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Mint plants could theoretically serve as companion plants (CPs) that attract enemies of herbivores in tritrophic interactions. In order to explore the traits of mint volatiles as attractant cues for enemies of two-spotted spider mites, we performed Y-tube olfactometer assays of predatory mites, Phytoseiulus persimilis and Neoseiulus californicus, towards three mint species, apple mint, candy mint, and spearmint, as odor source. Clean candy mint and spearmint were attractive to P. persimilis, when compared with clean air and undamaged Phaseolus vulgaris plants serving as the target crop. Moreover, clean candy mint plants were even more attractive than volatiles from P. vulgaris plants damaged by spider mites. These predator responses were induced additively by candy mint volatiles plus volatiles from damaged P. vulgaris plants, as shown using both Y-tube olfactometer and open-space assay systems. However, the number of spider mite eggs consumed by P. persimilis on P. vulgaris plants did not differ in the presence compared to the absence of mint volatiles, indicating that mint volatiles affect the attraction but not the appetite of P. persimilis. Together, these findings suggest that the use of candy mint and spearmint as CPs is an ideal platform for spider mite pest management via the attraction of predatory mites.

Mint plants enable improvement of pest management by attracting herbivore enemies to constitutively released mint volatiles. The generalist predator Nesidiocoris tenuis is used worldwide to control agricultural pests, but little is known about whether mint can serve as a companion plant that attracts this predator. To examine this, olfactory responses of N. tenuis were assessed using apple mint, candy mint, and spearmint as odor sources. Of the volatiles released by these mint species, candy mint volatiles alone were more attractive than those from undamaged eggplant, and were as attractive as volatiles from eggplant damaged with Spodoptera litura larvae. However, no prominent preference for particular volatile(s) among the mint volatiles was shown by O. strigicollis . When N. tenuis had been previously exposed to candy mint, the predator showed a stronger preference for candy mint volatiles than damaged eggplant volatiles. It was, however, irrelevant whether the predator received benefit or not by predating animal prey during the mint-experience period. In contrast, spearmint-experience increased the preference for spearmint volatiles only when the predator acquired prey during the mint-experience period. These findings suggest that previous exposure of N. tenuis to some particular mint species can increase its preference for volatiles from the conspecific mints.

We studied plant–plant communication in a system that included eggplants, herbivores as prey, and the omnivorous mirid Nesidiocoris tenuis . When uninfested eggplants were exposed to volatiles from conspecific plants infested by N. tenuis adults, the amounts of jasmonic acid (JA) and salicylic acid (SA) in the exposed plants remained to be similar to those in uninfested eggplants that were exposed to volatiles from uninfested conspecific plants (control eggplants). Subsequent artificial damage to the leaves of either the exposed or control eggplants using scissors led to a significant increase in JA content in the leaves. Furthermore, following the damage, the JA content in the exposed plants was significantly higher than in the control plants. In contrast, the amount of SA in the eggplants was not affected by either exposure or subsequent artificial damage. The fecundity of Kanzawa spider mites on the leaf disks of the exposed plants was significantly lower than that on the leaf disks of the control plants. The weight gain of 2nd stadium Spodoptera litura larvae on the exposed plants was significantly lower than on the control plants. However, the survival and fecundity of N. tenuis females on both exposed and control plants were not significantly different. This study demonstrates the potential variations in the tolerance of herbivorous and omnivorous arthropods to plant defenses in response to exposure to plant volatiles.

Nesidiocoris tenuis Reuter (Heteroptera: Miridae) is an omnivorous mirid bug that preys on diverse generalist herbivorous arthropods. N. tenuis adults are attracted to volatiles from plants induced by their prey, such as tobacco cutworms (CCW) ( Spodoptera litura larvae) and two-spotted spider mites ( Tetranychus urticae ). N. tenuis adults also induce volatiles when they infest plants. In this study, we focused on olfactory responses of N. tenuis males and females to volatiles from eggplants and sesame plants induced by conspecifics of the same or different gender by using a Y-tube olfactometer. Males were attracted to volatiles from plants of both species induced by either males or females. The male preference was biased to volatiles from plants of both species induced by females, probably because the biased response would facilitate their mate-finding. Females were attracted only to volatiles from plants of both species induced by females. Mating occurs multiple times in this species. Thus, the responses would indirectly affect mating of males and females. Slight but significant qualitative and quantitative differences were detected between the volatiles of plants of both species induced by N. tenuis females and those of the plants induced by conspecific males. N. tenuis might use such differences in their gender-specific responses.

We collected Solidago altissima clones to explore their leaf damage resistance, and as a result identified five accessions that exhibited variable defense abilities against the generalist herbivore Spodoptera litura . In order to characterize molecules involved in such natural variation, we focused on ethylene response factors (ERFs) that exhibited distinct transcription patterns in the leaves of the five accessions (e.g., S1 and S2) after wounding: the transcript of SaERF1 and SaERF2 was induced in wounded S1 and S2 leaves, respectively. Although transcription levels of SaERFs in leaves of the five accessions did not correlate with the accessions’ phytohormone levels, these transcription levels accorded with the possibility that ethylene and jasmonate signaling play crucial roles in wound-induced transcription of SaERF1 in S1 leaves, and SaERF2 in S2 leaves, respectively. SaERF1 was found to be a positive regulator of the GCC box and DRE element in the upstream regions of promoters of defense genes, whereas SaERF2 served as a negative regulator of genes controlled through the GCC box. Transgenic Arabidopsis plants expressing SaERF1 or SaERF2 showed enhanced and suppressed transcript levels, respectively, of a defensin gene, indicating that ERFs may be partly responsible for herbivore resistance properties of S. altissima accessions.

Nesidiocoris tenuis , an omnivorous arthropod, infests plants in either the absence or presence of prey arthropods. We studied whether plant-infestation experience of N. tenuis affected its subsequent prey-finding behavior. We used sesame plants and eggplants as food plants for N. tenuis , and common cutworm (CCW) ( Spodoptera litura larvae) as prey. We focused on their olfactory response to CCW-infested sesame plants versus CCW-infested eggplants in a Y-tube olfactometer. When N. tenuis adults experienced the infestation of sesame plants for one day, they preferred volatiles from CCW-infested sesame plants to those from CCW-infested eggplants. By contrast, when N. tenuis experienced the infestation of eggplants for one day, they showed no difference in their preference between the two odor sources. When the duration of the infestation of plants was increased to four days, N. tenuis that had experienced sesame plants showed a reversed response: they preferred CCW-infested eggplant volatiles, while those that had infested eggplants again showed no difference in their preference. Next, we studied the olfactory preference of N. tenuis that had previously infested plants with moth ( Ephestia kuehniella ) eggs. We found that irrespective of plant species and of duration of experience (either one or four days), N. tenuis adults that had previously experienced one plant species showed a significant preference for volatiles from CCW-infested plants of the same species. The blends of the volatiles emitted from CCW-infested sesame plants and those from CCW-infested eggplants were qualitatively different. Possibility to control the olfactory response of N. tenuis to certain prey-infested plant volatiles by adjusting their feeding history is discussed.

Aquatic plants play an important role in freshwater biodiversity, but the diversity of aquatic plants can be easily altered and is threatened by external factors. The water fern Azolla japonica has been designated as an endangered species in Korea, as it has been recently reported that natural habitats for this species are all lost. We investigated whether the species is found in Jeju, which has the warmest and stable weather in South Korea. We found four sites inhabited by populations of A. japonica . For conservation purposes, growth experiments were conducted. A. japonica showed maximum growth rate (about 12 times higher compared to the control) in the simplest treatment, distilled water with commercial soil bed treatment. However, liquid fertilizer and hoagland solution showed no statistical difference from the control. Therefore, we suggest a very simple growing method using commercial soil for A. japonica to contribute to its propagation. In addition, a new environmental governance approach is proposed, based on linking endangered species with local agricultural products for conservation and habitat restoration. Thus, we present a comprehensive and interdisciplinary method for restoring and conserving A. japonica populations.

Monoterpene alcohols function in plant survival strategies, but they may cause self-toxicity to plants due to their hydrophobic and highly reactive properties. To explore the role of these compounds in plant stress responses, we assessed transgenic tobacco plants overexpressing the monoterpene alcohol geraniol synthase (GES plants). Growth, morphology and photosynthetic efficiency of GES plants were not significantly different from those of control plants (wild-type and GUS-transformed plants). While GES plants’direct defenses against herbivores or pathogens were similar to those of control plants, their indirect defense (i. e., attracting herbivore enemy Nesidiocoris tenuis) was stronger compared to that of control plants. However, GES plants were susceptible to cold stress and even more susceptible to extreme heat stress (50°C), as shown by decreased levels of sugar metabolites, invertase activity and its products (Glc and Fru), and leaf starch granules. Moreover, GES plants showed decreased transcription levels of the WRKY33 transcription factor gene and an aquaporin gene (PIP2). The results of this study show that GES plants exhibit enhanced indirect defense ability against herbivores, but conversely, GES plants exhibit hypersensitivity to heat stress due to suppressed sugar metabolism and gene regulation for thermal stress tolerance.

Diurnal rhythm of volatile emissions from grasses in response to herbivory may temporally affect the oviposition behaviors of the conspecific herbivores and prey searching of natural enemies of the herbivores in a diurnal cycle of the ecosystem. We assessed volatiles emitted from the temperate grass Brachypodium distachyon L. (Poaceae) damaged by Mythimna separata Walker (Noctuidae), a specialist herbivore of Poaceae, in light/dark cycle conditions. Volatiles were preferentially emitted from the damaged plants in both light and dark phases, but their quantitative compositions were different. The generalist predator Nesidiocoris tenuis Reuter (Miridae) was attracted to the damaged plants in both light and dark conditions. However, adult females of M. separata preferred to oviposit on undamaged plants mostly in the dark owing to the cue of undamaged plant volatiles, partly in a circadian rhythm-dependent manner. The findings suggested that volatiles released in the dark contribute to both plant-herbivore and plant-herbivore enemy communications.

Although studies on microplastics are increasing every year, still very little is known about their toxicity. Especially for plant species, even studies of uptake of microplastics are only few, not to mention phytotoxicity of microplastics. Therefore, we conducted a pilot study on the phytotoxicity of 1-μm-sized fluorescent microplastics (FMPs) on the free-floating aquatic plants Spirodela polyrhiza and Salvinia natans and the emergent aquatic plant Phragmites australis using 0.1% and 0.01% FMP treatment. Furthermore, uptake of FMPs by plants was verified by detecting fluorescence of FMPs by laser. A free-floating aquatic plant S. polyrhiza and emergent aquatic plant P. australis showed significantly decreased harvested biomass after 3 weeks indicating phytotoxicity of FMPs, but S. natans did not show any differences of harvested biomass or chlorophyll contents among treatments. Detection of fluorescence from plant leaves provided evidence of active FMPs uptake by plants. The emission spectra of plant leaves in 0.1% FMP treatment showed similar peaks to those of free fluorescent microplastics, providing a firm evidence of FMPs uptake by plants. This study is one of the pioneering studies to explore fluorescent microplastic uptake and toxicity in aquatic plants and therefore provides a baseline for further studies.