Abstracts of Vol. 27 No. 3

Key words: 2-(substituted benzylideneaminooxymethyl)phenylacetamide derivatives, fungicide, strobilurin analogue.

Fungicidal characteristics of KC10017, an oxadiazole compound, were investigated in a greenhouse. KC10017 showed strong protective activity against rice blast. When KC10017 (0.5 μg/ml solution) was sprayed on leaves, rice blast was controlled almost completely. Its protective activity decreased temporally, reaching 54% of the control value at 14 days after treatment.　Further, its curative and systemic effects were not significant even at 100 μg/ml, and KC10017 was not active against the causal fungus, Magnaporthe grisea.　However, it inhibited the melanization of appressoria and mycelia in M. grisea.　KC10017 is the first oxadiazole compound showing an inhibitory effect on the biosynthesis of melanin in M. grisea.　It was further confirmed that the protective activity of KC10017 was counteracted by wound inoculation of M. grisea.　These results suggest that a compound with characteristics like KC10017 has potential as a new fungicide for rice blast.

Key words: melanin biosynthesis inhibitor, KC10017, an oxadiazole compound, rice blast.

The aerobic aquatic metabolism of fenitrothion and its oxon was studied in French lake and Japanese pond water-sediment to estimate their behavior in the natural aquatic environment.　The effect of aeration on the metabolic profiles of fenitrothion was examined by either passing air over the surface or gently bubbling the water phase.　Almost the same metabolic profiles were obtained under both conditions but the partition profiles of radioactivity between the aqueous and sediment phases differed slightly.　There was no significant difference in the metabolism of fenitrothion between French and Japanese sediments.　Fenitrothion mainly underwent cleavage of the P-O-aryl linkage to form the corresponding phenol and reduction of the nitro group followed by the subsequent acetylation of the amino group.　The oxidative desulfuration of fenitrothion to form the oxon was a minor route.　The increase in phenol and ¹⁴CO₂ with less reductive transformation under the bubbling of water with air was likely to originate at least in part from less anaerobicity.　The oxon derivative of fenitrothion rapidly underwent cleavage of the P-O-aryl linkage to form the phenol in the water-sediment system.

Key words: biodegradation, fenitrothion, water sediment system, reduction, nitro group, ester hydrolysis, oxidative desulfuration.

A plant uptake model was developed to estimate the residual amount of non-ionized pesticides in the edible roots of root crops.　An examination of the route of uptake of furametpyr (log Kow＝2.36) and pyriproxyfen (log Kow＝5.37) suggested that the more lipophilic of the two pesticides, pyriproxyfen, was mainly adsorbed by the root peel and incorporated by diffusion into the root core.　On the other hand, the less lipophilic pesticide, furametpyr, was mainly taken up via the transpiration stream into the core through the root hairs.　Based on the results, a mathematical model for the uptake of a pesticide into edible roots was developed based on the following route; (1) incorporation into the root core via the transpiration stream through the root hairs, (2) adsorption by the root peel, and (3) diffusion from the peel to the root core.　To test the model, residual amounts of furametpyr and pyriproxyfen were analyzed and compared to those predicted when the pesticides were treated at one-tenth of the concentration in the model construction.　Ratios of predicted to measured residual concentrations were 1.01‐1.38 and ?0.75‐1.28 for furametpyr and pyriproxyfen, respectively, showing the effectiveness of the model as a predictive tool.

Key words: plant uptake model, pesticide, root crop, furametpyr, pyriproxyfen.

Bivalent molecules of bis-imidacloprid with 2‐10 alkylene tethers as well as tethers containing an ethenylene, ethynylene, phenylene and oxide joint were prepared.　These dimeric chloronicotinyl molecules were highly insecticidal against American cockroaches on injection at 2‐30 nanomolar doses.　The minimum lethal dose of the most potent hexamethylene derivative was close to that of imidacloprid, and the potency was augmented up to about thirty-five-fold following pretreatment with metabolic inhibitors, while the binding affinity to ［³H］imidacloprid-binding sites on the nicotinic acetylcholine receptor was weaker than that of imidacloprid by a factor of 160.　The hexamethylene derivative elicited impulses in cockroach central nerves with an initial excitation and subsequent block at a potency comparable to imidacloprid.

Key words: neonicotinoid insecticides, imidacloprid, American cockroach, insecticidal activity, nerve-excitatory activity, alkylene-tethered bis-imidacloprid.

In order to search for a new systemic rice blast fungicide, a number of N-benzyl-α-cyanoacetamide derivatives and related compounds were prepared and their preventive activity against rice blast, Magnaporthe grisea was examined both in a foliar spray test and in a soil drench test.　Several N-[1-(substituted-phenyl)ethyl]- 2-cyano-3,3-dimethyl-butanamides and -2-pentenamides showed high activity in both tests.　Among them, (RS)-2-cyano-N-[(R)-1-(2,4-dichlorophenyl)ethyl]-3,3-dimethylbutyramide (diclocymet, S-2900) was selected as a practical new systemic rice blast fungicide, which shows potent fungicidal activity with little crop injury.

Key words: rice blast fungicide, systemic activity, α-cyanoacetamide derivatives, stereoisomer, diclocymet, S-2900.

Acyclic analogues of thiacloprid and related cyanoguanidine derivatives were prepared.　Their insecticidal activity against the American cockroach was determined by the injection method with or without metabolic inhibitor(s).　Thiacloprid along with two cyanoguanidine analogues showed the highest insecticidal potency without the inhibitors, which was one twentieth that of imidacloprid.　Metabolic inhibitors increased the activity by a factor of up to 100 for sulfur-containing compounds including thiacloprid, while the effect for the cyanoguanidine derivatives was much smaller.　Most of the test compounds elicited impulses in cockroach central nerves with an initial excitation and subsequent block.　Thiacloprid and its acyclic analogue were on a par with imidacloprid for blocking potency.　As the blocking activity increases, the insecticidal activity measured with the metabolic inhibitors tends to strengthen.

Key words: chloronicotinyl insecticide, thiacloprid, imidacloprid, American cockroach, insecticidal activity, neuroblocking activity.