In recent years, the research on the potential of using RNA interference (RNAi) to suppress crop pests has made an outstanding growth. However, given the variability of RNAi efficiency that is observed in many insects, the development of novel approaches toward insect pest management using RNAi requires first to unravel factors behind the efficiency of dsRNA-mediated gene silencing. In this review, we explore essential implications and possibilities to increase RNAi efficiency by delivery of dsRNA through non-transformative methods. We discuss factors influencing the RNAi mechanism in insects and systemic properties of dsRNA. Finally, novel strategies to deliver dsRNA are discussed, including delivery by symbionts, plant viruses, trunk injections, root soaking, and transplastomic plants.

Scientists have made significant progress in understanding and unraveling several aspects of double-stranded RNA (dsRNA)-mediated gene silencing during the last two decades. Now that the RNA interference (RNAi) mechanism is well understood, it is time to consider how to apply the acquired knowledge to agriculture and crop protection. Some RNAi-based products are already available for farmers and more are expected to reach the market soon. Tailor-made dsRNA as an active ingredient for biopesticide formulations is considered a raw material that can be used for diverse purposes, from pest control and bee protection against viruses to pesticide resistance management. The RNAi mechanism works at the messenger RNA (mRNA) level, exploiting a sequence-dependent mode of action, which makes it unique in potency and selectivity compared with conventional agrochemicals. Furthermore, the use of RNAi in crop protection can be achieved by employing plant-incorporated protectants through plant transformation, but also by non-transformative strategies such as the use of formulations of sprayable RNAs as direct control agents, resistance factor repressors or developmental disruptors. In this review, RNAi is presented in an agricultural context (discussing products that have been launched on the market or will soon be available), and we go beyond the classical presentation of successful examples of RNAi in pest-insect control and comprehensively explore its potential for the control of plant pathogens, nematodes and mites, and to fight against diseases and parasites in beneficial insects. Moreover, we also discuss its use as a repressor for the management of pesticide-resistant weeds and insects. Finally, this review reports on the advances in non-transformative dsRNA delivery and the production costs of dsRNA, and discusses environmental considerations.

Flavonoids are a group of polyphenols that provide health-promoting benefits upon consumption. However, poor bioavailability has been a major hurdle in their use as drugs or nutraceuticals. Low bioavailability has been associated with flavonoid interactions at various stages of the digestion, absorption and distribution process, which is strongly affected by their molecular structure. In this review, we use structure-activity/property relationship to discuss various flavonoid interactions with food matrices, digestive enzymes, intestinal transporters and blood proteins. This approach reveals specific bioactive properties of flavonoids in the gastrointestinal tract as well as various barriers for their bioavailability. In the last part of this review, we use these insights to determine the effect of different structural characteristics on the overall bioavailability of flavonoids. Such information is crucial when flavonoid or flavonoid derivatives are used as active ingredients in foods or drugs.

Since the discovery of RNA interference (RNAi), scientists have made significant progress towards the development of this unique technology for crop protection. The RNAi mechanism works at the mRNA level by exploiting a sequence-dependent mode of action with high target specificity due to the design of complementary dsRNA molecules, allowing growers to target pests more precisely compared to conventional agrochemicals. The delivery of RNAi through transgenic plants is now a reality with some products currently in the market. Conversely, it is also expected that more RNA-based products reach the market as non-transformative alternatives. For instance, topically applied dsRNA/siRNA (SIGS – Spray Induced Gene Silencing) has attracted attention due to its feasibility and low cost compared to transgenic plants. Once on the leaf surface, dsRNAs can move directly to target pest cells (e.g., insects or pathogens) or can be taken up indirectly by plant cells to then be transferred into the pest cells. Water-soluble formulations containing pesticidal dsRNA provide alternatives, especially in some cases where plant transformation is not possible or takes years and cost millions to be developed (e.g., perennial crops). The ever-growing understanding of the RNAi mechanism and its limitations has allowed scientists to develop non-transgenic approaches such as trunk injection, soaking, and irrigation. While the technology has been considered promising for pest management, some issues such as RNAi efficiency, dsRNA degradation, environmental risk assessments, and resistance evolution still need to be addressed. Here, our main goal is to review some possible strategies for non-transgenic delivery systems, addressing important issues related to the use of this technology.

In this study, 22 phenolic compounds were investigated to inhibit the angiotensin-converting enzyme (ACE). Tannic acid showed the highest activity (IC50 = 230 μM). The IC50 values obtained for phenolic acids and flavonoids ranged between 0.41 and 9.3 mM. QSAR analysis confirmed that the numbers of hydroxyl groups on the benzene ring play an important role for activity of phenolic compounds and that substitution of hydroxyl groups by methoxy groups decreased activity. Docking studies indicated that phenolic acids and flavonoids inhibit ACE via interaction with the zinc ion and this interaction is stabilized by other interactions with amino acids in the active site. Other compounds, such as resveratrol and pyrogallol, may inhibit ACE via interactions with amino acids at the active site, thereby blocking the catalytic activity of ACE. These structure-function relationships are useful for designing new ACE inhibitors and potential blood-pressure-lowering compounds based on phenolic compounds.

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Over the past few years, the use of RNA interference (RNAi) for insect pest management has attracted considerable interest in academia and industry as a pest-specific and environment-friendly strategy for pest control. For the success of this technique, the presence of core RNAi genes and a functional silencing machinery is essential. Therefore, the aim of this study was to test whether the Neotropical brown stinkbug Euschistus heros has the main RNAi core genes and whether the supply of dsRNA could generate an efficient gene silencing response. To do this, total mRNA of all developmental stages was sequenced on an Illumina platform, followed by a de novo assembly, gene annotation and RNAirelated gene identification. Once RNAi-related genes were identified, nuclease activities in hemolymph were investigated through an ex vivo assay. To test the functionality of the siRNA machinery, E. heros adults were microinjected with ~28 ng per mg of insect of a dsRNA targeting the V-ATPase-A gene. Mortality, relative transcript levels of V-ATPase-A, and the expression of the genes involved in the siRNA machinery, Dicer-2 (DCR-2) and Argonaute 2 (AGO-2), were analyzed. Transcriptome sequencing generated more than 126 million sequenced reads, and these were annotated in approximately 80,000 contigs. The search of RNAi-related genes resulted in 47 genes involved in the three major RNAi pathways, with the absence of sid-like homologous. Although ex vivo incubation of dsRNA in E. heros hemolymph showed rapid degradation, there was 35% mortality at 4 days after treatment and a significant reduction in V-ATPase-A gene expression. These results indicated that although sid-like genes are lacking, the dsRNA uptake mechanism was very efficient. Also, 2-fold and 4-fold overexpression of DCR-2 and AGO-2, respectively, after dsRNA supply indicated the activation of the siRNA machinery. Consequently, E. heros has proven to be sensitive to RNAi upon injection of dsRNA into its hemocoel. We believe that this finding together with a publically available transcriptome and the validation of a responsive RNAi machinery provide a starting point for future field applications against one of the most important soybean pests in South America. The Neotropical brown stink bug (BS), Euschistus heros (Hemiptera: Pentatomidae), is one of the most important Pentatomidae pests in South America 1 , especially in soybean (Glycine max) with a reduction in seed quality and yield 2. Stink bugs use their piercing/sucking mouthparts to inject enzymes into the plant tissues to digest plant components and remove pre-digested fluids 3. Although rarely reported before the 70s 2,4 , since then population outbreaks 2,5 and rapid population growth have allowed expansion of the range of E. heros to all the major South American soybean production regions, including Brazil 2 , Paraguay 2 , and Argentina 6 .