Pirimiphos-methyl Residues Research Articles

Persistence and activity towards Sitophilus zeamais (Coleoptera: Curculionidae) of pirimiphos-methyl sprayed at different temperatures on maize

The air temperature in storage units in tropical areas frequently exceeds 50°C during the warmest periods of the day. Since protectant insecticides are sprayed on grains under these conditions, such high temperatures may interfere with the insecticidal activity. To assess this possibility we sprayed maize grains with pirimiphos-methyl 500 EC (0.8 ml c.p./l and 1.5 l/t) at different temperatures (25°C, 30°C, 35°C, 40°C, 45°C, and 50°C) and 55% r.h. The grains were then maintained at 27±1°C and 55±5% r.h. throughout the experiment which lasted 90 days. Residues of pirimiphos-methyl on the sprayed grains were analyzed every 30 days. Grain samples were assessed every 15 days after the insecticide spraying for their effect on the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Insect mortality was evaluated after 24 and 48 h of exposure to the treated grain. The level of pirimiphos-methyl residue on maize grains decreased with an increase in storage period and air temperature during the insecticide spraying (varying from 11.0±0.1 to 1.1±0.1 ppm, corresponding to the residue levels at 25°C on the day of the spraying and after spraying at 50°C and 90 days of storage). The same trend was observed for mortality of the maize weevil, which dropped from 95.4±13.3% to 2.5±2.5% after 90 days storage after insecticide spraying at 50°C. These results indicate that temperature at spraying can affect insecticide persistence and activity during storage.

Periods of protection provided by different formulations of pirimiphos-methyl and etrimfos, when admixed with wheat, against four susceptible storage beetle pests

The periods of protection provided by emulsifiable concentrate (EC), dust (DP), microcapsule suspension (MS) and ultra low volume (UL) formulations of pirimiphos-methyl, and EC and DP formulations of etrimfos, were assessed at 25 °C and 70% relative humidity (r.h.), when admixed with wheat at 0.5, 1, 2 and 4 mg kg −1, against susceptible Tribolium castaneum (Herbst), Oryzaephilus surinamensis (L.), Sitophilus granarius (L.) and Rhyzopertha dominica (F.). One day and 1 week after treatment and then every 4 weeks for 36 weeks, samples of wheat were taken for pesticide residue analysis and insect bioassays. Insect mortality was assessed after 1, 7, 14, 21 and 28 days exposure. Against T. Castaneum, O. surinamensis and S. granarius the MS formulation of pirimiphos-methyl provided the longest periods of protection with shorter exposures required for complete mortality. The etrimfos DP was most effective against R. dominica. A reduction in etrimfos residues was detected over the 36 weeks, with pirimiphos-methyl residues fluctuating slightly, though a loss in biological effectiveness was observed.

Degradation and biological impact of chlorpyrifos-methyl on stored wheat and pirimiphos-methyl on stored maize in western Canada

Insecticide degradation and pest survival were monitored in treated stored wheat and maize in southern Manitoba. Wheat stored in two wooden bins each holding 2.4 tonnes of grain was treated with the insecticide chlorpyrifos-methyl at calculated levels of 5 ppm; untreated wheat was placed in two other identical bins in the same granary. Maize was simultaneously stored in four identical bins each holding 2.3 tonnes of grain in another granary and the maize in two of these bins was treated with the insecticide pirimiphos-methyl at calculated levels of 6 ppm. Monthly samples were taken from the top and at 1 m depths of the grain bulks for 18 months. Grain surface temperatures fluctuated with ambient air conditions, but at 1 m depth lagged behind top temperatures. Moisture content of the wheat ranged from 12.2 to 15.1% and the maize from 12.1 to 15.3% over 18 months. Chlorpyrifos-methyl residues on wheat declined 51 and 38% at the top and 1 m depths, respectively. Pirimiphos-methyl residues on maize did not decrease; however, after 8 months, pirimiphos-methyl began to appreciably lose effectiveness against the insect Tribolium castaneum (Herbst) in 24 h laboratory bioassays, and after a year against T. castaneum and the mite Tarsonemus granarius Lindquist within the granaries. Fat acidity values increased in both wheat and maize and insecticide treatments were not directly related to the increases. Under western Canadian conditions chlorpyrifos-methyl applied on wheat degraded with time, but at 4.6 ppm, offered effective insect control (>90%) for 10 months. Pirimiphos-methyl (5.6 ppm) on maize killed > 90% of insects for 8 months. It did not degrade at either the surface or 1 m depth, but became less effective with time, based on short-term exposure of adults, possibly because of translocation into the seed.

A comparison of the toxicity of pirimiphos-methyl and malathion to Typhaea stercorea (L.) when applied to stored maize

The toxicity of freshly applied and aged residues of pirimiphos-methyl and malathion were assessed against adult Typhaea stercorea (L.). Maize was treated with each pesticide at doses of 2, 4, 6, and 8 mg kg −1 and stored at a constant 25 °C and 70% r.h. for 12 weeks. All fresh deposits of pirimiphos-methyl produced 100% mortality as did malathion at 4, 6 and 8 mg kg −1. After four weeks storage pirimiphos-methyl still gave 100% mortality at 6 and 8 mg kg −1 but this dropped to 96% at 4 mg kg −1 and 60% at 2 mg kg −1, while mortality for malathion was less than 31% even at 8 mg kg −1. After 12 weeks storage only pirimiphos-methyl gave effective control with 78% mortality at the highest dose of 8 mg kg −1, while control by malathion had completely broken down. The effect of exposure time on T. stercorea for both pesticides at a single dose of 4 mg kg −1 was also assessed. Beetles were left in contact with treated maize for 2, 4, 6, 8 and 10 d. Fresh and four-week-old pirimiphos-methyl residues produced over 98% mortality at all exposure periods but on 12-week-old residues mortality had dropped and was only 61% following 10 d exposure. Only freshly applied malathion gave 100% mortality and even the maximum exposure of 10 d only produced 51% mortality of T. stercorea at four weeks and 39% at 12 weeks.

Efficiency of some technological processes on reducing the residues of malathion and pirimiphos methyl in mature broad bean seeds.

Residue study was performed on several insecticides which could contaminate local Egyptian beans. The effect of storage periods and various processing steps on lowering the residues of malathion and pirimiphos methyl in treated seeds and their processed products were investigated. The data indicated that malathion and pirimiphos methyl persisted for more than 90 days on and in stored mature dry broad beans after postharvest treatment. However, stored broad beans could be safely used for human consumption after 90 days when the insecticide residues reached safe levels. Washing removed 69 and 75% of malathion and pirimiphos methyl residues of treated broad beans, respectively. Malathion residue was not detected in various processed products. More than 89 and 99% of malathion residues were absent in dehulled and heated dehulled broad beans. In addition, pirimiphos methyl residues were reduced to 92, 97, 87, 99, 99, and 95% from the initial levels in treated beans following dehulling, cooking of dehulled beans, germination, cooking of germinated beans and cooking of the beans by the common method and under pressure, respectively.

Effect of Reduced Application Rates of Dicofol and Pirimiphos-methyl on Strawberries and Common Beans on Their Residue Content and Crop Production

Residues of dicofol and pirimiphos-methyl applied at different rates on strawberry and common beans, respectively, were monitored at different intervals. The rate of crop production of each rate was also studied. High-performance liquid chromatography was employed to detect both compounds and gas chromatography/mass spectrometry analysis was conducted for further confirmation. All tested rates produced residue levels below the respective maximum residue limits (MRL) of dicofol and pirimiphos-methyl. The highest two rates of dicofol (185 and 139 g of active ingredient/feddan) and of pirimiphos-methyl (750 and 562 g of active ingredient/feddan) produced comparable production rates of strawberry and common beans, respectively. Dicofol residues were 0.230 and 0.105 mg/kg, 1 and 2 weeks, respectively, after the application of the highest rate. The highest rate of pirimiphos-methyl produced a residue level of 0.399 mg/kg, 1 week after application. Keywords: Pirimiphos-methyl; dicofol; strawberry; common beans; HPLC; GC/MS

Residual effectiveness of pirimiphos-methyl on maize in small farm stores

A 2% dust formulation of pirimiphos-methyl applied at a nominal rate of 4.9 mg/kg on shelled maize stored in traditional small farmer's granaries was tested. Pesticide residues, mortality of Sitophilus zeamais (Motsch.) and Tribolium castaneum (Herbst) based on bioassays, damage levels and insect development on samples of treated grain from two areas were monitored over a 9-month storage period. The bioassays showed that the test insects were effectively controlled by the pirimiphos-methyl residues. 61.9% and 66.7% of the residues remained on maize after 9 months in storage in the two areas. Damage levels were kept below 8% throughout the experiment. Insect population was not eliminated though population growth was restrained.

Bioavailability and biological activity of bound residues of radiolabelled pirimiphos-methyl in maize grains.

Using a 14C-labelled pirimiphos-methyl preparation, the percentage of pirimiphos-methyl residues bound to maize grains after 32 weeks of storage was 13% of the applied dosage, or 38% of total terminal residues. Evidence is presented to show that bound residues of pirimiphos-methyl are bioavailable to the rat: 30%, 2% and approx. 6% of radioactivity were measured in urine expired air, and some organs respectively. A major portion of radioactivity (55%) was eliminated through faeces. Grain-bound pirimiphos-methyl residues (generated after storing whole maize grains with pirimiphos-methyl at concentrations of 10 ppm and 100 ppm) were administered to albino rats for 12 weeks. Body and organ weights, enzyme activities and blood chemistry were tested. There was a significant reduction in body weight gain in female rats. Also a significant reduction in blood cholinesterase activity was observed in both male and female rats fed on grain bound pirimiphos-methyl residues at two dose levels. The white blood cell count increased significantly in male rats fed on the high dose. No significant changes were observed in the other blood chemistry parameters tested. The results indicate that maize-bound pirimiphos-methyl residues can exert adverse biological effects in the rat.

Bioavailability to rats of bound [14C] pirimiphos-methyl in stored wheat.

Stored wheat treated with radiolabelled pirimiphos-methyl (0-2-diethyl-amino-6-methyl-pyrimidin-4-yl 0,0-dimethyl phosphorothioate) formed bound (nonextractable) 14C residues. Supercritical fluid extraction, gas chromatography and mass spectrometric techniques were used to identify and quantitate the 14C bound residues in wheat grains. The amount of bound 14C residues present after 28 weeks of storage was about 9.9% of the applied radioactivity. Pirimiphos-methyl accounted for 80% of the bound residue. Grain-bound residues were fed to rats for 5 days. After a total period of 8 days a substantially large percentage of the administered bound 14C residues (72.9%) was eliminated in urine while feces contained only 17.9%. Bound pirimiphos-methyl in wheat grain was metabolized in rats by processes involving hydrolysis, N-dealkylation and 0-demethylation. The results indicate that wheat-bound residues of pirimiphos-methyl are highly bioavailable to the rat and may possess a toxicological potential as manifested by a significant reduction in body weight gain.

Bioavailability and toxicity to rats of bound residues of 14C-pirimiphos-methyl in stored wheat.

Wheat grains were treated with 14C-pirimiphos-methyl to generate bound residues for testing their bioavailability to rats. Bound residues accounted for 25% of the applied dose (50 ppm) at the end of one year. When the grain bound residues were fed to rats for 48 hours the animals eliminated 30 and 40% of the administered dose in urine and feces respectively, after 5 days. Radioactivity in some selected organs and blood accounted for 37% of the administered dose after 2 days, which gradually declined to 1% after 5 days. These data indicate that wheat-bound pirimiphos-methyl residues are moderately bioavailable to rats. In a 90-day feeding study, inhibition of plasma cholinesterase and brain acetylcholinesterase strongly suggest that the bound residues possess a toxicological potential.

Small bin trials to determine the effectiveness of acid-activated kaolin against four species of beetles infesting paddy under tropical storage conditions

Control of populations of Rhyzopertha dominica, Sitophilus oryzae, Tribolium castaneum and Oryzaephilus surinamensis infesting paddy treated with acid-activated kaolin (AAK) at 0.75% w/w or with pirimiphos-methyl (PM) diluted with AAK to give 2 mg PM/kg paddy was compared with that in untreated paddy or paddy admixed with a 2% PM dust formulation on talc at 8 mg a.i./kg. Grain was stored in 45 kg lots in fibreboard drums for 250 days and subjected to periodic infestation with the beetles. All three treatments controlled adult populations of the insects up to 200 days post-treatment, but R. dominica populations started to increase at 250 days in the treatment using 2% PM dust, and this treatment gave progressively lower mortality of R. dominica and less suppression of progeny development in 7 day bioassays using samples taken through the trial than the other treatments. Mean % breakdown of PM formulated on AAK was about twice that on untreated kaolin in accelerated storage tests, and PM residues declined at a faster rate in paddy treated with the mixed dust formulations of AAK and PM than in paddy treated with the 2% PM dust formulation. The deactivator diethylene glycol could be incorporated at up to 10% w/w in AAK with negligible effect on the insecticidal activity of the dust to R. dominica.

Bioavailability and toxicological potential of wheat-bound pirimiphos-methyl residues in rats.

1. Wheat-bound residues of 14C-pirimiphos-methyl were fed to albino rats at 1.17 and 7.5 ppm in the diet for 3.5 months. 2. In toxicological tests, 1.17 ppm of bound residues caused an increase of rat alkaline phosphatase activity and blood urea nitrogen, and reduction in lymphocyte and monocyte counts. A dietary level of 7.5 ppm showed a significant decrease in serum cholinesterase activity and in lymphocytes and monocytes, and an increase in alkaline phosphatase activity and of urea nitrogen. 3. Bioavailability data indicate that wheat-bound pirimiphos-methyl residues are absorbed by rat.

Uptake of Malathion and Pirimiphos-methyl by Rye, Wheat, or Triticale Stored on Treated Surfaces

Rye, wheat, or triticale were stored for up to 8 months at 22°C in cylinders on fir plywood or galvanized steel panels treated with 0.5 g (AI)/m2 malathion or pirimiphosmethyl, or on untreated panels. Top (2–4 cm from the panel surface) and bottom (0–2 cm from the panel surface) samples were taken at regular intervals. Moisture content of the cereals was low, ranging from 6.1–9.6%. Bioassay of the cereals with adults of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), resulted in negligible mortality in top samples but high mortality in bottom samples. Mortality, which decreased with the length of the storage period, was often higher in the cereals on surfaces treated with malathion than on those treated with pirimiphos-methyl Insecticide residues did not exceed 0.8 ppm in top samples and generally declined between 1 and 8 months of storage while residues in bottom samples usually increased with time. Insecticide residues in top samples on both surfaces showed no significant differences at 8 months. Maximum insecticide levels in bottom samples were: 14.3 ppm malathion from wood, and 13.5 ppm pirimiphos-methyl from steel, in rye; 8.3 ppm malathion from steel, and 5.8 ppm pirimiphos-methyl from steel, in wheat; and 8.4 ppm malathion from steel, and 7.2 ppm pirimiphos-methyl from steel, in triticale. Insecticide levels were highest in rye and lowest in wheat.

Determination of Residues of Pirimiphos-methyl and Some of Its Degradation Products in Dates

ナツメヤシ樹にピリミホスメチル剤を施用し, 実中のピリミホスメチルとその分解物をガスクロマトグラフ法により定量した. ピリミホスメチルの残留量は施用後15日以内には急速に減少し, その後は全シーズンにわたって徐々に減少した. 分解物としてはヒドロキシピリミジン化合物のみが有為な量で検出され, オキソン体は根跡量が検出された. 脱エチルアミノ体やその他のピリミジノール化合物は検出されなかった.

Gas-chromatographic analysis of residues of pirimiphos-methyl in water, fish, and snails.

Gas-chromatographic analysis of residues of pirimiphos-methyl in water, fish, and snails.

Efficacy and Fate of Pirimiphos-Methyl Residue Applied at Two Dosage Rates to Wheat for Milling12

Pirimiphos-methyl was applied to cleaned, hard winter wheat as a water emulsion at 7.3 and 14.6 ppm AI. Samples of the treated wheat were stored for periods up to 12 months to determine the relative effectiveness of residues in controlling adult rice weevils, Sitophilus oryzae (L.), lesser grain borers, Rhyzopertha dominica (F.), red flour beetles, Tribolium castaneum (Herbst), and confused flour beetles, T. confusum Jacquelin duVal. Residues were determined on the whole wheat and on milled fractions.

Pirimiphos Methyl: Effect on Populations of Tribolium confusum and T. castaneum in Wheat13

Pirimiphos methyl at a rate of 7.8 ppm was more effective than malathion at a rate of 10.4 ppm as a protectant on hard winter wheat against the confused flour beetle, Tribolium confusum Jacquelin duVal, and the red flour beetle, T. castaneum (Herbst), in a 12-month 0.14 m3 small bin storage study. Malathion degraded to 16.3% of the initial deposit during the 12-month period but pirimiphos methyl residue degraded more slowlyas 83.1%of the initial residue remained on the wheat at 12 months post-treatment. Toxicity studies showed that the residues of pirimiphos methyl on wheat were very effective against both species of Tribolium .

Field Tests with Pirimiphos-Methyl as a Protectant for Farmers Stock Peanuts1

Abstract Farmers stock peanuts were treated with pirimiphosmethyl (0- [2- (diethvlamino)-6-methyl-4-pyrimidinyl 0,0-dimethyl phosphorothioate) applied at rates of 10, 20, and 30 ppm as a protectant against stored-product insects and stored in metal bins (4.5 metric tons) for 1 year. Similar peanuts were treated with malathion (diethyl mercaptosuccinate S-ester with 0,0-dimethyl phosphorodithioate) applied at a rate of 52.1 ppm as a standard for comparison. Although residues of pirimiphos-methyl decreased ca. 63% during the year (half of the decrease during the first 4 months), rates of 20 and 30 ppm gave excellent protection for 1 year, and a rate of 10 ppm gave protection for about 6 months. Malathion was relatively ineffective, either because it degraded so rapidly the first 2 months or because malathion-resistant strains of insects were present. Of the 16 species of stored-product insects found in the peanuts, red flour beetles, Tribolium castaneum (Herbst), and almond moths, Cadra cautella (Walker), were the predominant species.

Pirimiphos-methyl as a Protectant for Farmers Stock Peanuts2

Peanuts treated with 20.9. 36.4 or 52.2 ppm pirimiphos-methyl to assess effectiveness of the insecticide were held in open-top, 141.6-liter, cylindrical bins for 12 mo in a warehouse infested with 10 species of stored-product insects Peanuts treated at 52.2 ppm malathion were the standard. Pirimiphos-methyl was as effective or more effective than the standard in reducing the number of insects. Also, peanuts treated with pirimiphos-methyl had fewer insect-damaged kernels than those treated with malathion. Red flour beetles, Tribolium castaneum (Herbst), and almond moths, Cadra cautella (Walker), were the pre-dominant species found. Residues of pirimiphos-methyl decreased gradually at a rate ca. 33% less than malathion during the 12-mo period.

Pirimiphos Methyl as a Short Term Protectant of Grain Against Stored-Product Insects2

Pirimiphos methyl ( O -[2-(diethylamino)-6-methyl-4-pyrimidinyl] O, O -dimethyl phosphorothioate), applied as a water emulsion (5, 10, and 20 ppm) to hard winter wheat and shelled yellow corn killed all exposed adult rice weevils, Sitophilus oryzae (L.), red flour beetles, Tribolium castaneum (Herbst), confused flour beetles, T. confusum Jacquelin duVal, and lesser grain borers, Rhyzopertha dominica (F.) at 24 h and 1 month after treatment; no F1 progeny developed. After 3 months, a few red and confused flour beetles survived exposure to grain treated with 5 ppm, but no progeny developed. Also, some lesser grain borers survived, and F1 progeny and damage were recorded in wheat treated with 5 ppm and in corn treated with 5 and 10 ppm. Malathion, applied at a calculated dosage of 10 ppm as the chemical standard, gave complete protection to both grains for 3 months. The residues of pirimiphos methyl degraded gradually as the storage period lengthened except for the 20 ppm applied to shelled corn. The residues of malathion de-graded gradually on both grains.