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This article proposes an alternative method, using cloud-point extraction and gas chromatography, for extraction and determination of disulfoton in water samples. For cloud-point extraction, the nonionic surfactant Triton X-114 was used. Before gas chromatography, a cleanup stage for surfactant removal from the extracts was optimized. Cleanup used two columns, in series, containing silica gel and Florisil, with methanol:hexane (1 : 1) as eluent, resulting in the removal of more than 95% of the Triton X-114. Factors such as ionic strength (>0.5 mol L−1) and surfactant concentration (1.0% w/v) increased the extraction efficiency of the cloud-point methodology, yielding disulfoton recoveries of almost 100%. Compared with liquid–liquid extraction, the cloud-point methodology was more efficient, with a better detectability, and resulted in a significant reduction in solvent volume.

A multi-residue method for 122 pesticides in agricultural products was validated in accordance with Japanese guidelines for residual agricultural chemicals in food. The sample was extracted with acetonitrile. Co-extractives were removed by GPC-graphitized carbon column SPE, followed by silica gel/PSA cartridge column SPE. The pesticides in the test solution were determined by LC-MS/MS using scheduled MRM in combination with polarity switching. Validation tests were performed on spinach, brown rice, soybean, orange and tomato fortified at 0.01 and 0.1 μg/g. The pesticides at each level were analyzed in two samples per day on five different days. In conclusion, among 122 pesticides tested for each level, 121 pesticides (but not disulfoton) were found to meet all of the guideline criteria.

Repeated use of neonicotinoid insecticides has resulted in the first reported cases of Colorado potato beetle (Leptinotarsa decemlineata (Say)) resistance to imidacloprid. In the laboratory we determined susceptibility of the imidacloprid-resistant Colorado potato beetles from a population in Southern Maine to other insecticides currently registered for use on potato. This population was about 30-fold resistant to imidacloprid and could not be effectively controlled by its applications. Control mortality was significantly higher for the imidacloprid-resistant larvae than for the susceptible larvae, suggesting that fitness disadvantages may be associated with the resistance trait. Resistant larvae exhibited significantly less mortality than susceptible larvae when exposed to cyfluthrin, carbaryl, azinphosmethyl, and methamidophos. Their susceptibility to oxamyl was also somewhat reduced, although it did provide nearly 100% mortality at the highest concentration tested. Disulfoton was highly toxic to the resistant larvae. Oxamyl killed about 40% of the adults in greenhouse assays with potted potato plants, altered their feeding behavior (fewer adults up on plants), and reduced defoliation by more than 90%. Disulfoton was not lethal to adults, but significantly suppressed their feeding. In field trials with the resistant population, oxamyl and imidacloprid + spinosad provided the best beetle control. Novaluron had no detectable effect on beetle densities. There was little difference between the plots treated with imidacloprid or thiamethoxam and the untreated control. Our results suggest that insecticide rotation may be a valuable option for managing imidacloprid-resistant Colorado potato beetle populations. We also had a good consistency between the results of the Petri dish, greenhouse, and field experiments, indicating that screening under laboratory confinement may be useful when developing initial recommendations to potato growers in areas affected by resistance to neonicotinoids.

The reactions of thiometon and its ethyl analogue, disulfoton, with reduced sulfur species [e.g., bisulfide (HS-), polysulfide (S(n)2-), thiophenolate (PhS-), and thiosulfate (S2O3(2-))] were examined in well-defined aqueous solutions under anoxic conditions. The role of reduced sulfur species was investigated in the abiotic degradation of thiometon and disulfoton. Experiments at 25 degrees C demonstrated that HS-, S(n)2-, PhS-, and S2O3(2-) promoted the degradation of thiometon to a great extent while only S(n)2- and PhS- showed a small accelerating effect in the degradation of disulfoton. Reactions were monitored at varying concentrations of reduced sulfur species to obtain the second-order rate constants. The reactivity of the reduced sulfur species decreased in the following order: S(n)2- > PhS- > HS- approximately S2O3(2-). Transformation products were confirmed by standards or characterized by gas chromatography mass spectrometry. The results illustrate that multiple pathways occur in the reactions with reduced sulfur species, among which the nucleophilic attack at the alpha-carbon of the alkoxy group was the predominant pathway. Activation parameters of the reaction of thiometon and disulfoton with HS- were also determined from the measured second-order rate constants over a temperature range. DeltaH( not equal) values indicated that the reactivity of thiometon toward HS- was much greater than for disulfoton. Nucleophilic attack at the alkoxy group was more important for thiometon than disulfoton. When the measured second-order rate constants at 25 degrees C are multiplied by [HS-] and Sigma[S(n)2-] reported in saltmarsh porewaters, predicted half-lives show that reduced sulfur species present at environmentally relevant concentrations may present an important sink for thiometon in coastal marine environments.

Enzymes hydrolysing highly toxic organophosphate esters (OPs) are promising alternatives to pharmacological countermeasures against OPs poisoning. Bungarus fasciatus acetylcholinesterase (BfAChE) was engineered to acquire organophosphate hydrolase (OPase) activity by reproducing the features of the human butyrylcholinesterase G117H mutant, the first mutant designed to hydrolyse OPs. The modification consisted of a triple mutation on the (122)GFYS(125) peptide segment, resulting in (122)HFQT(125). This substitution introduced a nucleophilic histidine above the oxyanion hole, and made space in that region. The mutant did not show inhibition by excess acetylthiocholine up to 80 mM. The k(cat)/K(m) ratio with acetylthiocholine was 4 orders of magnitude lower than that of wild-type AChE. Interestingly, due to low affinity, the G122H/Y124Q/S125T mutant was resistant to sub-millimolar concentrations of OPs. Moreover, it had hydrolysing activity with paraoxon, echothiophate, and diisopropyl phosphofluoridate (DFP). DFP was characterised as a slow-binding substrate. This mutant is the first mutant of AChE capable of hydrolysing organophosphates. However, the overall OPase efficiency was greatly decreased compared to G117H butyrylcholinesterase.

Clomazone may be safely used in cotton to manage weeds when applied following treatments of the organophosphate insecticides phorate or disulfoton. The loss of chlorophyll and carotenoids with 6 days of 100 nM clomazone treatment of cotton seedlings was partially prevented with phorate in hydroponic solution in a rate-dependent manner. In a study to examine the timing of safening from a one-day clomazone (100 nM) treatment, maximum safening was achieved when phorate (50 μM) was applied the same day as clomazone. Phorate decreased metabolism of 14 C-clomazone to polar metabolites in excised cotton shoots and shoots of intact cotton plants. Microsomal studies of corn shoots showed an NADPH-dependent/cytochrome P450 reaction was inhibited by phorate. Additional studies with corn microsomes, corn seedlings and cotton seedlings supported the basis of clomazone safening is the inhibition of toxic clomazone metabolism by P450 inhibitors.

The hydrolysis of six selected pesticides has been studied in aqueous solution. Four organophosphorus pesticides (disulfoton, isofenfos, isazofos and profenfos) and two N-methylcarbamate derivatives (oxamyl and ethiofencarb) were selected. Hydrolysis was performed in purified buffered water at different pH in the range 7.0–10.0 (ionic strength = 2.5 mM, T = 25°C). At pH = 8.0, isofenfos and disulfoton (t 1/2 ≈ 4 years, t 1/2 ≈ 1 year, resp.) were found to be far more stable than isazofos (t 1/2 ≈ 5 months), ethiofencarb and profenofos (t 1/2

The acute toxicities of two organophosphorodithioate (dimethoate and disulfoton) and two organophosphorothioate (omethoate and demeton-S-methyl) insecticides were evaluated individually and in binary combination with the herbicide atrazine using fourth-instar larvae of the aquatic midge, Chironomus tentans. Atrazine alone up to 1000 μg/L did not show significant toxicity to the midges in a 48-h bioassay. However, atrazine concentrations as low as 1 μg/L in combination with dimethoate at EC25 (concentration to affect 25% of tested midges), 100 μg/L in combination with disulfoton (EC25), and 10 μg/L in combination with demeton-S-methyl (EC25) significantly enhanced the toxicity of each organophosphate insecticide. In contrast, atrazine concentrations of 10 μg/L and above in combination with omethoate (EC25) significantly decreased the toxicity of the insecticide. Biochemical analysis indicated that increased toxicity of dimethoate, disulfoton, and demeton-S-methyl in binary combination with atrazine correlated to the increased inhibition of acetylcholinesterase. Furthermore, cytochrome P450-dependent O-deethylation activity in the midges exposed to atrazine at 1000 μg/L was 1.5-fold higher than that in the control midges. Thus, atrazine appeared to induce cytochrome P450 monooxygenases in the midges. Elevated cytochrome P450 monooxygenase activity may increase the toxicities of dimethoate, disulfoton, and demeton-S-methyl by enhancing the oxidative activation of dimethoate into omethoate, and disulfoton and demeton-S-methyl into their sulfoxide analogs with increased anticholinesterase activity. In contrast, atrazine reduced the toxicity of omethoate possibly by enhancing the oxidative metabolic detoxification since omethoate does not require oxidative activation.

The photocatalysis reaction of three selected pesticide derivatives, namely methoxychlor (1), chlorothalonil (2) and disulfoton (3), has been investigated in an acetonitrile/water mixture in the presence of titanium dioxide and oxygen. The change as a function of irradiation time has been monitored using the UV spectroscopic analysis technique. An attempt has been made to identify the product formed during the photooxidation process through GC/MS analysis technique. The photolysis of methoxychlor (1) led to the formation of methoxychlor olefin (4) and 4,4′-dimethoxybenzophenone (9), whereas chlorothalonil (2) gave rise to 2,3,4,5-tetrachlorophenol (17) as the only product. On the other hand, the photolysis of disulfoton (3) under analogous conditions gave disulfoton sulfoxide (25) and phosphorodithioic acid (21). All the products have been identified by comparing the molecular ion and mass fragmentation peaks of the products with those reported in the library. A probable mechanism for the formation of the products has been proposed.

The photochemical transformation of four selected organophosphorus pesticides (OPs) has been studied in water. Because of their extensive use, disulfoton, isofenfos, isazofos and profenofos were chosen for this study. A solid phase extraction method has been developed to allow low-concentration experiments. Photolysis experiments have been performed both in purified water and in Capot river water (natural water from Martinique) using either monochromatic light at 253.7 nm (purified water) or polychromatic light greater than 285 nm (purified and Capot river waters). Kinetic investigations coupled with analytical studies (identification of degradation products) were performed for the four pesticides. Upon monochromatic irradiation, quantum yields of OP photolysis have been evaluated and in polychromatic irradiation experiments, apparent first-order kinetic constants have been determined. The reactivity is similar in purified and natural water, but differences are observed for each pesticide according to the role that natural organic matter (NOM) plays: filter effect of the light or photosensitizer. For each organophosphorus pesticide, experiments have been performed to identify the photodegradation products. Some photoproduct structures will be proposed according to mass spectral informations.

Field studies were conducted in 1992 and 1993 in Hermiston, Oregon, to evaluate nontarget impacts of transgenic Bt potato (Newleaf) expressing Cry3Aa protein derived from Bacillus thuringiensis (Bt) Berliner subsp. tenebrionis and conventional insecticides for control of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say). Pitfall traps were used to estimate the abundance of nontarget ground-dwelling arthropods in different treatment plots. There were no significant differences in the trap captures of major ground-dwelling coleopteran predators such as carabids (Coleoptera: Carabidae) and staphylinids (Coleoptera: Staphylinidae) among Bt and non-Bt potato fields treated with weekly sprays of a microbial Bt-based formulation containing Cry3Aa, biweekly applications of permethrin, early and mid season in-furrow applications of systemic insecticides (phorate and disulfoton), or no insecticides. While weekly sprays of permethrin significantly reduced the trap capture of ground-dwelling spiders (Araneae), there were no significant differences in the capture of spiders between Bt and non-Bt-potato fields treated with Bt sprays, systemic insecticides, or no insecticides. Significantly more springtails (Collembola: Entomobryidae and Hypogastruridae) were captured in potato fields treated with permethrin than with any other CPB control regime (transgenic Bt potato alone, microbial Bt formulation containing Cry3Aa, applications of systemic insecticides, or no action controls), among which there were no significant differences. The relevance of these findings to field evaluation of nontarget impacts of transgenic Bt crops is discussed.

Thiamethoxam- and imidacloprid-treated seed were evaluated for controlling infestations of potato leafhopper, Empoasca fabae (Harris), in snap bean in Minnesota in 2001 and in New York and Illinois in 2002. Efficacy of these seed treatments was assessed by rating leafhopper damage to foliage or by monitoring densities of nymphs through the season in small field plots. Thiamethoxam provided longer and more consistent protection of the crop from leafhoppers than imidacloprid. In thiamethoxam-treated plots, there was no damage to foliage and densities of nymphs were maintained below economically damaging levels from the seedling stage through bloom. Thiamethoxam at a rate of 30 g (a.i.)/100 kg of seed controlled leafhoppers for 31 d to over 38 d. Additionally, as the rate of thiamethoxam increased, the duration of protection also increased. In contrast, imidacloprid at a rate of 60 g (a.i.)/100 kg of seed protected early growth stages of the crop from leafhoppers in only 1 of 4 plantings. Snap bean seed treated with thiamethoxam will provide growers with an option for controlling potato leafhoppers that is safer and more environmentally friendly than using soil-applied, systemic organophosphate insecticides such as disulfoton or phorate. Furthermore, difficulty associated with properly timing foliar sprays, inadequate coverage and reduced efficacy often encountered when treating young snap bean plants are avoided using seed treatments.

Disulfoton and phorate applied in the seed furrow greatly reduce clomazone phytotoxicity to cotton in the field, whereas aldicarb does not. An experiment was conducted to determine the effect of aldicarb, disulfoton, and phorate on 14C-clomazone absorption, translocation, and metabolism by cotton grown in a sandy loam soil. Clomazone at 0.87 μg g−1 of soil alone or in combination with aldicarb at 0.6 μg g−1 of soil reduced cotton root and shoot growth 26 to 33%. Root and shoot growth were not reduced by clomazone plus disulfoton or phorate at 0.6 μg g−1 of soil. Protection of cotton against injury by clomazone was not explained by reduced absorption or translocation of clomazone or a metabolite to the shoot. Clomazone metabolism was reduced by disulfoton and phorate, thus indicating a clomazone metabolite may be more toxic to cotton. Nomenclature: Aldicarb; clomazone; disulfoton; phorate; cotton, Gossypium hirsutum L. ‘McNair 235’.

To assess the photodegradation extent of the organophosphorus pesticides, fenthion and disulfoton in the environment, degradation rates of their chemicals under irradiation by visible light and each region of the ultraviolet (UV) sources, UVA (320‐400 nm radiation), UVB (280‐320 nm radiation) and UVC (250‐260 nm radiation) in liquid- and solid-phases were determined and their photolysis products identified. Although visible light did not cause photodegradation of either fenthion or disulfoton even after the maximal irradiation of 8 hr in both phases, all the ranges of UV sources resulted in the photolysis of both pesticides, despite the solid-phase. The photolysis rates of fenthion under UVB and UVC irradiation in both phases were higher than that under UVA irradiation and also exceeded all of the degradation rates of disulfoton. This confirms that fenthion is more readily degraded than disulfoton in the UVB range. Fenthion sulfoxide and disulfoton sulfoxide were identified as oxidative photolysis products whose photolysis rates were considerably slower than parent compounds, and the oxidation reaction of both pesticides in the liquid-phase was superior to those on the solid-phase, indicating that dissolved oxygen in water is an important factor affecting the photolysis. These results suggest that fenthion in the environment is more rapidly degraded by UVB irradiation in natural sunlight than disulfoton, and sulfoxides of both pesticides remain stable as a photolysis product in the environment.

Comparative toxicity of selected organophosphate (OP) insecticides against resistant and susceptible clones of the greenbug, Schizaphis graminum, were studied both in vitro and in vivo. Two resistant (OR-1 and OR-2) clones of the greenbug showed marginal to high levels of resistance to all seven OPs tested, ranging from 11- to 327-fold greater than those of a susceptible (OSS) clone. The OR-1 clone showed lower levels of resistance to phenyl (parathion and parathion-methyl) and heterocyclic (chlorpyrifos) OPs than to aliphatic OPs (dimethoate, omethoate, disulfoton, and demeton-S-methyl), whereas the OR-2 clone showed a rather broad spectrum of resistance to nearly all OP insecticides examined. In vitro inhibition of acetylcholinesterase (AChE) using six selected OP oxon analogues showed that alterations of AChE were involved in resistance to all OP compounds examined in both the OR-1 and OR-2 clones. Although the levels of insensitivity of AChE to these OPs were relatively low, ranging from 1.1- to 3.8-fold, the insensitivity spectrum of AChE to different OPs was rather broad. The general esterase activity in the OR-1 and OR-2 clones was 1.3-8. 4-fold higher than that in the OSS clone, depending on the substrates used. The AChE activity in both the OR-1 and OR-2 clones was 1.8-fold higher than that in the OSS clone. High resistance levels of the OR-2 clone to phenyl and heterocyclic OPs appeared to be associated with the ability of the esterases to hydrolyze beta-naphthyl acetate and more hydrophobic substrates.

The damage–yield-loss relationships of Hessian fly, Mayetiola destructor Say, in soft red winter wheat, Triticum aestivum L., were examined using results of studies on Hessian fly management and yield loss that were conducted over a 9-yr period with various cultivars and planting times and at various locations in Georgia. Differences in grain yield and test weight of susceptible and resistant cultivars with or without a systemic insecticide (disulfoton or phorate) at planting were compared with the percentage of infested tillers in autumn (vegetative stage) and the percentage of infested stems or the number of immatures per stem in spring during grain filling. Grain yield loss increased linearly with increasing percentage of autumn-infested tillers and spring-infested stems. Infestations had little effect on grain test weight until infestations exceeded 20% of autumn-infested tillers or 38% of spring-infested stems. Grain yield and test weight losses were exponentially related to number of immatures per stem during grain filling, with proportionate loss increasing as immature numbers increased up to 6 immatures per stem. Analysis of grain yield components of headed stems found that injury reduced seeds per spike, spikelets per spike, seeds per spikelet, and seed weight. Gain thresholds indicated that, depending on commodity price, an application of a systemic insecticide at planting provided positive marginal returns for 68–74% of plot-years ( n = 50) on susceptible cultivars but only provided positive returns for 23–27% of plot-years ( n = 26) on resistant cultivars. Depending on control cost, economic damage occurred when autumn infestations exceeded 5–8% of infested tillers or when spring infestations exceeded 13–20% of infested stems, or 0.4–1.0 immatures per stem. These results provide a quantitative basis for Hessian fly damage loss assessment in wheat.

Organophosphorus hydrolase (OPH, EC 8.1.3.1) is a dimeric, bacterial enzyme that detoxifies many organophosphorus neurotoxins by hydrolyzing a variety of phosphonate bonds. The histidinyl residues at amino acid positions 254 and 257 are located near the bimetallic active site present in each monomer. It has been proposed that these residues influence catalysis by interacting with active site residues and the substrate in the binding pocket. We replaced the histidine at position 254 with arginine (H254R) and the one at position 257 with leucine (H257L) independently to form the single-site-modified enzymes. The double modification was also constructed to incorporate both changes (H254R/H257L). Although native OPH has two metals at each active site (four per dimer), all three of these altered enzymes possessed only two metals per dimer while retaining considerable enzymatic activity for the preferred phosphotriester (P-O bond) substrate, paraoxon (5-100% kcat). The three altered enzymes achieved a 2-30-fold increase in substrate specificity (kcat/Km) for demeton S (P-S bond), an analogue for the chemical warfare agent VX. In contrast, the substrate specificity for diisopropyl fluorophosphonate (P-F bond) was substantially decreased for each of these enzymes. In addition, H257L and H254R/H257L showed an 11- and 18-fold increase, respectively, in specificity for NPPMP, the analogue for the chemical warfare agent soman. These results demonstrate the ability to significantly enhance the specificity of OPH for various substrates by site-specific modifications, and it is suggested that changes in metal requirements may affect these improved catalytic characteristics by enhancing structural flexibility and improving access of larger substrates to the active site, while simultaneously decreasing the catalytic efficiency for smaller substrates.

Chemicals used in this study: acephate (Orthene 75 S) O,S-dimethyl phosphoramidothioate; bendiocarb (Turcam 76 W) 2,2-dimethyl­ 1,3-benzodioxol-4-yl methylcarbamate; bifenthrin (Talstar 0.2 G, Talstar F) 2-methyl (1,1'-biphenyl)-3-yl methyl 3-(2-chloro-3,3,3,­ trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate; carbofuran (Furadan 4 F) 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate; chlorpyrifos (Lorsban 15 G, Dursban Turf, SuSCon Green) O,O-diethyl O-(3,5,6-trichloro-2­ pyridinyl)phosphorothioate; disulfoton (Di-Syston 15 G) O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate; fipronil (Chipco Choice) 5-amino-1-(2,6-dichlorotrifluoro-p-tolyl)-4-trifluoromethylsulfinyl-pyrazole-3-carbonitrile; halofenozide (Mach 2 2SC) 4-chloro-2­ benzoyl-(l,l-dimethyl) hydrazide benzoic acid, imidacloprid (Marathon 60 W, Marathon 1 G) 1-[(6-chloro-3-pyridinyl)methyl]-N-nitro­ 2-imidazolidinimine; isofenphos (OftanoI2) 1-methylethyI2-[[ethoxy[(1-methylethyl) amino]-phophinothioyl]oxy]benzoate; tefluthrin (Fireban 1.5 G) 2,3,5,6-tetrafluoro-4-methylbenzyl cis-3-(Z-2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethylcyclopropanecarboxylate. Significance to the Nursery Industry White grubs, larvae of scarab beetles, damage and destroy roots of their hosts and can cause rejection of nursery stock for interstate and international commerce. Preplant incorpo­ ration ofFireban 1.5 G (tefluthrin) or Talstar 0.2 G (bifenthrin) can provide multi-year protection of container-grown nurs­ ery stock from these larvae. The labeled rate of Marathon 60 W (imidacloprid), drenched during mid-summer, also pro­ vided complete control of Japanese and oriental beetle lar­ vae during the year of application. Product cost for preplant incorporation of Talstar is about 1 cent per #1 container (2.5 liter), depending upon the bulk density of the growing me­ dium. The Talstar F drench treatment is about the same cost, and may be appropriate for established plants. Marathon 1 G preplant incorporation costs 17.5 cents per #1 container; the extra cost may be partially offset by the expected control of

Experiments were conducted in 1993 and 1994 to determine if seed treated with disulfoton at 3, 6, or 12 g ai kg−1 reduced bleaching of rice foliage caused by clomazone applied delayed preemergence at 0.56, 1.1, 1.7, or 2.2 kg ai ha−1 on silt loam and silty clay soils. Clomazone injured rice more on silt loam soil than on silty clay soil. Disulfoton reduced bleaching caused by clomazone. In additional field experiments conducted during 1995 and 1996, clomazone at rates as high as 2.2 kg ha−1 did not affect grain yield in seven of 10 experiments. Clomazone at rates below 1.7 kg ha−1 did not reduce grain yield in any of the experiments.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:02:21Z No. of bitstreams: 1 S0301-80591998000100017.pdf: 38452 bytes, checksum: c2b2db5691ca6f2b990cc9e90b8bc657 (MD5) Made available in DSpace on 2013-08-22T19:02:21Z (GMT). No. of bitstreams: 1 S0301-80591998000100017.pdf: 38452 bytes, checksum: c2b2db5691ca6f2b990cc9e90b8bc657 (MD5) Previous issue date: 1998-03-01 Made available in DSpace on 2013-09-30T17:51:43Z (GMT). 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No. of bitstreams: 2 S0301-80591998000100017.pdf: 38452 bytes, checksum: c2b2db5691ca6f2b990cc9e90b8bc657 (MD5) S0301-80591998000100017.pdf.txt: 22015 bytes, checksum: 959ccf8d7a86a39de08edda3c83d5998 (MD5) Previous issue date: 1998-03-01 Avaliou-se a eficiência de métodos de aplicação de inseticidas granulados sistêmicos para o controle das cigarras Quesada gigas (Olivier) e Dorisiana drewseni (Stål) do cafeeiro (Coffea arabica). O ensaio foi conduzido em cafezal cv. Mundo Novo com idade de seis anos, espaçamento de 3,5 X 1,5 m, com uma planta/cova, no ano agrícola 1992/1993. Utilizou-se um delineamento em blocos casualizados, com 21 tratamentos e 4 repetições, cada uma contendo parcelas de cinco plantas. Os tratamentos consistiram nas aplicações dos produtos triadimenol + disulfoton 1,5% + 7,5% (26 g/cova), aldicarb 150G (10,00 g/cova), ethoprophos 100G (30,00 g/cova), phorate 5G (80,00 g/cova) e terbufos 5G (40,00 g/cova) em quatro modalidades de aplicação: aplicador costal manual Mebuki TF8; canequinha, lançando o produto para o ápice da planta; aplicador tratorizado Kamaq CK2-AG; e sulcos em meia lua, abertos manualmente, na projeção da copa. As avaliações foram realizadas aos 70, 105 e 140 dias após aplicação dos produtos, onde foram efetuadas aberturas de trincheiras de 50 X 50 X 50cm por cova, procedendo-se a contagem do número de ninfas vivas. Concluiu-se que o aplicador costal manual e canequinha revelaram-se os mais eficientes (86,0 - 93,5% e 76,8 - 86,7%, respectivamente); aplicação tratorizada e sulcos na projeção de copa tiveram sua eficiência variável com o produto utilizado; terbufos apresentou maior redução da população (98,2 - 100%) e phorate (79,6 - 99,1%) e a mistura triadimenol + disulfoton (82,3 - 97,3%) apresentaram alta eficiência, não diferindo do terbufos. Aldicarb apresentou desempenho satisfatório (68,1 - 85,0%) conforme o modo de aplicação e ethoprophos não foi eficaz quando aplicado com o aplicador costal manual (58,4%), canequinha (45,1%) e sulco (31,9%). The influence of application methods on the efficacy of granular systemic insecticides used in the control of Quesada gigas (Olivier) and Dorisiana drewseni (Stål) attacking coffee (Coffea arabica) trees was studied. The trial was set up in a 6 years-old coffee cv. Mundo Novo plantation, planted in 3.5 X 1.5 m spacing, during 1992/1993. The experimental design used was randomized blocks, with 21 treatments replicated 4 times, each with 5 plants/ plot. The insecticides triadimenol + disulfoton 1.5% + 7.5% (26 g/tree), aldicarb 150G (10.0 g /tree), ethoprophos 100G (30.0 g/tree), phorate 5G ( 80.0 g/tree) and terbufos 5G (40.0 g/tree) were applied using four methods: manually operated knapsack applicator Mebuki TF8; throwing manually a mugfull of granules on the top of the canopy; tractor powered granule applicator, Kamaq CK2-AG, applying in furrow under the canopy; and in furrow manual application of granules. Assessment of control was carried out counting live nymphs at 70, 105 and 140 days after application, in a pit measuring 50 X 50 X 50 cm made underneath the plant canopy. The application method using the knapsack applicator and the mug showed to be the most effective (86.0 - 93.5% and 76.8 - 86.7%, respectively); application by tractor and in furrow under canopy afforded variable efficiency according to the chemical used; the performance of terbufos was the highest in reducing (98.2 - 100%) the cicadas population. Phorate (79.6 - 99.1%) and the mixture triadimenol + disulfoton (82.3 - 97.3%) were also effective, similar to terbufos; aldicarb gave a satisfactory control (68.1 - 85.0%) according to the application method and ethoprophos, did not control well the cicadas when applied with knapsack (58.4%), manually (45.1%) and in furrow (31.5%). UNESP FCAVJ Departamento de Defesa Fitossanitária UNESP FCAVJ Departamento de Ciências Exatas UNESP FCAVJ Departamento de Defesa Fitossanitária UNESP FCAVJ Departamento de Ciências Exatas

In order to know the photochemical behaviors of pesticides in natural water and on the surface of solids such as agricultural leaves and clay particles, the degradation patterns of 35 organophosphorus, 28 organonitrogens, 9 organochlorines and 7 pyrethroid pesticides in distilled water and on the silica gel plate during exposure to UV light (365 nm) for four hours were investigated. The percentages of the degradation of pyrethroid and organophosphorus pesticides were higher than those of organochlorine and organonitrogen pesticides under photoexposure in distilled water and on the silica gel plate. The percentages of degradation of all the pyrethroid pesticides were higher than 36%. Besides, the photochemical degradation on the thioether groups in disulfoton and fenthion were beyond 70%. Photochemical degradation products derived from disulfoton and fenthion were confirmed to be disulfoton sulfoxide and fenthion sulfoxide by GC-MS. The percentages of degradation of hormothion, disulfoton, fenthion, vamidothion, edifenfos and pyridafenthion on the silica gel plate were superior to those in distilled water. These findings suggested that those pesticides described above on the surface of solids such as agricultural leaves and clay particles were readily degradated as compared with those in natural water.

Milligram quantities of sulfoxides, sulfones, and oxygen analogue (oxon) sulfones of the insecticides disulfoton, phorate, and terbufos were prepared by selective oxidation. Pure insecticides or acetone extracts of granular formulations served as reactants. Structures of 9 compounds were confirmed by comparing their electron impact mass spectra (EI-MS), obtained by the direct inlet system with published data. Thin-layer chromatography (TLC) on silica gel was used to screen oxidation products and to purify products. Products were detected by spraying plates with PdCl2 reagent and exposing to iodine vapors. An esterase inhibition technique gave low detection limits, which are promising for residue analysis.

Insecticide resistance in insects often is associated with elevated acetylcholin esterases and carboxylesterases. Three greenbug, Schizaphis graminum (Rondani), strains with different general esterase patterns were tested for differences in insecticide response. The standard strain had no noticeable elevated esterase activity. Pattern 1 and pattern 2 strains had different elevated esterase patterns. Toxicity of 5 organophosphorous (chlorpyrifos, dimethoate, disulfoton, malathion, and parathion) and 2 carbamate (carbofuran and methomyl) insecticides were tested using surface residue bioassays. Esterase pattern 1 greenbugs had significantly higher LC50s for each of the organophosphorous insecticides, but the LC50 for the 2 carbamate insecticides were not higher than the standard strain. Esterase pattern 2 greenbugs had significantly higher LC50s for 4 of the 5 organophosphorus insecticides (chlorpyrifos, dimethoate, disulfoton, and parathion) and the 2 carbamate insecticides, but the LC50 for malathion was not higher than the standard strain. Pattern 2 greenbugs had significantly higher tolerance to disulfoton than did pattern 1 greenbugs. This indicates that certain strains of the greenbug are cross resistant to many of the organophosphorous and carbamate insecticides currently labeled for greenbug control in wheat and sorghum. There is an urgent need to find alternative control measures.

Abandoned landfill sites pose an uncertain threat to water quality and environmental health. These sites, often located in rural areas, historically had little or no regulation for use or maintenance, and it is often unknown what hazardous materials may have been discarded. Evaluation and remediation of these sites can be extremely costly. Numerical models of contaminant fate and transport can be a cost-effective tool for assessing the potential hazards that a site may pose and for evaluating potential remediation measures, but seldom are models available which can simulate all aspects of contaminant fate and transport under complex site conditions. A study is presented describing the site investigation and remediation of an abandoned landfill reported to contain unknown quantities of disulfoton, an acutely toxic pesticide. Depending upon disulfoton concentration, it may or may not be dissolved in the soil water; thus, it may be transported in the soil either in an aqueous (dissolved) phase solution with soil water or as a non-aqueous phase liquid (NAPL). Because of the complex nature of the site and contaminant, it was necessary to employ three different numerical models to analyze different aspects of the problem. The article focuses particular attention on the use of different models for contaminant transport modeling in support of a Remedial Investigation (RI). Model selection was based on the contaminant phase and soil conditions. Various scenarios were hypothesized due to the uncertainty of input parameters. Procedures are presented for site remediation based on site investigation, numerical modeling and risk assessment.

Organophosphates (OPs) are widely used as pesticides, and its urinary metabolites as well as the blood cholinesterases (ChEs) activity have been reported as possible biomarkers for the assessment of this pesticide exposure. Moreover, the OPs can induce mutagenesis, and the bone marrow micronucleus test is an efficient way to assess this chromosomal damage. This paper reports a study carried out to verify the correlation among the disulfoton exposure, blood ChEs activity, urinary diethyl thiophosphate (DETP), and diethyl dithiophosphate (DEDTP), as well as micronucleated polychromatic erythrocytes (MNPCEs) frequency. Four groups of rats (n=12) were exposed to disulfoton at 0, 2.8, 4.7, and 6.6 mg kg-1 body weight. The blood ChEs activity, urinary DETP and DEDTP concentrations, and MNPCEs frequency were determined. It was observed that the plasmatic and erythrocytary ChEs activity decreased from 2.9% to 0.5% and from 35.9 to 3.3%, respectively, when the disulfoton dose was increased from 0 to 6.6 mg kg-1 (correlation of 0.99). Urinary DETP and DEDTP concentrations, as well as the MNPCEs frequency, increased from 0 to 6.58 µg mL-1, from 0 to 0.04 µg mL-1, and from 0 to 1.4%, respectively, when the disulfoton dose was increased from 0 to 6.58 mg kg-1 body weight.Os organofosforados (OPs) são amplamente usados como praguicidas e a atividade da colinesterase sanguínea bem como os metabólitos urinários desses praguicidas têm sido reportados como biomarcadores eficazes para avaliar casos de exposição. Além disso, os OPs podem induzir mutagênese e o teste de micronúcleo de medula óssea é uma boa alternativa para avaliar os danos cromossômicos. Esse artigo reporta um estudo sobre a correlação entre a exposição a dissulfoton, a atividade da colinesterase sanguínea, a excreção urinária de dietil tiofosfato e dietil ditiofosfato e a frequência de micronúcleos em eritrócitos policromáticos. Quatro grupos de ratos (n=12) foram expostos a dissulfotom nas doses de 0, 2,8, 4,7, e 6,6 mg kg-1 de peso corpóreo. A atividade da colinesterase sanguínea as concentrações urinárias de dietil tiofosfato e dietil ditiofosfato e a frequência de micronúcleos foram determinadas. Os resultados demonstraram que as atividades da colinesterase plasmática e eritrocitária diminuíram de 2,9 para 0,5% e de 35,9 para 3,3% , respectivamente, quando a dose de dissulfoton foi aumentada de 0 para 6,6 mg kg-1 (correlação de 0,99). As concentrações urinárias de dietil tiofosfato e dietil ditiofosfato bem como a frequência de micronúcleos aumentaram de 0 a 6,56 µg mL-1, 0 a 0.04 µg mL-1 e de 0 a 1.4%, respectivamente, quando a dose de dissulfotom foi aumentada de 0 a 6,58 mg kg-1.

The 96-h toxicity of four organophosphates (thiometon, disulfoton, malathion, and demeton-S-methyl, the oxygen analogue of thiometon) in the freshwater bivalve mollusc Dreissena polymorpha was tested using different nominal concentrations ranging between 6 and 50 mg/L. No mortalities were observed in mussels exposed to malathion and demeton-S-methyl (26 mg/L and 6 mg/L, respectively), and at the lowest concentrations of thiometon and disulfoton (6 and 10 mg/L, respectively). At higher thiometon and disulfoton concentrations, mortalities occurred. At the highest concentrations of 50 mg thiometon/L and 30 mg disulfoton/L, mussel mortalities of 88 and 93%, respectively, were determined. Organophosphate concentrations of up to a factor 10 times higher than in the ambient water were found in exposed mussels, irrespective of whether they were alive or dead. The search for organophosphate metabolites via GC/MS analysis of mussel tissue extracts was negative, suggesting lacking or low oxidative activation of the insecticides used. The mollusc is highly resistant to toxic effects of organophosphate insecticides and their biological active oxygen analogues.

This study describe an analytical method employing gas chromatography (GC) using flame photometric detection that has been developed for the simultaneous determination of organophosphate pesticides (diazinon, disulfoton, parathion, chlorpyrifos and malathion) in strawberry samples. For this purpose, molecularly imprinted solid-phase extraction was applied as a sample preparation technique. The method was linear in the ranges from 0.10 to 1.00 μg g(-1), for diazinon, disulfoton, parathion and chlorpyrifos, and 0.10 to 2.00 μg g(-1) for malathion with r0.99. The detection limits (LD) ranged from 0.02 to 0.05 μg g(-1). Recovery studies yielded average recoveries in the range of 65.25 to 87.70 %. These results showed the potential of this technique for organophosphate residue monitoring in strawberry samples.

A liquid chromatography–tandem mass spectrometry method was developed and validated for simultaneous determination of disulfoton and five of its oxidative metabolites (disulfoton-sulfoxide, disulfoton-sulfone, demeton-S, demeton-S-sulfoxide and demeton-S-sulfone) in human whole blood and urine. Extraction was undertaken using a QuEChERS method, which is commonly used in food analysis. D 10 -Disulfoton was used as the internal standard. Separation was carried out using a CAPCELL-PAK MG II column (35×2.0mm i.d., 5μm, Shiseido) with a mobile phase of 10mmol/L ammonium formate and methanol. This method was applied in an autopsy case, and disulfoton and its oxidative metabolites were successfully detected in both blood and urine. The concentrations of disulfoton in the blood and urine were 360 and 23.8ng/mL, respectively. There was a relatively low concentration of demeton-S in both the blood (4.0ng/mL) and urine (45.7ng/mL). To date, there have been no reported cases of detection of demeton-S in human samples.

The toxicity of the organophosphorous insecticides thiometon and disulfoton as well as some of their degradation products was determined using Daphnia magna, Photobacterium phosphoreum (Microtox ® ) and an acetylcholinesterase (AChE) activity assay. For comparison, the toxicity of the organophosphorous insecticides dichlorvos, fenitrothion, parathion, etrimfos, propetamphos and quinalphos was measured. Although disulfoton and thiometon have a similar molecular structure they showed different inhibitory effects on D. magna and P. phosphoreum . Some of their degradation products (PO analogs) were stronger inhibitors of AChE than the parent compounds and showed also higher toxicity in the bioassay with D. magna. D. magna was less sensitive to the degradation products lacking the sulfur containing side-chain and to the low molecular weight sulfur compounds. A toxicological model was used to predict the toxicity of disulfoton and thiometon and their degradation products in soil leachates in the D. magna and P. phosphoreum bioassays. The predictions were based on the toxicity of the single compound and the concentration of each compound in the leachate. The predictions made showed good correlations with the determined toxicity for both bioassays.

The rate of loss of [14C]carbofuran, and the rate of formation of metabolites from it, were studied in a ‘treated’ soil, in which the insecticide was rapidly degraded. Metabolic inhibitors were added to the soil to study their effects upon these processes. The organophosphorus compounds paraoxon, chlorfenvinphos, and disulfoton, which, in their active forms, are inhibitors of ‘B’ esterases, all caused a temporary reduction of the rate of loss of carbofuran from the soil. However, within a period of 3–21 days, depending on the compound, the soil recovered its ability to break down carbofuran rapidly. The incorporation of both piperonyl butoxide (an inhibitor of oxidations catalysed by monooxygenases which contain cytochrome P450) and paraoxon into soil reduced the rate of loss to a greater extent and over a longer period than was found with paraoxon alone. Where soils were treated with paraoxon alone, or with paraoxon plus piperonyl butoxide, larger quantities of the primary oxidative metabolites 3-keto-carbofuran (< 4.1% of applied carbofuran) and 3-hydroxy-carbofuran (< 1.2% of applied carbofuran) were found than in control soils in which the corresponding values were < 0.54% and < 0.43% respectively. The results were consistent with the hypothesis that inhibition of microbial enzymes was the main reason for the stabilization of carbofuran in this soil following treatment with these compounds. The evidence suggested that esterase hydrolysis provided a major rate of breakdown, whilst oxidative metabolism provided a minor one. The higher levels of oxidative metabolites in soils treated with paraoxon and paraoxon plus piperonyl butoxide were thought to be due to the inhibition of their further metabolism. The possible use of certain of these compounds as ‘extenders’ for carbofuran in problem soils is discussed.

Five concentrations (0.0, 0.06, 0.03, 0.003, and 0.0003 g [AI]/liter) of esfenvalerate (pyrethroid) and five concentrations (0.0, 0.50, 0.25, 0,025, and 0.0025 g [Al]/liter) of disulfoton (organophosphate) changed the behavior of the blackmargined aphid, Monellia caryella (Fitch), the black pecan aphid, Melanocallis caryaefoliae (Davis), and the yellow pecan aphid, Monelliopsis pecanis Bissell. Esfenvalerate increased aphid activity (walking and changing position) and decreased the time spent by aphids on insecticide-treated leaves. All concentrations increased the number of aphids leaving the leaves. Black pecan aphids and yellow pecan aphids left the leaves either by walking or dropping off, but blackmargined aphids left the leaves mainly by flying off. Disulfoton had less effect on aphid behavior than esfenvalerate. Only some concentrations of disulfoton increased aphid activity with more time spent walking, but the time of walking was much shorter than the time spent settling. The blackmargined aphid and the yellow pecan aphid were less susceptible to each insecticide than the black pecan aphid.

The stability of the standard solutions for 20 organophosphorus, 19 organonitrogen and 7 pyrethroid pesticides during storage under different conditions (solvent, concentration of pesticides, with or without light) was investigated by gas chromatograph (GC). All of the investigated 46 pesticides were stable during twenty days under all conditions except storage under sunlight. It was found that 12 pesticides dissolved in acetone in low concentration decreased under sunlight. Photo-changed compounds of aldicarb, disulfoton, and fensulfothion in acetone were investigated by GC. It was clarified that these pesticides were gradually changed into their oxydative products (sulfoxide and sulfone). Consequently, it is recommendable that the standard solution for pesticides should be dissolved in hexane, in high concentration and kept in the dark.

Potatoes were grown from cut seed in Plainfield sand treated in-furrow with disulfoton (Di-Syston 15G, 3.36 kg AI/ha) in 1983 and from whole seed in similarly treated loam in 1991. Soils were contained in 2 m2 field plots. Soil, seed potato and foliage were analyzed for the insecticide and its sulfoxide and sulfone metabolites during the 8-12 wk following planting. Disulfoton disappeared at different rates from the two soils (ksand = 0.024 day-1, kloam = 0.056 day-1) with partial conversion to the sulfoxide and sulfone in both. Larger quantities of the three insecticidal components were absorbed by the seed potato in the cut-seed/sand combination. The relative amounts of these components in the seed potato also differed between treatments with disulfoton being the largest component of the cut-seed/sand and smallest in the whole-seed/loam. Disulfoton sulfoxide and sulfone were the major insecticidal components of the foliage and concentrations in the initial foliage (each ca. 10 ppm) were similar for both treatments. Sulfoxide concentrations in the foliage decreased more rapidly than the sulfone and the decrease in concentration of each of the components was similar for the two treatments.

The degradation of 10 organophosphorus pesticides in natural estuarine waters was studied. Estuarine water samples were spiked with organophosphorus pesticides at 50 μg/L level and were placed into 2-L Pyrex flasks being exposed outdoor to ambient sunlight and temperature. A sample of 10-75 mL of water was collected every week for analysis during a period of 5-6 weeks from January to March. The analytical determinations were performed by solid-phase extraction (SPE) with C 18 Empore disks followed by GC-NPD and GC-MS with El and by on-line SPE using PLRP-s exchangeable cartridges (Prospekt) followed by LC-DAD and LC-thermospray MS in PI mode. Five organophosphorus pesticides were stable for less than 1 week (disulfoton, fenamiphos, fenthion, malathion, and temephos), others had a half-life of ca. 1 week (chlorpyrifos-methyl, methidathion, and diazinon), and the rest showed a half-life of ca. 10 days (isofenphos and pyridafenthion). The half-life of three pesticide transformation products : disulfoton sulfoxide, disulfoton sulfone, and fenthion sulfoxide varied from 7 to 12 days.

Fifteen pesticides including some of their metabolites (disulfoton sulfoxide, ethoprophos, cadusafos, dimethoate, terbufos, disulfoton, chlorpyrifos-methyl, malaoxon, fenitrothion, pirimiphos-methyl, malathion, chlorpyrifos, terbufos sulfone, disulfoton sulfone and fensulfothion) were analysed in milled toasted wheat and maize as well as in wheat flour and baby cereals. The QuEChERS (quick, easy, cheap, effective, rugged and safe) methodology was used and its dispersive solid-phase extraction procedure was optimised by means of an experimental design with the aim of reducing the amount of co-extracted lipids and obtaining a clean extract. Gas chromatography with nitrogen phosphorus detection were used as the separation and detection techniques, respectively. The method was validated in terms of selectivity, recoveries, calibration, precision and accuracy as well as matrix effects. Limits of detection were between 0.07 and 34.8 µg kg(-1) with recoveries in the range of 71-110% (relative standard deviations were below 9%). A total of 40 samples of different origin were analysed. Residues of pirimiphos-methyl were found in six of the samples at concentrations in the range 0.08-0.47 mg kg(-1), which were below the MRLs established for this pesticide in cereal grains. Tandem mass spectrometry confirmation was also carried out in order to identify unequivocally the presence of this pesticide.

California’s surface water monitoring results from 1991 through 2010 were analyzed to determine whether 12 organophosphorus insecticides and herbicides (i.e., azinphos methyl, bensulide, dimethoate, disulfoton, ethoprop, fenamiphos, methamidophos, methidathion, methyl parathion, naled, phorate, and phosmet) and their degradates have been detected above maximum concentration limits (MCLs) in Pacific salmonid habitats. Methidathion, methyl parathion, phorate, phosmet, and the oxygen analogue of naled (DDVP) detections exceeded MCLs. Methyl parathion detections may be accounted for by monthly use trends, while methidathion detections may be explained by yearly use trends. There were inadequate phorate, phosmet, or DDVP data to evaluate for correlations with use.

Release of Periflus bioculatus (F.) (Hemiptera: Pentatomidae) nymphs at either 1.6/row-m (0.5/row-ft) or 9.8/row-m (3/row-ft) significantly reduced the number of both small and large larvae of the Colorado potato beetle in small plots. The number of Colorado potato beetle egg masses was significantly reduced by the high release rate as well as by the low rate in combination with a reduced spray schedule of Bacillus thuringiensis var. tenebrionis Berliner. Potato plant defoliation was significantly reduced by the high release rate. Three systemic soil insecticides (disulfoton, phorate, and aldicarb) caused significant mortality of P. bioculatus nymphs exposed to potato foliage 11 weeks after soil application. Four foliar insecticides had no effect on P. bioculatus nymphs exposed to recently sprayed foliage.

A 2-yr study of the effect of in-furrow application of aldicarb, disulfoton, carbofuran, and acephate on the level or frequency of resistance in the cotton aphid, Aphis gossypii Glover, revealed an increase in tolerance of survivors to bifenthrin (pyrethroid) and endosulfan (CHHC), two commonly used aphicides. With the exception of a low dose of acephate, all granular insecticides applied at planting increased the tolerance of surviving field-collected aphids and their offspring to both of these pesticides. Because alternative control measures may contribute more to the resistance problem than the use of granular insecticides at planting, the use of granular insecticides is still recommended as one of the steps to be taken in resistance management.

Field and greenhouse experiments evaluated interactions of soil-applied insecticides and imazaquin and imazethapyr on growth and development of cotton. Imazaquin and imazethapyr were applied PPI at 0 to 6 and 0 to 16 g ae ha7l, respectively, in the greenhouse (plus a no-insecticide control), and 0 to 72 g ha-1 in the field in combination with aldicarb, disulfoton, and phorate (without a no-insecticide control) applied in the seed furrow. Cotton shoot fresh weight in the greenhouse experiment decreased linearly as herbicide rates in- creased. Greater reductions in shoot fresh weight were noted with imazaquin than with imazethapyr. Compared with no insecticide, the methylcarbamate insecticide aldicarb and the organophosphate insecticides disulfoton and phorate did not affect cotton response to either herbicide. In the field, cotton injury increased while stand, yield, and maturity decreased as herbicide rates increased. Delayed maturity was due to a lower percent- age of bolls produced on sympodia from main stem nodes four to nine. Imazaquin caused greater injury, greater reductions in stand, greater delays in maturity, and lower yields than did imazethapyr. Earlier maturity was noted with aldicarb-treated cotton. Compared with aldicarb, disulfoton and phorate did not alter cotton response to imazaquin or imazethapyr. Nomenclature: Aldicarb, 2-methyl-2-(methylthio)propionaldehyde O-(methylcar- bamoyl)oxime; disulfoton, O,O-diethyl S-(2- (ethylthio)ethyl) phosphorodithioate; imazaquin, 2-(4,5- dihydro-4-methyl-4-(1-methylethyl)-5-oxo-lH-imidazol-2- yl)-3-quinolinecarboxylic acid; imazethapyr, (?)-2-(4,5- dihydro-4-methyl-4-(1-methylethyl)-5-oxo-lH-imidazol-2- yl)-5-ethyl-3-pyridinecarboxylic acid; phorate, O,O-diethyl S-(2-(ethylthio)-methyl phosphorodithioate; cotton, Gos- sypium hirsutum (L.) 'Deltapine 90', 'Stoneville Coker 304', 'Stoneville KC 380', and 'Stoneville McNair 235'. Additional index words: Pesticide interactions, maturity, plant mapping, fiber quality, aldicarb, disulfoton, phorate.

Characterization of Disulfoton-Induced Behavioral and Neurochemical Effects Following Repeated Exposure. Llorens, J., Crofton, K. M., Tilson, H. A., Ali, S. F., and Mundy, W. R. (1993). Fundam. Appl. Toxicol. 20, 163-169. These experiments examined the relationship between behavioral alterations and neurochemical changes in rats exposed repeatedly to disulfoton, an organophosphate cholinesterase inhibitor. Male Long-Evans rats were injected ip for 30 days with 0, 0.5, 1, or 2 mg/kg of disulfoton in corn oil. Clinical signs and motor activity were measured during the course of repeated exposure. Cognitive function, as measured in the Morris water maze, and passive avoidance procedures were assessed near the end of the dosing regimen. Regional brain acetylcholinesterase (ACHE) activity was measured during the course of dosing while the total number of muscarinic receptors was measured at the end of the dosing regimen. Tolerance developed rapidly to the clinical signs produced by disulfoton, but not to the disulfoton-induced decrease in motor activity. Disulfoton affected the acquisition of water maze performance, but had no effect on passive avoidance acquisition or retention. Repeated exposure to disulfoton decreased brain AChE activity and the number of [ 3 H]quinuclidinyl benzilate binding sites. These data indicate that, in spite of muscarinic receptor down-regulation that followed repeated exposure to disulfoton, animals become tolerant to only some of the functional effects produced by this chemical.

An experiment was conducted at four locations during 1990 and 1991 to determine the response of cotton to 1.12 kg ai ha-1 of clomazone applied PPI in combination with in-furrow application of 0.50 kg ai ha-1 of aldicarb plus 0.14, 0.28, and 0.56 kg ai ha-1 of either disulfoton or phorate. Early-season cotton injury ranged from 15 to 63% with clomazone plus aldicarb. Stands were reduced 31 and 61% at two locations, and yield was reduced 50% at one location. Applied in combination with aldicarb, all three rates of disulfoton and 0.28 and 0.56 kg ha-1 of phorate protected cotton from clomazone injury. Phorate at 0.14 kg ha-1 partially protected cotton from clomazone injury.

In 1979, a strain of spotted alfalfa aphid, Therioaphis trifolii (Monell) f. maculata (Buckton), from Tamworth, New South Wales, was resistant to pirimicarb (748- fold), disulfoton (48-fold), dimethoate (42-fold), thiometon (25-fold), demeton-S-methyl (20-fold), monocrotophos (11-fold), and omethoate (9.4-fold) compared with a susceptible reference strain at the LC50S Laboratory bioassays indicated low-order resistance to fen-valerate (2.8-fold) and methamidophos (2.6-fold). The strain was susceptible to several insecticides, including chlorpyrifos (ethyl), methidathion, and endosulfan. These three chemicals effectively controlled the resistant strain in the field. Chlorpyrifos was subsequently recommended for control of resistant populations. The same pattern of resistance was detected in strains of T. trifolii from several other areas of New South Wales and South Australia by 1981, Victoria by 1983, and Queensland by 1984. Chemical control of T. trifolii decreased substantially from the early 1980s because of the implementation of an integrated pest management program based on resistant alfalfa cultivars, imported biological control agents, cultural practices, and chemical control measures that were compatible with beneficial species. Control problems with insecticides were not reported from 1985 to 1990, when chlorpyrifos failed to control T. trifolii at Keith in South Australia. Laboratory tests indicated low-level resistance to chlorpyrifos.

Three methods were compared for applying the systemic insecticides, disulfoton and carbofuran, at planting to control the hessian fly [Mayetiola destructor (Say)] in winter wheat (Triticum aestivum L. em Thell). Liquid insecticides injected in furrow at planting with a microtube injection system were compared with granules placed in furrow and granules broadcast at planting. The injection of liquid formulations of both insecticides using a microtube system was as effective as in-furrow applications of granules when applied at the same rate. Broadcast applications of granules were less effective than both in-furrow methods for controlling hessian fly damage. The in-furrow injection of liquid insecticides using a microtube injection system is an effective alternative to granular insecticides for controlling the hessian fly in winter wheat.

The Hessian fly, Mayetiola destructor (Say), can cause severe damage to soft red winter wheat, Triticum aestivum L. em Theil, in the southeastern United States. The efficacy and cost effectiveness of in-furrow applications of disulfoton and phorate as alternatives to planting date modification and plant resistance for controlling Hessian fly damage in winter wheat was studied during the 1987-1988 and 1988-1989 seasons near Midville and Plains, Ga. The study consisted of a split-split plot design of two planting dates, three insecticide treatments, and four or six cultivars of soft red winter wheat. Populations were small and damage was minimal during the first season, but populations were large and damage was severe during the second season. Planting before the recommended planting date increased the severity of Hessian fly injury, but planting at the recommended date did not necessarily avoid Hessian fly damage during the fall. Applications of phorate and disulfoton were equally effective in controlling infestations in the fall and winter. Spring infestations also tended to be lower in treated than untreated plots. Plant resistance controlled Hessian fly damage throughout the season. Phorate reduced wheat seedling establishment in some trials, but this reduction did not adversely affect wheat productivity and economic returns. Low populations had little effect on wheat yield, test weight, and economic returns in 1987-1988. Hessian fly damage in 1988-1989 reduced grain yield, test weight, and straw weight in untreated susceptible cultivars. Use of a systemic insecticide at planting on Hessian fly susceptible cultivars provided a positive economic return regardless of planting date, and disulfoton and phorate provided similar economic benefits. When infestations were large, resistant cultivars provided a large economic benefit compared with an untreated susceptible cultivar. Insecticide use on a resistant cultivar was not economically justified. Planting a high-yielding, resistant cultivar without an insecticide provided similar or better economic returns than other management options. However, if high-yielding resistant cultivars are not available, use of a systemic insecticide at planting on susceptible cultivars in conjunction with proper cultural practices is a cost-effective alternative approach to managing the Hessian fly in wheat.

Life cycle studies showed that anthurium thrips, Chaetanaphothrips orchidii (Moulton) developed from egg to adult in 27.4 days. Studies confirmed that second‐instar nymphs migrated off the host plant and pupated in the media below. Insecticide granules were very effective in decreasing thrips‐injured flowers for 5 months. Aldicarb 10G and disulfoton 15G were most effective, followed by chlorpyrifos 2G and oxamyl 10G, respectively. As foliar sprays, bifenthrin 10W.P, cyfluthrin 2.0E.C and chlorpyrifos 1.0M.E were also effective in reducing thrips‐injured flowers; however, control did not persist after the last insecticide application. This study suggests the use of granular insecticides at 5‐month intervals or foliar sprays at 2‐week intervals to reduce anthurium thrips below economic injury levels in a pest management strategy.

Quantification of skin absorption is an essential step in reducing the uncertainty of dermal risk assessment. Data from literature indicate that the relative dermal absorption of substances is dependent on dermal loading. Therefore, an internal exposure calculated with absorption data determined at a dermal loading not comparable to the actual loading may lead to a wrong assessment of the actual health risk. To investigate the relationship between dermal loading and relative absorption in a quantitative manner, 138 dermal publicly available absorption experiments with 98 substances were evaluated (87 in vitro, 51 in vivo; molecular weight between 40 and 950, log P between -5 and 13), with dermal loading ranging mostly between 0.001 and 10 mg/cm2. In 87 experiments (63%) an inverse relationship was observed between relative dermal absorption and dermal loading, with an average decrease of factor 33 ± 69. Known skin irritating and volatile substances less frequently showed an inverse relationship between dermal loading and relative absorption. © 2009 Elsevier Inc. All rights reserved.

Quantification of skin absorption is an essential step in reducing the uncertainty of dermal risk assessment. Data from literature indicate that the relative dermal absorption of substances is dependent on dermal loading. Therefore, an internal exposure calculated with absorption data determined at a dermal loading not comparable to the actual loading may lead to a wrong assessment of the actual health risk. To investigate the relationship between dermal loading and relative absorption in a quantitative manner, 138 dermal publicly available absorption experiments with 98 substances were evaluated (87 in vitro, 51 in vivo; molecular weight between 40 and 950, log P between -5 and 13), with dermal loading ranging mostly between 0.001 and 10 mg/cm2. In 87 experiments (63%) an inverse relationship was observed between relative dermal absorption and dermal loading, with an average decrease of factor 33 ± 69. Known skin irritating and volatile substances less frequently showed an inverse relationship between dermal loading and relative absorption. © 2009 Elsevier Inc. All rights reserved.

A series of field studies was conducted to assess the feasibility of controlling spring infestations of the Hessian fly, Mayetiola destructor (Say), in winter wheat, Triticum aestivum L. em Thell, using foliarly applied insecticides. Systemic and nonsystemic insecticides were equally effective in 1986, suggesting that insecticides acted by killing ovipositing adults and neonate larvae exposed on the leaf surface. Single applications of disulfoton were not effective in reducing Hessian fly numbers or preventing yield losses when applied after plant spike emergence. Hessian fly numbers were partly reduced in some trials when a single spray was applied during the stem elongation stage of plant development and 1-2 wk before peak deposition of Hessian fly eggs. Repeated applications (four to six sprays) reduced spring infestations and prevented losses of grain yield if spraying began during stem elongation and before peak egg deposition. Gain threshold calculations indicated that the yield response to repeated insecticide applications justified up to three treatments of disulfoton. However, because of inconsistent efficacy, marginal economic benefit, and difficulty of predicting Hessian fly ovipositional activity, management of spring infestations of the Hessian fly using foliarly applied insecticides is not currently feasible.