Synergy between certain conventional chemical insecticides has been known for decades. However, heightened awareness and interest in bioinsecticides (microbials, botanicals and arthropod venoms) have led to numerous studies demonstrating synergy between bioinsecticides and conventional insecticides, between different bioinsecticides, and among specific constituents in botanicals, which are themselves chemically complex. At the same time, bioinsecticides have often been shown to be less deleterious to non-target organisms, particularly natural enemies and pollinators, although they are not entirely without negative impacts. However, the influence of synergy among these compounds, mixtures of bioinsecticides, or combinations of bioinsecticides and conventional insecticides on non-target species remains relatively unexplored. The taxonomic diversity of target (pest) insects for which such synergy has been documented suggests that this action could also occur in non-target species. However, the impact of this synergy on non-targets in actual field conditions remains difficult to predict.

Arthropods' resistance to synthetic pesticides and environmental issues has encouraged scientists to develop alternatives to these noxious materials. In this respect, botanical types have attracted lots of attention and among them, Rosmarinus officinalis from Lamiaceae family has been found as a versatile candidate. According to the literature, a wide range of research were conducted to prove the efficacy of R. officinalis against arthropods and this study aims to review, discuss, and consolidate their results by dividing them into four groups of stored product pests (SPP), medically important insects (MII), agricultural pests (AP), and other arthropods (OA). Most studies focused on pests as follows: SPP: Callosobruchus maculatus, Tribolium castaneum, Sitophilus granaries, Sitophilus oryzae, and Tribolium confusum, MII: Aedes aegypti, Culex pipiens, Culex quinquefasciatus, and Anopheles stephensi, AP: Tetranychus urticae, Trichoplusia ni, and Myzus persicae and OA: Phytoseiulus persimilis. Finally, some points and suggestions were provided for development of botanical insecticides.

The vegetable leafminer (VLM) Liriomyza sativae Blanchard is a troublesome pest of vegetable and ornamental plants worldwide. Resistance development and environmental pollution from the overuse of chemical insecticides have driven interest in alternative control strategies for this pest. Secondary metabolites derived from aromatic nonhost plants are recognised components of the plant defence system against herbivores. The essential oils derived from aromatic plants not only repel insects but also have toxic effects against various insect pests, yet little is known about their effects against leafminers. The major constituents of the essential oil extracted from rosemary leaves by hydrodistillation were identified by GC-MS. The behavioural responses of VLM adults to the rosemary essential oil (REO) were explored with Y-tube olfactometer experiments, and the oviposition and feeding deterrent effects of REO against adults were studied using no-choice cage tests. Dipping methods were used to determine the toxicity of REO and Matrine (a commercial botanical pesticide) against VLM eggs, larvae and pupae, while glass-vial bioassays were used for adults. The identified major constituents of the cineoliferum chemotype of REO were 1,8-cineole (23.53%), pinene (23.45%), (S)-(-)-verbenone (12.84%) and borneol (7.47%). REO repelled leafminer adults. Sublethal concentrations of REO deterred oviposition and feeding by adults. Adults were more susceptible than other developmental stages to toxicity of REO and Matrine. Female adults were more sensitive than males, based on EC50 values at 24 and 48 hr after treatment. Rosemary essential oil is a behaviour-modifying stimulus potentially useful in a "push-pull" strategy for L. sativae control, and as an alternative to synthetic chemical insecticides due to its low toxicity and high efficacy in the control of VLM.

Interest in the discovery and development of plant essential oils for use as bioinsecticides has grown enormously in the past 20 years. However, successful commercialization and utilization of crop protection products based on essential oils has thus far lagged far behind their promise based on this large body of research, most notably because with the exceptions of the USA and Australia, such products receive no special status from regulatory agencies that approve new pesticides for use. Essential oil-based insecticides have now been used in the USA for well over a decade, and more recently have seen use in the European Union (EU), Korea, and about a dozen other countries, with demonstrated efficacy against a wide range of pests and in numerous crop systems. For the most part these products are based on commodity essential oils developed as flavor and fragrance agents for the food and cosmetic industries, as there are formidable logistic, economic, and regulatory challenges to the use of many other essential oils that otherwise possess potentially useful bioactivity against pests. In spite of these limitations, the overall prospects for biopesticides, including those based on essential oils, are encouraging as the demand for sustainably-produced and/or organic food continues to increase worldwide.

The global biodiversity and climate emergencies demand transformative changes to human activities. For example, food production relies on synthetic, industrial and non-sustainable products for managing pests, weeds and diseases of crops. Sustainable farming requires approaches to managing these agricultural constraints that are more environmentally benign and work with rather than against nature. Increasing pressure on synthetic products has reinvigorated efforts to identify alternative pest management options, including plant-based solutions that are environmentally benign and can be tailored to different farmers' needs, from commercial to small holder and subsistence farming. Botanical insecticides and pesticidal plants can offer a novel, effective and more sustainable alternative to synthetic products for controlling pests, diseases and weeds. This Special Issue reviews and reports the latest developments in plant-based pesticides from identification of bioactive plant chemicals, mechanisms of activity and validation of their use in horticulture and disease vector control. Other work reports applications in rice weeds, combination biopesticides and how chemistry varies spatially and influences the effectiveness of botanicals in different locations. Three reviews assess wider questions around the potential of plant-based pest management to address the global challenges of new, invasive and established crop pests and as-yet underexploited pesticidal plants.

The diamondback moth, Plutella xylostella is a cosmopolitan pest that has evolved resistance to all classes of insecticide, and costs the world economy an estimated US $4-5 billion annually. We analyse patterns of variation among 532 P. xylostella genomes, representing a worldwide sample of 114 populations. We find evidence that suggests South America is the geographical area of origin of this species, challenging earlier hypotheses of an Old-World origin. Our analysis indicates that Plutella xylostella has experienced three major expansions across the world, mainly facilitated by European colonization and global trade. We identify genomic signatures of selection in genes related to metabolic and signaling pathways that could be evidence of environmental adaptation. This evolutionary history of P. xylostella provides insights into transoceanic movements that have enabled it to become a worldwide pest.

Maize weevils, Sitophilus zeamais, are stored product pests mostly found in warm and humid regions around the globe. In the present study, acute toxicity via contact and residual bioassay and fumigant bioassay of 28 essential oils as well as their attraction–inhibitory activity against the adults of S. zeamais were evaluated. Chemical composition of the essential oils was analyzed by gas chromatography-mass spectrometry, and a compound elimination assay was conducted on the four most active oils (cinnamon, tea tree, ylang ylang, and marjoram oils) to identify major active constituents. Amongst the oils examined, cinnamon oil was the most active in both contact/residual and fumigant bioassays, and exhibited strong behavioral inhibitory activity. Based on the compound elimination assay and chemical analyses, trans-cinnamaldehyde in cinnamon oil, and terpinen-4-ol in tea tree and marjoram oils were identified as the major active components. Although cinnamon oil seemed promising in the lab-scale bioassay without rice grains, it failed to exhibit strong insecticidal activity when the container was filled with rice. When a cinnamon oil-based product was applied both in an empty glass jar and a rice-filled container, all weevils in the empty jar were killed, whereas fewer than 15% died in the rice-filled container.

Insecticidal action of plant essential oils has been an area of intensive research in the new millennium, according to a recent bibliometric analysis. Despite this overwhelming research effort, commercialization of bioinsecticides based on essential oils has lagged far behind, although such products have now been used in the USA for over a decade, and in the EU in the last 4–5 years. Recent progress in commercialization of these products is reviewed here. Essential oils and their mono- and sesquiterpenoid constituents are fast-acting neurotoxins in insects, possibly interacting with multiple receptor types. These compounds also display potentially important sublethal behavioural effects in pest insects, including feeding and oviposition deterrence and repellence. Synergy among essential oil terpenoids appears to be a common phenomenon, and a mechanism for this action in rosemary oil has recently been demonstrated. Commercial development of bioinsecticides based on plant essential oils can follow several different pathways producing products with active ingredients differing in their genesis. These include products whose active ingredients consist of (1) a mixture of essential oils; (2) a single essential oil, or a single terpenoid constituent; (3) a blend of terpenoids, synthetically produced, that emulate those in a plant essential oil; and (4) a novel (non-natural) blend of terpenoids obtained from different plant sources. Examples of each of these are provided.

Academic interest in plant natural products with insecticidal properties has continued to grow in the past 20 years, while commercialization of new botanical insecticides and market expansion of existing botanicals has lagged considerably behind. Insecticides based on pyrethrum and neem (azadirachtin) continue to be standard bearers in this class of pesticides, but globally, their increased presence is largely a consequence of introduction into new jurisdictions. Insecticides based on plant essential oils are just beginning to emerge as useful plant protectants. Some countries (such as Turkey, Uruguay, the United Arab Emirates, and Australia) have relaxed regulatory requirements for specific plant extracts and oils, while in North America and the European Union, stricter requirements have slowed progress toward commercialization of new products. Botanicals are likely to remain niche products in many agricultural regions and may have the greatest impact in developing countries in tropical regions where the source plants are readily available and conventional products are both expensive and dangerous to users.

SPECIALTY GRAND CHALLENGE article Front. Agron., 13 December 2019Sec. Pest Management Volume 1 - 2019 | https://doi.org/10.3389/fagro.2019.00002

Oliveria decumbens is an aromatic plant traditionally used for treatment of infections and gastrointestinal diseases. In the present study, the volatile oil of the plant was obtained by hydrodistillation and analyzed by GC-MS. In addition, antibacterial and anti-Helicobacter pylori activities of this essential oil were determined using disc diffusion and agar dilution methods, respectively. Insecticidal activity was assessed through topical and fumigation application of the essential oil to cabbage looper larvae. Acetylcholinesterase (AChE) inhibition by the essential oil was examined using Ellman's method. Furthermore, its cytotoxic potential against three different cancer cell lines was assessed using the MTT assay. The phenolic monoterpenoids, thymol (38.79%), and carvacrol (36.30%) were identified as major constituents of the essential oil. We observed significant antibacterial activity of the essential oil against H. pylori (MIC=20.4 µg /mL) as well as other tested bacteria, except for Pseudomonas aeruginosa. O. decumbens essential oil showed significant toxicity to cabbage looper larvae with LD50 value of 52.1 µg /larva following topical and fumigant administration. O. decumbens essential oil was considerably inhibitory to acetylcholinesterase activity (IC50 = 0.117 µg/mL). Cytotoxic assay of the volatile oil resulted in IC50 = 0.065, 0.104, and 0.141 μg/mL for MCF-7, T47D and MDA- MB-231 cell lines, respectively. According to our data, this species with high concentrations of thymol and carvacrol could be considered as a natural source for pharmaceutical products.

California Department of Pesticide Regulation's Pesticide Use Report (PUR) and Pesticide Label databases provide a unique opportunity to analyze trends in the plant-derived (botanical) pesticide industry in California based on product registration and commercial usage. While the role of botanical pesticides in commercial pest control remain minor, the number of registered botanical pesticide products (indicating registrants' confidence in their marketability) and the mass of botanicals used commercially have seen marked increases in recent years. Registered product counts (as total number of products by 7/7/2017) are high and usage remains steady for the classical botanicals pyrethrins (4,862 products, 250,000 kg products/yr) and strychnine (617 products, 50,000 kg products/yr). By 2015, registration and usage had grown for some newer botanicals, including azadirachtin (65 products, 150,000 kg/yr) and limonene (145 products, 40,000 kg/yr). Pesticidal activity of essential oils often require multiple components, and the 37 different essential oils registered for use in California have achieved only marginal implementation according to PUR usage. As in the pyrethrin/pyrethroid story that began in the 1960s, natural products continue to serve as leads for new high-usage synthetics. For example, a unique intracellular calcium receptor class, discovered using the natural alkaloid ryanodine, has been used to develop the synthetic ryanoid insecticides chlorantraniliprole, cyantraniliprole and flubendiamide. Entering the California market in 2009, ryanoids achieved 350,000 kg of product usage in 2015. These trends underscore the importance of continuing the search for plant natural products with potent insecticidal activities, as they may lead to powerful synthetics with new modes of action in order to mitigate resistance to existing high-use pesticides.

Increasing population growth is estimated to reach at least 9 billion by 2050 will result in additional demand for food globally. Conventional animal protein sources including beef, pork, and chicken meat may be insufficient to meet this need, subsequently opening a door to alternative sources. Edible insects show great potential as an environmentally friendly choice for future food systems. There are several beneficial aspects of utilizing insects as a sustainable food source including their high nutritional content. Besides fats and proteins, insects are also an excellent source of vitamins and minerals. Insects have greater food conversion efficiency and produce lower greenhouse gas emissions (GHGEs), while requiring less water and land compared with their vertebrate counterparts in traditional animal husbandry. The consumption of insects therefore contributes positively to the environment, food and nutritional security, and a healthy life for present and future generations.

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Interest in, and research on, bioactivities of plant essential oils to insects has exploded in the past 15 years, according to a recent bibliometric analysis. However, commercial exploitation of this knowledge is being realized much more slowly although essential oil-based pesticides have begun to establish a market presence at least in the USA. The volatility of essential oils makes them especially suitable as fumigants in protected environments and for protection of stored products, but they also have demonstrated utility for protection of horticultural crops. Many essential oils and their major constituents, monoterpenes and sesquiterpenes, have contact toxicity to insects and mites, but their utility is broadened owing to their sublethal behavioral effects as deterrents and repellents. These bioactivities result from neurotoxicity of the terpenes, with at least two distinct mechanisms of action identified thus far. One intriguing aspect of the toxicity of some essential oils in insects is synergy among particular terpenes within an oil, thus enhancing bioactivity. Although many essential oils display bioactivity against insects when tested in the laboratory, only a few commodity oils – those used extensively in the flavor and fragrance industries – have been developed for use as pesticides. These include certain oils from the families Lamiaceae, Lauraceae, Myrtaceae, and Poaceae. Their potential as protectants for horticultural crops is discussed.190