Acibenzolar-S-methyl (ASM), a functional analogue of salicylic acid, induces systemic acquired resistance and restricts infection by several RNA viruses, yet its mechanisms against DNA viruses remain unknown. By examining the accumulation of tomato yellow leaf curl virus (TYLCV) DNA in inoculated leaves of Nicotiana benthamiana, we investigated whether ASM suppresses begomovirus infection. TYLCV was inoculated by agroinfiltration, and virion-sense (VS) and complementary-sense (CS) strands of TYLCV DNA were quantified separately using two-step strand-specific qPCR. ASM pretreatment significantly reduced the total TYLCV DNA accumulation at 1, 2, and 3 days post-inoculation. To determine whether this reduction reflected a direct effect on TYLCV rather than impaired Agrobacterium-mediated T-DNA delivery, we used a replication-defective mutant (TYLCVΔC1) as a delivery control and confirmed that ASM did not affect T-DNA delivery. Both VS and CS strands of wild-type TYLCV were substantially reduced by ASM treatment, providing the first direct evidence that ASM suppresses begomovirus infection by targeting viral DNA accumulation at the replication stage.

Microbial secondary metabolites have historically provided numerous agrochemicals with novel chemical scaffolds and distinctive modes of action, contributing substantially to modern pesticide science. However, the long-term accumulation of natural product screening efforts has resulted in the frequent rediscovery of known compounds, and this issue, combined with the global spread of pesticide-resistant pests and pathogens, has become a serious challenge in agrochemical research. This commemorative review summarizes the research achievements of the author focusing on the discovery of pesticide seed compounds from microbial secondary metabolites. Particular emphasis is placed on two original strategies developed by the author: the activation of silent biosynthetic gene clusters in filamentous fungi via introduction of the global transcriptional regulator laeA and the construction of innovative bioassay platforms for antifungal and insecticidal screening using drug-hypersensitive model organisms. These approaches successfully expanded accessible chemical diversity, markedly improved hit rates, and enabled the identification of bioactive compounds with novel molecular targets. Collectively, these studies demonstrate a practical and versatile framework for natural-product-based pesticide discovery that supports sustainable crop protection.

The fall armyworm, Spodoptera frugiperda, is a major invasive pest causing severe damage to maize. This study evaluated the efficacy of emamectin benzoate (EB) as a seed-coating insecticide and examined its systemic movement within maize plants. EB coatings did not affect seed germination or seedling vigor. Larval mortality was significantly higher in EB-treated plants, with PRIME GREEN G106 (PG)+EB at 0.5–1.0% producing 69–72% mortality at 20 days after germination. Leaf injury in treated plants remained below 25%, as compared with more than 40% in controls. Synchrotron FTIR (SR-FTIR) and principal component analysis (PCA) confirmed EB absorption and upward translocation from roots to leaves. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) detected EB residue in leaf tissues up to 30 days, while stems showed no detectable levels, indicating preferential foliar accumulation. Overall, EB seed coating provides adequate early-season protection against S. frugiperda and represents a promising component of sustainable maize pest management.

Pyrimisulfan is a highly effective, water-soluble, and paddy herbicide used against various annual weeds, such as Echinochloa spp. Pyrimisulfan was released into surface water, and it migrated into soil water; it formed a herbicide-treated layer within seven days of the water-holding period upon the application of granules with uncontrolled formulation under the flooded condition. Although pyrimisulfan efficacy declined under overflow conditions before forming the herbicide-treated layer, the decrease in herbicidal activity was suppressed after layer formation. In addition to uncontrolled formulation, a controlled-release formulation was tested. Although time for the formation of the herbicide-treated layer increased, water fluctuation resistance improved. As a benchmark, the concentration of pyrimisulfan in soil water on the target date, after adsorption equilibrium, was 57.6 ppb. Although herbicidal activity generally decreases in soils with high organic carbon content, pyrimisulfan showed no loss of activity. This study provides fundamental insights into the mechanism of herbicide-treated layer formation.

Oxazosulfyl is the first insecticide in the sulfyl (alkylsulfone) class developed for rice protection. While the vesicular acetylcholine transporter (VAChT) has been proposed as its primary molecular target, its mode of action has not yet been extensively examined in major agricultural pests. In this study, we investigated the binding affinity of oxazosulfyl to VAChT derived from the brown planthopper (BPH), a significant rice pest, and evaluated the relationship between its insecticidal activity and binding affinity. Oxazosulfyl bound to VAChT, heterologously expressed in cultured cells, with a K_d of 1.7 nM. The displacement potency of its analogs strongly correlated with their insecticidal activity against BPH in a rice foliar spray test. Combined with the observation that oxazosulfyl blocks excitatory synaptic transmission in the cercal reflex circuit of the American cockroach, these results indicate that oxazosulfyl functions as a synaptic transmission inhibitor, exerting potent insecticidal activity against BPH, primarily through VAChT inhibition.