Volatiles Induced from Hypolepis punctata (Dennstaedtiaceae) by Herbivores Attract Sclomina erinacea (Hemiptera: Reduviidae): Clear Evidence of Indirect Defense in Fern

Microbial-type terpene synthases significantly contribute to the terpene profile of glandular trichomes of the fern Dryopteris fragrans (L.)

Ferns, known for their adaptability and widespread presence, form a diverse group of plants. However, the mechanisms underlying terpenoid production, which are often linked to plant adaptation, are not well understood in ferns. Here, we report that Dryopteris fragrans (D. fragans) produces diverse terpenoids in glandular trichomes (GTs) through the activities of microbial-type terpene synthases. Using microscopy methods, capitate GTs were found to occur on various organs throughout the development of D. fragrans. In D. fragrans leaves, 13 terpenoids, most being sesquiterpenoids, were identified. By comparing the terpenoid chemistry of intact leaves, GT-removed leaves, and isolated GTs, GTs were concluded to be the main site of terpenoid storage. Next, transcriptomes of D. fragrans leaves and GTs were created and mined for genes of the terpenoid biosynthetic pathway. Among them were nine putative full-length microbial terpene synthase-like (MTPSL) genes designated DfMTPSL1-9. Using in vitro enzyme assays, six of the nine DfMTPSLs were demonstrated to have sesquiterpene synthase activities. Of them, DfMTPSL1 catalyzes the formation of (-)-9-epi-presilphiperfolan-1-ol, the most abundant sesquiterpenoid in leaves. DfMTPS2 produces α-muurolene, another major sesquiterpenoid from D. fragrans. The catalytic activities of DfMTPSLs together with the GT-enriched expression of their respective genes support that GTs are also the main site of terpenoid biosynthesis in D. fragrans. Methyl jasmonate treatment induced the expression of DfMTPSL genes and the emission of terpenoid volatiles, suggesting that GT-produced terpenoids play a role in defense against biotic stresses in D. fragrans, similar to their counterparts in seed plants.

Fractionation, identification of chemical constituents, and biological properties of cashew (Anacardium occidentale L.) leaf extracts

The current study aimed to identify the chemical constituents and bioactivities of the crude ethanolic extract (CEE) and its fractions (ethyl acetate (EAF), hexane (HEF), and aqueous (AEF)) from leaves of cashew (Anacardium occidentale L.) grown in Vietnam. A total of 31 compounds which belong to alkanes, hydrocarbons, iodine, terpenoids, phenolics, and flavonoids were determined by a gas chromatography-mass spectrometry (GC-MS) analysis, with bis(2-ethylhexyl) phthalate being the most prevailing compound. The highest total phenolic and flavonoid contents were obtained in the EAF, followed by HEF, CEE, and AQF. All samples showed promising in vitro antibacterial activity, enzyme inhibition, and anticancer activity. Among the samples tested, the EAF exhibited the highest enzyme inhibition activity against α-amylase and α-glucosidase (IC50 values of 51.24 μg/mL and 99.29 μg/mL, respectively), cytotoxicity activity against HeLa cells (IC50 value of 79.49 μg/mL), and antibacterial activity against Bacillus subtilis and Escherichia coli with MIC values of 5 mg/mL and 2.5 mg/mL, respectively. These findings suggest that the leaves of A. occidentale cultivated in Vietnam are a promising source of bioactive components and that EAF is a promising bioactive material warranting further pharmaceutical investigation.

Tritrophic Interactions among Arthropod Natural Enemies, Herbivores and Plants Considering Volatile Blends at Different Scale Levels

Herbivore-induced plant volatiles (HIPVs) are released by plants upon damaged or disturbance by phytophagous insects. Plants emit HIPV signals not merely in reaction to tissue damage, but also in response to herbivore salivary secretions, oviposition, and excrement. Although certain volatile chemicals are retained in plant tissues and released rapidly upon damaged, others are synthesized de novo in response to herbivore feeding and emitted not only from damaged tissue but also from nearby by undamaged leaves. HIPVs can be used by predators and parasitoids to locate herbivores at different spatial scales. The HIPV-emitting spatial pattern is dynamic and heterogeneous in nature and influenced by the concentration, chemical makeup, breakdown of the emitted mixes and environmental elements (e.g., turbulence, wind and vegetation) which affect the foraging of biocontrol agents. In addition, sensory capability to detect volatiles and the physical ability to move towards the source were also different between natural enemy individuals. The impacts of HIPVs on arthropod natural enemies have been partially studied at spatial scales, that is why the functions of HIPVs is still subject under much debate. In this review, we summarized the current knowledge and loopholes regarding the role of HIPVs in tritrophic interactions at multiple scale levels. Therefore, we contend that closing these loopholes will make it much easier to use HIPVs for sustainable pest management in agriculture.

Plant Volatiles and Herbivore Induced Plant Volatiles from Chili Pepper Act as Attractant of the Aphid Parasitoid Aphelinus varipes (Hymenoptera: Aphelinidae)

Plants have evolved a number of different chemical defenses, covering nearly all classes of (secondary) metabolites, that represent a major barrier to herbivory: some are constitutive; others are induced after attacks from herbivores (HIPVs) and may elicit the attraction of predators and parasitoids. Here, we studied how the female solitary endoparasitoid Aphelinus varipes responds to plant and host aphid volatiles in a series of experiments on five commercially important vegetables that were either healthy or infested with the aphid Myzus persicae: chili pepper, eggplant, crown daisy, Chinese cabbage and cabbage. The results for the olfactory responses of A. varipes showed that the presence of M. persicae increased the attraction of the endoparasitoid to the infested plants. In a second experiment, volatiles from highly attractive and repellent plants were obtained via headspace collection to investigate volatiles from healthy and aphid-damaged plants. The results for the differences in volatile profiles in response to aphid infestation in chili pepper cultivar were dominated by the volatile blends, including α-pinene, decanal and phthalic acid, while in cabbage they were dominated by isophorone. Moreover, when HIPVs with different concentrations were compared, α-pinene at a dose rate of 100 ng/μL attracted more parasitoids, and the comparison was useful to understand the mechanisms of plant secondary volatiles during aphid infestation and to provide new resources to control this insect pest. Overall our study shows how HIPVs can bolster tritrophic interactions by enhancing the attractiveness of parasitoids.