Organophosphorothioates and synergised synthetic pyrethroids as grain protectants on bulk wheat

Organophosphorothioates and synergised synthetic pyrethroids were used in duplicate field trials carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays using malathion-resistant strains of insects were carried out on samples of treated grain at intervals over 9 months. These established that all treatments were generally effective. Deltamethrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1), fenitrothion (12 mg kg^?1)+ fenvalerate (1 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1), fenitrothion (12 mg kg^?1)+ phenothrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) and pirimiphos-methyl (4 mg kg^?1)+ permethrin (1 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) controlled common field strains of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.). Against a highly resistant strain of S. oryzae, deltamethrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) was superior to the remaining treatments. All treatment combinations completely prevented progeny production in Tribolium castaneum (Herbst), T. confusum Jacquelin du Val and in Ephestia cautella (Walker). Residues of deltamethrin, fenvalerate, permethrin and phenothrin were determined and shown to be highly persistent on stored wheat. During milling, residues accumulated in the bran fractions and were reduced in white flour. They were not significantly reduced during baking.     

Chlorpyrifos-methyl plus bioresmethrin; Methacrifos; Pirimiphos-methyl plus bioresmethrin; and synergised bioresmethrin as grain protectants for wheat

Field trials with various pesticide combinations were carried out on bulk wheat in commercial silos in Queensland, South Australia and Western Australia. Laboratory bioassays on samples of treated grain at intervals over 8 months using malathion-susceptible and malathion-resistant strains established the following orders of efficacy: against Sitophilus oryzae (L.), chlorpyrifos-methyl 10 mg kg^?1 + bioresmethrin 1 mg kg^?1 = methacrifos 15 mg kg^?1 in aerated storage > pirimiphos-methyl 4 or 6 mg kg^?1 + bioresmethrin 1 mg kg^?1 = bioresmethrin 4 mg kg^?1 + piperonyl butoxide 16 mg kg^?1; against Rhyzopertha dominica (F.), bioresmethrin 4 mg kg^?1 + piperonyl butoxide 16 mg kg^?1 > methacrifos 15 mg kg^?1 > chlorpyrifos-methyl 10 mg kg^?1 + bioresmethrin 1 mg kg^?1 = pirimiphos-methyl 4 or 6 mg kg^?1 + bioresmethrin 1 mg kg^?1. All treatments completely prevented production of progeny in Sitophilus granarius (L.), Tribolium castaneum (Herbst), T. confusum Jackquelin du Val and Oryzaephilus surinamensis (L.). The biological efficacy of methacrifos was greater and the rate of degradation lower in aerated than in non-aerated storage. Residue levels of all compounds were determined chemically and were below proposed international residue levels to be considered by the Codex Alimentarius Commission.     

Organophosphorus and synergised synthetic pyrethroid insecticides as grain protectants for stored sorghum

A field experiment was carried out on bulk sorghum stored for 26 weeks in concrete silos in South Queensland. No natural infestation occurred. Laboratory bioassays of treated grain, in which malathion-resistant strains of insects were added to grain samples, indicated that all the treatments were generally effective. Deltamethrin (2mg kg⁻¹)+piperonyl butoxide (8mg kg⁻¹), fenitrothion (12mg kg⁻¹)+fenvalerate (1 mg kg⁻¹)+piperonyl butoxide (8mg kg⁻¹), and fenitrothion (12mg kg⁻¹)+phenothrin (2mg kg⁻¹)+piperonyl butoxide (8mg kg⁻¹) controlled typical malathion-resistant strains of Sitophilus oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneum (Herbst) and Ephestia cautella (Walker). Pirimiphos-methyl (6mg kg⁻¹)+permethrin (1mg kg⁻¹)+piperonyl butoxide (8mg kg⁻¹) allowed some survival of adults and progeny production by S. oryzae after 12 weeks, and by one strain of R. dominica throughout. Chemical assays established that the residues and rates of breakdown of these grain protectants on sorghum conformed to the general pattern on other cereal grains. Residues at the conclusion of the experiment were below the individual Maximum Residue Limits recommended by the Codex Alimentarius Commission.     

Grain protectants for the control of malathion-resistant insects in stored sorghum

Duplicate experiments were carried out on bulk sorghum stored in South Queensland and in Central Queensland. Bioassays of treated grain, conducted during 6 months' storage, established that fenitrothion (12 mg kg^?1)+ bioresmethrin (1 mg kg^?1), and pirimiphos-methyl (4 mg kg^?1)+ carbaryl (8 mg kg^?1), controlled typical malathionresistant strains of Sitophilus oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneum (Herbst), and Ephestia cautella (Walker). Chlorpyrifos-methyl (10 mg kg^?1)+ pyrethrins (1.5 mg kg^?1)+ piperonyl butoxide (12 mg kg^?1), and fenitrothion (12 mg kg^?1)+ (1R)-phenothrin (1 mg kg^?1), also controlled the strains of S. oryzae, T. castaneum and E. cautella, but were only partly effective against R. dominica. Methacrifos (15 mg kg^?1) controlled all the tested species except E. cautella. Chemical assays established that the residues and rates of breakdown of these grain protectants on sorghum conformed to the general pattern for other cereal grains; residues from the above treatments were below the individual Maximum Residue Limits recommended by the Codex Alimentarius Commission.     

Extensive pilot use of the grain protectant combinations,fenitrothion plus bioresmethrin and pirimiphos-methyl plus bioresmethrin

Each of the combinations, bioresmethrin (1 mg kg^?1) plus pirimiphos-methyl(6 mg kg^?1) or fenitrothion (12 mg kg^?1), was applied in 1976 to grain in 21 commercial storages. Grain condition and protectant residues were regularly monitored. Three storages became infested with Rhizopertha dominica (F.), but all storages remained free of other insect species. In two of the three infested storages, application of protectant was uneven, and the third became infested only after 8 months of storage. Despite some variations in recovered residues between sites, the mean residue levels were accurately described by predictive models. Falls in temperature during storage varied considerably, and were related to factors other than climate and bin size. There was a marked effect by aeration with ambient cold air on both the grain temperature and the rate of loss of residues. Results of collaborative studies on the determination of residues indicate a need for regular check programmes of analysis, and confirm previous conclusions that residues of fenitrothion and pirimiphos-methyl can be accurately and conventionally determined.     

Combinations of pirimiphos-methyl and carbaryl for stored grain protection

In laboratory experiments, whole wheat was treated with pirimiphos-methyl or carbaryl or combinations of these two insecticides; the treated grain was then adjusted to a 12% moisture content and stored at 25°C for bioassay at various intervals over a period of 39 weeks. Pirimiphos-methyl at 5.1 mg kg^?1 effectively controlled Sitophilus granarius (L.) and Tribolium confusum Jacquelin du Val but was ineffective against Rhyzopertha dominica (F.) CRD 118, a strain showing malathion resistance. Conversely, carbaryl at 6.5 mg kg^?1 (but not at 3.1 mg kg^?1) was effective against R. dominica, but ineffective against the other two species. A combination of pirimiphosmethyl + carbaryl, at 1.8 + 5.1 mg kg^?1, controlled S. granarius and R dominica but not T. confusum, whilst a 4.2 + 3.4 mg kg^?1 combination was relatively more effective against T. confusum but less so against R. dominica. In a separate experiment, whole wheat was treated with carbaryl at 2.5, 5.0 and 7.5 mg kg^?1 (nominal rates). Samples were stored and, at various times after the treatments, were bioassayed with R. dominica CRD 2, at 20, 25, 30 and 35°C. The results were comparable with those for the CRD 118 strain, but efficacy was reduced at higher temperatures. The combination of pirimiphos-methyl at 4–5 mg kg^?1 and carbaryl at 5–6 mg kg^?1 is suggested as a potentially useful grain protectant where R. dominica is a problem and long term storage is required. These results are discussed in relation to the protection of stored grain in Australia.     

Potential of piperonyl butoxide‐synergised pyrethrins against psocids (Psocoptera: Liposcelididae) for stored‐grain protection

BACKGROUND: Piperonyl butoxide (PB)‐synergised natural pyrethrins (pyrethrin:PB ratio 1:4) were evaluated both as a grain protectant and a disinfestant against four Liposcelidid psocids: Liposcelis bostrychophila Badonnel, L. entomophila (Enderlein), L. decolor (Pearman) and L. paeta Pearman. These are key storage pests in Australia that are difficult to control with the registered grain protectants and are increasingly being reported as pests of stored products in other countries. Firstly, mortality and reproduction of adults were determined in wheat freshly treated at 0.0, 0.75, 1.5, 3 and 6 mg kg^?1 of pyrethrins + PB (1:4) at 30 ± 1 °C and 70 ± 2% RH. Next, wheat treated at 0.0, 1.5, 3 and 6 mg kg^?1 of pyrethrins + PB (1:4) was stored at 30 ± 1 °C and 70 ± 2% RH and mortality and reproduction of psocids were assessed after 0, 1.5, 3 and 4.5 months of storage. Finally, the potential of synergised pyrethrins as a disinfestant was assessed by establishing time to endpoint mortality for adult psocids exposed to wheat treated at 3 and 6 mg kg^?1 of synergised pyrethrins after 0, 3, 6, 9 and 12 h of exposure. RESULTS: Synergised pyrethrins at 6 mg kg^?1 provided 3 months of protection against all four Liposcelis spp., and at this rate complete adult mortality of these psocids can be achieved within 6 h of exposure. CONCLUSION: Piperonyl butoxide‐synergised pyrethrins have excellent potential both as a grain protectant and as a disinfestant against Liposcelidid psocids. Copyright © State of Queensland, Department of Employment, Economic Development and Innovation, 2010. Published by John Wiley and Sons, Ltd.     

Residues of synthetic pyrethroid insecticides on horticultural crops

Foliar applications of synthetic pyrethroids were made to several crops to determine residue levels at various intervals after application. On onions, residues of cypermethrin, permethrin and fenvalerate were negligible > 0.1 mg kg^?1, 7 days after application. On lettuce, residues of fenvalerate and permethrin were 0.8 mg kg^?1. On celery, residues of fenvalerate did not decline and ranged from 0.12 to 0.25 mg kg^?1 during the 14-day period. On green bush-beans, residues of permethrin and cypermethrin did not decline during the 14-day period and ranged from 0.1 to 0.6 mg kg^?1. By day 7, residues of cyfluthrin, cypermethrin, deltamethrin, fenvalerate and permethrin on strawberries were less than the acceptable maximum tolerance of 0.1 mg kg^?1 with the exception of cypermethrin, applied at the rate of 0.14 kg a.i. ha^?1 which gave a residue of 0.14 mg kg^?1.     

Fenitrothion plus (1R)-phenothrin,and pirimiphos-methyl plus carbaryl,as grain protectant combinations for wheat

Duplicate field trials were carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays on samples of treated grain at intervals over 9 months, using malathion-resistant strains of insects, established that treatments were generally effective. Fenitrothion (12 mg kg^?1)+ (1R)-phenothrin (2 mg kg^?1) was more effective than pirimiphos-methyl (6 mg kg^?1) + carbaryl (10 mg kg^?1) against Sitophilus oryzae (L.) and Ephestia cautella (Walker); the order of effectiveness was reversed for S. granarius (L.). Against Rhyzopertha dominica (F.), Tribolium castaneum (Herbst), T. confusum Jackquelin du Val and Oryzaephilus surinamensis (L.), both treatments effectively prevented the production of progeny. The order of persistence was pirimiphos-methyl> (1R)-phenothrin>carbaryl or fenitrothion. During processing from wheat to white bread, residues were reduced by 98% for carbaryl, >44% for (1R)-phenothrin, 98% for fenitrothion and 85% for pirimiphosmethyl.     

Residues of zeta‐cypermethrin in bovine tissues and milk following pour‐on and spray application

The depletion of zeta‐cypermethrin residues in bovine tissues and milk was studied. Beef cattle were treated three times at 3‐week intervals with 1 ml 10 kg^?1 body weight of a 25 g litre^?1 or 50 g litre^?1 pour‐on formulation (2.5 and 5.0 mg zeta‐cypermethrin kg^?1 body weight) or 100 mg kg^?1 spray to simulate a likely worst‐case treatment regime. Friesian and Jersey dairy cows were treated once with 2.5 mg zeta‐cypermethrin kg^?1 in a pour‐on formulation. Muscle, liver and kidney residue concentrations were generally less than the limit of detection (LOD = 0.01 mg kg^?1). Residues in renal‐fat and back‐fat samples from animals treated with 2.5 mg kg^?1 all exceeded the limit of quantitation (LOQ = 0.05 mg kg^?1), peaking at 10 days after treatment. Only two of five kidney fat samples were above the LOQ after 34 days, but none of the back‐fat samples exceeded the LOQ at 28 days after treatment. Following spray treatments, fat residues were detectable in some animals but were below the LOQ at all sampling intervals. Zeta‐cypermethrin was quantifiable (LOQ = 0.01 mg kg^?1) in only one whole‐milk sample from the Friesian cows (0.015 mg kg^?1, 2 days after treatment). In whole milk from Jersey cows, the mean concentration of zeta‐cypermethrin peaked 1 day after treatment, at 0.015 mg kg^?1, and the highest individual sample concentration was 0.025 mg kg^?1 at 3 days after treatment. Residues in milk were not quantifiable beginning 4 days after treatment. The mean concentrations of zeta‐cypermethrin in milk fat from Friesian and Jersey cows peaked two days after treatment at 0.197 mg kg^?1 and 0.377 mg kg^?1, respectively, and the highest individual sample concentrations were 2 days after treatment at 0.47 mg kg^?1 and 0.98 mg kg^?1, respectively. © 2001 Society of Chemical Industry     

A rapid high-pressure liquid chromatographic method for the determination of carbaryl residues in wheat grain

Carbaryl residues in wheat grain have been determined in methanol extracts using normal-phase high-pressure liquid chromatography (h. p. l. c.) with ultraviolet detection. A single-injection, clean-up and analysis technique was used to allow more rapid analysis of samples after extraction. A detection limit of 0.1 mg kg^?1 in a 50 g sample of wheat was achieved. Recoveries of 86% at the 1 mg kg^?1 level and 90-99% at the 5 mg kg^?1 level were obtained for fortified grain samples. Methanol was found to be a superior extractant for carbaryl from wheat when compared with hexane, acetone and dichloromethane. Twelve samples containing aged carbaryl residues were analysed by the h. p. l. c. technique and by a colorimetric procedure which allowed statistical analysis of errors. For the h. p. l. c. method (excluding sampling error), a relative standard deviation of 4.4% was obtained.     

Comparative purification methods for determination of triadimenol residues in plant material

Two procedures are described for the determination of residues of triadimenol and compared on cereal material. After extraction, purification is carried out by Florisil column chromatography in method I and by semi-preparative High-Performance Liquid Chromatography in method II. Triadimenol residues are quantified by gas chromatography with a thermoionic detector. With method I, interference was observed but not with method II. This specific procedure has been tested on other plant materials. Recoveries in the range of 90–98% indicate that this procedure is suitable for residue analysis of this fungicide with detection limits of 0·008 mg kg^?1 in wheat grains, 0·03 mg kg^?1 in wheat straw and 0·004–0·008 mg kg^?1 in other plants. Maximum residue limits in France are: 0·1 mg kg^?1 in grain, 2·0 mg kg^?1 in straw and 1·0 mg kg^?1 in other vegetables and fruit.     

Pharmacokinetics of Intravenous Fenvalerate in Cattle Treated Topically with a Low Dose of Piperonyl Butoxide

Experiments were conducted to identify pharmacokinetic interactions between topically applied piperonyl butoxide and intravenous fenvalerate in cattle (Angus steers). Intact fenvalerate in plasma was derivatized by condensation with acetone and measured by negative chemical ionization gas chromatography/mass spectrometry. Noncompartmental pharmacokinetic analyses indicated that the elimination-phase rate constant (β, 0·00069 (±0·00006) min^-1), mean residence time (172 (±14) min), systemic clearance (10·4 (±0·7) ml min^-1 kg^-1) or volume at steady state (1800 (±230) ml kg^-1) were not changed (P>0·05) after topical application of a low dose of piperonyl butoxide. These data indicate that topical application of a low dose of the metabolic synergist piperonyl butoxide would not be expected to modify the in-vivo disposition of fenvalerate in cattle. © of SCI.     

The effects of low-volume aeration on the residues and biological effectiveness of chlorpyrifos-methyl applied to wheat

The effects of low-volume ventilation on the persistence and biological efficacy of chlorpyrifos-methyl applied to English wheat were investigated. Four 20-tonne batches of wheat were treated with a dose of 2.5 mg kg^?1 chlorpyrifos-methyl. After treatment, two of the batches were aerated continuously at a rate of 17 m³ h^?1 tonne^?1 (10 cfm tonne^?1) for 16 weeks. The remaining two batches were not aerated. Samples were collected from both aerated and non-aerated wheat at intervals over the 16-week storage period and subjected to biological assay using laboratory multi-organophosphorus-resistant strains of Tribolium castaneum, Sitophilus granarius, Sitophilus oryzae and Oryzaephilus surinamensis. The samples were also analysed for chlorpyrifos-methyl residues. No differences in either the biological efficacy or the rate of chemical decomposition were detected between the aerated and non-aerated wheat.     

Residues of Mecoprop in Post-emergence-Treated Wheat and Oat

The dissipation of mecoprop in wheat (Triticum aestivum L.) and oat (Avena sativa L.) was monitored over a growing season following post-emergence application of the dimethylamine salt of mecoprop to each crop at 1·1 kg ha^?1. Residues of mecoprop, as its methyl ester, were determined gas chromatographically using electrolytic conductivity detection. Initial residues in wheat (119 (±20) mg kg^?1) and oat (95·3 (± 10·0) mg kg^?1) on the day of application (four-leaf stage of wheat and four- to five-leaf stage of oat) decreased to 0·1 to 0·2 mg kg^?1, respectively, within six weeks. Residues were non-detectable in the mature seed of both crops. Recoveries of mecoprop were in the order of 90% from the green tissue and seed of both crops fortified at 0·05 mg kg^?1.     

The behaviour of residues of benzoylprop-ethyl and its breakdown products in wheat

Samples of wheat grain and straw have been analysed from trials with the wild oat herbicide benzoylprop-ethyl ( I ) in several countries. Following recommended commercial treatments (application of 1.0–1.6 kg ha^?1 at Feekes growth stage G-J), total residues of I and its hydrolysis product N-benzoyl-N-(3,4-dichlorophenyl)-DL - alanine (free and conjugated) were low and in the majority of instances they were < 0.01 mg kg^?1 in samples of grain from the UK, although rather higher residues were detected in some grain samples from other countries. Residues in straw were higher, but normally did not exceed 2 mg kg^?1, and were rather variable, possibly as a result of differences in agricultural practice.     

An Example of Cross-resistance to Pyrethroids in DDT-resistant Aedes aegypti

Comparisons of the susceptibility of several strains of adult Aedes aegypti were made. Mosquitoes from Bangkok and Jakarta were found to be highly resistant to DDT and resistant to pyrethroids relative to a laboratory strain. A strain from Singapore, where less DDT has been used, was susceptible to DDT and pyrethroids. Two strains from the Caribbean had LC₅₀ values to DDT 3 times that of the reference strain while the LC₅₀ values against bioresmethrin synergised with piperonyl butoxide were 1 1/2 times raised. Another two strains from central Africa were 2 times tolerant of DDT and 1 1/2 times tolerant of bioresmethrin plus piperonyl butoxide. Agents which block DDT-dehydrochlorinase, esterases and oxidases each caused small increases in the mortality of the Bangkok strain due to DDT and bioresmethrin as well as augmenting toxicity to the susceptible reference strain. It is tentatively suggested that resistance in the Bangkok strain is due to a combination of the actions of these and perhaps other resistance mechanisms.     

Pyrethroid residues in sediment and water samples from mesocosm and farm pond studies of simulated accidental aquatic exposure

This paper describes the residue analysis of water and hydrosoil samples taken from two separate large-scale aquatic ecotoxicology trials designed to assess the environmental fate and effects of the pyrethroids lambda-cyhalothrin and cypermethrin. Comparison of the results demonstrates the high degree of reproducibility of the chemical residue found the day after treatment using experimental mesocosms (lambda-cyhalothrin) as opposed to an in-use farm pond (cypermethrin). Both studies showed that pyrethroid residues were rapidly lost from the water column: residues of lambda-cyhalothrin were less than 2 ng litre^?1 following the final application of a cumulative seasonal exposure equivalent to twelve ?drift’? and six ?run-off’? events, each delivering a dose equivalent to that expected from a typical event under field conditions. Hydrosoil appeared to act as a sink for pyrethroid residues and, under the stringent test conditions of the mesocosm study, lambda-cyhalothrin residues reached 3.2 μg kg^?1 following the seasonal exposure described above. The cypermethrin farm-pond study illustrated the localised pattern of exposure expected under natural field conditions, with site topography and cultivation practices which represent an average ?worst case’?. Residues in hydrosoil reached a maximum level of approximately 25 μg kg^?1 in one sampling zone at one interval, and thereafter declined to a level of < 9 μg kg^?1 within four months.     

Ethyl formate plus methyl isothiocyanate--a potential liquid fumigant for stored grains

BACKGROUND: Methyl bromide is being phased out for use on stored commodities, as it is listed as an ozone‐depleting substance, and phosphine is the fumigant widely used on grains. However, phosphine resistance occurs worldwide, and phosphine fumigation requires a long exposure period and temperatures of > 15 °C. There is an urgent requirement for the development of a fumigant that kills insects quickly and for phosphine resistance management. This paper reports on a new fumigant formulation of 95% ethyl formate plus 5% methyl isothiocyanate as an alternative fumigant for stored grains. RESULTS: The formulation is stable for at least 4 months of storage at 45 °C. A laboratory bioassay with the formulation showed that it controlled all stages of Sitophilus oryzae (L.), Sitophilus granarius (L.), Tribolium castaneum (Herbst), Rhyzopertha dominica (F.), Trogoderma variabile Ballion and Callosobruchus maculatus (Fabricius) in infested wheat, barley, oats and peas at 80 mg L^?1 for 5 days, and in canola at both 40 mg L^?1 for 5 days and 80 mg L^?1 for 2 days at 25 ± 2 °C. After an 8–14 day holding period, residues of ethyl formate and methyl isothiocyanate in wheat, barley, peas and canola were below the experimental permit levels of 1.0 and 0.1 mg kg^?1. However, fumigated oats needed an 18 day holding period. CONCLUSIONS: The findings suggest that the ethyl formate plus methyl isothiocyanate formulation has potential as a fumigant for the control of stored‐grain insect pests in various commodities. Copyright © 2011 Society of Chemical Industry     

Excretion and residues of the pyrethroid insecticide cypermethrin in laying hens

Laying hens were treated daily for 14 days with oral doses of [¹⁴C-phenoxy]cypermethrin (1.52 mg day^?1, 0-7 mg kg^?1) formulated on a small quantity of diet. Radioactivity in the eggs reached a plateau value of 0.05 μg equivalents g^?1 8 days after the start of dosing. Most of the residue was found in the yolk and was a mixture of cypermethrin and material which was closely associated with neutral lipids and phosphatidyl cholines. Four and a half hours after the last dose, the birds were killed and selected tissues were taken for analysis. The highest residue was found in the liver. This was composed of cypermethrin and a mixture of very polar metabolites which were not hydrolysed to significant amounts of 3-phenoxybenzoic acid or its 4-hydroxy derivative.