Abstracts of Vol. 24 No. 4

Original Articles

Predicting the Dissipation of Bensulfuron Methyl and Azimsulfuron in Rice Paddies Using the Computer Model EXAMS2

A computer model scenario using EXAMS2 was developed to estimate concentrations of sulfonylurea herbicides, bensulfuron methyl and azimsulfuron in paddy water. The rapid disappearance of the two chemicals from water could be described only when indirect photolysis (represented by hydroxyl radical reactions) was included as a dissipation pathway in the modeling scenario with partitioning to soil, hydrolysis, direct photolysis and metabolism. The model scenarios were calibrated against paddy water dissipation data from two 1m2 simulated paddies to obtain values for the dispersion coefficient and oxidative radical concentration in each plot.
 The EXAMS2 scenario successfully predicted the partitioning and degradation that led to half-lives in paddy water of 3‐4 days observed in field studies conducted in Japan. Verification of the EXAMS2 model by comparison with field results was necessary for establishing realistic environmental concentrations of bensulfuron methyl and azimsulfuron in paddy water.

Key words: environmental fate, modeling, paddy, sulfonylurea, herbicides.

Negatively Correlated Cross-Resistance between N-Methyl Carbamate and Monocrotophos in Green Rice Leafhopper, Nephotettix cincticeps Uhler

Although monocrotophos showed strong inhibition to N-methyl carbamate resistant acetylcholinesterase in the green rice leafhopper, Nephotettix cincticeps, the toxicity was not so high to Nakagawara populations of the leafhopper. The different results between in vitro and in vivo experiments were thought to be caused by an increase of aliesterase activity in Nakagawara strains which are resistant to both organophosphorus
insecticides and N-methyl carbamates. Thus, MC-R strain which has only N-methyl carbamate resistance gene was bred by introducing N-methyl carbamate resistance gene of Nakagawara-3-C strain to susceptible Shiraoka strain. Then monocrotophos showed negatively correlated cross resistance against N-methyl carbamates in Shiraoka and MC-R strains under both in vitro and in vivo conditions.
Key words: acetylcholinesterase, aliesterase, negatively correlated cross-resistance, Nephotettix cincticeps, methyl carbamate, monocrotophos.

Enhancement of Phytoalexin Synthesis during Rice Blast Infection of Leaves by Pre-treatment with Carpropamid

Carpropamid{(1RS, 3SR)-2,2-dichloro-N-[1-(4-chlorophenyl) ethyl-1-ethyl-3-methyl cyclopropanecarboxamide], which is considered as a melanin biosynthesis inhibitor, enhanced the accumulation of the phytoalexins momilactone A and sakuranetin in the rice leaves subsequently inoculated with the blast pathogen (Pyricularia oryzae). Carpropamid and its two diastereo-isomers, A(1R,3S) and B(1S,3R), did not stimulate phytoalexin production directly, but they potentiated rice plants to produce the two phytoalexins more rapidly and much amounts in response to blast infection. This phenomenon was also observed in rice leaves treated with WL28325 (2,2-dichloro-3,3-dimethylcyclopropane carboxylic acid), a resistance inducer. The calculation data of the correlation among accumulation of phytoalexins, concentrations of chemicals and biological effects suggested that the correlation pattern of isomer A resembled that of WL28325. The main mode of action of isomer A appears to be an enhancement of phytoalexin synthesis during blast infection (EPAS mode) similar to that of WL28325, rather than the inhibition of melanin biosynthesis (MBI mode). In contrast, the main mode of action of isomer B was found to be MBI, although EPAS probably also contributes to its biological activity. Carpropamid is assumed to control rice blast through a combination of MBI and EPAS activities.

Key words: carpropamid, phytoalexin, momilactone A, sakuranetin, plant resistant inducer, Pyricuralia oryzae.

Effect of Temperature on Quinclorac-Induced Ethylene Production from Corn Leaves

Effect of temperature ethylene evolution from corn leaves, which was induced by on the herbicide quinclorac (3,7-dichloro-8-quinolinecarboxylic acid), was investigated. The results indicated that not only the temperature after quinclorac treatment but also that prior to the treatment significantly influenced the quinclorac-induced ethylene production from corn leaves. Furthermore, a rapid cooling (from 30℃ to 20℃) caused suppression of quinclorac-induced ethylene production, depending on the cumulative temperature after the herbicide-application. On the contrary, a rapid warming (from 20℃ to 30℃) during quinclorac application increased significantly the ethylene production more than the estimates accounted for by the cumulative temperature, suggesting that a rapid warming may increase the amount of ethylene biosynthesis enzyme induced by quinclorac under light exposure.
Key words: quinclorac, temperature, ethylene, light, chlorotic discoloration.

Prodigiosin Produced by Serratia marcescens Enhances the Insecticidal Activity of Bacillus thuringiensis delta-Endotoxin (Cry1C) against Common Cutworm, Spodoptera litura

Synergistic effects of chitinases A, B and C1, chitin binding protein and prodigiosin from Serratia marcescens on the insecticidal activity of delta-endotoxin, Cry1C, of Bacillus thuringiensis against the common cutworm, Spodoptera litura, were investigated. Only prodigiosin showed a potent synergistic activity with Cry1C on both the lethal and growth inhibitory activity. In the previous paper (Asano et al., 1999) a synergistic effect in the supernatants of S. marcescens culture on the insecticidal activity of Cry1C was described. The supernatants from S. marcescens and partially purified prodigiosin showed a similar synergistic activity on the insecticidal activity of Cry1C. The content of prodigiosin in the supernatants was estimated as 10% according to the absorbance at 467 nm where prodigiosin showed a peak and the content seemed to be enough to explain the synergistic activity of the supernatants on the activity of Cry1C.
Key words:  synergism, Serratia marcescens, Bacillus thuringiensis, Cry1C, delta-endotoxin, prodigiosin, Spodoptera litura.

Natural Fluctuation of Microbial Activity Related to Nitrogen Cycle in Rice Paddy Soils as a Basis for Assessing the Side-Effect of Pesticides on Soil Ecosystem

Soil microbial parameters of two different rice paddies were monitored, from May 1997 to Dec. 1998 (20 months). During the two growing seasons, the natural variability in the microbial communities activity were monitored in order to assess the effects of pesticide usage on rice paddy soils. The study focused mainly on the effect of pesticides on the nitrogen cycle such as nitrification, ammonification, protease activity and ammonium oxidizing bacterial population (AOB) being what was monitored.
 The coefficient of variation(CV) was the statistical tool used to monitor the variability in the study. During the two growing seasons, the CV for nitrification, ammonification, protease activity and AOB were 16-20, 39-53, 31-62 and 88-174%, respectively, which reflects the fluctuation caused by the natural stresses as well as anthropologic stresses. These results were much wider than the fluctuation observed in the short period or in laboratory studies and should be used as reference when conduct risk assessments of pesticides to the microflora in rice paddy soil.
Key words: nitrification, ammonification, protease activity, ammonium oxidizer, risk assessment, long-term monitoring.


Synthesis and Insecticidal Activity of N-(Tolyloxybenzyl)-pyrazolecarboxamide Derivatives

Key words: insecticidal activity, Myzus persicae, Plutella xylostella, N-tolyloxybenzylpyrazolecarboxamides, tolfenpyrad, OMI-88.

Glycosides of a Phenylpropanoid and Neolignans: Oviposition Stimulants in Pine Inner Bark for Cerambycid Beetle, Monochamus alternatus

Key words: Monochamus alternatus, Pinus densiflora, oviposition stimulant, dihydroconiferyl alcohol glucoside, neolignan glycoside.

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