Neonicotinoids are the only major new class of insecticides introduced in the past three decades. They act as selective agonists at the insect nicotinic acetylcholine receptor and are therefore highly toxic towards important insect pests but relatively safe to mammals. However, the excellent selective toxicity may not be evident with their metabolites or analogous compounds. The aim of this paper is to consider the effects of neonicotinoids and derivatives in mammalian cells and mice involving up-regulation of nicotinic receptor levels and activation of the intracellular signal integration cascade elicited by chronic or sustained exposure and analgesic and toxic effects in mice.

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Studies on brassinosteroid (BR) function in dicot plants have provided definitive proof that BRs regulate a broad range of cellular responses, and revealed that BRs are essential for plant development and growth. However, prior to our studies of BR mutants of rice, there had been no reports dealing with the molecular biological function of BRs in monocot plants. We have isolated and characterized three independent BR-related mutants of rice. All three exhibit a common phenotype: erect leaves, shortened internodes, and constitutive photomorphogenesis in the dark. The erect leaves with shortened culms suggested that the BR-related phenotype might improve crop architecture and, thereby, increase crop yield. Indeed, recently, it was revealed that a semi-dwarf barley cultivar, uzu, contains a single nucleotide mutation in the BR receptor gene, BRI1.

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Ecdysone receptor (EcR) and ultraspiracle (USP) of the lepidopteran Chilo suppressalis were expressed using a wheat germ cell-free protein synthesis system, and the functions of the expressed proteins were analyzed. In a gel mobility shift assay, the EcR/USP heterodimer bound to the Drosophila melanogaster hsp27 ecdysone response element. In ligand-receptor binding assays, a potent ecdysteroid, ponasterone A, bound to the EcR/USP complex with a high affinity (K_D=2.1 nM). For a series of ecdysteroids and N-tert-butyl-N,N′-dibenzoylhydrazines, the binding activity toward the in vitro expressed EcR/USP complex using a wheat germ system was linearly correlated with that to the endogenous receptor proteins in the cell-free preparation of C. suppressalis integument. These results indicate that functional ecdysteroid receptor proteins were successfully expressed in a wheat germ protein synthesis system. © Pesticide Science Society of Japan

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A combination of two conventional methods of porphyrins analysis revealed a significant accumulation of protoporphyrinogen IX (Protogen) prior to protoporphyrin IX (Proto IX) in cucumber (Cucumis sativus L.) cotyledons immediately after the foliar application of a protoporphyrinogen IX oxidase (Protox)-inhibiting herbicide, pyraflufen-ethyl. The accumulation of Protogen peaked at 4 to 7 hr and then decreased with the increase of Proto IX. Although a similar time-course of Protogen accumulation was observed in cucumber cotyledons treated with another Protox-inhibiting herbicide, acifluorfen, the amount of Proto IX accumulated was 2 to 3 times lower than that after the pyraflufen-ethyl treatment. Furthermore, a foliar application of pyraflufen-ethyl caused a significant accumulation of Protogen rather than Proto IX in cleavers (Galium aparine L.) after 7 hr, while little accumulation of Protogen and Proto IX took place in wheat (Triticum aestivum L.). © Pesticide Science Sociey of Japan

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O-Syn and O-anti benzyl epoxycyclopentyl ethers were synthesized and their herbicidal activity was investigated. The O-syn isomers were found to be active, and the O-anti isomer was inactive. Thus, benzyl epoxycycopentyl ethers require two oxygens with the syn stereochemistry for herbicidal activity. The O-syn configuration should be considered in addition to the geometrical 1,4-relationship to optimize herbicidal activity. © Pesticide Science Society of Japan

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A series of 5-aryl-1,3,4-oxadiazole-2-thiols was found to inhibit trans-cinnamate 4-hydroxylase (C4H) from Populus kitakamiensis, which was expressed in yeast. 5-Phenyl-1,3,4-oxadiazole-2-thiol showed inhibitory activity comparable to 2-hydroxy-1-naphthoic acid, a known C4H inhibitor. Studies on the structure-activity relationship indicated that the presence of a thiol group was significant for stronger activity. Of the compounds tested, 5-(3-fluorophenyl)-1,3,4-oxadiazole-2-thiol was the most active. © Pesticide Science Society of Japan

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Foliar sprays of validamycin A (VMA) controlled cabbage black rot effectively in pot and field trials. In a pot test, VMA reduced the number of Xanthomonas campestris pv. campestris (Xcc) in leaves. VMA inhibited the production of extracellular polysaccharide (EPS) on yeast-peptone (YP) agar containing carbohydrates. Injection of EPS from Xcc on medium containing VMA produced fewer lesions than that without VMA. These results suggested that VMA might inhibit the multiplication of Xcc in plants and affect the quantity and quality of EPS. © Pesticide Science Society of Japan

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Thiobencarb (S-4-chlorobenzyl diethylthiocarbamate) is a thiocarbamate herbicide used for weed control in rice production. After screening, a strain able to degrade thiobencarb, identified as Aspergillus niger van Tieghem, was successfully isolated. Optimal conditions for thiobencarb degradation in culture were at pH 5.5 and 30°C. The strain also showed the ability to degrade the herbicides molinate and butachlor. © Pesticide Science Society of Japan

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Oat leaves produce phytoalexins, avenanthramides, in response to pathogen infection and elicitor treatment. Feeding experiments with labeled precursors and measuring enzyme activities revealed the biosynthetic pathway for avenanthramides. In addition, the enzyme that catalyzes the final biosynthetic reaction was identified. An accumulation of similar hydroxycinnamic acid amides was found in maize and barley under stress, suggesting the generality of the defense reaction that involves hydroxycinnamic acid amides. The metabolism of avenanthramides was analyzed using labeled compounds. Avenanthramides were metabolized by the oat leaf itself and were incorporated into cell walls. The elicitor treatment induced peroxidase activity that accepts avenanthramides as substrates. These findings suggested that avenanthramides serve as substrates for the reinforcement of cell walls.

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Cytochrome P450 monooxygenases are important metabolic enzymes involved in catalyzing a number of compounds and thus are essential for most creatures. One of the major roles of P450s in insects is detoxification or activation of pesticides including pyrethroid insecticides. In this paper, our recent attempts to elucidate the role of P450s in mechanisms of pyrethroid resistance in Culex mosquitoes, houseflies and fruit flies are summarized. Possible applications to insect pest management and to the development of novel insect regulators are also discussed.

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The binding affinity of neonicotinoids for housefly head membranes was evaluated to elucidate the physicochemical features of the compounds involved in the ligand-nicotinic acetylcholine receptor (nAChR) interactions. Both steric and electrostatic factors of the substituents on the aromatic and imidazolidine rings were found to influence the binding affinity. [¹⁴C]Imidacloprid was employed to clarify the metabolism of imidacloprid in the flies. It was found that the compound was degraded, and the metabolites were then excreted from the flies in a short period after administration. Agonist actions of neonicotinoids on nAChRs were evaluated to examine their relationships with the binding and insecticidal activities. High correlations were observed among these activities, suggesting that the channel opening of nAChRs resulting from the neonicotinoid binding is likely to cause the insecticidal actions.

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