Insecticidal Activity and Cuticular Penetration of Indoxacarb and Its N-Decarbomethoxylated Metabolite in Organophosphorus Insecticide-Resistant and -Susceptible Strains of the Housefly, Musca domestica (L.)
Indoxacarb, the novel oxadiazine insecticide showed potent insecticidal activities in insecticide-susceptible (SRS) and organophosphorus insecticide-resistant (R-OP) strains of the housefly, Musca domestica (L.). The R-OP strain showed slightly less susceptibility to indoxacarb with the tolerance ratio of 2.5. N-Decarbomethoxylated metabolite of indoxacarb (DCJW) also showed insecticidal activity that was more potent than indoxacarb in both SRS and R-OP strains. Similar to indoxacarb, the R-OP strain showed less susceptibility to DCJW with the tolerance ratio of 6.1. Cuticular penetration experiments revealed that the R-OP strain showed more external persistency and less internal accumulation of indoxacarb and DCJW than the susceptible strain. The reduced cuticular penetration could account for the less susceptibility of the R-OP strain to indoxacarb and DCJW. Further analyses revealed that DCJW was excreted more slowly than indoxacarb which could be one of the factors of differences in insecticidal activity between the two chemicals.
Key words: Cuticular penetration, indoxacarb, resistant mechanism, housefly, reduced penetration, DCJW.
Synthesis and Acaricidal Activities of New Benzophenone O-Methyloximes
We synthesized newly developed benzophenone O-methyloxime derivatives (I) and assessed their acaricidal activities. Studies of the structure-activity relationship revealed that the strongest acaricidal activity was achieved when position-2 in the left phenyl moiety was substituted with a 5-trifluoromethyl-2-pyridyloxymethyl group. Among the geometrical isomers at the oxime moiety, the Z-isomers were more active than the E-isomers. When the right phenyl moiety was substituted with a 4'-chloro, 4'-bromo or 4'-trifluoromethyl group, good acaricidal activity was obtained. Among the compounds examined, 4'-chloro-2-(5-trifluoromethyl-2-pyridyloxymethyl)benzophenone O-methyloxime (21) showed the most potent activity against Tetranychus urticae and Tetranychus kanzawai.
Key words: Benzophenone O-methyloxime, (α-alkoxyiminobenzyl)isoxazole, acaricidal activity, Tetranychus urticae, Tetranychus kanzawai.
Natural Fluctuation of Microbial Biomass and Population in Rice Paddy Soils as a Basis for Assessing the Side-Effect of Pesticides on Soil Ecosystem
The ranges of usual fluctuation of several parameters on microbial biomass, population and environmental conditions in low input and conventional rice paddy soils were monitored for two years in order to establish criteria to assess the abnormality of short-term effect of pesticide on soil microorganisms. The fluctuation patterns of the parameter in both paddies were generally similar. Any obvious change that would be considered to be due to the pesticides and chemical fertilizers applied in the conventional paddy was not recognized. It is considered that the fluctuation in the conventional paddy also had not been caused by the chemicals but by the agricultural practices common to low input paddy such as flooding and draining. The fluctuation range and pattern of the parameters in the paddies were mostly in agreement with the previous observation. Therefore, it is considered that the fluctuation of the microbial biomass and population in the soils was typical enough in Japanese paddies to be used as the criterion to assess pesticide effects. The usual fluctuation rate of the parameters ranged from 0.86 to 1.21 times/week for the biomass and from 0.80 to 1.40 times/week for the population. The fluctuation rates are proposed as the criteria to assess the abnormality of short-term effect by pesticide.
Key words: paddy soil, microbial biomass, microbial population, natural fluctuation, risk assessment of pesticide, long-term monitoring.
Synthesis of Antifungal 2-Anilino-4-phenylthiazoles and Their Inhibitory Activities on Sterol Biosynthesis
We previously reported that 1,2,4-thiadiazole derivatives such as 5-(4-chloroanilino)-3-(2,6-dichlorophenyl)-1,2,4-thiadiazole showed high antifungal activities in vitro against Trychophyton mentagrophytes and Botrytis cinerea, and accumulated squalene remarkably. In view of the Nussbaumer's model of squalene epoxidase inhibitors, we synthesized the corresponding thiazole derivatives in which 2-nitrogen atom of 1,2,4-thiadiazole was replaced by carbon in order to explore the structural requirement of the heteroaromatic moiety for fungicidal activity. We further synthesized the related thiazoles having various substituents to investigate the structure-activity relationships. Antifungal activities and squalene accumulation of the thiazole compounds were well correlated. Among the compounds synthesized, 2-(4-chlorophenylamino)-4-(2,6-dichlorophenyl)thiazole (5) showed the highest antifungal activity against T. mentagrophytes and B. cinerea, and was more active than tolnaftate, a clinically used thiocarbamate. The compound (5) inhibited squalene epoxidase remarkably in a cell free assay using S. cerevisiae. These experimental results indicate that the primary mode of action of the thiazole derivatives is the inhibition of squalene epoxidase in the sterol biosynthesis.
Key words: squalene epoxidase inhibitor, antifungal activity, Trychophyton mentagrophytes, Botrytis cinerea, 2-anilino-4-phenylthiazoles.
Inhibitory Activity of N-Substituted-2-piperidones with a 1,4-Benzodioxan Ring on Germination of Barnyardgrass
A variety of 3-substituted-2-piperidones and related compounds were evaluated for their activity to inhibit germination of barnyardgrass (Echinochloa utilis) seeds. 3-[1-(1,4-Benzodioxan-6-yl)-1-hydroxymethyl]-N-benzyl-2-piperidone (22) showed extremely high inhibitory activity. Studies on the structure-activity relationship indicated that a 1,4-benzodioxan ring, a hydroxy substituent at the α-position of the benzyl group and a 2-piperidone ring were significant for higher activity. Of the compounds tested, 3-[1-(1,4-benzodioxan-6-yl)-1-hydroxymethyl]-N-cinnamyl-2-piperidone (55) was the most effective, showing more than 90% germination inhibition at 1 nM. In both compounds 22 and 55, only erythro isomers inhibited germination of barnyardgrass seeds, while threo isomers were inactive even at 1 μM. This result indicated that the stereochemistry of 1,4-benzodioxan moiety in the erythro isomer, which is fixed by an intramolecular hydrogen bond between the hydroxy group and the carbonyl group, was essential for activity. The erythro-22 and 55 were less active against rice seeds when compared to barnyardgrass.
Key words: 2-piperidones, 1.4-benzodioxan, germination, barnyardgrass.
Effects of N-Demethylation of Pamamycins on Aerial Mycelium-Inducing and Growth Inhibition Activities
Using a combination of ODS and NH2 HPLCs, we isolated new pamamycin derivatives from the culture broth of Streptomyces alboniger IFO 12738. MS spectroscopy showed that their structures were de-N-methylpamamycins with the aid of labeled compounds prepared in a methionine-methyl-d3 feeding culture of S. alboniger. De-N-methylpamamycins had stronger aerial mycelium-inducing activity and weaker growth-inhibition activity than the corresponding pamamycin with the same alkyl group arrangement.
Key words: morphological differentiation, aerial mycelium, pamamycin, Streptomyces alboniger.
Phytotoxicity of Leaves of Japanese Pear in the Greenhouse Culture by Application Timing of Insecticides and Acaricides
Key words: phytotoxicity, insecticide, acaricide, Japanese pear, leaf rolling, leaf chlorosis.
Correlation of Pyrethroid Structure and Resistance Level in Culex quinquefasciatus Say from Saudi Arabia
Key words: cross-resistance, pyrethroid, Culex quinquefasciatus, mosquito, kdr, cytochrome P450 monooxygenase.
Synthesis and Herbicidal Activity of Sulfonylurea Compounds with Imidazo [1,2-a]pyridine Moiety
Key words: sulfonylurea, herbicidal activity, fused heterocycles, TKM-19, Bromus tectorum L.
Relation between Penetration Rates of Pesticides and Partition Coefficients in Topical Application to Spodoptera litura
Key words: penetration rates, Spodoptera litura, partition coefficient.
Synthesis and Fungicidal Activities of 2-(α-Methoxyiminobenzyl)-1-methylimidazole Derivatives
Key words: 2-(α-Methoxyiminobenzyl)-1-methylimidazole, fungicidal activity, powdery mildew, downy mildew.
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