordings performed on insect cells (Sf9) showed that the oxyopinins produce a drastic reduction of cell membrane resistance by opening non-selective ion channels. Additionally, a new paralytic neurotoxin named Oxytoxin 1 was purified from the same spider venom. It contains 69 amino acid residue cross-linked by five disulfide bridges. Application of mixtures containing oxyopinins and Oxytoxin 1 to insect larvae showed a potentiation phenomenon, by which an increase lethality effect is observed. These results suggest that the linear amphipathic peptides in spider venoms and neuropeptides cooperate to capture insects efficiently.

Amino Acid Sequence↗

PubMed2007

Knockdown of aminopeptidase-N from Helicoverpa armigera larvae and in transfected Sf21 cells by RNA interference reveals its functional interaction with Bacillus thuringiensis insecticidal protein Cry1Ac.

Aminopeptidase-N (APN) and cadherin proteins located at the midgut epithelium of Helicoverpa armigera have been implicated as receptors for the Cry1A subfamily of insecticidal proteins of Bacillus thuringiensis. Ligand blot analysis with heterologously expressed and purified H. armigera Bt receptor with three closely related Cry1A proteins tentatively identified HaAPN1 as an interacting ligand. However, to date there is no direct evidence of APN being a functional receptor to Cry1Ac in H. armigera. Sf21 insect cells expressing HaAPN1 displayed aberrant cell morphology upon overlaying with Cry1Ac protein. Down-regulating expression of HaAPN1 by RNA interference using double-stranded RNA correlated with a corresponding reduction in the sensitivity of HaAPN1-expressing cells to Cry1Ac protein. This clearly establishes that insect cells expressing the receptor recruit sensitivity to the insecticidal protein Cry1Ac, and their susceptibility is directly dependent on the amount of HaAPN1 protein expressed. Most importantly, silencing of HaAPN1 in H. armigera in vivo by RNA interference resulted in reduced transcript levels and a corresponding decrease in the susceptibility of larvae to Cry1Ac. BIAcore analysis of HaAPN1/Cry1Ac interaction further established HaAPN1 as a ligand for Cry1Ac. This is the first functional demonstration of insect aminopeptidase-N of H. armigera being a receptor of Cry1Ac protein of B. thuringiensis.

Animals↗

PubMed1996

Effects of carbamate insecticides in a rat medium-term bioassay for hepatocarcinogens.

Ethiofencarb and pirimicarb, widely used insecticides, were investigated for hepatocarcinogenesis-modifying effects using a medium-term bioassay system for carcinogens. F344 male rats were given a single intraperitoneal injection of diethylnitrosamine (DEN, 200 mg/kg) and then, starting 2 wk later, received ethiofencarb in the diet at concentrations of 500 or 250 ppm, pirimicarb at 400 or 200 ppm, or a combination of ethiofencarb (250 ppm) and pirimicarb (200 ppm) for 6 wk. Control groups received DEN (200 mg/kg) or carbamate insecticides alone as stated earlier, without DEN. All rats were subjected to two-thirds partial hepatectomy at wk 3 and were killed at wk 8. Development of preneoplastic lesions, glutathione S-transferase placental form-positive foci, in the liver was significantly increased in terms of number receiving 500 ppm ethiofencarb. The results thus indicate that ethiofencarb at high dose possesses promoting activity for rat liver carcinogenesis.

Animals↗

PubMed2007

A simple empirical model to predict forest insecticide ground-level deposition from a compendium of field data.

Deposit data from 205 aerial forest insecticide applications conducted in field trials by the Canadian Forest Service, Great Lakes Forestry Centre over a 15-year period are summarized. Deposit measurements were taken under "worst case" scenarios in the sense that direct applications were made over water bodies, and ground samplers were intentionally placed in open or cleared areas of forest. The median % deposit on shoreline collectors (32 separate applications) was 5.7%, on mid-stream collectors (44 separate applications) was 6.2%, and on forest floor collectors (129 separate applications) was 4.9%. Forest floor deposit was most closely associated with application rate and droplet size (r = 0.624, p < 0.001 and r = 0.662, p = 0.011, respectively) but these variables combined only explained 44% of the variation in deposit. Data from all three collector types were grouped by 10% deposit increments and combined to provide a data set from all deposition scenarios. A negative exponential model was fitted to the proportion of these combined sites regressed on % deposit in 10% increments and plotted as a deposit probability distribution curve (p < 0.001, r2 = 0.992). The probability distribution curve indicated that 5-10% deposit would be expected about 57-91% of the time, whereas 50% deposit or greater would be expected about 2% of the time or less. In a probabilistic risk assessment for aerially applied insecticides in a conifer-dominated forest environment, the probability distribution curve based on empirical data presented here can be used to refine the characterization of exposure scenarios from which effects estimates can be derived.

Environmental Monitoring↗

PubMed1976

The evaluation of a radio gas-chromatographic system for the detection of trace amounts of labelled insecticides.

A radio gas-chromatographic system consisting of a gas chromatograph, combustion furnace, proportional counter and guard scintillation counter has been studied for the analysis of trace amounts of 14C-labelled organophosphorus insecticides. The proportional detector is a concentration sensitive detector requiring strict flow control. Sensitivity depends on the concentration of the quenching gas used. Using 14C-ethyl parathion and 14C-metamidophos as model compounds a linear range of 3500-5000 was measured. A sensitivity of 0.98 cpm/pCi and a detection limit of 24pCi were obtained which allows the detection of 0.33 ng if the specific activity of the insecticide is 21.5 mCi/mMol. The system must be decontaminated in order to achieve optimum detection levels by passage of oxygen through the combustion tube and by periodically injecting the corresponding non-labelled compound into the column. A solvent effect was found to interfere in the analysis due to the sudden production and expansion of CO2. This effect was eliminated by choosing column conditions to prevent elution near the solvent. The system was tested by analyzing a mixture of 37 ppb and 23 ppb of ethyl parathion and its oxygen analog in orange juice.

Chemical Phenomena↗

PubMed1981

Detection of incipient effects of anticholinesterase insecticides in rats and humans by electromyography and cholinesterase assay.

Rats, fed low levels of diazinon (0.5 and 5.0 mg/kg) and parathion (0.1, 0.5 and 1.0 mg/kg) daily for 26 weeks, and agricultural workers chronically exposed to anticholinesterase insecticides, were monitored by electromyographic (EMG) and blood cholinesterase determinations. The two diazinon-fed and the highest parathion-fed groups of rats gained less weight, whereas the lowest parathion-fed group gained more weight than the control; rats fed 0.5 mg/kg parathion daily did not show any difference in weight gain when compared to the control. In addition, the two diazinon-fed groups of rats gained significantly less weight than the three parathion-fed groups. Both erythrocyte acetylcholinesterase (AChE) and plasma cholinesterase (ChE) activities were severely inhibited in the treated groups. However, parathion inhibited ChE much less than diazinon, and slight recovery of both enzymes was evident in the parathion-treated groups. No changes in amplitudes of EMGs were observed in the treated rats. Agricultural workers were examined monthly during one growing season. Although there was high variation in the data, EMG amplitudes and AChE levels were lower in the workers than in persons not exposed to pesticides; ChE levels were statistically different only once. These results have demonstrated that the rat is not suitable for investigating the use of EMG as a method for monitoring exposure to anticholinesterase insecticides, but that EMG (or AChE) may be used to monitor such exposures in humans.

Acetylcholinesterase↗

PubMed1982

Effect and mechanism of action of methomyl and cypermethrin insecticides on kynurenine metabolizing enzymes of mouse liver.

The effect of methomyl and cypermethrin insecticides on the B6-dependent kynurenine hydrolase (KH) and kynurenine aminotransferase (KATE) was studied. These insecticides induced pronounced inhibition on the (KH) and (KATE) enzymes after single dose treatment. Repeated doses of methomyl induced inhibition on the (KH) and (KATE) activities, whereas repeated treatment with cypermethrin had no effect on the activities of these enzymes. In vitro methomyl inhibited (KH) and (KATE) enzymes at 10(-6)M up to 10(-3)M, through a competitive mechanism. Methomyl and cypermethrin are capable of causing alterations in the kynurenine metabolizing enzymes of mouse liver.

Animals↗

PubMed1983

Development of insecticidal cyclic phosphoryl compounds through chemical and biochemical approaches.

Chemical and biochemical studies on three types of cyclic phosphoryl compounds are discussed in connection with the development of insecticides. They are five-membered cyclic phosphoramidates (I), six-membered cyclic phosphates (II) and bridged bicyclic phosphates (III). Development of I has started from the finding of L-leucine as a neuroactive substance in silkworm blood, followed by its combination with chemically active five-membered cyclic phosphates. Studies on the metabolism of neurotoxic tri-o-tolyl phosphate caused the invention of the insecticide salithion in the series of II. Salithion was chemically converted into its thiolo isomers, which is a convenient phosphorylating agent useful to synthesize biologically interesting phosphate esters. III does not inhibit acetylcholin-esterase but acts as an anti-GABA agent.

Amino Acids↗

PubMed1990

Effects of some insecticides on several enzymes of tryptophan metabolism in rats.

The activities of tryptophan 2,3-dioxygenase (EC 1.13.11.11), indoleamine 2,3-dioxygenase (EC 1.13.11.17), kynurenine 3-hydroxylase (EC 1.14.13.9), kynureninase (EC 3.7.1.3), kynurenine transaminases, and pyridoxal phosphokinase (EC 2.7.1.35) in the liver, kidney and lung rats were measured after administration of a single dose and repeated doses of dimethoate, carbaryl and fenvalerate, respectively. Ten percent LD50 of each insecticide was orally administered to a rat for a single dose, while 5% LD50 was orally given for five consecutive days as repeated doses. The control animals received the same volume of vehicle (polyethylene glycol 300). Body weight and organs weight losses were recognized only after repeated doses of dimethoate, while protein content remained constant compared to control animals. Repeated administration of dimethoate caused significant decrease in the activity of kynurenine 3-hydroxylase (28.3% decrease in liver, and 32.5% in kidney), kynurenine-pyruvate transaminase (EC 2.6.1.7) (40% in liver, and 24.2% in kidney), kynurenine- pyruvate transaminase (EC 2.6.1-) (24.5% in kidney) and pyridoxal phosphokinase (36.1% in liver). Repeated doses of carbaryl resulted in a significant decrease in the activity of apo-tryptophan 2,3-dioxygenase (42.8%), kynurenine-2-oxoglutarate transaminase (40% in liver), kynurenine-pyruvate transaminase (30.6% in liver), and serine-glyoxylate transaminase (EC 2.6.1.51) (47.9% in liver). Externally added insecticides at different concentrations to the incubation mixture resulted in an inhibition to tryptophan 2,3-dioxygenase, while the other enzymes examined showed no change in their activities.

Animals↗

PubMed1995

Organophosphate insecticide degradation by non-amended and cupric ion-amended Fenton's reagent in aqueous solution.

Improper treatment and disposal of pesticide-contaminated wastewaters raise concerns for soil and water contamination. Based on the pilot studies described here, chemical treatment via Fenton's reagent (ferrous ion plus hydrogen peroxide) of three organophosphorus insecticides in aqueous solution appears promising. Results show that the Fenton dark reaction degrades methyl parathion, malathion, and methamidophos, and in many cases their breakdown products as well. Addition of cupric ion greatly accelerates insecticide disappearance. To maximize degradation, further studies of the influence of 1) pesticide structure, 2) reagent ratios, and 3) breakdown product competition on reaction rates are necessary.

Copper↗

PubMed1997

Treatment of two insecticides in an electrochemical Fenton system.

The ability of an electrochemical Fenton system to degrade the organophosphorous insecticides malathion and methyl parathion was studied. A combination of hydrogen peroxide and electrochemically-generated iron was found to be successful in degrading the two insecticides, and optimization of the system was pursued. Augmentation with near UV light at an intensity of 1.67 x 10(17) quanta/sec and centered at a wavelength of 370 nm improved the degradation of malathion at low iron concentrations but did not affect other treatments. Adding the hydrogen peroxide slowly over the course of treatment rather than all at once at the beginning of each treatment did, however, greatly improve the system. Removal efficiencies of 98.0% or greater were achieved for both pesticides.

Carbon Dioxide↗

PubMed1998

Mother's milk protein profile, a possible biomarker for human exposure to persistent insecticides.

The electrophoretic protein profile and residue levels of selected persistent insecticides were investigated in 160 mother's milk samples representing 20 different locations in Egypt. Nine major protein bands were detected in all of the samples. These protein bands were designated as lactoferrin, albumin, SIgA heavy chain, casein I, casein II, SIgA light chain, casein III, lysozyme and alpha-lactalbumin. Residue levels of DDT and its metabolites as well as lindane and its other hexachlorocyclohexane isomers were determined using electron capture gas chromatography and confirmed by gas chromatography/mass spectrometric analysis. Samples containing relatively higher residue levels of the DDT group (DDT, DDE and DDD) showed significant effects on the levels of lysozyme and alpha-lactalbumin bands relative to samples with low or no residue levels. On the other hand, the casein subunits were mostly affected by the residue levels of hexachlorocyclohexane isomers (alpha, beta, gamma and delta isomers). The two patterns showed characteristic dose response correlation suggesting that the protein profile of human milk may serve as a quick biomarker for exposure to persistent insecticides.

Albumins↗

PubMed2006

Two new insecticidal sesquiterpene polyol esters from Celastrus angulatus.

Two new insecticidal sesquiterpene polyol esters with a beta-dihydroagarofuran sesquiterpene skeleton, celangulatin A (1), B (2), and two known compounds, celangulin IV (3) and V (4), were isolated from the leaves of Celastrus angulatus by bioassay-guided fractionation. Their chemical structures were elucidated mainly by analyses of the NMR and MS spectral data. Their insecticidal activities against Mythimna separate were demonstrated with the KD50 value of 68.5 and 215.8 microg g(-1), respectively.

Animals↗