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PubMed1994

The effect of multiple soil applications of disulfoton on enhanced microbial degradation in soil and subsequent uptake of insecticidal chemicals by potato plants.

Potatoes were grown during 1992 in 2 m2 plots of loam which had received 1, 2 or 3 annual treatments of Di-Syston 15G, equivalent to 3.36 kg AI/ha, in furrow at planting. The presence of enhanced degradative activity to the sulfoxide and sulfone metabolites of disulfoton in the soil treated in the previous two years was confirmed by laboratory tests prior to the 1992 treatments. Soil, seed potato and foliage from the three treatments were analyzed for disulfoton and its sulfoxide and sulfone metabolites for 12 wk following planting/treatment. Disulfoton was the major insecticidal component of the soil, a minor component of the seed piece and was not detected (< 0.02 ppm) in potato foliage. Disulfoton concentrations in each of the three substrates sampled were similar for the three treatments. Disulfoton sulfoxide and sulfone were the major insecticidal components of the seed piece and foliage. Their maximum concentrations in 1st year soil, seed pieces and foliage were ca. 2x, 2x and 6x, respectively, those measured in the 2nd and 3rd year treatments. The results demonstrate that enhanced microbial degradation of relatively minor insecticidal compounds in the soil can profoundly affect insecticide levels in the plant when these compounds are the major insecticidal components accumulated. The broader implications for crop protection using soil-applied systemic insecticides are discussed.

Biodegradation, Environmental↗

PubMed1981

Persistence of four pyrethroid insecticides in a mineral and an organic soil.

Permethrin, cypermethrin, fenpropanate and fenvalerate (emulsifiable concentrates) were applied at 280 g AI/ha and incorporated into mineral and organic soil contained in small field plots. Radishes and carrots were grown to serve as indicators of insecticide uptake. Similar plots were treated with the same insecticides at 140 g AI/ha and the soil surface was left undisturbed following application. Soil cores were removed at appropriate intervals and the crops were harvested when mature. The insecticide concentration in all samples was determined by gas-liquid chromatography. The amount of insecticide in the soil declined rapidly to less than 50% of the initial value in 1 month or less for most material-soil-treatment combinations and within 2 months for all cases. Concentrations remained in excess of 0.01 ppm in the organic soil for at least six months for all material-treatment combinations but fell below this level over 2-5 months in the mineral soils. Organic soil incorporated fenvalerate was the most persistent combination overall with 25, 17 and 7% remaining at 6, 18 and 28 months respectively. The trans-isomers of permethrin and cypermethrin disappeared more quickly than the cis-isomers but the insecticidally active IR isomers were not preferentially degraded relative to the inactive 1S. No residues (less than 0.01 ppm) were found in the radish or carrot crops. First order disappearance rates were not constant for any of the combinations. A comparison of partial rate constants showed: 1) 0-1 mo rates were generally greater in mineral than organic soil, 2) 1-6 mo rates in organic soil were lower than 0-1 mo rates, 3) 1-6 mo rates for surface applications to organic soil were generally less than for incorporated applications. In laboratory experiments, 0-1 mo rates for fenvalerate disappearance in a mineral soil were 2-3x greater for 0.5 ppm than for 10 ppm while 1-6 mo rates were independent of insecticide concentration but were 1.5x greater for 0.5% moisture than for 5%.

Biodegradation, Environmental↗

PubMed1992

[Modification and expression of insecticidal protein structural gene of Bacillus thuringiensis var. aizawai 7-29].

The regulative region (181bp) and the fifth toxic active domain (217bp) were removed from the insecticidal protein gene of Bacillus thuringiensis var. aizawai 7-29. After the synthesis of the adaptor (15bp) that contains initiation codon (ATG) and the PCR synthesis of the fifth toxic active domain (229bp) that contains stop codon (TAA), were inserted into on 5' truncated and 3' truncated of the coding fod N-terminal peptid's DNA fragment, that to become a modified structural gene. The modified structural gene can be play initiatic translation-function and stop translation-function during translation of insecticidal protein. The insecticidal protein was determined by western blotting, showed the expression of modified structural gene in Escherichia coli JM 103. The bioassay of insecticidal proteins showed the 3' truncated and 5' truncated of insecticidal gene was higher toxic active than the 3' truncated of insecticidal gene in Escherichia coli JM 103.

Bacillus thuringiensis↗

PubMed1999

Comparative effect of fenitrothion treatment on intracellular protease activities in insecticide-resistant and susceptible strains of Musca domestica L.

In order to further elucidate the biochemical mechanisms responsible for insecticide resistance in insects, we have determined changes in the activity levels of a comprehensive range of proteolytic enzymes (cytoplasmic and lysosomal proteinases and peptidases, which play a key role in normal cell functioning) in fenitrothion-resistant (571ab) and susceptible (Cooper) strains of Musca domestica following in vivo exposure to the insecticide fenitrothion. Untreated insects of the resistant strain had significantly higher levels (20-100%) of activity for many protease types compared to the susceptible strain (whole body analysis). Exposure to fenitrothion resulted in further activity increases for most proteases at some point during the subsequent 24 h period in resistant strain insects; susceptible strain insects were also capable of similar increases in protease activities. We therefore suggest that it must be the combination of intrinsically higher protease levels (prior to pesticide exposure), together with the capacity to further increase protease activities following insecticide exposure, which is important in the mechanism by which proteases may confer survival advantages in insecticide resistant insects. We further speculate that this mechanism may involve increased supply of precursor amino acids from proteolytic degradation products to the intracellular pool, prior to de novo synthesis of detoxifying enzymes following insecticide exposure.

Animals↗

PubMed1999

The insect voltage-gated sodium channel as target of insecticides.

Examination of the function, chemistry, and pharmacology of the voltage-gated insect sodium channel (ISC) reveals that the ISC closely resembles its vertebrate counterpart in electrophysiology and ion conductance, primary structure and allocation of all functional domains, and its pharmacological diversity and flexibility exhibited by the occurrence of different allosterically coupled receptor-binding sites for various neurotoxicants. The toxicants include several groups of insecticides, namely DDT and its analogues, pyrethroids, N-alkylamides, and dihydropyrazoles, which affect channel gating and ion permeability. Despite their similarity, the insect and vertebrate channels are pharmacologically distinguishable, as revealed by the responsiveness of the heterologously expressed Drosophila para clone to channel modifiers and blockers and the occurrence of the insect-selective sodium channel neurotoxins derived from arachnid venoms presently used for the design of recombinant baculovirus-mediated selective bioinsecticides. The pharmacological specificity of the ISC may lead to the design of insect-selective toxicants, and its pharmacological flexibility may direct the use of ISC insecticides for resistance management. Insecticide resistance [such as knockdown resistance (KDR)] is acquired by natural selection and operated by increased metabolism, channel mutagenesis, or both. The resistance issue can be dealt with in several ways. One is by simultaneous application of low doses of synergistic, allosterically coupled mixtures (thus delaying or preventing the onset of resistance). An alternative is to replace an insecticide to which resistance was acquired by channel mutation with a different ISC toxicant to which increased susceptibility was conferred by the same mutation. Such a possibility was exemplified by a significant increase in susceptibility to N-alkylamides, as well as an insect-selective neurotoxin revealed by KDR insects. Third, both of these methods can be combined. Thus owing to its pharmacological uniqueness, the ISC may serve as a high-priority target for future selective and resistance-manageable insecticides.

Animals↗

PubMedDate not supplied

Evaluation of insecticide resistance and biochemical mechanisms in a population of Culex quinquefasciatus (Diptera: Culicidae) from São Paulo, Brazil.

To establish an insecticidal resistance surveillance program, Culex quinquefasciatus mosquitoes from São Paulo, Brazil, were colonized (PIN95 strain) and analyzed for levels of resistance. The PIN95 strain showed low levels of resistance to organophosphates [malathion (3.3-fold), fenitrothion (11.2-fold)] and a carbamate [propoxur (3.0-fold)]. We also observed an increase of 7.4 and 9.9 in alpha and beta esterase activities, respectively, when compared with the reference IAL strain. An alteration in the sensitivity of acetylcholinesterase to insecticide inhibition was also found in the PIN95 mosquitoes. The resistant allele (Ace.1R), however, was found at low frequencies (0.12) and does not play an important role in the described insecticide resistance. One year later, Cx. quinquefasciatus mosquitoes were collected (PIN96 strain) at the same site and compared to the PIN95 strain. The esterase activity patterns observed for the PIN96 strain were similar to those of the PIN95 mosquitoes. However the occurrence of the Ace.1R allele was statistically higher in the PIN96 strain. The results show that esterase-based insecticide resistance was established in the PIN95 Cx. quinquefasciatus population and that an acethylcholinesterase based resistant mechanism has been selected for. A continuous monitoring of this phenomenon is fundamental for rational mosquito control and insecticide application programs.

Animals↗

PubMed1998

Susceptibility status of malaria vectors to insecticides in India.

The use of chemical insecticides for control of malaria vector populations continues to be the mainstay of malaria control strategy in India. Monitoring vector susceptibility to chemical insecticides is an important activity under the National Malaria Eradication Programme to ensure judicious and effective use of chemical Insecticides. 72 entomological zones were established under NMEP in 1977 for undertaking entomological studies in the malaria problematic areas. These zones have been generating insecticide susceptibility data in respect of the various malaria vectors. In this paper the insecticide susceptibility data, in respect of major vectors of malaria as on 1997, is presented.

Animals↗

PubMed1994

What role for insecticides in vector control programs?

Vector-borne diseases including dengue, yellow fever, Japanese encephalitis, malaria, leishmaniasis, and filariasis remain severe public health problems in most of the countries in which they are endemic. In some cases, their incidence is increasing and they are spreading to new geographic areas. For a number of the infections, the most effective manner of controlling their transmission is through control of their vectors. However, in some instances, such as dengue and Chagas' disease, there is no alternative. Most countries that are endemic for vector-borne diseases maintain vector control services, and most large tropical and semitropical cities also have pest control programs, mainly against pest mosquitoes. Virtually all of the vector and pest control programs depend on the use of insecticides formulated as larvicides, adulticides, baits, or insecticide impregnated bed nets. For many years, the development of new insecticides for use in public health programs was encouraged and supported by multilateral and bilateral health agencies, including the implementation of field trials in endemic areas. Due to the development of insecticide resistance, toxicologic and environmental considerations, and the cost of development and of registration, the number of compounds available for use has declined while the number of new insecticides submitted for laboratory and field trials to the World Health Organization has dwindled even more. The recrudescence of vector-borne diseases, the rapid pace of urbanization, lagging development of environmental services in many tropical cities, and difficulties encountered in ensuring the community's cooperation in its own protection through environmental measures make imperative the continued availability of pesticides for public health use. Since only the pesticide manufacturing industry has the combination of technical and financial resources to promulgate the research and development of new pesticides and pesticide groups, it is suggested that governments, bilateral, and multilateral organizations explore the manner in which they can assist industry in the development of new compounds and guarantee the continued availability of effective and safe pesticides for vector-control programs.

Animals↗

PubMed2001

Multi-residue determination of 41 insecticides in garlic by gas chromatography and ion trap mass spectrometry using the selective ion storage technique.

A method is described for determining 41 insecticide residues in garlic (Allium sativum L.), including organophosphorus, organochlorine, carbamate, and synthetic pyrethroid insecticides. These insecticides were extracted from samples with acetone and dichloromethane, and co-extractives removed using a charcoal/Celite/alumina column. Analysis was performed by gas chromatography with ion trap mass spectrometry in selective ion storage (SIS) mode. Retention times and specific ions (m/z values) were used to confirm insecticides. Recoveries for most insecticides (blank samples spiked at 0.05, 0.2 and 1 microg mL(-1) levels) ranged from 70% to 110%, the coefficient of variation (CV) of the method was <20% for every case, and the limit of detection (LOD), defined in terms of 3 times baseline noise, varied between 0.01 and 0.16 mg kg(-1), depending on the compound.

Food Contamination↗

PubMed1993

Insecticide action at the GABA-gated chloride channel: recognition, progress, and prospects.

Three billion (3 x 10(9)) pounds of hexachlorocyclohexanes, polychlorobornanes, and chlorinated cyclodienes (such as lindane, toxaphene, and endosulfan, respectively) were used to control pest insects before their mode of action was established as blocking the GABA-gated chloride channel. With the restricted use or demise of these polychlorocycloalkanes (each approximately 50 to approximately 75% by weight of chlorine), the GABAergic system is for now an underutilized target of insecticide action. Newer compounds with outstanding potency at this receptor and as toxicants to houseflies are suitably-substituted 2,6,7-trioxabicyclo[2.2.2]-octanes, particularly the bicycloorthobenzoates, and 1,3-dithianes, including those with no halogenated substituents. Picrotoxinin analogs and alkynylphenyl-silatranes also act at this target but are of lower insecticidal activity. [3H]n-Propyl-ethynylbicycloorthobenzoate ([3H]EBOB) is for now the best radioligand for this insecticidally-relevant binding site in insects. Macrocyclic lactones such as the avermectins and moxidectin act at a different binding site to disrupt chloride flux and they have a different spectrum of insecticidal activity and no cross resistance with cyclodienes in houseflies. The search for new insecticides has provided the incentive and probes for a better understanding of the insect GABAergic system.

Animals↗

PubMed1995

Relationship of aquatic natural organic material characteristics to the toxicity of selected insecticides.

Toxicities of the commercial insecticide formulations of azinphos methyl, chlorpyrifos, fenvalerate, and methyl parathion were evaluated in streamwater samples containing natural organic material (NOM) using a modification of a bacterial bioluminescence assay. Toxicity reduction of azinphos methyl was significantly (P < 0.05) correlated with water sample nonvolatile total solids (NVTS) concentration. Toxicity reductions of fenvalerate and of methyl parathion were significantly correlated to E4/E6 absorbance ratio of NOM, and to the proportion of NOM having molecular weight greater than 3700 Da. Toxicity reductions of fenvalerate and methyl parathion had significant correlations to the concentration of NVTS in water samples. Linear regressions of insecticide EC50 values to these NOM characteristics were used to mathematically model the effect of NOM on insecticide toxicity. Insecticide logKOW values were significantly correlated to the slopes of the EC50-total organic carbon (TOC) concentration regression lines. This confirms that the level of association of some nonionic organic contaminants with NOM is a function of the contaminant's water solubility. No single NOM characteristic was the best predictor of toxicity for all insecticides examined. However, these findings suggest that the influence of NOM on toxicity results primarily from differences in TOC content and abundance of larger molecular size NOM.

Animals↗

PubMed2001

Acute toxicity of locust insecticides to two indigenous invertebrates from Sahelian temporary ponds.

During desert locust plagues large amounts of insecticides are used for control operations. Drift from these treatments and accidental overspraying may contaminate small surface waters such as temporary ponds. The present study describes methods for static acute toxicity tests with two abundant organisms that occur in temporary ponds in the African Sahel region: the fairy shrimp Streptocephalus sudanicus Daday (Branchiopoda, Anostraca, Streptocephalidae) and the backswimmer Anisops sardeus Herrich-Schåffer (Hemiptera, Notonectidae). The organisms were captured in the field and 48-h static toxicity tests were conducted in the laboratory. The assays were used to screen the toxicity of 11 formulated synthetic insecticides used in desert locust control and of spores of the mycopesticide Metarhizium anisopliae var. acridum. Most of the synthetic insecticides tested were highly toxic to both organisms (LC50 or EC50<1 mg/L). Exceptions were the toxicity of diflubenzuron to A. sardeus (moderately toxic: 1<LC50<10 mg/L), and that of fenitrothion (moderately toxic) and malathion (slightly toxic: 10<EC50<100 mg/L) to S. sudanicus. M. anisopliae var. acridum was moderately toxic to S. sudanicus and only slightly toxic to A. sardeus. EC50 values of the insecticides for S. sudanicus were not significantly correlated with L(E)C50 values for Daphnia magna collected from the literature. For A. sardeus a significant correlation with D. magna was found, but even in this data set the two species had widely differing sensitivities to some insecticides.

Animals↗

PubMed1975

[Residues of organochlorine insecticides in sediments of a high estuary of Fleuve St-Laurent].

In order to determine the distribution and levels of organochlorine insecticide residues in sediments of the upper estuary of the St. Lawrence River, we have carried out the first analyses in Quebec of these compounds in samples from different parts of this region. The recovery of these residues was conducted by continuous Soxhlet extraction of the samples with 100 ml of a mixture of acetone and n-hexane (50:50). The insecticide-containing extract was cleaned up by column chromatography on activated florisil. Elution with 100 ml of n-hexane and then 150 ml of a mixture of n-hexane and ether (85:15) gave two fractions. The analyses were performed by gas liquid chromatography using an electron-capture detector with a radioactive 63Ni source. In the two series of samplings (June and July 1973), DDT and its metabolites were detected in appreciable amounts at nearly all sampling sites while the other insecticides: alpha-BHC, gamma-BHC, heptachlor and dieldrin, were found only in a few and at very low concentrations: beta-BHC, aldrin and heptachlor epoxide were absent at all sites. In general, the insecticide levels at the various sites show a slight variation in time. However, in some, the concentration of organochlorine insecticides is much lower than in others; in these cases it is presumed that this is due to a greater rate of sedimentation in the absence of current and also to local agriculture and sediment texture.

Canada↗

PubMed1996

Heterogeneity of the glutathione transferase genes encoding enzymes responsible for insecticide degradation in the housefly.

One of the four glutathione-S-transferases (GST) that is overproduced in the insecticide-resistant Cornell-R strain of the housefly (Musca domestica) produces an activity that degrades the insecticide dimethyl parathion and conjugates glutathione to lindane. In earlier work, it was shown that the resistant Cornell-R carries an amplification, probably a duplication, of one or more of its GST loci and that this amplification is directly related to resistance. Using polymerase chain reaction (PCR) amplification with genomic DNA, multiple copies of the gene encoding the parathion-degrading activity (called MdGst-3) were subcloned from both the ancestral, insecticide-susceptible strain BPM and from the insecticide-resistant Cornell-R. In BPM, three different MdGst-3 genes were identified while in Cornell-R, 12 different MdGst-3 sequences were found that, though closely related to ancestral genes, had diverged by a few nucleotides. This diversity in MdGst-3 genomic sequences in Cornell-R is reflected in the expressed sequences, as sampled through a cDNA bank. Population heterozygosity cannot account for these multiple GST genes. We suggest that selection for resistance to insecticides has resulted in not only amplification of the MdGst-3 genes but also in the divergence of sequence between the amplified copies.

Animals↗

PubMed1999

Multiple origins of cyclodiene insecticide resistance in Tribolium castaneum (Coleoptera: Tenebrionidae).

The number of origins of pesticide resistance-associated mutations is important not only to our understanding of the evolution of resistance but also in modeling its spread. Previous studies of amplified esterase genes in a highly dispersive Culex mosquito have suggested that insecticide resistance-associated mutations (specifically a single-gene duplication event) can occur a single time and then spread throughout global populations. In order to provide data for resistance-associated point mutations, which are more typical of pesticide mechanisms as a whole, we studied the number of independent origins of cyclodiene insecticide resistance in the red flour beetle Tribolium castaneum. Target-site insensitivity to cyclodienes is conferred by single point mutations in the gene Resistance to dieldrin (Rdl), which codes for a subunit of a gamma-aminobutyric acid (GABA) receptor. These point mutations are associated with replacements of alanine 302 which render the receptor insensitive to block by the insecticide. We collected 141 strains of Tribolium worldwide and screened them for resistance. Twenty-four strains contained resistant individuals. After homozygosing 23 of these resistance alleles we derived a nucleotide sequence phylogeny of the resistant strains from a 694-bp section of Rdl, encompassing exon 7 (which contains the resistance-associated mutation) and part of a flanking intron. The phylogeny also included six susceptible alleles chosen at random from a range of geographical locations. Resistance alleles fell into six clades and three clades contained both resistant and susceptible alleles. Although statistical analysis provided support at only the 5-6% level, the pattern of variation in resistance alleles is more readily explained by multiple independent origins of resistance than by spread of a single resistance-associated mutation. For example, two resistance alleles differed from two susceptible alleles only by the resistance-associated mutation itself, suggesting that they form the susceptible ancestors and that resistance arose independently in several susceptible backgrounds. This suggests that in Tribolium Rdl, de novo mutations for resistance have arisen independently in several populations. Identical alleles were found in geographically distant regions as well, also implying that some Rdl alleles have been exported in stored grain. These differences from the Culex study may stem both from differences in the population genetics of Tribolium versus that of mosquitoes and differences in mutation rates associated with point mutations versus gene duplication events. The Tribolium data therefore suggest that multiple origins of insecticide resistance (associated with specific point mutations) may be more common than the spread of single events. These findings have implications for the way in which we model the evolution and spread of insecticide resistance genes and also suggest that parallel adaptive substitutions may not be uncommon in phyletic evolution.

Animals↗

PubMed1982

Interactions of chlorinated hydrocarbon insecticides with membranes.

Chlorinated hydrocarbon insecticides quench the fluorescence of N-alkyl derivatives of carbazole. We used phospholipids with covalently attached carbazole as probes for the interactions of chlorinated hydrocarbon insecticides with lipid bilayers, the object being to understand better the toxicities of chlorinated hydro-carbons. Fluorescence quenching measurements revealed the lipid-water partition coefficients of the chlorinated hydrocarbons, their diffusion coefficients in the membranes, and the binding capacities of the membranes for the chlorinated hydrocarbons. Active insecticides were compared with inactive analogues to test whether activities correlated with chlorinated hydrocarbon-membrane interactions. Thus DDT and methoxychlor were compared with inactive DDE, and insecticidal gamma-lindane was compared with three less active stereoisomers. The partition coefficients, diffusion coefficients and membrane saturation capacities did not correlate with insecticidal potency. The partition coefficients of these chlorinated hydrocarbons were larger in bilayers containing unsaturated fatty acyl chains as compared to bilayers containing saturated fatty acyl chains. Interestingly, neural membranes are known to contain a large percentage of unsaturated lipids. Our results indicate that the activities of chlorinated hydrocarbons are not a result of specific interactions of these compounds with the lipids of membranes. However, the neurotoxicity of chlorinated hydrocarbons may be amplified by selective partitioning in the unsaturated neural membranes.

Diffusion↗

PubMed1984

Interference by DDT and cyclodiene types of insecticides with chloroplast-associated reactions.

The effects of DDT, some of its analogs, and selected cyclodiene insecticides on isolated spinach (Spinacea oleracea L.) thylakoids were identified, characterized, and compared to responses induced by selected herbicides. Except for endrin, the insecticides inhibited light-induced electron transport, altered chlorophyll fluorescence transients, and competitively displaced [14C]atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], a known photosystem II inhibitor, from the membranes. The insecticides appeared to act at, or near B, the secondary electron acceptor of photo-system II. Binding of DDT and dieldrin was estimated at 900 and 2200 molecules, respectively, per photosynthetic unit (490 chlorophyll molecules). The insecticides also inhibited valinomycin-induced swelling of the thylakoid membrane. Whereas inhibition of electron transport can be attributed to interaction by the insecticides with a proteinaceous component of the thylakoid membrane, interference with the action of valinomycin may involve interaction with lipoidal constituents of the membrane.

Binding, Competitive↗

PubMed1983

Influence of pretreatment with various insecticides on the N-demethylation of dimethylnitrosamine.

The effects of various classes of insecticides were studied on the N-demethylation of dimethylnitrosamine (DMN) by mouse liver enzymes. Organochlorine insecticides, represented by lindane, DDT, and endrin, increased the activities of DMN demethylase I and II. The latter enzyme was more susceptible to the inducive action of the tested chlorinated insecticides. On the other hand, the synthetic pyrethroids, fenvalerate and flucythrinate, did not alter the activity of either enzyme. While pretreatment with carbaryl, a carbamate derivative, was without effect, moderate elevation in the activity of both demethylases was observed following administration of carbofuran. Dimethoate, representing organophosphorus compounds, was the only insecticide tested to inhibit the N-demethylation of DMN, with more pronounced effect on DMN demethylase I. Since DMN requires metabolic activation for its hepatotoxic and carcinogenic actions, alterations in the activities of its metabolizing enzymes as a sequela of exposure to certain insecticides may change susceptibility to its toxicity and/or carcinogenicity.

Animals↗