Control of insects in cotton crops in africa with some pyrethroid

Cotton yield results are presented for trials in Senegal, the Ivory Coast, Chad and Morocco in which the pyrethroids permethrin, biopermethrin, 3-phenoxybenzyl (1R,cis)-3-(2,2-dichlorovinyl)-2, 2-dimethylcyclopropanecarboxylate (NRDC 167) and (S)-α-cyano-3-phenoxybenzyl (1R,1 S)-cis,trans-3-(2,2-dibromovinyl-2, 2-dimethylcy-clopropanecarboxylate (NRDC 156) were compared with the compounds currently used for insect control. NRDC 156 gave marked yield increases at rates as low as 12.5 g.a.i./ha, the other pyrethroids needing higher rates to give comparable results. Control of mites, Hemitarsonemus lata and Tetranychus urticae was not satisfactory, however.     

α-氰基-3-苯氧基苄醇乙酸酯立体选择性水解酯酶产生菌的筛选及酶学特性初探

经过酵母菌富集培养,以α-氰基-3-苯氧基苄醇乙酸酯为唯一碳源培养和分离,并进一步用手性HPLC法复筛,得到了两株优先立体选择性水解(S)-α-氰基-3-苯氧基苄醇乙酸酯的酵母菌菌株S11和S25。两株酵母菌均能产生耐酸酯酶,在pH 3.0时对α-氰基-3-苯氧基苄醇乙酸酯进行立体选择性水解,产物对映体过量值(ee/em>p)均在95％以上,转化率(C)分别达50％和46％。测定了菌株S11的生长曲线,并对其产酶特性进行了初探,发现其所产酶为生长偶联型的胞内酶。     

The pyrethrins and related compounds. Part XXII. Preparation of isomeric cyano-substituted 3-phenoxybenzyl esters

Preparation of 3-phenoxybenzyl chrysanthemates and their dihalovinyl analogues substituted with a cyano group at the 2-, 6-, (R)-α-, or (S)-α- positions is described. The (R)- and (S)- isomers of α-cyano-3-phenoxybenzyl esters of 2,2-difluoro-, -dichloro-, and -dibromo-vinyl analogues of cis- and trans- chrysanthemic acid are separated chromatographically, as are the separate pairs of enantiomers of fenvalerate, (RS)-α- cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate. An optically active ester of α-cyano-3-phenoxybenzyl alcohol (obtained using D -oxynitrilase) with 2,2,3,3-tetramethylcyclopropanecarboxylic acid is synthesised.     

Photolysis of flucythrinate

Photolysis of flucythrinate ((RS)-α-cyano-3-phenoxybenzyl (S)-2-(4-difluoromethoxyphenyl)-3-methylbutyrate) in solution (methanol) by UV light (> 290 nm) and as a thin film on glass by exposure to sunlight yields products resulting from ester cleavage. The major product in solution is formed via photo-induced decarboxylation. When thin films are exposed to sunlight, flucythrinate has a half life of 8 days on glass and 3 days on a leaf surface.     

Separation and identification of short-lived free radicals formed by photolysis of the pyrethroid insecticide fenvalerate

Using a spin-trap reagent 3-nitrosodurene (1,2,4,5-tetramethyl-3-nitrosobenzene), the short-lived free radicals generated by ultraviolet irradiation of fenvalerate [(RS)-α-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate] in degassed benzene or dichloromethane, were scavenged as the more stable nitroxide radicals. These radicals were separated by high-performance liquid chromatography and identified individually by electron-spin resonance spectroscopy, as well as by gas chromatography/mass spectrometry. As a result, they were found to be the spin adduct mixtures of the 4-chloro-α-isopropylbenzyl and α-cyano-3-phenoxybenzyl radicals, which are involved in the photo-induced decarboxylation process of fenvalerate. Discrimination of the radicals was also performed by the isotope-labelling method whereby the benzylic proton in the acid moiety was deuteriated. The spin numbers of the nitroxides decreased by about five-fold when photolysis was carried out in oxygenated benzene solution. N-Benzylidene-tert-butylamine N-oxide trapped both radicals but much less efficiently. The nitroxide of the 4-chloro-α-isopropylbenzyl radical was predominant at 25°C or –40°C, but the proportion of the α-cyano-3-phenoxybenzyl nitroxide radical increased at the lower temperature.     

2-anilino-3-methylbutyrates and 2-(isoindolin-2-yl)-3-methylbutyrates,two novel groups of synthetic pyrethroid esters not containing a cyclopropane ring

A new series of substituted 2-anilino-3-methylbutyrates has been prepared; bioassay data for these compounds on Heliothis virescens, Musca domestica, Aphis fabae and Tetranychus urticae are presented and discussed. Some unexpected relationships were observed between the nature of the substituents and the biological activity. Increases in foliar stability were noted with certain substitution patterns. Both α-cyano-3-phenoxybenzyl 3-methyl-2-(α, α, α,2-tetrafluoro-p-toluidino)butyrate and the corresponding 2-(2-chloro-α, α, α-trifluoro-p-toluidino)-3-methylbutyrate showed good stability in air and light, and exhibited biological activities of a similar nature and potency to those of previously known synthetic pyrethroids. Esters of the (R)-2- anilino-3-methylbutyric acids are far more active than those prepared from the (S)-enantiomers. The (R)-configuration at C-2 in these acids is sterically equivalent to the active absolute configuration at the chiral carbon α to the carboxylate group in both the permethrin and the fenvalerate types of pyrethroids. A new class of insecticidal 2-(isoindolin-2-yl)alkanoates is also reported. In this series the most biologically active analogue was α-cyano-3-phenoxybenzyl 3-methyl-2-(4,5,6,7-tetrafluoroisoindolin-2-yl)butyrate. These esters were considerably less stable than the anilino analogues on exposure to air and light.     

The action of pyrethroids in the insect central nervous system. I. Features of molecular structure associated with toxicity to cockroaches and to their giant fibre axons

To investigate relationships between the molecular structure of pyrethroids and their mode of action, toxicities to adult male Periplaneta americana by topical application and injection were compared with toxicities to their giant fibre nerve axons. From the tests against intact insects it was concluded that: (i) although ED₅₀S ranged from 0.04 to 65 μg/insect, each compound was equally toxic, with one exception, when administered by either route; (ii) esters of (1 R)-cis- were more toxic than esters of the corresponding (1 R)-trans-3-substituted-2, 2-dimethylcyclopropanecarboxylic acids; (iii) α-cyano-3-phenoxybenzyl esters were more toxic than the corresponding 3-phenoxybenzyl esters; (iv) changes in the alcoholic component of some compounds (particularly trans-isomers of esters of 5-benzyl-3-furylmethanol and esters of α-cyano-3-phenoxybenzyl alcohol) affected a recovery phase in their ED₅₀/time curves more than changes in the acid component; (v) the amount of recovery was positively correlated with molecular polarity. The concentration required to decrease the amplitude of the action potential of giant fibres by 30% in 1 h ranged from 0.26 μM for the most active compound to 100 μM for the least active. There was no clear relationship between neurotoxicity and toxicity to whole insects and little association between neurotoxicity and features of molecular structure. Neurotoxicity was, however, positively correlated with polarity. Giant fibre axons seem unlikely to be critical sites of action of pyrethroids.     

Structure—activity relationships in pyrethroid esters derived from substituted 2-phenoxy-3-methylbutanoic acids

Non-cyclopropane pyrethroid esters of different substituted 2-phenoxy-3-methylbutanoic acids have been synthesised using the three alcohols—3-phenoxybenzyl alcohol, α-cyano-3-phenoxybenzyl alcohol and 3, 4-methylene-dioxybenzyl alcohol. Among the 35 esters synthesised and tested against Culex quinquefasciatus Say, the Bancroftian filariasis vector, for both larvicidal and adulticidal activities, α-cyano-3-phenoxybenzyl 2-(4-fluorophenoxy)-3-methylbu-tanoate, with an LC₅₀ value of 2.5 × 10^?3 mg litre^?1 for larvicidal activity, and α-cyano-3-phenoxybenzyl-2-(4-chlorophenoxy)-3-methylbutanoate, with an LD₅₀ value of 30 times; 10^?4 ug insect^?1 for adulticidal activity, were found to be as effective as fenvalerate, a well-known non-cyclopropane pyrethroid ester. Structure-activity studies showed that the insecticidal activity is dependent on the nature and position of the substituent in the phenyl ring of the acid moiety and also on the type of alcohol moiety.     

Metabolism of the cis- and trans-isomers of cypermethrin in mice

Metabolism in mice of the separated cis- and trans-isomers of the pyrethroid insecticide cypermethrin (NRDC 149), (RS)-α-cyano-3-phenoxybenzyl (1RS)-cis, trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate, was investigated in each case with preparations that were ¹⁴C-labelled in the benzyl and cyclopropyl moieties. Radioactivity from the trans-isomer was mainly excreted in the urine and that from the cis-isomer in the faeces. Elimination of both isomers was rapid except for a small portion (approximately 2%) of the cis-isomer which was released from the fat with a half-life of approximately 13 days. Metabolism of cypermethrin occurred mainly by ester cleavage and elimination of the cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethyl- cyclopropanecarboxylic acid moieties as glucuronide conjugates. The α-cyano-3-phenoxybenzyl alcohol released by ester cleavage was mainly converted to 3-phenoxy-benzoic acid which was partly eliminated unchanged, partly conjugated with aminoacids (mainly taurine) and glucuronic acid, and partly oxidised to 3-(4-hydroxyphenoxy) benzoic acid which was excreted as the sulphate conjugate. Metabolites retaining the ester linkage were formed by hydroxylation at various sites in the molecule with more hydroxylation of the cis- than of the trans-isomer occurring.     

The pyrethrins and related compounds; Part XXIV: synthesis, 13C-nuclear magnetic resonance spectra and insecticidal activity of cycloalkyl analogues of fenvalerate

Close isosteres of fenvalerate [(RS)-α-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate], in which cyclopropyl groups replace isopropyl have insecticidal activity close to or greater than the parent compounds, and diminished intravenous toxicity to rats. A direct toxicological relationship of these compounds to fenvalerate itself and to chrysanthemate esters is indicated by the consistently greater activity of esters from one of an enantiomeric pair of acids. Other esters with larger alkyl or cycloalkyl groups, or spiropentane analogues of chrysanthemates are less active insecticides. ¹³C-Nuclear magnetic resonance spectra suggest that in the α-cyanobenzyl esters there is an intramolecular through-space interaction in solution. The relationships between the chemical structures of the compounds synthesised and their relative activities to different insect species and toxicity to rats are discussed.     

The activity of some pyrethroids against Periplaneta americana and Blattella germanica

The knockdown and contact killing actions of various pyrethroids were compared using Blattella germanica and Periplaneta americana. A wide range of knockdown activity was found; 5-benzyl-3-furylmethyl (1R)-cis-3-(dihydro-2-oxo-3-thienylidenemethyl)-2,2-dimethylcyclopropanecarboxylate (RU 15525) acted fastest, more rapidly than pyrethrins, against B. germanica as well as having a low LD₅₀ value. Topical application and direct spray tests showed that (S)-α-cyano-3-phenoxybenzyl (1R)-cir-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate (NRDC 161) was more active as a killing agent, by an order of magnitude, than cismethrin, the next most active compound, and also had considerable knockdown activity. Piperonyl butoxide generally had little synergist effect. Female P. americana were over three times more tolerant than males to a range of insecticides applied topically. Residual knockdown action in the WHO resistance test was observed to provide baseline data. There was little overlap in speed of action between pyrethroids and other insecticides among the compounds tested.     

Insecticidal activity of the pyrethrins and related compounds. VII. Insecticidal dihalovinyl analogues of cis and trans chrysanthemates

Eighteen esters of resolved cis- and trans-3-(2,2-difluoro, -dichloro or -dibromovinyl)-2,2-dimethylcyclopropanecarboxylic acids with 5-benzyl-3-furylmethyl, 3-phenoxybenzyl and α-cyano-3-phenoxybenzyl alcohols were prepared and evaluated for insecticidal activity against Musca domestica L. and Phaedon cochleariae Fab. Chlorine and bromine substituted esters are more active, in general, than those with fluorine, and in the most active esters, the cis isomer is more effective than the trans.     

The vinylogous relationship in some pyrethroids

Attention is drawn to a vinylogous relationship between the structure of certain biologically-active pyrethroids. A series of racemic α-cyano-3-phenoxybenzyl 2-(2,2-dichlorovinyl)-1-phenylcyclopropanecarboxylates, based on this relationship, were synthesised and were found to be only moderately toxic to Musca domestica, Spodoptera littoralis and Leptinotarsa decemlineata.     

Interception and persistence of parathion and fenvalerate on cotton plants as a function of application method

Parathion (O,O-diethyl O-4-nitrophenyl phosphorothioate) and fenvalerate [(RS)-α-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate] were applied by controlled droplet applicators (CDAs) and conventional hydraulic nozzles in refined soybean oil, soybean oil + water, or water, to mature cotton plants (Gossypium hirsutum L.) as ULV (ultra-low volume, < 5 litre ha^?1), VLV(very low volume, 5-50 litre ha^?1), or LV(low volume, 50–200 litre ha^?1) carrier rates. The use of CDA or soybean oil applied as ULV and VLV sprays did not produce greater deposition or persistence for either insecticide during the 49-h test period following application. In general, insecticide persistence was greatest when applied with water or soybean oil + water as LV sprays using the conventional TX8 hydraulic nozzle.     

The optical isomers of α-cyano-3-phenoxybenzyl 3-(1,2-dibromo-2,2-dichloroethyl)-2,2-dimethylcyclo-propanecarboxylate and their insecticidal activities

Bromination of the dichlorovinyl group of cypermethrin yielded a new compound which is a highly potent insecticide. This dibromo adduct has four asymmetric centres and therefore can exist as a mixture of 16 stereoisomers. To establish the influence of the absolute configuration at the chiral centres on the biological activities of these isomers, each of the isomers was isolated; their insecticidal activities against larvae of Heliothis virescens, and adult Calliphora erythrocephala and Blattella germanica were then determined and compared with those of (S)-α-cyano-3-phenoxybenzyl (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate (deltamethrin NRDC 161), of fenvalerate, and of the eight stereoisomers of cyper methrin.     

Synthesis and insecticidal activity of 3-(haloalkyl-1,3-dienyl)-2,2-dimethylcyclopropanecarboxylates

New 2,2-dimethylcyclopropanecarboxylic acids bearing halogenated 1,3-alkadienyl substituents at position 3 of the cyclopropane ring were synthesised and the insecticidial activities of their 3-phenoxybenzyl and α-cyano-3-phenoxybenzyl esters against housefly (Musca domestica), Colorado potato beetle (Leptinotarsa decemlineata) and Egyptian cotton leafworm (Spodoptera littoralis) were determined. The activity of these compounds varied according to the relative position of the halogen substituents on the diene chain. The observed changes of activity with the structure of the side chain are discussed in terms of the coplanarity of the conjugated double bonds.     

Response of susceptible and resistant peach-potato aphids Myzus persicae (Sulz.) to insecticides in leaf-dip bioassays

The response of susceptible (S), moderately resistant (R₁) and strongly resistant (R₂) peach-potato aphids, Myzus persicae (Sulz.) to organophosphorus, carbamate and pyrethroid insecticides was tested by a leaf-dip bioassay. The aphids were placed on potato leaves (dipped in insecticide solutions 1–2 or 24 h before infestation) and their mortality examined 48 h later. R₁ aphids were virtually susceptible to most of the carbamates, demephion and acephate, but were slightly to moderately resistant (2.1–9.4 times) to permethrin, cypermethrin and (S)-α-cyano-3-phenoxybenzyl (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate (I), (NRDC 161), to 5,6,7,8-tetrahydro-2-methylquinolin-4-yl dimethylcarbamate (II), (Hoechst 25 682) and demeton-S-methyl. R₂ aphids resisted more strongly or very strongly (between 65 and 1280 times) the pyrethroids, demeton-S-methyl (×94), II (×83) and demephion (×9), and were slightly to moderately (2–5 times) resistant to acephate, pirimicarb, ethiofencarb and 2-(dimethylcarbamoyloxyimino)-3-methoxyimino-N,N- dimethylbutyramide (III), (DPX 3853). Both resistant strains were susceptible to nitrilacarb [4,4-dimethyl-5-(methylcarbamoyloxyimino)pentanenitrile] complex (1:1) with zinc chloride (IV), (AC 85 258). The implications of these results in terms of practical aphid control are discussed.     

Pyrethroid toxicology: Mouse intracerebral structure-toxicity relationships

Mouse intracerebral (ic) toxicity studies with 29 pyrethroids confirm earlier mouse intraperitoneal (ip) and rat oral and intravenous findings in three respects: α-cyano-3-phenoxybenzyl esters produce choreoathetosis, convulsions, and salivation, whereas compounds lacking the α-cyano group yield tremors and convulsions; high stereospecificity is involved in inducing both poisoning syndromes; large toxicity differences for (1R,trans) vs (1R,cis) resmethrin and permethrin do not extend to ethanomethrin and the cyanophenoxybenzyl esters. The ic investigations further establish that: profuse salivation is not unique for pyrethroids with the α-cyano group; the inactivity of (1R,trans) resmethrin in the brain is not due to detoxification; pyrethroids acting most rapidly in the brain are those with the highest knockdown activity for insects; the cyanophenoxybenzyl esters, in comparison with the non-cyano pyrethroids, have a high ic toxicity relative to their synergized ip toxicity indicating the importance of the brain in the Type II poisoning syndrome.     

The metabolism of fenvalerate in plants: The conjugation of the acid moiety

The metabolism of the pyrethroid insecticide fenvalerate [(RS)-α-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate] ( I ), and of its most insecticidal (αS,2S) isomer ( II ), has been examined in cabbage plants grown and treated under laboratory conditions with [¹⁴C]chlorophenyl- and [ring-¹⁴C]benzyllabelled preparations of the two compounds. Both insecticides disappeared from the treated leaves with similar half-lives of approximately 12–14 days; they underwent ester cleavage to a significant extent, together with some hydroxylation at the 2- or 4-position of the phenoxy ring, and hydrolysis of the nitrile group to amide and carboxyl groups. Most of the carboxylic acids and phenols thus produced occurred as glycoside conjugates. In separate experiments, the uptake and metabolism of 2-(4-chlorophenyl)-3-methylbutyric acid ( X ), the acidic half of the molecule, were examined in the laboratory, using abscised leaves of kidney bean, cabbage, cotton, cucumber and tomato plants. The acid X was found to be readily converted, mainly into glucose and 6-O-malonylglucose esters in kidney bean, cabbage and cucumber plants, into glucosylxylose, sophorose and gentiobiose esters in cotton, and into two types of triglucose esters with differing isomerism in tomato. One of the acetyl derivatives of the trisaccharide conjugates was identical with the synthetic deca-acetyl derivative of the [1 → 6]-triglucose ester.