2,4-滴异辛酯的水解及光解特性

为明确2,4-滴异辛酯的环境行为规律,采用室内模拟试验方法,研究了2,4-滴异辛酯在不同温度、pH值、水体及初始浓度下的水解特性及其在不同pH值、水体、光源和初始浓度下的光解特性。结果表明:中性 (pH = 7) 条件下,初始质量浓度为5 mg/L的2,4-滴异辛酯在15、25 和35 ℃ 下的水解半衰期分别为346.6、231.0和173.3 h;25 ℃下,5 mg/L的2,4-滴异辛酯在pH值分别为4、7 和9 的缓冲溶液中的水解半衰期分别为77.0、231.0 和138.6 h;2,4-滴异辛酯在稻田水、自来水和河水中的水解速率高于其在蒸馏水中的水解速率,4 种条件下的半衰期分别为23.1、25.7、40.8 和63.0 h;初始质量浓度分别为1、3和5 mg/L的2,4-滴异辛酯在pH值为7的缓冲溶液中的水解半衰期分别为231.0、173.3和138.6 h。300 W汞灯照射下,2,4-滴异辛酯在酸性条件下的光解速率大于其在中性和碱性条件下,半衰期分别为49.5、77.0 和138.6 h;2,4-滴异辛酯在河水和稻田水中的光解速率高于其在自来水和蒸馏水中的光解速率,4 种条件下的半衰期分别为6.7、7.6、43.3 和46.2 h;2,4-滴异辛酯在不同光源下的光解速率依次为500 W汞灯 > 300 W汞灯 > 500 W氙灯;初始质量浓度分别为1、3和5 mg/L的2,4-滴异辛酯在pH值为7的缓冲溶液中的光解半衰期分别为63.0、43.3和40.8 h。2,4-滴异辛酯水解及光解的主要产物是2,4-滴,其降解机制主要是酯水解反应。研究结果可为2,4-滴异辛酯的合理使用及其环境风险评估提供参考。     

Substrate-specificity and toxicological significance of pyrethroid-hydrolyzing esterases of mouse liver microsomes

An esterase or esterases in acetone powder preparations of mouse liver microsomes hydrolyze the cyclopropanecarboxylate ester linkage of pyrethroid insecticide chemicals derived from primary alcohols. The rate of cleavage of (+)-trans-chrysanthemates with various alcohol moieties decreases in the following order: 5-propargyl-2-furylmethyl; 5-benzyl-3-furylmethyl (bioresmethrin); 3-phenoxybenzyl; tetrahydrophthalimidomethyl esters. The hydrolysis rate of benzylfurylmethyl esters with various acid moieties decreases in the order: (+)- or (?)-trans-chrysanthemate; (+)-trans-ethanochrysanthemate; tetramethylcyclopropanecarboxylate; (+)- or (?)-cis-chrysanthemate or (+)-cis-ethanochrysanthemate. The trans-isomers of chrysanthemates and ethanochrysanthemates are hydrolyzed from 2.6- to more than 50-fold more rapidly than the corresponding cis-isomers. This enzyme system does not hydrolyze secondary alcohol esters, i.e., allethronyl (+)-trans- and (+)-cis-chrysanthemates.On intraperitoneal administration to mice, the (+)-trans-chrysanthemate and -ethanochrysanthemate of benzylfurylmethanol are of very low toxicity relative to the corresponding (+)-cis-isomers and the tetramethylcyclopropanecarboxylate. S,S,S-tributyl phosphorotrithioate (DEF) pretreatment increases the toxicity of these five compounds by 2.6- to more than 188-fold, with the exception of bioresmethrin whose toxicity is not altered. When the toxicity is increased, it is probably the result of esterase inhibition since DEF strongly inhibits the esterase activity of fresh liver microsomes while the mixed-function oxidase system remains active. The oxidase system metabolizes the chrysanthemates more rapidly than the ethanochrysanthemates of benzylfuryl-methanol. Depending upon the pyrethroid involved, the esterase or the mixed-function oxidase system, or both may be responsible for limiting the toxicity of these pyrethroids to mice.     

The effect of pretreatment with S,S,S-tributyl phosphorotrithioate on deltamethrin resistance and carboxylesterase activity in Aphis gossypii (Glover) (Homoptera: Aphididae)

The synergism of S,S,S-tributyl phosphorotrithioate (DEF) and its effect on carboxylesterase activity were investigated in deltamethrin-selected resistant (DRR) and susceptible (DSS) strains of cotton aphids, Aphis gossypii (Glover). Compared to the DSS strain, the DRR strain showed 23,900-fold resistance to deltamethrin, and 7560- and 99-fold cross-resistance to bifenthrin and ethofenprox, respectively. The synergist, DEF, increased the toxicity of both deltamethrin and bifenthrin, but not of ethofenprox when DEF was pretreated of 15 h. DEF exhibited significant inhibition on the carboxylesterase activity in the DRR strain, but no significant effect on that of the DSS strain in vitro. After the cotton aphids exposing to DEF, the carboxylesterase activity decreased gradually until 15 h and then gradually recovered until 24 h in the DRR strain, which fluctuated according to the effect of DEF on the deltamethrin toxicity detected using DEF pretreatment in the DRR strain. Therefore, our studies suggested that the effect of DEF on carboxylesterase was associated with deltamethrin resistance in the DRR strain.     

Response of wheat and oat seedlings to root-applied diclofop-methyl and 2,4-dichlorophenoxyacetic acid

Roots of wheat and oat seedlings were treated with diclofop-methyl (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate) in a specially designed Plexiglas treatment apparatus. Diclofopmethyl severely inhibited the root growth of susceptible oat seedlings but roots of resistant wheat seedlings were unaffected. Diclofop-methyl at 0.3 μM reduced the growth of oat roots to 50% of the control. Direct contact between diclofop-methyl and the inhibited root zone was necessary for growth inhibition since other parts of the seedling (roots and shoots) isolated from contact with diclofop-methyl solution by a physical barrier were unaffected. Diclofop (2-[4-(2′,4′-dichlorophenoxy)phenoxy]propionic acid), the free acid metabolite of diclofop-methyl, was somewhat more phytotoxic than the parent compound. The herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), which engenders auxin responses, slightly enhanced the inhibition of oat root growth by diclofop-methyl. The primary wheat metabolite, ring-hydroxylated diclofop, was nonphytotoxic to oat root growth, whereas the acetylated derivative of the primary water-soluble oat metabolite (neutral glucose ester of diclofop) inhibited oat root growth to the same extent as diclofop-methyl. These results support the hypothesis that the basis for selectivity between resistant wheat and susceptible oat is the metabolism of diclofop-methyl by aryl hydroxylation and conjugation but not glucose ester conjugation. Translocation is also not an important factor in the phytotoxic activity of diclofop-methyl.     

The hydrolysis of herbicidal phenoxyalkanoic esters to phenoxyalkanoic acids in Saskatchewan soils

The hydrolysis of the iso-propyl, n-butyl-and iso-octyl esters of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), the n-bytyl ester of 2,4-dichlorophenoxybutyric acid (2,4-DB) and the iso-octyl ester of 2,4-dichlorophenoxypropionic acid (2,4-DP) was studied in four prairie soils of differing textures and pH at 25±1°C. The esters were analysed using gas chromatography. After 24 h in soils at wilting point moisture, and above, less than 20% of the applied iso-propyl and n-butyl esters could be recovered from one soil type and none from the remaining three. Loss of the iso-cotyl esters was slower; however, no trace of the 2,4,5-T and 2,4-DP esters was observed in any of the moist soils after 48 and 72 h respectively. In all cases loss of all esters from air-dried soils minimal. The phenoxyalkanoic acid hydrolysis products were recovered from all soil types, treated with the various esters and identified using thin-layer chromatography.     

Mitochondrial impacts of insecticidal formate esters in insecticide‐resistant and insecticide‐susceptible Drosophila melanogaster

BACKGROUND: Previous research on insecticidal formate esters in flies and mosquitoes has documented toxicity profiles, metabolism characteristics and neurological impacts. The research presented here investigated mitochondrial impacts of insecticidal formate esters and their hydrolyzed metabolite formic acid in the model dipteran insect Drosophila melanogaster Meig. These studies compared two Drosophila strains: an insecticide‐susceptible strain (Canton‐S) and a strain resistant by cytochrome P450 overexpression (Hikone‐R). RESULTS: In initial studies investigating inhibition of mitochondrial cytochrome c oxidase, two proven insecticidal materials (hydramethylnon and sodium cyanide) caused significant inhibition. However, for insecticidal formate esters and formic acid, no significant inhibition was identified in either fly strain. Mitochondrial impacts of formate esters were then investigated further by tracking toxicant‐induced cytochrome c release from mitochondria into the cytoplasm, a biomarker of apoptosis and neurological dysfunction. Formic acid and three positive control treatments (rotenone, antimycin A and sodium cyanide) induced cytochrome c release, verifying that formic acid is capable of causing mitochondrial disruption. However, when comparing formate ester hydrolysis and cytochrome c release between Drosophila strains, formic acid liberation was only weakly correlated with cytochrome c release in the susceptible Canton‐S strain (r² = 0.70). The resistant Hikone‐R strain showed no correlation (r² < 0.0001) between formate ester hydrolysis and cytochrome c release. CONCLUSION: The findings of this study provide confirmation of mitochondrial impacts by insecticidal formate esters and suggest links between mitochondrial disruption, respiratory inhibition, apoptosis and formate‐ester‐induced neurotoxicity. Copyright © 2009 Society of Chemical Industry     

Metabolic mechanisms of insecticide resistance in the western flower thrips, Frankliniella occidentalis (Pergande)

The interactions between six insecticides (methiocarb, formetanate, acrinathrin, deltamethrin, methamidophos and endosulfan) and three potential synergists (piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM)) were studied by topical exposure in strains selected for resistance to each insecticide, and in a susceptible strain of Frankliniella occidentalis (Pergande). In the susceptible strain PBO produced appreciable synergism only of formetanate, methiocarb and methamidophos. Except for endosulfan, PBO synergized all the insecticides to varying degrees in the resistant strains. A very high level of synergism by PBO was found with acrinathrin, which reduced the resistance level from 3344- to 36-fold. PBO slightly synergized the carbamates formetanate (4.6-fold) and methiocarb (3.3-fold). PBO also produced a high synergism of deltamethrin (12.5-fold) and methamidophos (14.3-fold) and completely restored susceptibility to both insecticides. DEF did not produce synergism with any insecticide in the resistant strains and DEM was slightly synergistic to endosulfan (3-fold). These studies indicate that an enhanced detoxification, mediated by cytochrome P-450 monooxygenases, is the major mechanism imparting resistance to different insecticides in F occidentalis. Implications of different mechanisms in insecticide resistance in F occidentalis are discussed.     

Selection and characterization of spinosad resistance in Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae)

The cross-resistance and biochemical mechanism of the beet armyworm, Spodoptera exigua (Hübner), to spinosad was studied in the laboratory. S. exigua population were collected from Shanghai suburb. After five generations of selection, the resistance of S. exigua to spinosad increased 345.4 times compared with the susceptible strain. There was no cross-resistance between spinosad and fenvalerate, phoxim, methomyl, abamectin, and cyfluthrin. When the inhibitors, PBO, TPP, DEF, and DEM were used as synergist in the susceptible strain and resistant strain, the synergistic ratio was 0.7-, 0.5-, 1.0-, and 0.6- fold for the susceptible strain, and 9.8-, 1.5-, 2.6-, and 1.5-fold for the resistant strain, respectively. The results revealed that PBO had significant synergistic effect on the resistant strain. The activity in vitro of microsomal-O-demethylase and glutathione S-transferase in the resistant strain was 5.2- and 1.0-fold of the susceptible strain, respectively. The results implied that microsomal-O-demethylase might be important in conferring spinosad resistance in the S. exigua population.     

THE HYDROLYSIS OF 2,4-DICHLOROPHENOXY- ACETATE ESTERS TO 2,4-DICHLOROPHENOXYACETIC ACID IN SASKATCHEWAN SOILS

Summary. The hydrolysis of the iso-propyl, n-butyl and iso-octyl esters of 2,4-dichloro-phenoxyacetic acid to the free acid was studied in aqueous solutions and on three prairie soils. The esters were analysed using electron-capture gas chromatography following extraction from solution with benzene, and from soils, using either 10% aqueous aceto-nitrile or a 2:1 mixture of benzene and iso-propanol.
Ester hydrolysis in 0·1 n sodium hydroxide solution was very rapid, more than 50% of all the esters being hydrolysed in less than 1 min. In 0·1 n sodium carbonate solution the times for 50% hydrolysis at 25°C were < 5, 5 and 30 min for the n-butyl, iso-propyl and iso-octyl esters respectively. In distilled water negligible hydrolysis occurred over a 5 h period.
The iso-propyl and n-butyl esters underwent a very facile hydrolysis on soils. Shaking the treated soils with 0·1 M calcium chloride solution for 30 min at 25°C resulted in extensive hydrolysis to the acid as determined spectrophotometrically. Under similar conditions negligible hydrolysis of the iso-octyl ester occurred.
After 1·5 h at 25±1°C on soils at their wilting point moisture levels, and greater, less than 15% of the applied iso-propyl or n-butyl esters could be recovered using either extraction procedure, indicating rapid hydrolysis to the acid. After 24 h no iso-propyl or n-butyl ester residues could be detected in any of the soils. Loss of the iso-octyl ester was slower under these conditions with approximately 20–30% of the ester remaining after 24 h, and 10% after 48 h.
L'hydrolyse des esters de 2,4 dichlorophénoxyacétates en acide 2,4 dichlorophénoxyacétique dans les sols du saskatchewan.     

The effect of O,S,S,-trimethyl phosphorodithioate on the in vivo metabolism of phenthoate in the rat

The in vivo metabolism of phenthoate (O,O-dimethyl S-[α-(carboethoxy)benzyl]phosphorodithioate) was followed in rats after oral administration of a nontoxic dose of 100 mg/kg. The same metabolic study was conducted following coadministration of 0.5% O,S,S-trimethyl phosphorodithioate (OSS-Me). When administered alone, phenthoate was metabolized principally by carboethoxy ester hydrolysis and cleavage of the PO and CS bonds, resulting in at least six metabolites. The primary urinary metabolite excreted was phenthoate acid. Coadministration of 0.5% OSS-Me did not alter the types of metabolites excreted. However, a reduction of the carboxylesterase-catalyzed product (phenthoate acid) was observed, indicating that the enzyme responsible for the major pathway of phenthoate detoxication was inhibited. Alternate detoxication processes did not compensate for the reduction in carboxylesterase-catalyzed detoxication. It was concluded that inhibition of the carboxylesterase enzymes is the major cause of the potentiation of phenthoate toxicity by OSS-Me.     

THE ADSORPTIVE BEHAVIOUR OF ACID AND ESTER FORMS OF 2,4-D ON SOILS

Summary. The adsorption of acid, n-butyl, and iso-octyl ester forms of 2,4-D (2,4- dichloiophenoxyacetic acid) was studied for several Canadian prairie soils. The k values for the acid ranged from 0·09 to 1·30 and were correlated to the soil organic matter and not to the clay content. The Q , values (μg adsorbed/g of organic matter) for the acid were 7–2±l. The n-butyl and the iso-octyl esters hydrolysed to the acid form in the aqueous medium and this process was accelerated in the presence of the moist soil. Consequently, the k values for the esters, using slurry type adsorption experiments, or their distribution coefficients, using leaching columns, could not be determined. It was concluded that the adsorptive behavior of the two esters in moist soil was similar to that of the acid form.
Comportement des formes actde, et ester du 2,4-D quant à leur adsorption dans tes sols     

Esterases and resistance to synthetic pyrethroids in the Egyptian cotton leafworm

Esterases hydrolyzing α-naphthyl acetate (α-NA), β-naphthyl acetate (β-NA), and p-nitrophenyl acetate (p-NPA) were investigated colorimetrically in larval homogenates of synthetic pyrethroid susceptible (S) and resistant (R) strains of Spodoptera littoralis (Boised). The hydrolytic activity towards the three substrates in cybolt, decamethrin, and fenvalerate R strains were from 3 to 6.5 times as high as in the S strain. The increase in esterase activity was closely associated with the development of resistance in the R strains. DEF (S,S,S-tributyl phosphorotrithioate) proved to be an inhibitor for all esterases, with a particularly potent action on p-NPA-hydrolyzing enzymes. The inhibitory action was more pronounced in R strains than in the S strain. Pretreatment with DEF increased the toxicity of pyrethroid compounds in the R strains more than in the S strain and hence decreased the levels of resistance in these strains. This is evidence that the esterases contribute to the resistance against synthetic pyrethroids in S. littoralis larvae.     

STUDIEN ZUR VERTEILUNG VON 14C-MARKIERTEM 2,4-D IN VERSCHIEDEN EMPFINDLICHEN UNKRÄUTERN

Studies of the absorption and translocation of ¹⁴C-2,4-D in Chenopodium album L., Galinsoga parviflora Cav., Datura stramonium L. and Galium aparine L. in relation to their susceptibility gave the following results: In G aparine (resistant) there was little transport of 2,4-D applied to the leaves, and a probable relationship between resistance and the immediate binding of the 2,4-D in the treated leaf. D. stramonium (relatively resistant) transported 2,4-D in considerable amounts alter uptake through the leaf, while C. album (very susceptible) and G. parviflora (susceptible) were intermediate in respect of 2,4-D translocation. No relationship between susceptibility of these four species and 2,4-D uptake and translocation from the leaves could be established. After application to the root systems of the four species, 2,4-D was taken up and translocated in the shoot to varying extents. In G. aparine much 2,4-D was taken up and translocated. In contrast to leaf application, the herbicide was not immediately converted into a strongly-held immobile form. In C. album, G. parviflora and D. stramonium, however, no 2,4-D was translocated in the shoot. There was thus no correlation between susceptibility and shoot transport of 2,4-D in the four species studied. Distribution du 2,4-D marqué au ¹⁴C dans des espèces de mauvaises herbes présentant des sensibilités diverses     

Toxic effects of novel organophosphorus insecticide (RPR-V) on certain biochemical parameters of euryhaline fish, Oreochromis mossambicus

The euryhaline fish, Oreochromis mossambicus was exposed to sub-lethal concentration (0.017 mg L⁻¹) of a novel phosphorothionate, 2-butenoic acid-3-(diethoxy phosphinothionyl) ethyl ester (RPR-V) for 30 days and allowed to recover for 7 days. Important biomarker enzymes were assayed in plasma, brain, gill, liver, kidney, and muscle during exposure tenures of day-3, -7, -15, -30, and also at 7 days (withdrawal) after stopping treatment. Acetylcholinesterase (AChE) activities of brain, gill, and muscle were strongly inhibited by 67, 75, and 66%, respectively, on day-30. Exposure (time) dependent increases in alanine aminotransferase (ALAT), and aspartate aminotransferase (ASAT), acid phosphatase (AcP), and alkaline phosphatase (AkP), activities in plasma and kidney; AcP and AkP activities in gill were noticed. However, significant decrease in ALAT, ASAT, AcP, and AkP activities in liver was observed. The depletion of glycogen was observed in liver, brain, and gill tissues, an indication of typical stress related response of the fish with pesticide. A significant increase in lactate dehydrogenase (LDH) activity in gill and brain was observed and decreased in liver and muscle, indicating tissue damage and muscular harm. Depletion of glutathione (GSH) was observed in the above tissues, there by enhancing the lipid peroxidation resulting in cell damage. The induction in hepatic glutathione-S-transferase (GST) levels indicates the protection against the toxicity of xenobiotic-induced lipid peroxidation. There was a significant recovery in all the above biochemical parameters, in all the tissues of fish after a recovery period of 7 days. These results revealed that RPR-V affects the intermediary metabolism of O. mossambicus and the increase of biomarker enzymes in plasma, might be due to the necrosis of liver.     

Kinetic efficiency of mutant carboxylesterases implicated in organophosphate insecticide resistance

Resistance to organophosphorus (OP) insecticides in Lucilia cuprina arises from two mutations in carboxylesterase E3 that enable it to hydrolyse the phosphate ester of various organophosphates, plus the carboxlyester in the leaving group in the case of malathion. These mutations are not found naturally in the orthologous EST23 enzyme in Drosophila melanogaster. We have introduced the two mutations (G137D and W251L) into cloned genes encoding E3 and EST23 from susceptible L. cuprina and D. melanogaster and expressed them in vitro with the baculovirus system. The ability of the resultant enzymes to hydrolyse the phosphate ester of diethyl and dimethyl organophosphates was studied by a novel fluorometric assay, which also provided a sensitive titration technique for the molar amount of esterase regardless of its ability to hydrolyse the fluorogenic substrate used. Malathion carboxylesterase activity was also measured. The G137D mutation markedly enhanced (>30-fold) hydrolysis of both classes of phosphate ester by E3 but only had a similar effect on the hydrolysis of dimethyl organophosphate in EST23. Introduction of the W251L mutation into either gene enhanced dimethyl (23-30-fold) more than diethyl (6-10-fold) organophosphate hydrolysis and slightly improved (2-4-fold) malathion carboxylesterase activity, but only at high substrate concentration.     

Interactions between S,S,S-tributyl phosphorotrithioate (DEF) and growth regulator herbicides. II.—Further studies

Additional results are presented from experiments with poplar and privet discussed in a previous paper. At 9 months after application mixtures of picloram and S,S,S-tributyl phosphorotrithioate (DEF) caused more severe effects than either compound applied alone. This result was in agreement with earlier assessments of phytotoxicity. The earlier synergism of DEF with the triethylamine salt of 2,4,5-T on privet diminished or disappeared, however. Mixtures of DEF with 2,4,5-T iso-octyl ester were antagonistic both in their shortand longer-term phytotoxic effects. Further experiments with guava plants grown in a glasshouse have demonstrated synergism in mixtures of DEF with salt or amine formulations ofpicloram, 2,4,5-T or mecoprop and antagonism between DEF and ester formulations of these herbicides. 2-Butyne-1,4-diol had no effect on the phytotoxicity of picloram ester. Xylene and a non-ionic emulsifying agent (Triton B 1956) did not appreciably increase the effects of picloram if a wetting agent was also present. Synergism was reduced when DEF was applied to guava leaves 2–4 h before or after picloram, and the compounds did not interact when they were introduced directly into the vascular system of this plant.     

Synergism of insecticides provides evidence of metabolic mechanisms of resistance in the obliquebanded leafroller Choristoneura rosaceana (Lepidoptera: Tortricidae)

The interactions between six insecticides (indoxacarb, cypermethrin, chlorpyrifos, azinphosmethyl, tebufenozide and chlorfenapyr) and three potential synergists, (piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM)) were studied by dietary exposure in a multi-resistant and a susceptible strain of the obliquebanded leafroller, Choristoneura rosaceana (Harris). The synergists did not produce appreciable synergism with most of the insecticides in the susceptible strain. Except for tebufenozide, PBO synergized all the insecticides to varying degrees in the resistant strain. A very high level of synergism by PBO was found with indoxacarb, which reduced the resistance level from 705- to 20-fold when PBO was administered alone and to around 10-fold when used in combination with DEF. DEF also synergized indoxacarb, cypermethrin, chlorpyrifos, azinphosmethyl and tebufenozide in the resistant strain. DEM produced synergism of indoxacarb, chlorpyrifos, azinphos-methyl and chlorfenapyr in the resistant strain. DEM was highly synergistic to cypermethrin, and to some extent to tebufenozide in both the susceptible and resistant strains equally, implying that detoxification by glutathione S-transferases was not a mechanism of resistance for these insecticides. The high level of synergism seen with DEM in the case of cypermethrin may be due to an increase in oxidative stress resulting from the removal of the antioxidant, glutathione. These studies indicate that enhanced detoxification, often mediated by cytochrome P-450 monooxygenases, but with probable esterase and glutathione S-transferase contributions in some cases, is the major mechanism imparting resistance to different insecticides in C. rosaceana.     

2,4-Dichlorophenoxyacetic acid (2,4-D) and paranitrophenol (PNP) interactions with gills of Anodonta californiensis and Mytilus californianus: Uptake and effects on membrane fluxes

The effects of pesticides and their breakdown products on membrane fluxes is a subject of interest in assessing the potential ecological impact of these substances. As part of a continuing program we have examined the effects of 2,4-dichlorophenoxyacetic acid (2,4-D) and paranitrophenol (PNP) on divalent cation and primary amine losses from and glycine uptake by gills of the bivalve molluscs Anodonta californiensis (fresh water) and Mytilus californianus (marine). Both 2,4-D and PNP reduce glycine influx into gills of M. californianus. This observation is consistent with the view that glycine is bound to the gill surface as a Mg²⁺ complex prior to active transport.For gills of A. californiensis, Ca²⁺ and Mg²⁺ losses are increased by 10^?3M 2,4-D relative to that into distilled water. Primary amine losses are increased for both A. californiensis and M. californianus gills at low 2,4-D concentrations.For A. californiensis and M. californianus gills the uptake of both 2,4-D and PNP are reduced by increasing concentrations of Ca²⁺ and Mg²⁺. In the case of A. californiensis, Ca²⁺ has a larger effect than Mg²⁺, which is consistent with the demonstrated stabilizing effect of Ca²⁺ on biological membranes. The uptake of PNP is larger than that of 2,4-D and glycine for gills of A. californiensis. The uptake of 2,4-D is reduced by the presence of an excess concentration of glycine but this is probably a physical effect. The uptake of 2,4-D, PNP, and glycine are all passive processes for A. californiensis gills. Glycine does not reduce 2,4-D uptake into M. californianus gills. For M. californianus the transport mechanism for glycine is not the same as that for 2,4-D; the former being active transport and the latter passive transport. However, 2,4-D does interfer with the active transport of glycine.     

Metabolism of methyl bromide by susceptible and resistant strains of the granary weevil, Sitophilus granarius (L.)

Methyl bromide was metabolized by susceptible and resistant strains of adult granary weevil, Sitophilus granarius (L.), mainly by conjugation with glutathione. S-Methyl glutathione and S-methyl cysteine were produced by both strains and S-methyl glutathione sulfoxide was identified as a metabolite in the resistant strain. In the untreated insects, no significant difference was observed in glutathione S-transferase activity but the resistant contained approximately twice as much glutathione per insect as the susceptible strain. When the insects were treated with methyl bromide, the glutathione content of both strains was lowered; proportionally, however, the decrease was considerably higher in the susceptible than in the resistant strain. These results indicate that conjugation of methyl bromide with glutathione is a major detoxication pathway and tolerance to this fumigant is related, in part at least, to the level of glutathione in the granary weevil.     

Esterase-mediated bifenthrin resistance in a multiresistant strain of the two-spotted spider mite, Tetranychus urticae

A field-collected multiresistant strain of Tetranychus urticae Koch exhibiting high resistance to bifenthrin was investigated in comparison with a susceptible laboratory strain. The esterase inhibitor S,S,S-tributyl-phosphorotrithioate (DEF) was able strongly to synergise bifenthrin toxicity in the resistant strain. Optimal conditions for determining esterase activities in T. urticae were determined, and a higher esterase activity towards several artificial substrates was found in this resistant strain, which had a preference for hydrolysing 4-nitrophenyl butyrate. Bifenthrin was able to bind the active centres of T. urticae esterases in vitro, as was determined after competition experiments by a Dixon plot, revealing a higher affinity of bifenthrin in the resistant strain. Bifenthrin-hydrolysing activity in the resistant and susceptible strains was examined in vitro and quantified with gas chromatography. A 7.2-fold higher metabolising rate was found in the resistant strain.