The biological activity of tralomethrin against larvae of the tobacco cutworm, Spodoptera litura, was evaluated by injection, topical application and electrophysiological studies, and compared to that of deltamethrin. By injection, tralomethrin was almost as potent as deltamethrin. By topical application, tralomethrin delayed the onset of moribund symptoms longer than deltamethrin. Tralomethrin increased miniature excitatory postsynaptic potentials at neuromuscular junctions less often than deltamethrin. The electrophysiological studies suggested that tralomethrin per se was less active than deltamethrin at the target site. The observed in vivo activities of tralomethrin may have arised from deltamethrin present in tralomethrin samples, or from deltamethrin converted from tralomethrin in the insect, or from both.

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Absorption, traslocation and metabolism of two arsenical fungicides, MAF (iron methanearsonate; dust formulation) and MAFA (ammonium iron methanearsonate; liquid formulation) were studied using rice seedlings following root and foliar applications. After 7 days, root uptake of arsenic (As) by the seedlings was 5.1% for MAF and 16.6% for MAFA. The translocation of both applied arsenicals to the shoots was restricted; over 90% of the absorbed As remained in the roots. In foliar treatment with MAF, neither absorption nor translocation of monomethyl-arsenic (MM-As) through the treated leaves was observed. Following foliar treatment with MAFA, a measurable amount of MM-As was found in the untreated leaves and shoots, the roots and the nutrient solutions. The chemical analysis of As species in the plant extracts and the nutrient solutions indicated that both arsenicals were scarcely transformed to methylated and demethylated As species in the plant. Absorption, translocation and metabolism of a related compound, DSMA (disodium methanearsonate), and possible metabolites [arsenate, arsenite, DMAA (dimethylarsinic acid) and TMA=O (trimethylarsine oxide)] were also studied.

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Hydrolysis of pyrazolate, [4-(2, 4-dichlorobenzoyl)-1, 3-dimethylpyrazol-5-yl] p-toluenesulfonate, was studied in buffer solutions in a range of pH 1.0-9.0 at 25°C, and in artificial gastric and intestinal fluids (pH 1.5 and 7.5) at 37°C. The hydrolysis proceeded predominantly through base- and acid-catalyzed processes in the regions above pH 7 and below pH 3, respectively, whereas both reactions occurred between pH 3 and pH 7. The half-life (hr) of pyrazolate ranged from 4.3 (pH 9.0) to 106.0 (pH 5.0) at 25°C, and was 2.3 (pH 7.5) and 7.8 (pH 1.5) at 37°C. Hydrolysates of pyrazolate in the wide range of pH at both temperatures were p-toluenesulfonic acid and 4-(2, 4-dichlorobenzoyl)-1, 3-dimethyl-5-hydroxypyrazole; i. e., destosyl pyrazolate (DTP).

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Sixty-five N-aryl-4-carboxy- and N-aryl-4-hydroxy-phthalimides having various substituents on the N-aryl moiety were prepared, and their preventive activity against clubroot of Chinese cabbage caused by Plasmodiophora brassicae was examined. Among these compounds, only 2, 6-dialkyl derivatives showed high preventive activity, which depended on the position-specific substituent effect, and both the presence of the α-branching and the number of carbon atoms in the alkyl groups on the N-aryl ring.

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Optical isomers of ten 1, 3, 2-oxazaphospholidine 2-sulfides and two 1, 3, 2-benzodioxaphosphorin 2-sulfides, including a commercial insecticide, salithion, were topically applied to an organophosphate-susceptible strain of housefly. Of all the oxazaphospholidines, (S)_C(R)_P isomers showed the highest insecticidal activity, and the potency decreased with configuration in the order of (S)_C(R)_P>(S)_C(S)_P>(R)_C(R)_P>(R)_C(S)_P. In the benzodioxaphosphorins, the (S)_P configuration was favorable for high insecticidal activity. Some optical isomers were also tested against the onion maggot, two species of planthopper and an organophosphateresistant strain of housefly. The relationship between configuration and insecticidal activity was similar in the susceptible and resistant strains of housefly, but varied with species of insect.

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The photodegradation of pentachlorophenol (PCP) in hexane was investigated under xenon lamp irradiation. PCP was easily decomposed by 33.3min (500 counts) irradiation. The maximal degradation of PCP was observed at 292.1nm in the 100ppm solution and in a range of 252.6nm to 318.6nm in the 10ppm solution by 33.3min irradiation. At these wavelengths, PCP was completely degraded. Reductive dechlorination and replacement reaction of a chlorine atom with a hexyl group derived from the solvent used were observed. As the photodegradation products of PCP, 2, 3, 4, 5-tetrachlorophenol (TeCP), 2, 3, 4, 6-TeCP, 2, 3, 5, 6-TeCP, 2, 3, 4-trichlorophenol (TrCP), 2, 4, 5-TrCP, 3, 4, 5-TrCP, 2, 4-dichlorophenol (DCP), 3, 4-DCP, 3, 5-DCP and 3-chlorophenol were identified by gas chromatography-mass spectrometry. Besides the above compounds, three isomers of monohexyltetrachlorophenol and three isomers of monohexyltrichlorophenol were also tentatively identified.

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The acute inhalation toxicity of chloropicrin (CP) vapor was determined by exposing male Fischer 344 rats to CP vapor. The determination showed that the 4-hr median lethal concentration (LC₅₀) was 11.9ppm (80.0mg/m³), and the development of deaths was biphasic. The first phase was within 24hr after exposure, and the second phase between days 8 and 10 of the 14-day observation period. Major effects, such as dyspnea (labored breathing, gasping), cyanosis, diffuse pulmonary edema and emphysema, and large increase in absolute lung weight were observed in both phases, while rhinorrhea, salivation and hydrothorax were observed in the first phase only. The results indicate that the main target organ of CP vapor upon acute inhalation exposure is the respiratory tract, and that the cause of deaths in both phases is a respiratory failure due to injuries of the respiratory tract. In addition, the 30-min exposure study was performed to investigate the relationship between the duration of exposure and the acute inhalation toxicity. The results suggest that the acute inhalation toxicity for a 30-min exposure is similar in quality to that for a 4-hr exposure, but higher judging from the lethal CT (concentration × time) products.

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Distribution, metabolism and excretion of [O-ethyl-1-¹⁴C] isofenphos were examined in rats. When rats were orally administered with ¹⁴C-isofenphos, the ¹⁴C-compounds were distributed over the whole body 6hr after administration and decreased gradually with time. ¹⁴C-Compounds in the liver were persistent. Greater part of radiocarbon excreted from rats was recovered from the urine, and smaller part from the feces and the expired air. When metabolites in the urine and feces were partitioned between benzene and water, most of radiocarbon was recovered from the water fraction, and only small part from the benzene fraction and unextractable residues. Aminoisofenphos and isofenphos-oxon were identified as benzene soluble metabolites, and six metabolites were identified as water soluble metabolites, which include O-ethyl hydrogen phosphoramidate, O-ethyl hydrogen isopropylphosphoramidothioate and others. The results suggested that cleavage of P-O-aryl linkage took place dominantly in isofenphos metabolism in rats compared with that of P-N linkage.

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For better control of brown planthoppers (BPH), the insecticide susceptibility and deposition on BPH by dust application were examined in laboratory and in paddy rice field, respectively. When carbaryl was topically applied, the LD₅₀ value was 1.9μg/g for the susceptible strain (S-strain) and 14.6μg/g for the Yamaguchi population (Y-population). When a mixture of carbaryl (NAC) and fenitrothion (MEP) (1.5:2) was applied by the bell-jar dusting method, the LD₅₀ value was 23.1μg/g for the Y-population, from which the LD₅₀ value of NAC was estimated to be 10.2μg/g, similar to the value obtained by topical application. When the dust was applied to the Y-population in paddy rice field, the MEP deposit on BPH was 0.1 to 210μg/g, showing logarithm normal distribution. The mean deposits of MEP by different dusting methods were 3.5 to 25.3μg/g, and those of NAC were estimated to be 2.6 to 18.5μg/g. These values are similar to or smaller than the LD₅₀ value of NAC. From the dosage-mortality curves and the distribution of deposits, it could be inferred that the mortality of Y-population was considerably low, while that of S-strain was high. Such experimental results support the assumption that insecticides here become less effective against BPH because the lethal dose has increased as insecticide resistance developed and because the conventional dust application does not deposit sufficient amounts of insecticides.

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[in Japanese]

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Selection of larvae of field-collected strains (SHR₈₄, OKR₈₄ and KAR₈₄) of the diamondback moth, Plutella xylostella L. with fenvalerate produced very high levels of resistance to the selecting agent. After 8-9 generations of continuous selection, resistance factor (Rf) values of LD₅₀ and LD₉₅ in the selected strains, SHR₈₄-FR, OKR₈₄-FR and KAR₈₄-FR, became 54.9 and 315, 580 and 7960, and 3500 and 125, 000, respectively. Rapid development of resistance to fenvalerate within a short period might explain that field populations of P. xylostella in Japan possess high gene frequencies for fenvalerate resistance.

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[in Japanese]

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Selection for susceptibility with phenthoate was conducted in the OKR and OSS strains of the diamondback moth, Plutella xylostella L. for nine generations. The third instar of the selected OKR (OKR-S) and OSS (OSS-S) strains exhibited 0.12 and 0.05, and 0.41 and 0.24 times higher LD₅₀ and LD₉₅ values to phenthoate than the non-selected OKR (OKR) and OSS (OSS) strains, respectively. The adults of the OKR-S and OSS-S strains showed 0.48 and 0.39, and 0.50 and 0.32 times higher LD₅₀ and LD₉₅ values than those of the OKR and OSS strains, respectively. The selected strains had also shown higher susceptibility to various insecticides in comparison with the non-selected strains, i. e. generally lower LD₅₀ and LD₉₅ values with a larger slope of regression equations (SREs).

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The mode of action of phosphine (PH₃) was investigated principally using adult maize weevil, Sitophilus zeamais. Mortality of the insects did not increase with an increase in PH₃ concentration. High PH₃ concentrations narcotized the insects by decreasing the respiratory rate. There was a significant relation between the oxygen uptake and the mortality. The results of in vitro experiments led to the conclusion that PH₃ inhibited the cytochrome oxidase activity as in the case of HCN. However, PH₃ showed a low inhibitory effect on state 4 respiration of both mitochondria of the maize weevil and the rat liver, and a weak action on the reduced form of cytochrome oxidase obtained from the beef heart. In vivo experiments demonstrated that PH₃ inhibited the activity of cytochrome oxidase in mitochondria obtained from the insects treated at lower PH₃ concentrations more effectively than that in mitochondria from the insects narcotized at higher PH₃ concentrations. A special factor to absorb PH₃ was detected in a soluble fraction obtained from the homogenate of flour beetles, Tribolium castaneum. This factor may act as a catalyst to promote a reaction between oxygen and PH₃ to produce an oxygen radical. The effect of PH₃ on the insects varied with the concentration. PH₃ at higher concentrations exerted a narcotic effect on the insects by decreasing the oxygen uptake as the mitochondria reached state 4 respiration and cytochrome oxidase was reduced, thus making the target site insensitive to PH₃. PH₃ at lower concentrations did not exert a narcotic effect on the insects, leaving the target site sensitive to PH₃ as the mitochondria exhibited state 3 respiration and cytochrome oxidase was oxidized. In addition, the reaction to produce an oxygen radical at the cellular level and the anoxic condition of the insects may account for the action mechanism of PH₃.

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Since the invention of phenoxyacetic acid herbicides with clear activity on broad-leaf plants, the development of a herbicide with reverse selectivity has been a long-pending problem from the practical viewpoint of removing grasses from broad-leaf crops. Based on the results of the long-term studies to improve the unfavorable characters of diphenyl ether herbicides, the authors have successfully developed fluazifop which is capable of killing grasses, including perennials, without damaging broad-leaf crops. Since diphenyl ether herbicides selected as a lead-compound do not translocate in plants but kill only the tissues directly exposed to the herbicides, an oxyalkanoate side-chain characteristic to the phenoxyacetic acid auxin herbicides, which are able to translocate in plant tissues, was introduced to the 3′-position adjacent to the nitro group on the diphenyl ether structure. Thus-prepared esters improved the translocation but not satisfactorily enough for the practical use. Therefore, the following attempts were made for optimization: 1) introduction of a trifluoromethyl group as a substituent on the 4-position, 2) alteration of one of the benzene rings to a pyridine nucleus, 3) elimination of the nitro group on the 4-position which had been regarded indispensable, 4) migration of oxyalkanoate on the 3-position to the 4-position, 5) selection of lactate out of alkanoates to obtain optimum herbicidal activity, and 6) modification of an ester moiety. Thus-prepared fluazifop-butyl, endowed with selectivity of killing grass weeds without damaging broad-leaf crops and with excellent translocatability in plant tissues to the extent of killing the subterranean stems of perennial grasses even in case of foliar treatment, is now marketed for the use in cotton, soybean and beet fields. Structure-activity relationship studies on fluazifop and its related analogs indicated that the trifluoromethylpyridinyloxy group played an important role in the hydrophobicity and total molecule structure to obtain optimum herbicidal activity and in enhancing the systemic activity to let the molecule reach a target organ through plant tissues.

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Hexythiazox [trans-5-(4-chlorophenyl)-N-cyclohexyl-4-methyl-2-oxothiazolidine-3-carboxamide] is a new miticide effective for control of various kinds of mites. Discovery of a compound with weak miticidal activity among thiazolo [2, 3-b] triazine derivatives, which had fungicidal activity on diseases caused by Phycomycetes, initiated this study, and trials of cleavages at a few parts of the triazine ring led to an invention of 2-thiazolidone compounds with outstandingly high acaricidal activity. In regard to the diastereoisomers at the 4- and 5-positions of the thiazolidine ring, the trans-form was found to be crucial for their miticidal activity. Introduction of various substituents, especially halogen atoms, onto the phenyl ring at the 5-position resulted in a remarkable improvement of the activity. A compound was selected from a large number of the derivatives, which has been in the market under the common name of hexythiazox. Hexythiazox had broad miticidal spectrum and excellent ovicidal, larvicidal and nymphcidal actions. It showed hatching inhibition through adult females and acted as both stomach and contact poisons on larvae. Immature mites treated with the compound did not die at the motile stage but died at the next chrysalis. Hexythiazox, possessed good residual activity and was successful in controlling citrus red mites for about 70 days in the field trial when used at very low concentrations of 25-50ppm. It has been confirmed that the miticide gives no lethal effect on predacious mites.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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