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PubMed2005

The X-ray structure of a hemipteran ecdysone receptor ligand-binding domain: comparison with a lepidopteran ecdysone receptor ligand-binding domain and implications for insecticide design.

The ecdysone receptor is a hormone-dependent transcription factor that plays a central role in regulating the expression of vast networks of genes during development and reproduction in the phylum Arthropoda. The functional receptor is a heterodimer of the two nuclear receptor proteins ecdysone receptor (EcR) and ultraspiracle protein. The receptor is the target of the environmentally friendly bisacylhydrazine insecticides, which are effective against Lepidoptera but not against Hemiptera or several other insect orders. Here we present evidence indicating that much of the selectivity of the bisacylhydrazine insecticides can be studied at the level of their binding to purified ecdysone receptor ligand-binding domain (LBD) heterodimers. We report the crystal structure of the ecdysone receptor LBD heterodimer of the hemipteran Bemisia tabaci (Bt, sweet potato whitefly) in complex with the ecdysone analogue ponasterone A. Although comparison with the corresponding known LBD structure from the lepidopteran Heliothis virescens (Hv) ecdysone receptor revealed the overall mode of ponasterone A binding to be very similar in the two cases, we observed that the BtEcR ecdysteroid-binding pocket is structured differently to that of HvEcR in those parts that are not in contact with ponasterone A. We suggest that these differences in the ligand-binding pocket may provide a molecular basis for the taxonomic order selectivity of bisacylhydrazine insecticides.

Amino Acid Sequence↗
PubMed2004

Genetic diversity and insecticide resistance of Myzus persicae (Hemiptera: Aphididae) populations from tobacco in Chile: evidence for the existence of a single predominant clone.

The tobacco-feeding race of Myzus persicae (Sulzer), formerly known as M. nicotianae Blackman, was introduced into Chile during the last decade. In order to evaluate the genetic diversity and insecticide resistance status of Chilean tobacco aphid populations, a field survey was conducted in 35 tobacco fields covering a 300 km latitudinal survey. The populations sampled were characterized using microsatellite markers and morphometric multivariate analysis. Insecticide resistance levels were assessed through a microplate esterase assay and the mutation status of the kdr gene. All samples collected corresponded to the same anholocyclic aphid genotype, and showed morphological variation within the range expected for the tobacco-feeding race of M. persicae. Esterase activity showed the level and variability expected for an R1 clone lacking mutations in the sodium channels (susceptible kdr), thus corresponding to a type slightly resistant to organophosphate and carbamate, and susceptible to pyrethroid insecticides.

Animals↗
PubMed2005

Reduced response of insecticide-resistant aphids and attraction of parasitoids to aphid alarm pheromone; a potential fitness trade-off.

Response to the alarm pheromone, (E)-beta-farnesene, produced by many species of aphids, was assessed in laboratory bioassays using an aphid pest, Myzus persicae (Sulzer), and its primary endoparasitoid, Diaeretiella rapae (McIntosh). This was done in three separate studies, the first investigating responses of a large number of M. persicae clones carrying different combinations of metabolic (carboxylesterase) and target site (kdr) insecticide resistance mechanisms, and the other two investigating the responses of young virgin female adult parasitoids. In M. persicae, both insecticide resistance mechanisms were associated with reduced repellence suggesting that each has a pleiotropic effect on aphid behaviour. In contrast, D. rapae females were attracted to the alarm pheromone source. The implications of this apparent fitness trade-off for the evolution and dynamics of insecticide resistance, and the potential for using beneficial insects to combat resistance development are discussed.

Animals↗
PubMedDate not supplied

Termite control and other determinants of high body burdens of cyclodiene insecticides.

Breast milk fat concentrations of three cyclodiene insecticides--dieldrin, heptachlor epoxide, and oxychlordane--were measured in 797 primiparous women, and sources of exposure that contributed significantly to high body burdens were investigated. All three distributions were highly skewed to the right, with median concentrations falling between 0.007 and 0.039 mg/kg. Termite control of residence was associated consistently with being in the high-body-burden group for all three compounds, but the association was greatest for heptachlor. Age, socioeconomic status, residential area, smoking, and home use of insecticides were also associated with high body burden of one or more of the compounds, but the odds ratios were lower than those for termite control; the findings were inconsistent for the three compounds. The results for termite control remained statistically significant when we adjusted for the other factors; therefore, termite control of residence is an important risk factor for cyclodiene insecticide absorption.

Adipose Tissue↗
PubMed1975

Entomopathogens as insecticides.

Entomopathogens, diseases of insects, are suggested as a possible new generation of safe, selective insecticides. Over a thousand pathogens have been isolated from insects. Many of these, associated with major insect pests, are potential candidates for development into microbial insecticides. Phases in the development of a microbial insecticide are discussed as well as factors (production, safety, efficacy, registration, non-technical) which may influence this development.

Bacteria↗
PubMedDate not supplied

Residues of insecticides and fungicides on Ontario-grown vegetables, 1986-1988.

Between 1986 and 1988, 433 composite vegetable samples representing 16 commodities were collected from farm deliveries to the marketplace in Ontario, Canada. All samples were analysed for insecticides and fungicides. The analyses included organochlorine, organophosphorus, synthetic pyrethroid, and N-methylcarbamate insecticides and dithiocarbamate, dicarboximide, and organochlorine fungicides. The commodities tested included asparagus, beans, carrots, celery, cole crops, cucumbers, lettuce, onions, peppers, potatoes, radishes, rutabagas and tomatoes. In 64% of samples, no pesticide residues were identified to the limits of detection which ranged from 0.005 to 0.05 mg/kg. A further 22% had combined insecticide and fungicide residues below 0.1 mg/kg. Most of the positive findings were a fraction of the Maximum Residue Limit permitted for each commodity under the Canadian Food and Drugs Act and Regulation. Three samples (0.7%) had residues that exceeded the MRL. These involved diazinon and parathion on celery and chlorothalonil on peppers. While some commodities had no detectable residues others had measurable residues of up to three separate pesticides. The most were found on celery, lettuce and field tomatoes.

Food Analysis↗
PubMed1979

Occupational effect of phosfolan insecticide on spraymen during field exposure.

Phosfolan (Cyolane), 2-(diethoxy phosphinylimino)-1,3-dithiolane is one of the widely used insecticides in Egypt specially to protect cotton plants. The hazard of exposure of the spray workers team in the field was estimated in terms of the amount of Phosfolan insecticide retained on workmen body pads during field spraying. The health effect of such exposure was determined through recording of the AChE inhibition in the red blood cells at different intervals after exposure. The calculated percentage of the toxic dose received per every spraying day for each worker varied with the type of job in the range of 0.008 to 0.03 percent. The body of the mixer received the maximum exposure with 10 to 12 fold that of the assistants. The highly exposed group of workers suffered from 31 to 44 percent RBC's AChE inhibition. About half of the inhibited enzyme activity recovered after 48 hours. Then it took more than 3-4 weeks to reach complete recovery. Thus the RBC's AChE activity can be recommended as a criterion for the level of exposure to organophosphorous insecticides.

Acetylcholinesterase↗
PubMed1989

Toxic and developmental effects of organophosphorus insecticides in embryos of the South African clawed frog.

Four organophosphorus insecticides and the active metabolites of two phosphorothionate insecticides were tested for their toxic and teratogenic effects on embryos of Xenopus laevis. All compounds caused dose-dependent developmental defects, such as abnormal pigmentation, abnormal gut development, notochordal defects and reduced growth. Malathion, malaoxon, parathion, and paraoxon produced severe defects, while monocrotophos and dicrotophos produced considerably milder defects. All compounds reduced NAD+ levels to a similar extent, regardless of the severity of the defects induced. Thus some commonly used organophosphorus insecticides and their metabolites are teratogenic to Xenopus embryos, but reduced NAD+ level does not appear to be important in causing the developmental defects.

Animals↗
PubMed1996

Regional distribution of organochlorine insecticide residues in human milk from Egypt.

The organochlorine insecticide residues in 60 human milk samples from 20 Egyptian governorates were analyzed by gas chromatography/electron capture and gas chromatography/mass spectrometry. The results showed that the main detected organochlorine insecticides were p,p'-DDE and lindane. Other HCH isomers, p,p'-DDT and endosulfan I residues were detected in some samples, but aldrin and endrin were not detected in most of the samples. The mean values for p,p'-DDE, lindane, endosulfan I and p,p'-DDT levels in the milk samples of the 20 governorates studied were 21.37 ppb, 8.42 ppb, 4.84 ppb and 2.93 ppb respectively, which are lower than the levels reported, a number of years ago, in most of the developed countries. Relatively higher levels of organochlorine insecticide residues were recorded in the samples from intensive agricultural activity regions.

Chromatography, Gas↗
PubMed2001

Insecticidal diarylheptanoid from Alpinia oxyphylla against larvae of Drosophila melanogaster.

In the course of screening for novel naturally occurring insecticides from Chinese crude drugs, a MeOH extract of Alpinia oxyphylla was found to give an insecticidal activity against larvae of Drosophila melanogaster Meigen. From the extract, an insecticidal compound was isolated by bioassay-guided fractionation and identified as yakuchinone A (1) by GC, GC/MS, 1H and 13C NMR spectroscopy.

Animals↗
PubMed2005

Pyrethroid insecticides, fenvalerate and permethrin, inhibit progesterone-induced alkaline phosphatase activity in T47D human breast cancer cells.

Pyrethroid insecticides exhibited a weak estrogenic activity by stimulation of MCF-7 cell proliferation and induction of alkaline phosphatase (AlkP) enzyme activity in cultured Ishikawa cells. Previously it was reported that fenvalerate and permethrin significantly inhibited the 17beta-estradiol-induced MCF-7 BUS cell proliferation. Although certain pyrethroid insecticides exert estrogenic or antiestrogenic activities, it is not clear whether pyrethroid insecticides act as progesterone agonists or antagonists. Therefore, the aim of this study was to evaluate the effects of fenvalerate and permethrin on AlkP activity as a progesterone-specific response in T47D cells. In the present study, the stimulation of AlkP activity was concentration dependent with addition of progesterone, and maximum activity was observed at concentration of 1 x 10(-8) M. Both fenvalerate (1 x 10(-6) M) and permethrin (1 x 10(-6) M) did not stimulate the AlkP activity, but progesterone (1 x 10(-8) M)-induced AlkP activity was significantly inhibited at 1 x 10(-6) M concentration of fenvalerate and permethrin, respectively. Progesterone receptor (PR) levels in cytosolic protein of T47D cells were studied to determine the relationship between cellular PR expression and AlkP activity. Similar to AlkP activity, progesterone (1 x 10(-8) M) significantly increased PR protein levels compared to control. However, PR protein levels were not affected in T47D cells cultured with fenvalerate and permethrin alone, whereas fenvalerate and permethrin significantly decreased progesterone-induced PR protein levels. Our data indicate that fenvalerate and permethrin exhibit antiprogestagenic activity in T47D human breast cancer cells.

Alkaline Phosphatase↗
PubMed1976

Joint action of insecticides against houseflies.

Mixtures of DDT, lindane, endrin, isobenzan, malathion, thiometon, and carbaryl were formulated on an equitoxicity basis. The joint action of 14 mixtures of insecticides was studied against the female housefly (Musca nebulo L.) by a topical application method. In general, the intragroup combinations of the chlorinatophosphate plus a chlorinated hydrocarbon insecticide exhibited no loss in either potency or synergism. An independent joint action was observed only in those mixtures containing DDT and either malathion or thiomethon. The toxicity of all the formulations containing carbaryl and a chlorinated hydrocarbon insecticide was found to be more than additive. The mixture of isobenzan plus carbaryl exhibited the highest degree of synergism of all the combinations tested, while those containing carbaryl and either malathion or thiometon showed a slight antagonism.

Animals↗
PubMedDate not supplied

Induction of sister chromatid exchanges in Chinese hamster ovary cells by organophosphate insecticides and their oxygen analogs.

Induction of sister chromatid exchanges (SCEs) in cultures of Chinese hamster ovary cells by 10 anticholinesterase organophosphate insecticides was investigated. The insecticides were two phosphates (dichlorvos and dicrotophos), four sulfur-containing organophosphates (malathion, parathion, leptophos, and diazinon), and four oxygen analogs of the latter (malaoxon, paraoxon, leptophosoxon, and diazoxon). All of the compounds except diazinon induced statistically significant increases in SCE frequencies at concentrations between 0.03 and 1.0 mM. These results suggest that SCE induction is a common property of organophosphate insecticides. Compared to the sulfur-containing organophosphates, the oxygen analogs consistently produced higher SCE frequencies and had stronger antiproliferative activity. Compared to two known genotoxicants, doxorubicin and ethyl methanesulfonate, the ability of organophosphates to produce SCEs is much weaker.

Animals↗
PubMed1982

Effect of the insecticides toxaphene and carbaryl on induction of lung tumors by benzo[a]pyrene in the mouse.

The insecticides toxaphene and carbaryl, when fed in the diet alone for 20 wk, were not tumorigenic to female A/J mice. Dietary levels of these insecticides were investigated for their effects on the incidence of lung tumors induced by oral administration of benzo[a]pyrene (BP). A significant reduction in BP-induced lung tumors was found after feeding 100 ppm toxaphene for 12 wk or 200 ppm for 20 wk. In contrast, 1000 ppm carbaryl fed for 20 wk caused a significant enhancement of BP-induced lung tumors. Mice that received toxaphene in the diet alone, or toxaphene and BP, showed an increase in BP hydroxylase activity in the liver and a decrease in enzyme activity in the lung. Carbaryl and BP increased BP hydroxylase activity in the lung without altering enzyme activity in the liver. Inhibition of lung BP hydroxylase activity was paralleled by a reduction in BP-induced lung tumors in mice fed toxaphene. Conversely, increased lung BP hydroxylase activity was associated with an enhancement of BP-induced lung tumors in animals fed carbaryl. The metabolism of BP by organs susceptible to BP-induced tumors and possible mechanisms for interactions with the insecticides are discussed.

Animals↗
PubMed1986

Effects of insecticides on GABA-induced chloride influx into rat brain microsacs.

The actions of different insecticides known to affect binding of ligands to gamma-aminobutyric acid (GABA) receptors were studied on the function of GABAA receptors in rat brain as assayed by GABA-induced 36Cl- influx into membrane microsacs. This flux was inhibited by the competitive antagonist bicuculline and the noncompetitive antagonist t-butylbicyclophosphorothionate, and the GABA effect was potentiated by the tranquilizer flunitrazepam and the depressant pentobarbital, as expected for effects on a GABAA receptor. The GABA-induced 36Cl- flux was inhibited by several cyclodienes and gamma-hexachlorocyclohexane (gamma-BHC) with the following order of decreasing potency: endosulfan I greater than endrin greater than endosulfan II greater than dieldrin greater than heptachlor epoxide greater than gamma-BHC greater than heptachlor. The noninsecticidal beta-BHC had no effect, while the IC 50 values for gamma-BHC and endrin were 1 and 0.2 microM, respectively. The four pyrethroids tested also inhibited the GABA-induced 36Cl- flux with the following decreasing potencies: 1R,cis,alpha S-cypermethrin greater than 1R,trans, alpha S-cypermethrin greater than fluvalinate greater than allethrin. Avermectin B1a was the only insecticide tested that, in the absence of GABA, stimulated 36Cl- flux in a dose-dependent manner, and this flux was inhibited by bicuculline. The stereospecific inhibition of the GABA-induced 36Cl- influx by the cyclodienes and gamma-BHC supports previously published data on their binding to mammalian brain GABAA receptor and suggests that these insecticides inhibit this receptor's function. It is also suggested that type II pyrethroids are potent inhibitors of the same receptor. However, avermectin B1a appears to act as a partial agonist of GABAA receptors.

Animals↗
PubMed1988

Effect of selected insecticides on rat brain synaptosomal adenylate cyclase and phosphodiesterase.

Previous reports from our laboratory and others clearly indicated that organochlorine insecticides such as chlordecone and DDT are potent inhibitors of ATPases involved in active ion transport. The present studies were initiated to study the effect of plictran, chlordecone, toxaphene, aldrin, dieldrin, endrin, isodrin, and telodrin on enzymes involved in cyclic AMP metabolism. Rat brain synaptosomes were prepared by Ficoll-sucrose gradient centrifugation method. Adenylate cyclase activity, which is involved in anabolism of cAMP, was determined using the radioactive method by measuring [32P]cAMP formed during hydrolysis of [32P]ATP. Phosphodiesterase activity, which is involved in the catabolism of cAMP, was estimated by measuring [3H]adenosine formed using [3H]cAMP as a substrate. Synaptosomal adenylate cyclase activity was inhibited significantly by plictran with an IC50 of 25 microM, and a maximum inhibition of 30% was observed with 50 microM chlordecone. Toxaphene, aldrin, dieldrin, endrin, isodrin, and telodrin did not affect the adenylate cyclase activity. Similarly, none of the insecticides studied inhibit the activity levels of synaptosomal phosphodiesterase. The significant inhibition of adenylate cyclase observed with plictran might be due to the tin component, since several heavy metals affect cAMP metabolism. The lack of inhibition of adenylate cyclase and phosphodiesterase with other compounds tested clearly supports our postulation that these organochlorine insecticides exert their neurotoxic action by the selective inhibition of ATPases in synaptosomes.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1989

Epidemiologic study of insecticide exposures, obesity, and risk of bladder cancer in household dogs.

A case-control study of household dogs was conducted to determine if exposure to sidestream cigarette smoke and chemicals in the home, use of topical insecticides, and obesity are associated with the occurrence of bladder cancer. Information was obtained by interview from owners of 59 dogs with transitional-cell carcinoma of the bladder and 71 age- and breed size-matched control dogs with other chronic diseases or neoplasms. Bladder cancer risk was unrelated to sidestream cigarette smoke and household chemical exposures. Risk was significantly increased by topical insecticide use (OR = 1.6 for 1-2 applications per year and OR = 3.5 for greater than 2 applications per year; chi 2 trend; p = .008). This risk was enhanced in overweight or obese dogs. Further studies of this canine model may facilitate identification of specific carcinogens present in insecticides commonly used on pet animals and in the environment.

Administration, Cutaneous↗
PubMed1990

Chlorinated hydrocarbon insecticides in Colorado beef cattle serum--a pilot environmental monitoring system.

A pilot project was initiated to test an existing animal disease surveillance system for use in monitoring environmental pollutants. Eleven chlorinated hydrocarbon insecticides were assayed to provide an indication of environmental contamination. A total of 241 bovine serum samples from 53 Colorado beef ranches was tested; 123 samples (51%) were found to contain detectable concentrations of 1 or more of 11 chlorinated hydrocarbons. There were a total of 203 occurrences of a compound being found at a level exceeding the detection limit. Heptachlor, heptachlor epoxide, lindane, and oxychlordane were the insecticides detected most frequently in bovine sera. This pilot study supports the use of domestic food-producing animals as sentinels of environmental contamination with insecticides.

Animals↗