Disposition and metabolism of [14C]chlorpyrifos in the black imported fire ant, Solenopsis richteri Forel

The short-term disposition and metabolism of topically administered [¹⁴C]chlorpyrifos was assessed in the black imported fire ant (Solenopsis richteri Forel) in the presence and absence of the mixed-function oxidase inhibitor piperonyl butoxide. Chlorpyrifos is readily absorbed into an internal organosoluble fraction which was quickly converted into a water-soluble fraction. The radioactivity was slowly excreted over a 24-hr period. Piperonyl butoxide slowed the conversion of the internal organosoluble radioactivity to the water-soluble fraction. Thin-layer chromatography indicated that piperonyl butoxide slowed the conversion of chlorpyrifos to material remaining at the origin, presumably water-soluble metabolites. The results of acid hydrolysis studies indicated that the water-soluble radioactivity was comprised mainly of conjugates. Although very little chlorpyrifos oxon was recovered in the metabolism experiments, in vitro studies on fire and head homogenates showed the compound to be an extremely potent anticholinesterase, with an I₅₀ of 4.6 × 10^?10M, while a major metabolite, 3,5,6-trichloropyridinol, was an ineffective acetylcholinesterase inhibitor.     

Distribution and metabolism of abamectin in larval stages of Spodoptera littoralis boisduval and Heliothis armigera hübner (Lepidoptera: Noctuidae)

Comparisons were made between the amounts of abamectin and total radioactivity recovered from Spodoptera littoralis and Heliothis armigera larvae after topical application of [³H]abamectin. Penetration (as shown by wash-off experiments) did not differ significantly between the Spodoptera instars. Significantly more abamectin was recovered from ventral nerve cord samples of larvae showing symptoms of poisoning than from larvae not showing these symptoms. Fifth-instar S. littoralis larvae had a significantly lower proportion of radioactivity as abamectin in the ventral nerve cord than in sixth-instar S. littoralis or fifth- and sixth-instar H. armigera. The proportion of radioactivity present as abamectin (but not total radioactivity) was significantly increased when the fifth-instar S. littoralis larvae were pre-treated with piperonyl butoxide (PB) suggesting that the relative insensitivity of fifth-instar S. littoralis larvae to abamectin is due at least in part to greater metabolism, particularly by microsomal oxidases. Fat body samples consistently had a greater proportion of radioactivity as abamectin than the nerve cord and the former may act as storage sites for abamectin.     

Microsomal oxidase activity of three blowfly species and its induction by phenobarbital and β-naphtoflavone

Induction of the microsomal oxidase system by dietary phenobarbital and β-naphthoflavone was examined in three blowflies, Phormia regina (Mg.), Lucilia illustris (Mg.), and Eucalliphora lilica (Walk.). Responses were similar in adults and larvae of all species. Phenobarbital increased cytochrome P-450 levels up to 9-fold and aldrin epoxidase up to 138-fold. Increases in cytochrome P-450 and aldrin epoxidase caused by β-naphthoflavone were minor relative to those produced by phenobarbital. In toxicity experiments with carbaryl and propoxur tolerance was associated with the amount of microsomal oxidase activity. Using piperonyl butoxide to synergize carbaryl and propoxur there was no clear indication for the use of either the synergist ratio or synergist difference as an indicator of microsomal oxidase activity.     

Microsomal oxidases in the flesh fly (Sarcophaga bullata Parker) and the black blow fly [Phormia regina (Meigen)]

The microsomal oxidase system in the flesh fly (Sarcophaga bullata Parker) and the black blow fly [Phormia regina (Meigen)] was examined using aldrin as substrate. In both species the oxidase requires NADPH and is inhibited by CO and by piperonyl butoxide. The enzyme activity changes significantly during larval development, reaching a maximum shortly before puparium formation then declining during the pupal stage and increasing again in adults. Dietary sodium phenobarbital at 0. 1– 0.5% increases the oxidase activity up to 60- and 56-fold in the larvae of blow flies and flesh flies, respectively.     

Phorate sulfoxidation by plant root extracts

Soybean root homogenates were found to oxidize phorate to phorate sulfoxide. Neither PO nor sulfone derivatives of phorate were detected. Fractionation of soybean root homogenate indicates that the enzyme(s) which oxidize phorate to the sulfoxide are largely (72%) in the 25,000g pellet. In vitro studies of the 25,000g pellet indicate a linear reaction rate at 34°C for periods of up to 2 h at the pH optimum of 5.5. Soybean and bean root 25,000g pellets were twice as active on a mg protein basis as those from barley, corn, wheat, sorghum and over ten times more active than tomato.In vitro studies indicate that Counter, disulfoton, fenthion, aldrin, heptachlor, piperonyl butoxide, sulfoxide, atrazine, SKF525A and p-chlorothioanisole when present at a 10:1 ratio with phorate significantly inhibited soybean root phorate sulfoxidation.     

A comparison of permethrin and methomyl insecticides for the control of a multiresistant strain of houseflies (Musca domestica)

A methomyl sugar bait formulation and permethrin residual spray were compared for the control of a multi-insecticide resistant strain of housefly in a UK pig farm. The methomyl was applied as a granular scatter bait at the manufacturer's recommended rate of 25 mg m^?2 active ingredient (a.i.) to the treated floor area. Permethrin was applied at 32, 64 and 128 mg m^?2 a.i. to structural surfaces. The highest deposit rate of permethrin used was four times that recommended by the manufacturer for the control of flying insects. The methomyl bait gave effective control but the permethrin spray failed at all deposit rates tested. The use of permethrin increased resistance to this compound at the KD50 level from x 13 to x 560 within 10 weeks and significantly increased the proportion of flies resistant to natural pyrethrins synergised with piperonyl butoxide (P<0.01).     

Metabolism of trifluralin,profluralin, and fluchloralin by rat liver microsomes

Three structurally related [¹⁴C]dinitroaniline herbicides, trifluralin, profluralin, and fluchloralin, were extensively metabolized in vitro by both normal and phenobarbital-induced rat liver microsomes. Identification of the metabolites in the ethyl acetate extracts indicated that aliphatic hydroxylation, N-dealkylation, reduction of a nitro group, and cyclization were the predominant metabolic routes for these herbicides in vitro. Of particular interest was the formation of a benzimidazole metabolite.     

Development of resistance to pyrethroids in insects resistant to other insecticides

Resistance to pyrethroids in insects is rare, but its recent rapid development in the field suggests that this resistance may be facilitated by previous exposure to or by resistance to insecticides of unrelated groups. To test this houseflies of strain 49_r2b, originally resistant to dimethoate in the field, were selected eight times during ten generations with either pyrethrum extract or bioresmethrin with or without piperonyl butoxide or with dimethoate. Selecting with any of the pyrethroids led to resistance to these insecticides and in particular to pyrethrum/piperonyl butoxide. Selecting with pyrethrum/piperonyl butoxide resulted in strongest resistance to the pyrethroids tested, whereas selecting with bioresmethrin/piperonyl butoxide resulted in least resistance. These results show that dimethoate-resistant flies selected with pyrethroids can readily develop resistance to these insecticides, but development of resistance can be minimised by using bioresmethrin/piperonyl butoxide. The implications of these findings on the sequential use of insecticides are discussed.     

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.     

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.     

Toxicity of chlordimeform and amitraz to the egyptian cotton leafworm (Spodoptera littoralis) and the tobacco budworm (Heliothis virescens)

The relative toxicity (μg a.i. g^?1 body wt) of the formamidine insecticide chlordimeform (CDM) and the triazapentadiene insecticide amitraz was examined in two species of noctuid moth Spodoptera littoralis and Heliothis virescens. When applied topically, there was an unexpected and marked difference in the toxicity of CDM base and its hydrochloride to adults of both species, the salt being appreciably more toxic. For H. virescens at least, this difference in toxicity could not be explained by differences in penetration. This trend was reversed for larval instars of S. littoralis; while there was relatively little difference in the toxicity of the base to adult and larval stages, the salt was at least 1000-fold more toxic to adults than to larvae. N¹-Demethylchlordimeform (DCDM) was the only metabolite of CDM to show biological activity against either species, but was much less toxic than the parent compound. Amitraz was far less toxic than either CDM or DCDM; like the CDM salt, it appeared to be more toxic to adult than larval stages of S. littoralis. Application of piperonyl butoxide significantly increased the toxicity of the CDM salt, DCDM and amitraz to adult H. virescens, the synergist being particularly effective with DCDM and amitraz. In contrast, piperonyl butoxide had no significant effect on the toxicity of DCDM, and slightly antagonised the toxicity of DCDM to fourth-instar larvae of S. littoralis.     

Environmental degradation of the insect growth regulator methoprene. IX. Metabolism by bluegill fish

The accumulation, persistence, and metabolism and/or elimination of methoprene (isopropyl (2E, 4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate) was examined for bluegill sunfish (Lepomis macrochirus) contained in a dynamic flow-through system and a model aquatic ecosystem. The fish in the dynamic flow-through system acquired moderate residues of largely unmetabolized methoprene when continuously exposed to about 30 times anticipated environmental levels of methoprene, but residues were rapidly eliminated (93–95%) within 2 weeks when fish were transferred to flowing uncontaminated water. When bluegill were treated with methoprene in a model aquatic ecosystem, fish showed a highly misleading accumulation of ¹⁴C residues since residual radioactivity was found almost exclusively in radiolabeled natural products, including cholesterol, free fatty acids, glycerides, and protein. Less than 0.1% of the total radioactivity in fish could be attributed to unmetabolized methoprene or its primary metabolites; thus, simple radioassay procedures in ecosystem studies can be severely compromised unless coupled with more sophisticated analytical techniques.     

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.     

Bimodal effect of methylenedioxyphenyl compounds on detoxifying enzymes in the housefly

Thirteen methylenedioxyphenyl (MDP) compounds, including commercial insecticide synergists and juvenile hormone analogs, were compared in their effect on detoxifying enzymes in the housefly (Musca domestica). Flies were fed a diet containing 1% of the compounds for 3 days. Enzymes were then assayed in vitro for their activity using aldrin and DDT as substrates. Piperonyl butoxide (PB), sesamex, propyl isome, sulfoxide, safrole, isosafrole, 6,7-epoxy-3,7-diethyl-1-[3-4(methylenedioxy) phenoxy]-2-octene (MDP-JH I) and 6,7-epoxy-3-methyl-7-ethyl-1-[3,4-(methylenedioxy) phenoxy]-2-octene (MDP-JH II) all caused a bimodal effect, inhibiting microsomal epoxidase and inducing DDT-dehydrochlorinase in the resistant Isolan-B strain. Two of these, PB and MDP-JH I, gave similar results with the susceptible strain, stw;w⁵ and two resistant strains, Fc-B and Orlando-DDT. However, o-safrole, piperonylic acid, piperonal, 3,4-methylenedioxybenzyl acetate and methyl-(3,4-methylenedioxy) benzoate had little or no effect on the enzyme systems studied. The standard susceptible strain (WHO-SRS) responded to these compounds very differently. Among those tested, piperonyl butoxide, sesamex, safrole, and isosafrole were inducers of microsomal epoxidase, a 4-fold increase occurring after treatment with sesamex. Only MDP-JH II showed a marked inhibition of the epoxidase. These treatments did not effect DDT-dehydrochlorinase activity in this strain.The enhancement of DDT-dehydrochlorinase activity by the MDP compounds is associated with an increased rate of DDT dehydrochlorination in vivo. The stimulatory effect could be blocked by treatment with actinomycin D or cycloheximide.     

Insecticidal activity of synthetic 2-carboxylbenzofurans and their coumarin precursors

Several 2-carboxylbenzofurans and their coumarin precursors, compounds 1 – 6 , and the novel compound 7 were synthesized and their insecticidal activity studied using adult sweet potato weevils (Cylas formicarius elegantulus (Summer)) at 24 μg, 48 μg and 72 μg per insect in 0.5 ml litre^?1 piperonyl butoxide (PPB) in acetone. The order of toxicity of the compounds as judged by the percentage mortality at 24 μg per insect at 48 h was 2 (100%) > 6 (95%) > 7 (85%) > 4 (75%)) > 3 (65%) > 1 (60%) > 5 (45%) > piperonyl butoxide (0.0%). Compound 2 was equitoxic to 24 μg of technical grade dimethoate. When administered in acetone alone, however, the compounds were only moderately active (i.e. > 120 μg per insect was required for 60% mortality at 48 h). The test compounds were more active at lower doses (48–72 μg per insect) when dissolved in dimethylsulfoxide or in an oil extract obtained from the fruit of Blighia sapida Koenig.     

Monooxygenase mediated pyrethroid detoxification in sea lice (Lepeophtheirus salmonis)

The role of monooxygenases in detoxification of the pyrethroids cypermethrin and deltamethrin was examined. Four strains of sea lice (Lepeophtheirus salmonis Krøyer) with normal or moderately reduced sensitivity towards the pyrethroids were tested in bioassays by exposure to the pyrethroid alone and in combination with an oxygenase inhibitor, piperonyl butoxide (PBO). The normal (baseline) sensitivity was considered as the sensitivity range for the two most sensitive strains. Pre‐treatment with PBO elevated the sensitivity (P < 0.01) compared with groups exposed to the pyrethroid only. A positive, but not statistically significant, correlation between the activity of haem peroxidases and the pyrethroid concentration immobilizing 50% of the parasites was demonstrated (ρ = 0.500 for deltamethrin and ρ = 0.310 for cypermethrin). The results indicate that cytochrome P450 monooxygenases are involved in detoxification of pyrethroids in sea lice. ¹⁴C‐Deltamethrin was absorbed in a lesser amount in a group of sea lice exposed to a mixture of the compound and PBO than in a group exposed to ¹⁴C‐deltamethrin alone. A significant difference could be demonstrated both immediately after exposure (P < 0.01) and 24 h after exposure (P < 0.05). No significant differences were found between groups pre‐treated with PBO and groups exposed to ¹⁴C‐deltamethrin only. ¹⁴C‐Deltamethrin was taken up mainly through the cuticle, especially the cuticle on the extremities of the ventral surface, and subsequently distributed throughout the body of the parasite. Copyright © 2005 Society of Chemical Industry     

Effect of liver enzyme induction on paraoxon metabolism in the rat

Orally administered [1-¹⁴C]ethyl paraoxon, O,O-diethyl-O-p-nitrophenyl phosphate, is readily absorbed from the gastrointestinal tract of male albino rats. Radioactivity is essentially eliminated in 72 hr by excretion into urine and feces and by expiration as ¹⁴CO₂. Compounds with radioactivity in the urine are tentatively identified as diethyl phosphoric acid, desethyl paraoxon, ethanol, metabolites conjugated with amino acids, and paraoxon; the first compound is the predominant radioactive metabolite. Intraperitoneally injected phenobarbital, DDT, dieldrin, and endrin are inducers of microsomal enzymes that degrade paraoxon. The aryl phosphate-cleaving activity in vitro is not dependent on the addition of NADPH. O-Dealkylation of paraoxon is catalyzed by microsomal enzymes that require NADPH and oxygen and are inhibited by carbon monoxide. Microsomal enzymes from rats pretreated with enzyme inducers give an increased rate of O-dealkylation of paraoxon. Reduced glutathione has little or no effect on paraoxon degradation by either microsomal or soluble enzymes. Actinomycin D inhibits O-dealkylation of paraoxon in vivo, as indicated by reduction of ¹⁴CO₂ formation, and in vitro, as indicated by decreased activity of microsomal O-dealkylase. The role of microsomal mixed-function oxidases and NADPH-dependent O-dealkylase in the metabolism of organophosphorus insecticides is discussed.     

Toxicology and metabolism of chloromethiuron in Boophilus microplus larvae

The toxicity of the acaricide chloromethiuron, 3-(4-chloro-o-tolyl)-1,1-dimethyl- (thiourea), and of nine related compounds to Boophilus microplus larvae was determined by a spray-tower method. Four of these compounds were toxic but only chloromethiuron and its N-demethyl derivative were of practical importance. Metabolism of [¹⁴C]chloromethiuron, in the formamidine-susceptible but organo-phosphorus-resistant Mt. Alford strain, was compared with that in a chlordimeform-selected Mt. Alford strain, which in laboratory tests was two to three times resistant to chloromethiuron, chlordimeform and amitraz. The latter strain produced smaller quantities of the toxic N-demethyl derivative than the Mt. Alford strain; this was the only resistance mechanism determined. Rates of degradation of chloromethiuron were the same in both strains. Piperonyl butoxide strongly antagonised the toxicity of chloromethiuron by 18 to 33 times and depressed the production of the N-demethyl derivative in both strains (0.3 times that of the control), while degradation rates of chloromethiuron itself were halved by piperonyl butoxide in both strains. These results indicated that the parent material was not toxic until oxidised to the N-demethyl derivative. As, in addition, some symptoms of chloromethiuron toxicosis in larvae were similar to those caused by formamidine acaricides, a common mode of lethal action is suggested.     

Microsomal sulfoxidation of phorate in the fall armyworm,Spodoptera frugiperda (J. E. Smith)

Microsomal sulfoxidation in fall armyworm (Spodoptera frugiperda) larvae was examined using phorate as substrate. The system required NADPH and was inhibited by CO and by piperonyl butoxide. Sulfoxidase activity was found in the alimentary canal, fat body, and Malpighian tubules, with the midgut being the most active. Microsomal substrates such as aldrin, heptachlor, biphenyl, and methyl parathion significantly inhibited the enzyme activity whereas p-nitroanisole and p-choloro-N-methylaniline had no effect. Enzyme activity increased during larval development, reaching a maximum shortly before pupation. Allelochemicals (monoterpenes, indoles, and flavones), drugs (phenobarbital and 3-methylcholanthrene), and host plants (corn cotton, parsnip, and parsley) significantly increased the enzyme activity. Increased phorate sulfoxidation through enzyme induction was found to decrease oral toxicity of phorate to the larvae. Analyses of internal insecticide revealed that, at various intervals, induced larvae retained less phorate and its oxidative metabolites than the controls. It was concluded that induction of phorate sulfoxidase activity results in an overall increase in the rate of phorate detoxication in this insect.     

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.