RNA interference technology in crop protection against arthropod pests,pathogens and nematodes

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. © 2017 Society of Chemical Industry     

Sublethal effects of kaolin and the biopesticides Prestop-Mix and BotaniGard on metabolic rate,water loss and longevity in bumble bees (Bombus terrestris)

Kaolin is an inert material with a broad range of applications, e.g. as an insecticide and as a filling substance in the formulation of biopesticides. Hence, bees that dispense biopesticides to the field in the context of entomovectoring are exposed to elevated risks because of side-effects of those products. Here, we investigated with use of bumble bee workers of Bombus terrestris L. the lethal and sublethal effects of (i) pure kaolin, (ii) the biofungicide Prestop-Mix containing the parasitic fungus Gliocladium catenulatum and kaolin and (iii) the bioinsecticide BotaniGard containing the entomopathogenic fungus Beauveria bassiana and compared with wheat flour powder that we considered safe for bumble bees. As the most important result, treatment with kaolin increased the cuticular water loss and reduced the survival of treated bumble bees, while Prestop-Mix had no negative effect on longevity. BotaniGard caused mortality in the bumble bees because of the entomopathogenic spores it contained. In conclusion, our data indicated that substances used as ‘inert materials’ and in biocontrol agents which are used in IPM and organic farming systems may bring higher risks to bumble bees used in entomovector technology.     

Towards dsRNA-integrated protection of medical Cannabis crops: considering human safety,recent- and developing RNAi methods,and research inroads

Owing to the expanding industry of medical Cannabis, we discuss recent milestones in RNA interference (RNAi)-based crop protection research and development that are transferable to medical Cannabis cultivation. Recent and prospective increases in pest pressure in both indoor and outdoor Cannabis production systems, and the need for effective nonchemical pest control technologies (particularly crucial in the context of cultivating plants for medical purposes), are discussed. We support the idea that developing RNAi tactics towards protection of medical Cannabis could play a major role in maximizing success in this continuously expanding industry. However, there remain critical knowledge gaps, especially with regard to RNA pesticide biosafety from a human toxicological viewpoint, as a result of the medical context of Cannabis product use. Furthermore, efforts are needed to optimize transformation and micropropagation of Cannabis plants, examine cutting edge RNAi techniques for various Cannabis–pest scenarios, and investigate the combined application of RNAi- and biological control tactics in medical Cannabis cultivation. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Action of the ecdysteroid agonist tebufenozide in susceptible and artificially selected beet armyworm

Toxicity assays with tebufenozide, the first commercial non-steroidal ecdysteroid agonist, against a laboratory strain of the beet armyworm, Spodoptera exigua (Hübner), demonstrated the promise of this new compound for the control of this important pest. Experiments to select insects artificially from the laboratory strain by continuous exposure of larval instars to corresponding LC₂₅ doses of tebufenozide for over 12 generations (G₀→G₁₂: 14–15 months), revealed no loss in susceptibility to the insecticide for up to five generations. Moreover, retention and fate of ¹⁴C-labelled tebufenozide were investigated using G₆ larvae from the selection experiments and the results compared with those for the susceptible (G₀) larvae. In addition, piperonyl butoxide, an inhibitor of monooxygenases, when ingested by larvae along with tebufenozide, increased the susceptibility of intoxicated larvae to this ecdysteroid agonist, indicating its oxidative metabolism in Spodoptera larvae. © 1998 Society of Chemical Industry.     

Improvements in larviculture of Crangon crangon as a step towards its commercial aquaculture

The European brown shrimp, Crangon crangon, is a highly valued commercial species in Europe. These shrimp fisheries are characterized by strong seasonal variations in average landings. Attempts to ‘catch and hold’ wild adults in land‐based rearing systems have been proven to be very difficult, due to inadequate feed, slow growth and high mortality. In this study, we have optimized design and operation procedures of a small‐scale static larval rearing system for the culture of C. crangon larvae. Focus was on optimizing larval survival via water temperature, feed selection, feeding regime and density. This is the first report that shows that C. crangon larvae can be reared at high densities of 300 larvae L^‐1 with high survival of 73.5 (± 5.4)% under laboratory conditions. In these systems, larvae can be fed exclusively Artemia nauplii according to a feeding regime which is adjusted based on major moulting events. Addition of microalgae may further increase survival by 10%. The information gathered during this research can be applied to further optimize larval development in either flow‐through or recirculation systems.     

RNA‐based biocontrol compounds: current status and perspectives to reach the market

Facing current climate challenges and drastically reduced chemical options for plant protection, the exploitation of RNA interference (RNAi) as an agricultural biotechnology tool has unveiled possible new solutions to the global problems of agricultural losses caused by pests and other biotic and abiotic stresses. While the use of RNAi as a tool in agriculture is still limited to a few transgenic crops, and only adopted in restricted parts of the world, scientists and industry are already seeking innovations in leveraging and exploiting the potential of RNAi in the form of RNA‐based biocontrol compounds for external applications. Here, we highlight the expanding research and development pipeline, commercial landscape and regulatory environment surrounding the pursuit of RNA‐based biocontrol compounds with improved environmental profiles. The commitments of well‐established agrochemical companies to invest in research endeavours and the role of start‐up companies are crucial for the successful development of practical applications for these compounds. Additionally, the availability of standardized guidelines to tackle regulatory ambiguities surrounding RNA‐based biocontrol compounds will help to facilitate the entire commercialization process. Finally, communication to create awareness and public acceptance will be key to the deployment of these compounds. © 2019 Society of Chemical Industry     

Toxicity and kinetics of methoxyfenozide in greenhouse-selected Spodoptera exigua (Lepidoptera: Noctuidae)

Methoxyfenozide (RH-2485) was found to be 7.5-fold less toxic in terms of LD50 values against last-instar larvae of a greenhouse-selected strain of the beet armyworm Spodoptera exigua (Hübner) that was collected in July 2001 in an experimental greenhouse for resistance at Murcia in southern Spain, in comparison with a laboratory susceptible strain. To date, the compound is the newest member of this new group of moulting hormone accelerating IGRs to reach the marketplace against Lepidoptera. To understand this different potency in the greenhouse-selected S exigua, oxidative metabolism and acetylcholinesterase activities were measured in last-instar larvae and adults. In addition, we determined, by the use of 14C-labelled methoxyfenozide, the pattern of absorption in body tissues and excretion via faeces in last-instar larvae of the greenhouse-selected strain and compared the results with those from the laboratory susceptible strain. It was striking that the rate of excretion was about twice as high in the greenhouse-selected strain, resulting in a more rapid clearance of insecticide amounts from the insect body. Data are discussed in relation to mechanisms of lower toxicities for this new group of IGRs.