Assessment of the grain protectants chlorpyrifos-methyl plus bioresmethrin,fenitrothion plus (1R)-phenothrin,methacrifos and pirimiphos-methyl plus carbaryl under practical conditions in Australia

Methacrifos (22.5 g t^?1) and the three protectant combinations chlorpyrifos-methyl (10 g t^?1) plus bioresmethrin (1 g t^?1), fenitrothion (12 g t^?1) plus (1R)-phenothrin (2 g t^?1) and pirimiphos-methyl (4 g t^?1) plus carbaryl (8 g t^?1) were each applied to grain that was stored in at least 15 silos. Grain temperature and levels of protectant were regularly monitored, and samples from 12 storages using each treatment were taken for laboratory assays against Rhyzopertha dominica and Tribolium castaneum. Grain condition did not deteriorate during storage. Grain remained free of insects in 60 of the 63 storages treated; partial failure in the other 3 storages was attributed to low or irregular levels of protectant. The mean and range of residue values of all protectants were recorded as a function of time and the mean observed values corresponded to predicted values. In laboratory bioassay, the order of effectiveness against T. castaneum was methacrifos > chlorpyrifos-methyl plus bioresmethrin > fenitrothion plus (1R)-phenothrin = pirimiphos-methyl plus carbaryl. The order of effectiveness against R. dominica was carbaryl plus pirimiphos-methyl = (1R)-phenothrin plus fenitrothion > methacrifos > bioresmethrin plus chlorpyrifos-methyl.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

A new resistance to pyrethroids in tribolium castaneum (herbst)

The characteristics of a new high-level, field-derived resistance to pyrethroids in Tribolium castaneum (Herbst) were investigated using impregnated-paper and treated-grain assays. Piperonyl butoxide almost completely suppressed the resistance, suggesting that the major resistance mechanism was microsomal oxidation. Resistance extended to all pyrethroids tested and to carbaryl but not to organophosphorus insecticides or to methoprene. Resistance was strongest against α—CN phenoxybenzyl cyclopropanecarboxylate pyrethroids and was correlated with structural modifications of the pyrethroid molecule, results also consistent with oxidative resistance. This resistance will ultimately result in failures to control T. castaneum if pyrethroids, such as deltamethrin, cypermethrin or cyfluthrin, are used in the field, even if they are synergised with piperonyl butoxide. The resistance does not jeopardise organophosphorus materials (e.g. fenitrothion, chlorpyrifos-methyl, pirimiphos-methyl, methacrifos) or methoprene.     

Synergised cyfluthrin and cypermethrin as grain protectants on bulk 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 8 or 9 months storage using malathion-resistant strains of insects established that treatments were generally effective. Cyfluthrin (2 mg kg^?1) plus piperonyl butoxide (10 mg kg^?1) and cypermethrin (4 mg kg^?1) plus piperonyl butoxide (10 mg kg^?1) completely controlled two strains of Sitophilus oryzae L. Control of a third strain by the cypermethrin combination was incomplete after 11/2 months and neither controlled a multi-resistant laboratory strain. Both combinations were effective against Rhyzopertha dominica F., Tribolium castaneum Herbst and Ephestia cautella Walker. No natural infestation developed in the treated grain in any silo. Mean residues of cyfluthrin and cypermethrin after 9 months storage were 58% and 52% of the calculated application rates, respectively. Compared with overall concentrations in the wheat, residue levels were higher in bran and pollard and lower in white flour. During baking, residues decreased by up to 29%. Operators experienced respiratory irritation associated with exposure to both combinations and alternative formulations would be required for use of these materials in grain storage.     

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.     

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     

The persistence and activity of insecticide spary deposits on woven polypropylene fabric

Wettable powder formulations of the organophosphorus insecticides, fenitrothion and pirimiphos-methyl, and the pyrethroids, permethrin and deltamethrin, have been compared for persistence and activity on woven polypropylene fabric; the residues produced in maize kept under the test sheets have also been measured. The test insects were Sitophilus oryzue (L.) and Tribolium custuneum (Herbst). Permethrin at 41 and 83 mg m^?2 was completely effective for the full 12 weeks of the experiment. Deltamethrin at 6.2 and 12.5 mg m^?2 was almost equally effective but after 4 weeks the deposit was slower acting against S. oryzae. The organophosphorus compounds were effective only up to 2 weeks at 250 mg m^?2 and up to 4 weeks at 500 mg m^?2. No residues could be detected under the pyrethroids but the organophosphorus insecticides gave residues of 2–4 mg kg^?1 on a thin layer of grain. This residue was biologically effective against the test insects.     

Cockroach control in sewers in Singapore using bioresmethrin and piperonyl butoxide as a thermal fog

Cockroaches have considerable importance as vectors of disease. In tropical areas, large populations of Periplaneta americana may be found in sewers and the refuse chutes of large apartment blocks. These cockroach populations are not accessible to residual insecticide treatment with sprays but may be controlled with thermal fogs of pyrethroids. An experiment on the use of bioresmethrin (5-benzyI-3-furyimethyl-(+)-trans chrysanthemate) as 0.15% and 0.25% w/v solutions with equal amounts of synergist in kerosene discharged from a TIFA fog generator was made at Toa Payoh in Singapore. Effective control was obtained with 0.15% bioresmethrin plus 0.55% piperonyl butoxide in kerosene blown into the sewers and waste chutes initially, at four weeks, at eight weeks later and then followed by treatment every two months.     

Efficacy of Surface Dust Treatments of Pirimiphos-Methyl and Etrimfos when Applied to Commercially Stored Wheat and Barley

Commercially stored wheat and barley were surface treated with dust formulations of pirimiphos-methyl and etrimfos at the manufacturer's recommended application rate. Samples were taken at four-weekly intervals for 32 and 16 weeks for wheat and barley respectively. Pesticide efficacy was determined using insect bioassays and chemical analysis of residues. There was no evidence to suggest a decline in residue levels of either pesticide over the experimental period. However, considerable variation was observed in the residue levels recorded at different sample points and also between residue levels recorded for the same point over the trial period. Control of susceptible strains of Tribolium castaneum (Herbst), Oryzaephilus surinamensis (L.) and Sitophilus granarius (L.) was achieved where recovered pesticide residues remained above 1 mg kg⁻¹ pirimiphos-methyl and 1·6 mg kg⁻¹ etrimfos.     

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.     

Spirosultam LY219048: A new chemical class of insecticide acting upon the GABA receptor/chloride ionophore complex

This study assessed the toxicity and mode of action of a new experimental insecticide, LY219048 in insects and mammals. LY219048 produced rapid convulsions in mice and had LD₅₀ values of 0.7 mg kg^?1 and 4 mg kg^?1 after intracerebral and intraperitoneal injection, respectively. In initial screens against insects, LY219048 showed low activity against the German cockroach (Blatella germanica L.). Lethality from dietary exposure required one to two weeks, even at concentrations as high as 10000 mg kg^?1 (LC₅₀ = 485 mg kg^?1). In contrast, it had an LC₅₀ value of 8.3 mg kg^?1 against insecticide-susceptible Drosophila melanogaster (Meig.) when synergized with piperonyl butoxide. Significant resistance to LY219048 (> 12-fold) was detected in a cyclodiene-resistant strain of D. melanogaster possessing an altered target site resistance mechanism. This finding suggested that LY219048 blocked the 4-aminobutyric acid (GABA)-gated chloride channel in a manner similar to that of the cyclodienes. In physiological studies in larval D. melanogaster central neurons, LY219048 antagonized the reduction of firing caused by 1 mM GABA. Dose-response experiments showed that the ED₅₀ for blocking inhibition under these conditions was c. 1 μ. Studies of ³⁶CI uptake into bovine brain synaptosomes found that LY219048 was a potent antagonist. At 10 μ it completely blocked chloride flux stimulated by 50 μM GABA. LY219048 competitively displaced [³H]TBOB binding from bovine brain membranes, with an IC₅₀ of 42 nM, which was comparable to values determined for TBPS (35 nM) and picrotoxinin (267 nM). There was little or no displacement (<25%) of [³H]flunitrazepam or [³H]muscimol binding by 10 μM LY219048. Taken together, these results provide strong evidence that this new chemical class of insecticide manifests its acute toxicity by blocking the GABA-gated chloride channel.     

The effects of temperature and humidity on the toxicity of three organophosphorus insecticides to adult Oryzaephilus surinamensis (L.)

The toxicities, to a laboratory susceptible strain and to a resistant strain of Oryzaephilus surinamensis (L.), of water-dispersible powder formulations of pirimiphos-methyl, fenitrothion or chlorpyrifos-methyl under constant conditions of 25°C and 70% r. h. were compared to the toxicities when the insects were exposed to a diurnal cycle of 12.5–20–12.5°C and 70–50–70% r. h. to simulate grain store conditions in the UK during spring and autumn. All the insecticides were more effective at 25°C and 70% r. h. The LD₅₀ values for the susceptible strain were low, being 4.4 and 1.4 mg m^?2 at 12.5-20°C and 25°C, respectively, for chlorpyrifos-methyl, 18.3 and 4.1 mg m^?2, respectively, for pirimiphos-methyl, and 4.0 and < 1.O mg m^?2, respectively, for fenitrothion. The LD₅₀ values obtained from the two sets of environmental conditions for a resistant strain (484) differed by factors of 1.8 for chlorpyrifos-methyl, 4.8 for pirimiphos-methyl, and 7.3 for fenitrothion. Toxicity studies were also made with chlorpyrifos-methyl under various constant conditions of temperature and humidity from 5–30°C (5°C intervals) and 30, 50, 70 and 90% r. h., and also at O°C and 60% r. h. Chlorpyrifos-methyl was very effective and there was little or no cross resistance to chlorpyrifos-methyl in the resistant strain. From 15 to 30°C, mortality was high, and differences in mortality at the LD₅₀ level for the various humidities were slight, but there was a decrease in mortality with decreasing humidity at any one temperature, in particular, at 5°C, 50 and 70% r. h., and 10°C and 50% r. h. Chlorpyrifosmethyl was more toxic to both strains at the highest humidity (90%) throughout the whole temperature range. The LD₅₀ values for each strain decreased at each temperature as the water vapour concentration was increased. At O°C and 60% r. h., all the insects from both strains died but the cause of death was not clear.     

An assessment of chlorpyrifos-methyl,etrimfos, fenitrothion and pirimiphos-methyl as grain protectants

Trials were carried out over two consecutive years to compare the efficacy of chlorpyrifos-methyl, etrimfos, fenitrothion and pirimiphos-methyl against susceptible and organophosphorus-resistant strains of Tribolium castaneum Herbst, Sitophilus granarius L. and Oryzaephilus surinamensis L., gamma-HCH-resistant strains of Acarus siro L. and Glycyphagus destructor Schrank, and a susceptible strain of Tyrophagus longior Ger-vais. Pirimiphos-methyl was not evaluated against the three mite species as data on the efficacy of this material had previously been published. Etrimfos and pirimiphos-methyl were also tested against a susceptible and an organophosphorus-resistant strain of Sitophilus oryzae L. Each pesticide was applied to two separate 20-tonne batches of English wheat and stored under ambient conditions for 36 weeks. The efficacy of the pesticides was assessed regularly over the storage period using established bioassay techniques. However, chlorpyrifos-methyl and fenitrothion were assessed against susceptible and resistant strains of S. granarius for 32 weeks only. Each of the four pesticides produced >95% mortality of the susceptible strain of all insect species tested for the entire duration of the trial with the exception of fenitrothion, when survival of T. castaneum increased after 32 weeks. Only fenitrothion failed to give 100% mortality of the resistant strain of S. granarius throughout the trial, but even so, the mortality was always >95%. Chlorpyrifos-methyl, etrimfos and pirimiphos-methyl gave much better control of the resistant T. castaneum than fenitrothion, and etrimfos gave slightly better control of resistant O. surinamensis than pirimiphos-methyl which was in turn better than chlorpyrifos-methyl at 36 weeks. Both etrimfos and pirimiphos-methyl gave 100% mortality of the susceptible and resistant strains of S. oryzae. None of the pesticides maintained 100% kill of A. siro throughout the trial and fenitrothion failed to achieve this level of mortality after only 4 weeks. Etrimfos produced 100% mortality of the other two mites species tested throughout the trial, whereas both chlorpyrifos-methyl and fenitrothion achieved this level of mortality for 32 weeks.     

Synthetic pyrethroids: Toxicity and synergism on dietary exposure of Tribolium castaneum (Herbst) larvae

The potency of six dietary pyrethroids, as toxicants and inhibitors of weight gain in first- and fourth-instar Tribolium castaneum (Herbst) larvae, decreased in the order of cis-cypermethrin and deltamethrin > trans-cypermethrin and cis-permethrin > fenvalerate and trans-permethrin. Dosages that reduced larval weight also delayed pupation and emergence, probably due to their antifeeding activity. Three oxidase inhibitors (piperonyl butoxide, O, O-diethyl O-phenyl phosphorothioate, and O-isobutyl O-prop-2-ynyl phenylphosphonate), at a dietary concentration of 100 mg kg^?1, had little or no effect on the toxicity of trans-permethrin, but strongly synergised the toxicity of cis-cypermethrin by about 3-, 3- and 10-fold, respectively. Piperonyl butoxide also synergised the toxicity of cis-permethrin, trans-cypermethrin and deltamethrin, but not that of fenvalerate. On the other hand, an esterase inhibitor, profenofos, did not enhance the potency of any of the α-cyano-3-phenoxybenzyl pyrethroids. Oxidases appear to be more important than esterases in pyrethroid detoxification by T. castaneum larvae.