Molecular and pharmacological analysis of an octopamine receptor from American cockroach and fruit fly in response to plant essential oils

Influence of molecular descriptors of plant volatilomics on fumigant action against the three major stored product beetle pests

Plant volatilomics such as essential oils (EOs) and volatile phytochemicals (PCs) are known as potential natural sources for the development of biofumigants as an alternative to conventional fumigant pesticides. This present work was aimed to evaluate the fumigant toxic effect of five selected EOs (cinnamon, garlic, lemon, orange, and peppermint) and PCs (citronellol, limonene, linalool, piperitone, and terpineol) against the Callosobruchus maculatus, Sitophilus oryzae, and Tribolium castaneum adults. Furthermore, for the estimation of the relationship between molecular descriptors and fumigant toxicity of plant volatiles, quantitative structural activity relationship (QSAR) models were developed using principal component analysis and multiple linear regression. Amongst the tested EOs, garlic EO was found to be the most toxic fumigant. The PCs toxicity analysis revealed that terpineol, limonene, linalool, and piperitone as potential fumigants to C. maculatus (< 20 µL/L air of LC50), limonene and piperitone as potential fumigants to T. castaneum (14.35 and 154.11 µL/L air of LC50, respectively), and linalool and piperitone as potential fumigants to S. oryzae (192.27 and 69.10 µL/L air of LC50, respectively). QSAR analysis demonstrated the role of various molecular descriptors of EOs and PCs on the fumigant toxicity in insect pest species. In specific, dipole and Randic index influence the toxicity in C. maculatus, molecular weight and maximal projection area influence the toxicity in S. oryzae, and boiling point and Dreiding energy influence the toxicity in T. castaneum. The present findings may provide insight of a new strategy to select effective EOs and/or PCs against stored product insect pests.

Design, Synthesis, and Biological Evaluation of Pyrido [1,2-α] Pyrimidinone Mesoionic Derivatives Bearing Propenylbenzene as the Vector Control Insecticide

A series of novel pyrido [1,2-α] pyrimidinone mesoionic derivatives bearing a propenylbenzene group at the 1-position were synthesized on the basis of the structure of mesoionic insecticides triflumezopyrim and dicloromezotiaz via a rationally conceived pharmacophore model and evaluated for their insecticidal activities against three insect vectors. The bioassay results showed that some compounds exerted remarkable insecticidal activities against M. domestica, Ae. albopictus, and B. germanica. Particularly, compound 26l displayed outstanding insecticidal activity against Ae. Albopictus, with an LC50 value of 0.45 μg/mL, far superior to that of imidacloprid (LC50 = 1.82 μg/mL) and equivalent to that of triflumezopyrim (0.35 μg/mL). Meanwhile, compound 34l presented a broad insecticidal spectrum, with LC50 values of 1.51 μg/g sugar, 0.52 μg/mL and 0.14 μg/adult, which were about 2.88, 3.50, and 1.50 times better than that of imidacloprid (LC50 = 4.35 μg/g sugar, 1.82 μg/mL and 0.21 μg/adult against M. domestica, Ae. albopictus, and B. germanica, respectively) and equivalent to that of triflumezopyrim against M. domestica (1.13 μg/g sugar) and Ae. albopictus (0.35 μg/mL) but lower than the potency against B. germanica (0.06 μg/g sugar). The molecular docking study by energy minimizations revealed that introducing propenylbenzene at the 1-position of compounds 26l and 34l could embed into the binding pocket of nicotinic acetylcholine receptors and form pi-alkyl interaction with LEU306. These results demonstrated that compounds 26l and 34l could be promising candidates for vector control insecticides, which deserved further investigation.

Bioactivities of thymol and p-cymene from the essential oil of Adenosma buchneroides against three stored-product insects

The adverse effects of relying solely on synthetic pesticides have become increasingly evident, leading many countries to explore alternatives sourced from plant-based green economies. Essential oil (EO) from stems and leaves of Adenosma buchneroides Bonati (A. buchneroides) was distilled by using hydrodistillation and subjected to gas chromatography-mass spectrometry (GC-MS) for component identification. Subsequently, EO as well as its main constituents (thymol and p-cymene) were tested for their insecticidal activity against the red flour beetle (Tribolium castaneum), the cigarette beetle (Lasioderma serricorne), and the booklouse (Liposcelis bostrychophila). The joint action of thymol and p-cymene produced an additive or synergistic effect. A. buchneroides essential oil (BHO) and the fixed ratio of the main compounds, thymol, and p-cymene both showed significant toxic activity against the target pests. This toxic effect is not simply the sum of individual effects, as it is influenced by various factors such as insect species and mode of action. These findings imply that the BHO and its phytoconstituents possess great potential to develop plant-derived biopesticides that will be safe for humans and the environment.

Plants and Their Derivatives as Promising Therapeutics for Sustainable Control of Honeybee (Apis mellifera) Pathogens

The most important pollinator for agricultural crops is the Western honeybee (Apis mellifera). During the winter and summer seasons, diseases and stresses of various kinds endanger honeybee numbers and production, resulting in expenses for beekeepers and detrimental effects on agriculture and ecosystems. Researchers are continually in search of therapies for honeybees using the resources of microbiology, molecular biology, and chemistry to combat diseases and improve the overall health of these important pollinating insects. Among the most investigated and most promising solutions are medicinal plants and their derivatives. The health of animals and their ability to fight disease can be supported by natural products (NPs) derived from living organisms such as plants and microbes. NPs contain substances that can reduce the effects of diseases by promoting immunity or directly suppressing pathogens, and parasites. This literature review summarises the advances that the scientific community has achieved over the years regarding veterinary treatments in beekeeping through the use of NPs. Their impact on the prevention and control of honeybee diseases is investigated both in trials that have been conducted in the laboratory and field studies.

Bio-molluscicidal potential and biochemical mechanisms of clove oil and its main component eugenol against the land snail, Theba pisana

The land snail, Theba pisana is a serious pest that adversely affects various crops in sustainable agriculture. Essential oils and their constituents represent an environmentally sound alternative to synthetic pesticides. Our study aimed to investigate the lethal and sub-lethal toxicity of clove oil and its main component eugenol to understand the mechanisms underlying its toxic action against T. pisana. The GC-MS profile of the clove oil composition was characterized. In the laboratory experiment, LD₅₀ of clove oil and eugenol via the contact testing were determined after 48 and 72 h. Moreover, sub-lethal effects of clove oil or eugenol on the survivors following the exposure of snails to the 25 and 50% of the LD₅₀/48 and 72 h were evaluated through using snail tissues for biochemical measurments. The GC-MS analysis showed that eugenol (64.87%) was the major constituent present in the oil. The results also showed that LD₅₀ values at 48 and 72 h were 2006.5 and 1493.5 μg/g b.w for oil and 239.6 and 195.3 μg/g b.w for eugenol, respectively. Compared to control, the sub-lethal effects of clove oil or eugenol at 48 and 72 h showed a significant increase in reduced glutathione (GSH) levels. Catalase (CAT) and glutathione-S-transferase (GST) activities significantly elevated in oil- or eugenol-treated snails, except at low dose after 48 h. After two exposure times, snails exposed to oil or eugenol at both sub-lethal effects had considerably higher γ-glutamyltransferase (γ-GT) and aspartate aminotransferase (AST) activities. Moreover, markedly augmentation in alkaline phosphatase (ALP) and alanine aminotransferase (ALT) activities at all exposure times, with the exception of snails treated with low dose of eugenol after 48 h was observed. Both clove oil and eugenol at the tested doses caused a significant inhibition in acetylcholinesterase (AChE) activity at two exposure times. Our findings highlight the potential of clove oil and eugenol, as an efficient natural molluscicide alternative to its synthetic counterparts for snail control.

In Vitro Efficacy of Terpenes from Essential Oils against Sarcoptes scabiei

The mite Sarcoptes scabiei is responsible for the emerging or re-emerging skin disease called scabies in humans and sarcoptic mange in animals. Essential oils represent an appealing alternative strategy for the control of Sarcoptes infections, but the commercial development of essential oils may be hampered by their inconsistency in efficacy due to their varied chemical compositions. In order to address this issue, we assessed the efficacy of six components (carvacrol, eugenol, geraniol, citral, terpinen-4-ol, and linalool) against S. scabiei. At a concentration of 0.5%, carvacrol presented the best miticidal efficacy, with a median lethal time (LT₅₀) value of 6.7 min, followed by eugenol (56.3 min), geraniol (1.8 h), citral (6.1 h), terpinen-4-ol (22.3 h), and linalool (39.9 h). The LC₅₀ values at 30 min for carvacrol, eugenol, and geraniol were 0.24, 0.79, and 0.91%, respectively. In conclusion, carvacrol, eugenol, and geraniol represent potential complementary or alternative agents for S. scabiei infections in humans or animals. Our study provides a scientific basis for the development of scabicidal products based on essential oils.

Essential Oils in Urban Insect Management-A Review

The allures of city life have culminated in the rise of urban populations resulting in conditions that promote the establishment of certain insect pests. Globally, the public health significance of these urban insect pests is enormous, ranging from billions of dollars to loss of lives. Most chemical insecticides no longer provide the anticipated level of control, and significant insecticide resistance has been reported. Therefore, there has been a spike in interest for alternatives to conventional insecticides. Among them, natural products from plants such as essential oils (EOs) and essential oil components (EOCs) have enjoyed the most attention owing to widespread reports of efficacy and toxicity even against insecticide-resistant urban insects. Yet, there is no comprehensive synthesis on the extent and impact of the management of urban insects using EOs or EOCs. Such a review is highly relevant since it provides a means to assess the extent of progress made, shortfalls, limitations, and prospects. More so, we hope it can be used to make informed decisions and develop relevant policies reliably. We present the ranges of insecticidal effects of EOs, EOCs, and commercially available EO-based products from laboratory and field studies. Finally, we discuss the gaps in our knowledge and prospects for the sustainable use of EOs.

Exploring the Antioxidant and Bioinsecticidal Activity of Spontaneous Flora Vegetal Extracts for Plant Protection and Prevention of Soil Contamination

The purpose of this article was to evaluate the application of different plant extracts with bioinsecticidal action and antioxidant activity for plants and soil protection, by substitution of the application of synthetically formulated pesticides with eco-friendly compounds. In this framework, this research focused on the utilization of plant extracts from the spontaneous flora of Moldova (Romania) as bioinsecticides for the control of field pests of the species Leptinotarsa decemlineata and their antioxidant activity. Plant extracts of oregano (Origanum vulgare), yarrow (Achillea millefolium), wormwood (Artemisia absinthium), and cowslip (Primula veris) were assessed for their antioxidant activity by the microplate spectrophotometric-based method (for polyphenols and flavonoids content and for 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenger activity) and were characterized by FTIR spectroscopy spectra. To evaluate the bioinsecticidal properties of the plant extracts, the mortality (%) and neuroleptic manifestations appearing in the middle of the monitoring period for larvae and adults of the Leptinotarsa decemlineata species were identified. Mortality (%) was statistically analyzed using a one-way analysis of variance (ANOVA) and the resulting experimental results were compared with the LSD-Fisher’s test (p < 0.05). The highest mortality (%) was observed after 24 h of treatment with extracts of Origanum vulgare at 100% concentration, while the maximum effect was recorded after 48 h for Origanum vulgare at 60% and 100% concentrations.

Essential Oil of Rosmarinus officinalis Ecotypes and Their Major Compounds: Insecticidal and Histological Assessment Against Drosophila suzukii and Their Impact on a Nontarget Parasitoid

Essential oils (EOs) produced by plants in the Lamiaceae family may provide new insecticidal molecules. Novel control compounds are needed to control Drosophila suzukii (Matsumura), a severe economic invasive pest of thin-skinned fruit crops. Thus, we characterized the main compounds of EOs from three rosemary Rosmarinus officinalis ecotypes (ECOs) and evaluated their toxicity to D. suzukii adults, deterrence of oviposition behavior, and histological alterations in larvae. Additionally, we analyzed the lethal and sublethal effect on the pupal parasitoid Trichopria anastrephae. The main compounds identified in the R. officinalis ECOs were α-pinene, camphor and 1,8-cineole. In bioassays via topical application or ingestion, ECOs and their major compounds showed high toxicity on D. suzukii adults and a lower concentration could kill 50% and 90% of flies compared to spinetoram. The dry residues of a-pinene, 1,8-cineole, and camphor provided a repellent effect by reducing D. suzukii oviposition by ~47% compared to untreated fruit. Histological sections of 3rd instar larval D. suzukii posttreatment revealed damage to the fat body, Malpighian tubules, brain, salivary gland, and midgut, which contributed to high larval and pupal mortality. Survival and parasitism by adult T. anastrephae were not affected. Thus, R. officinalis EO and their compounds have potential for developing novel insecticides to manage D. suzukii.

Chemical Composition and Insecticidal Properties of Moroccan Lavandula dentata and Lavandula stoechas Essential Oils Against Mediterranean Fruit Fly, Ceratitis capitata

The current study describes the chemical composition and insecticidal activities of the essential oils (EOs) extracted from Lavandula dentata L. and Lavandula stoechas L. against the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), a worldwide fruit pest. Gas chromatography (GC) and GC-mass spectrophotometry (GC-MS) analyses revealed that L. dentata oil contained camphor (50.8%), 1,8-cineole (6.6%), β-selinene (5%), and borneol (3.2%) as major components. On the other hand, L. stoechas EO was characterized by high contents of camphor (44%), camphene (14.8%), fenchone (9.1%), and 1-10-diepi-cubenol (4.6%). The toxic impact of EOs against C. capitata was evaluated through ingestion and contact methods. All of the EOs were toxic to C. capitata, and insect mortality was dose and time-dependent. In ingestion toxicity assays, L. dentata was the most toxic oil with an LC₅₀ (lethal concentration for 50% mortality) of 6.54% for males and 10.21% for females. Topical applications revealed that all the EOs had a good insecticidal activity at 24 h. The results of this study show that L. dentata and L. stoechas EOs may reduce the risks associated with the use of synthetic insecticides and may also be considered as a potent source for the production of botanical insecticides against C. capitata.

When Scent Becomes a Weapon—Plant Essential Oils as Potent Bioinsecticides

Crop protection still mostly relies on synthetic pesticides for crop pest control. However, the rationale for their continued use is shaded by the revealed adverse effects, such as relatively long environmental persistence that leads to water and soil contamination and retention of residues in food that brings high risks to human and animal health. As part of integrated pest management, biopesticides may provide crop protection, being eco-friendly and safe for humans and non-target organisms. Essential oils, complex mixtures of low-molecular-weight, highly volatile compounds, have been highlighted as major candidates for plant-derived bioinsecticides that are up to the sustainable biological standard. In this review, we screened the insecticidal activity of essential oils or their purified compounds, with focus given to their modes of action, along with the analyzed advantages and problems associated with their wider usage as plant-derived insecticides in agriculture.

Octopamine drives honeybee thermogenesis

In times of environmental change species have two options to survive: they either relocate to a new habitat or they adapt to the altered environment. Adaptation requires physiological plasticity and provides a selection benefit. In this regard, the Western honeybee (Apis mellifera) protrudes with its thermoregulatory capabilities, which enables a nearly worldwide distribution. Especially in the cold, shivering thermogenesis enables foraging as well as proper brood development and thus survival. In this study, we present octopamine signaling as a neurochemical prerequisite for honeybee thermogenesis: we were able to induce hypothermia by depleting octopamine in the flight muscles. Additionally, we could restore the ability to increase body temperature by administering octopamine. Thus, we conclude that octopamine signaling in the flight muscles is necessary for thermogenesis. Moreover, we show that these effects are mediated by β octopamine receptors. The significance of our results is highlighted by the fact the respective receptor genes underlie enormous selective pressure due to adaptation to cold climates. Finally, octopamine signaling in the service of thermogenesis might be a key strategy to survive in a changing environment.

Amino Alcohols from Eugenol as Potential Semisynthetic Insecticides: Chemical, Biological, and Computational Insights

A series of β-amino alcohols were prepared by the reaction of eugenol epoxide with aliphatic and aromatic amine nucleophiles. The synthesized compounds were fully characterized and evaluated as potential insecticides through the assessment of their biological activity against Sf9 insect cells, compared with a commercial synthetic pesticide (chlorpyrifos, CHPY). Three derivatives bearing a terminal benzene ring, either substituted or unsubstituted, were identified as the most potent molecules, two of them displaying higher toxicity to insect cells than CHPY. In addition, the most promising molecules were able to increase the activity of serine proteases (caspases) pivotal to apoptosis and were more toxic to insect cells than human cells. Structure-based inverted virtual screening and molecular dynamics simulations demonstrate that these molecules likely target acetylcholinesterase and/or the insect odorant-binding proteins and are able to form stable complexes with these proteins. Encapsulation assays in liposomes of DMPG and DPPC/DMPG (1:1) were performed for the most active compound, and high encapsulation efficiencies were obtained. A thermosensitive formulation was achieved with the compound release being more efficient at higher temperatures.

Assessment of lipid profile in fat body and eggs of Rhipicephalus microplus engorged females exposed to (E)-cinnamaldehyde and α-bisabolol, potential acaricide compounds

In the present study, the lipid profile from the fat body and eggs of Rhipicephalus microplus was evaluated after exposure of engorged females to (E)-cinnamaldehyde and α-bisabolol, substances which have acaricide potential according to the literature. Engorged females collected from artificially infested cattle were immersed in a concentration of 10.0 mg/mL of each substance. Dissection of the female fat bodies was performed at different times (72 h and 120 h), for subsequent lipid extraction. In addition, on the fifth day of oviposition, were collected 50.0 ml50.0 mL aliquots of the egg mass of each treatment to perform the same lipid extraction procedure. To assess the lipid profiles, the samples were submitted to the thin layer chromatography (TLC) and gas chromatography-mass spectrometry (GCMS) analysis. Furthermore, an in silico analysis was performed using PASS online® software to predict the possible molecular targets of (E)-cinnamaldehyde and α-bisabolol. As result, the main lipids identified from the fat body were triacylglycerides, fatty acids, and cholesterol, whereas, triacylglycerides (TAG), fatty acids (FA), and cholesterol (CHO) and cholesterol esters (CHOE), were identified in the eggs. The results also showed a significant increase (p < 0.05) of CHO in the fat body in the group exposed to (E)-cinnamaldehyde at 72 h (0.12 μg/fat body) and 120 h (0.46 μg/fat body), in the eggs from females treated with this same substance, there was a significant reduction (p < 0.05) in the amount of CHO (0.21 μg), compared to the water control group (0.45 μg). In the GCMS technique, 5 chemical classes were found, and variations were observed between these substances, mainly hydrocarbons and steroids, in the different groups, and (E)-cinnamaldehyde promoted the greatest changes. From the predictions of the in silico study, 38 and 20 targets were selected, respectively, which are mainly related to alterations in lipid metabolism, immune system and nervous system. This study provides the first report of changes in lipid metabolism of R. microplus exposed to (E)-cinnamaldehyde and α-bisabolol, as well as presenting possible activity on the molecular targets of these substances, expanding knowledge for the potential use of these compounds in the development of botanical acaricides.

Binary combinations of thymol, carvacrol and eugenol for Amblyomma sculptum control: Evaluation of in vitro synergism and effectiveness under semi-field conditions

This study aimed to investigate the in vitro acaricidal effect of thymol, carvacrol and eugenol (binary combinations) and their synergistic effect on unfed larvae and nymphs of Amblyomma sculptum, estimate the cost to prepare a formulation with these compounds, and evaluate the formulations under semi-field conditions against A. sculptum larvae. To evaluate the acaricidal effect of the compounds alone or their binary combinations (1:1 ratio) the larval packet test was performed using six concentrations (0.3125 to 10.0 mg/mL) for larvae and seven concentrations (2.5 to 20.0 mg/mL) for nymphs. The cost to produce 1 L of thymol, carvacrol and eugenol solutions, combined or alone, was estimated. In the semi-field test, formulations were sprayed on Panicum maximum plots experimentally infested with unfed A. sculptum larvae. In the in vitro tests with larvae, a synergistic effect (synergism and moderate synergism) was observed for thymol + eugenol at all concentrations tested, while thymol + carvacrol and eugenol + carvacrol showed a synergistic effect at the concentration of 5.0 mg/mL. In the in vitro tests with nymphs, thymol + eugenol, thymol + carvacrol and carvacrol + eugenol showed a synergistic effect (synergism and moderate synergism) at a concentration of 5.0 mg/mL and higher. Combining the compounds reduced the concentrations required to obtain mortality rate above 95%, resulting in lower costs. Under semi-field conditions, the treatments with thymol + eugenol and carvacrol + eugenol showed efficacies of 63.2% and 42.6%, respectively. We conclude that, depending on the concentrations, the binary combinations of thymol, carvacrol and eugenol have a synergistic acaricidal effect on unfed A. sculptum larvae and nymphs, and under semi-field conditions the associations between thymol + eugenol and carvacrol + eugenol were effective against A. sculptum larvae.

Plant-Derived Pesticides as an Alternative to Pest Management and Sustainable Agricultural Production: Prospects, Applications and Challenges

Pests and diseases are responsible for most of the losses related to agricultural crops, either in the field or in storage. Moreover, due to indiscriminate use of synthetic pesticides over the years, several issues have come along, such as pest resistance and contamination of important planet sources, such as water, air and soil. Therefore, in order to improve efficiency of crop production and reduce food crisis in a sustainable manner, while preserving consumer's health, plant-derived pesticides may be a green alternative to synthetic ones. They are cheap, biodegradable, ecofriendly and act by several mechanisms of action in a more specific way, suggesting that they are less of a hazard to humans and the environment. Natural plant products with bioactivity toward insects include several classes of molecules, for example: terpenes, flavonoids, alkaloids, polyphenols, cyanogenic glucosides, quinones, amides, aldehydes, thiophenes, amino acids, saccharides and polyketides (which is not an exhaustive list of insecticidal substances). In general, those compounds have important ecological activities in nature, such as: antifeedant, attractant, nematicide, fungicide, repellent, insecticide, insect growth regulator and allelopathic agents, acting as a promising source for novel pest control agents or biopesticides. However, several factors appear to limit their commercialization. In this critical review, a compilation of plant-derived metabolites, along with their corresponding toxicology and mechanisms of action, will be approached, as well as the different strategies developed in order to meet the required commercial standards through more efficient methods.

The potential of Apiaceae species as sources of singular phytochemicals and plant-based pesticides

The Apiaceae Lindl. (=Umbelliferae Juss.), which includes several economical important vegetables, herbs, and spices, is one of the most numerous plant family. Umbelliferous crops (namely anise, fennel, carrot, coriander, parsley, etc.) are also valuable sources of botanical flavoring agents and fragrances. In addition, Apiaceae species yield a wide variety of distinctive specialized metabolites (i.e, volatile phenylpropanoids, furanocoumarins, sesquiterpene coumarins, polyacetylenes, and phthalides), some of them been described as uncommon natural phytochemicals exclusive of the family, which offers a great potential for bioprospection. Numerous studies have pointed out the outstanding biological activity of extracts and several classes of phytochemicals from Apiaceae species. Emphasis has been given to essential oils (EOs) and their constituents activities, most likely because this type of plant added value product benefits from a larger acceptance and application potential in integrated pest management (IPM) and integrated vector management (IVM) programs. Several species of the family offer a variety of unique compounds with great potential as biopesticidal and/or synergizing agents. Investigations covering their activity toward agricultural pests and phytopathogens have increased in the last years, nevertheless the interest remains strongly focus on arthropod species, predominantly those acting as vectors of human diseases. From our survey, it is patent the gap of knowledge concerning the potential molluscicidal properties of Apiaceae extracts/phytochemicals, as well as their herbicidal activities against invasive plant species. In this review, we propose to highlight the potential of Apiaceae species as suitable sources of bioactive phytochemicals with great relevance within the frame of plant-based pesticides R&D, and will discuss their applicability in real-world scenarios considering the recent developments regarding the design of stable formulations incorporating Apiaceae bioactive products. We expect that this review will encourage researchers to consider undervalued Apiaceae species as alternative sources of bioactive compounds and will give a contribute to the field by suggesting new research topics.

Control of red flour beetle (Tribolium castaneum) in feeds and commercial poultry diets via using a blend of clove and lemongrass extracts

The insects' infestation decreases the nutritive value of the stored grains and causes losses in its weight, quality, or economic values. The aim of the present study was to investigate the efficiency of a natural product of clove and lemongrass extracts in controlling of red flour beetle (Tribolium castaneum) in different feedstuffs and commercial poultry diets. Different concentrations of the tested product (5, 10, 20, 50, 100 mg) were mixed with 10 g of different feedstuffs and poultry diets, and incubated at different time points. The percent repellency (PR), toxicity effect, and antifeedant activity of the plant extracts compound were assessed. The PR was detected depending on the choice method. It was found that the PR was dose and time dependent. The highest doses (50 or 100 mg/10 g feed) achieved the highest repellency effect reaching 70% at 24 h post-application (PA). The minimal PR was reported by the lowest dose of 5 mg/10 g feed reaching 50% at 24 h PA. Moreover, the PR was found to decrease by time. The toxicity effect of this natural product on T. castaneum was cumulative, not acute, in which it was recorded after 1 month of application. Besides, this effect needs high doses of the product (at dose 500 or 1000 mg/50 g feed). The used product achieved a clear antifeedant activity against T. castaneum, as the feeding deterrent index (FDI %) for corn grains was 98.5% at 1.0 and 2.0% concentration, whereas for wheat grains there was a significant difference between both concentration (96.0 vs. 74.4%). In addition, the weight loss of control corn and wheat grains was higher than the treated ones, and it was about 3.15% and 2.0% per month for corn and wheat, respectively. In conclusion, the clove and lemongrass extracts had a repellency effect reaching to 70%. Moreover, it had a lethal effect on T. castaneum. In addition, it can reduce the weight loss of the infested feeds and consequently increasing its FDI %. Therefore, the clove and lemongrass extract blend can be used to protect the feedstuffs from the damage by this insect.

Monoterpenes alter TAR1-driven physiology in Drosophila species

Monoterpenes are molecules with insecticide properties whose mechanism of action is, however, not completely elucidated. Furthermore, they seem to be able to modulate the monoaminergic system and several behavioural aspects in insects. In particular, tyramine (TA) and octopamine (OA) and their associated receptors orchestrate physiological processes such as feeding, locomotion and metabolism. Here, we show that monoterpenes not only act as biopesticides in Drosophila species but also can cause complex behavioural alterations that require functional type 1 tyramine receptors (TAR1s). Variations in metabolic traits as well as locomotory activity were evaluated in both Drosophila suzukii and Drosophila melanogaster after treatment with three monoterpenes. A TAR1-defective D. melanogaster strain (TAR1PL00408) was used to better understand the relationships between the receptor and monoterpene-related behavioural changes. Immunohistochemistry analysis revealed that, in the D. melanogaster brain, TAR1 appeared to be mainly expressed in the pars intercerebralis, lateral horn, olfactory and optic lobes and suboesophageal ganglion lobes. In comparison to wild-type D. melanogaster, the TAR1PL00408 flies showed a phenotype characterized by higher triglyceride levels and food intake as well as lower locomotory activity. The monoterpenes, tested at sublethal concentrations, were able to induce a downregulation of the TAR1 coding gene in both Drosophila species. Furthermore, monoterpenes also altered the behaviour in wild-type D. suzukii and D. melanogaster 24 h after continuous monoterpene exposure. Interestingly, they were ineffective in modifying the physiological performance of TAR1-defective flies. In conclusion, it appears that monoterpenes not only act as biopesticides for Drosophila but also can interfere with Drosophila behaviour and metabolism in a TAR1-dependent fashion.

Toxicity and physiological effects of ajwain (Carum copticum, Apiaceae) essential oil and its major constituents against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

The effects of Ajwain essential oil and its major constituents were investigated against newly fourth instar larvae of Tuta absoluta, a major pest of tomato cropping in Iran and other parts of the world. The study included individual efficacy of each compound and determination of their synergistic or antagonistic efficacy. We also determined the activities of detoxifying enzymes in treated insects. According to the results, the Ajwain essential oil and thymol showed the highest toxicity against T. absoluta larvae (LC₅₀ = 6.14 and 7.72 μL/mL, respectively, and LC₃₀ = 3.05 and 3.57 μL/mL, respectively). The ɤ-terpinene and p-cymene had lesser toxicity compared to other compounds. The larvicidal potency increased by binary mixtures of active constituents, such as thymol + p-cymene and thymol + ɤ-terpinene. On the other hand, ɤ-terpinene + p-cymene mixture demonstrated antagonistic effect on the larvae. The esterases and glutathione S-transferases were significantly increased in all treatments. Finally, our results revealed a significant inhibition of AChE activity in the treated larvae by all treatments except for ɤ-terpinene + p-cymene. In vitro experiments representing AChE inhibition with IC₅₀ values were recorded 0.370, 0.457, 0.528, 1.094 and 1.323 μL/mL for thymol + p-cymene, thymol + ɤ-terpinene, thymol, ɤ-terpinene and p-cymene, respectively. Thymol demonstrated significant potential as a controlling agent of T. absoluta larvae, both larvicidal, compatible with other compounds with strong AChE inhibition properties. These finding could pave the way for development of new botanicals based on EO constituents which should be completed with preparation of an efficient formulation and field trials.

Insecticidal activity of the essential oil of Perovskia artemisioides Boiss

This work reports the phytochemical profile and insecticidal properties of Perovskia artemisioides Boiss essential oil (PAEO) collected in Baluchestan, Iran. Totally, twenty-six substances were identified with 1,8-cineole (25.81%), geranyl acetate (13.00%) and linalool (10.21%) as dominant chemical metabolites by GC-MS analysis. PAEO possessed fumigant toxicity against various growth stages of Phthorimaea operculella. P. operculella adults showed considerable sensitivity (LC₅₀ = 0.58 µL/L air) in comparison to eggs (LC₅₀ = 5.87 µL/L air) and neonate larvae (LC₅₀ = 1.23 µL/L air). Finally, molecular docking of major components of PAEO was performed against detoxification enzymes, including cytochrome P450 and glutathione S-transferase activities. Humulene, β-caryophyllene, and α-cadinol exhibited the most interactions with the P450 and GST. It can be concluded that PAEO has the potential for development into natural insecticides for the control of storage pests.

Deterrent Effects of Essential Oils on Spotted-Wing Drosophila (Drosophila suzukii): Implications for Organic Management in Berry Crops

Simple Summary

Spotted-wing drosophila (Drosophila suzukii Matsumura; SWD) poses a significant threat to small fruit production world-wide. Though frequent applications of insecticides is the dominant strategy to manage this pest, insecticide resistance is a concern. Resistance has already been reported for one of the only consistently effective insecticides labeled for organic production systems, spinosad, underscoring the need to diversify management strategies. Botanical products, such as essential oils, contain volatile organic compounds (VOCs) which could interfere with SWD preference for or ability to locate host fruit. We conducted laboratory and field studies to determine the efficacy of botanical products (lavender oil, catnip oil, KeyPlex Ecotrol^® PLUS, and KeyPlex Sporan^® EC²) on preventing SWD infestation in raspberry and blueberry crops. Under laboratory conditions lavender oil, Ecotrol, and Sporan deterred SWD from diet. In the field trials, Ecotrol deterred SWD from raspberries; however, no differences were seen in blueberry infestation. To optimize essential oil deterrents for SWD, such as how to maintain effective concentrations for longer periods of time, further research is needed. Botanical deterrents represent a promising alternative pest management strategy that could be implemented without additional equipment investment from growers, while decreasing the use of broad-spectrum insecticides.

Abstract

Due to concerns about frequent applications of spinosad and other broad spectrum insecticides for managing spotted-wing drosophila (Drosophila suzukii Matsumura, SWD), we investigated the use of essential oils as an alternative to current insecticides. Essential oils from a number of plant species have been studied for their attraction and deterrence of SWD. However, these botanical products have not been thoroughly tested in the field. We conducted laboratory and field studies to determine the efficacy of botanical products, including lavender (Lavandula angustifolia Mill.) oil, catnip (Nepeta cataria L.) oil, KeyPlex Ecotrol^® PLUS, and KeyPlex Sporan^® EC² on preventing SWD infestation in raspberry (Rubus idaeus L.) and blueberry (Vacciniumcorymbosum L.) crops. In a two-choice laboratory bioassay, lavender oil, Ecotrol, and Sporan treatments deterred SWD from a yeast-cornmeal-sugar based fly diet. In the field trials, raspberry fruit treated with Ecotrol had lower SWD infestation (6%), compared to the control (17%), and was comparable to spinosad (6%). No differences were seen in blueberry infestation. The combination of essential oils in Ecotrol may work to decrease SWD fruit infestation under certain conditions in the field, however more research is needed on the longevity of these products.

Volatile Essential Oils Can Be Used to Improve the Efficacy of Heat Treatments Targeting the Western Drywood Termite: Evidence from a Laboratory Study

Use of heated air to create lethal temperatures within infested wood serves as a nonchemical treatment option against western drywood termites, Incisitermes minor (Hagen). When treating a whole or large portion of the structure, however, the presence of hard-to-heat areas (structural heat sinks) and potential risk of damaging heat-sensitive items are recognized as important challenges. To address these challenges, we tested if the incorporation of a volatile essential oil would increase the overall efficacy of heat treatments against the drywood termites. To choose an essential oil for use, we tested the volatile action of several candidate compounds against individual termites using a fumigant toxicity assay. As a proof-of-concept experiment, field-collected termites were housed in small wooden arenas and subsequently subjected to 2-h heat treatment at various air temperatures within a gas chromatography oven. A simulated heat sink and essential oil treatment was also included in the experimental design. Analyses of lethal temperatures (LTemp50 and LTemp99 values), probabilities of mortality, and survivorship data over time suggested that 1) the presence of a heat sink significantly increased the minimum air temperature needed for complete kill of the termites and 2) the volatile essential oil added at the site of a heat sink effectively counteracted the impact of the heat sink. The use of volatile essential oils makes it possible to effectively kill drywood termites even in areas which might not reach lethal temperatures (~50°C), potentially improving the overall efficacy of heat treatments while reducing the risk of heat damage.

Comparison of sublethal effects of natural acaricides carvacrol and thymol on honeybees

The parasitic mite Varroa destructor is a threat to beekeeping colonies. Among naturally derived acaricides, the monoterpenoid essential oil compound thymol is used in beekeeping for varroa mite control, but adverse impacts on honeybees has been already documented. Carvacrol, another monoterpenoid, also has a high acaricidal potential and could thus be promising for regular use in beekeeping, but information is scarce regarding the effects of prolonged systemic administration of carvacrol on honeybees. In this study, we evaluate and compared the sublethal effects of long term consumption of carvacrol and thymol on Carnolian honeybee workers (Apis mellifera carnica). Survival and feeding rate were determined preliminary to assess sublethal concentrations. The sublethal effects were analysed by the activity of the acetylcholinesterase (AChE), enzyme involved in the control of neurotransmission, and the activity of detoxifying enzyme glutathione S-transferase (GST) in heads and thoraces. We found that, thymol and carvacrol, caused mortality only at the highest concentrations tested, 1% and 5% respectively. As demonstrated by others, both substances could be effective against varroa at concentrations ten times lower than those causing significant honeybee mortality. However, we demonstrated sublethal effects at the 0.05% carvacrol and thymol exposure concentrations evidenced as increased activity of AChE and GST in the honeybee heads. In conclusion, prolonged treatment with thymol and carvacrol affects bee nervous system and induce detoxification processes possibly resulting in a limited use for acaricidal purposes. We postulate that under the same chronic exposure conditions carvacrol and thymol will have similar sublethal effects on honeybees.

Disentangling the ecotoxicological selectivity of clove essential oil against aphids and non-target ladybeetles

The plant-based biopesticides have been proposed as insect pest control tools that seem to be safer for the environment and human health when compared to synthetic conventional molecules. However, such assumptions are generally made without considering the absence of detrimental effects on sublethally-exposed non-target organisms or showing the physiological basis of the selective action of such botanical products. Thus, by using in silico-based and in vivo toxicological approaches, the present investigation aimed to disentangle the ecotoxicological selectivity of clove, Syzygium aromaticum, essential oil against the aphid Rhopalosiphum maidis and the non-target ladybeetle, Coleomegilla maculata. We also investigated whether the sublethal exposure to clove essential oil would affect the locomotory and predatory abilities of C. maculata. We found that the clove essential oil concentration estimated to kill 95% (LC₉₅: 0.17 μL/cm²) of the aphids was lethal to <18% of C. maculata. Indeed, our in silico results reinforced such differential susceptibility, as it predicted that eugenol and β-caryophyllene (i.e., the clove essential oil major components) bound to three potential molecular targets (i.e., transient receptor potential (TRP) channels, octopamine, and gamma-aminobutyric acid (GABA) receptors) of the aphids but only to the octopamine receptors of the ladybeetles. Additionally, the ladybeetles that were exposure to the clove essential oil exhibited unaffected abilities to locomote and to prey upon R. maidis aphids when compared to unexposed ladybeetles. Thus, by displaying lower toxicity against the ladybeetles, the clove essential oil represents a safer alternative tool to be integrated into programs aiming to manage aphid infestations.

Rubio R, Coviella C, Santo Orihuela PL, Vassena CV, Lucia A. Surfactantless Emulsions Containing Eugenol for Imidacloprid Solubilization: Physicochemical Characterization and Toxicity against Insecticide-Resistant Cimex lectularius

Synthetic insecticides have been used for a long time as one of the most effective tools for insect pest control. However, the re-emergence of insect pests and their fast development of resistance, as has occurred for pyrethroid-resistant bed bugs Cimex lectularius L., make it necessary to develop new and safe strategies for effective pest control. This has fostered the research on new eco-sustainable formulations based on essential oils, which allows reducing the impact associated with the intensive use of synthetic insecticides on the environment and their effects on human health. This research explores the stability of water/eugenol/ethanol surfactantless emulsions loaded with imidacloprid (0.003 wt%), and their toxicity against a resistant bed bug strain. The results have shown that these emulsions enable the solubilization of a poorly water-soluble drug, such as the imidacloprid, without any significant modification of their stability. Furthermore, the application of the obtained formulations against the pyrethroid-resistant bed bug results in mortality in the 50-85% range upon topical and spray applications, with the increase of the eugenol content enhancing the effectiveness of the formulations. It may be expected that the ternary water/eugenol/ethanol mixtures could be further developed in the preparation of ready to use formulations, enabling the dispersion of insecticides for pest control.

Modulation of Drosophila suzukii type 1 tyramine receptor (DsTAR1) by monoterpenes: a potential new target for next generation biopesticides

This study proposes a biochemical and molecular model for the interaction between the Drosophila suzukii type 1 tyramine receptor (DsTAR1) and monoterpenes. A preliminary molecular and functional characterization of DsTAR1 cDNA revealed that a 1.8 kb long ORF codes for a 600 amino acid polypeptide featuring seven transmembrane domains, as expected for a GPCR. A stable HEK 293 cell line expressing DsTAR1 was tested for responsiveness to tyramine (TA) and octopamine (OA). In intracellular calcium mobilization studies, TA led to a concentration-dependent increase in [Ca²⁺]_i (pEC₅₀ ~ 6.40), completely abolished by pre-incubation with the antagonist yohimbine 1 μM. Besides, in dynamic mass redistribution (DMR) studies, TA evoked a positive DMR signal in a concentration-dependent manner (pEC₅₀ ~ 6.80). The recombinant cell line was then used to test three monoterpenes (thymol, carvacrol and α-terpineol) as putative ligands for DsTAR1. The terpenoids showed no agonist effects in both DMR and calcium mobilization assays, but they increased the potency of the endogenous ligand, TA, acting as positive allosteric modulators. Moreover, expression analysis on adults D. suzukii, exposed for 24, 72 or 120 h to a sublethal concentration of the three monoterpenes, showed a downregulation of DsTAR1. This evidence has led to hypothesize that the downregulation of DsTAR1 might be a compensatory mechanism in response to the positive allosteric modulation of the receptor induced by monoterpenes. Therefore, these findings might be useful for the development of a new generation of biopesticides against Drosophila suzukii, targeting TAR1.

Topical Toxicity Profiles of Some Aliphatic and Aromatic Essential Oil Components Against Insecticide-Susceptible and Resistant Strains of German Cockroach (Blattodea: Ectobiidae)

Toxicity profiles of four aliphatic (α-pinene, cyclononanone, limonene, nerolidol), four aromatic (β-thujaplicin, carvacrol, eugenol, tropolone) essential oil components (EOCs), and permethrin were investigated against three strains of German cockroach, Blattella germanica (L.). The strains include a susceptible strain (S), and two multi-resistant strains - strains D and E. Also, a synergism bioassay, using piperonyl butoxide (PBO) was conducted. The most toxic EOCs were aromatic EOCs carvacrol, eugenol, and tropolone, followed by aliphatic EOC limonene; all had LD50 values of <0.7 mg/µl. Four of the EOCs were equally toxic against all the strains, with carvacrol being the most toxic, followed by eugenol, tropolone, and α-pinene. The other four EOCs were more toxic against strain S than against the two resistant strains. Permethrin was significantly more toxic to strain S (LD50 = 0.056 µg/µl) compared with the resistant strains (D = 2.138 µg/µl, E = 1.730 µg/µl). Toxicity of aliphatic EOCs correlated positively with their molecular weight against strain E only, whereas both molecular weight and vapor pressure of aromatic EOCs correlated significantly with toxicity in all strains. Strain D exhibited the greatest resistance (RR of 6.7) to EOCs, and synergism to the aliphatic EOC cyclononanone. Clear synergism with PBO was observed in permethrin against resistant strains, but not in all of the EOCs, suggesting multiple resistance mechanisms in the resistant cockroaches. These findings give insight on the potential of EOCs to be incorporated as parts of an IPM approach to managing insecticide resistant German cockroaches.

Ultrasound assisted formation of essential oil nanoemulsions: Emerging alternative for Culex pipiens pipiens Say (Diptera: Culicidae) and Plodia interpunctella Hübner (Lepidoptera: Pyralidae) management

Over the last years, nanotechnology has contributed to the development of new botanical insecticides formulations based on essential oils (EO), which are safe for the human health and the environment. Nanoemulsions (NEs) can enhance the bioactivity of the EO to prevent the premature volatility and degradation of the active ingredients. In our work, geranium EO (Geranium maculatum L.) was used to develop micro and nanoemulsions adding Tween 80 as surfactant. For NEs formulation, ultrasound was applied and the physicochemical and ultrasound parameters were optimized: oil: surfactant ratio = 1:2, ultrasound power = 65 W, sonication time = 2 min, cycles = 30 on/20 off and ultrasonic probe distance = 3.7 cm. The NEs obtained had 13.58 nm and polydisperse index (PDI) values of 0.069. They were stored at 25 °C and were stable for 60 days. The present study also demonstrated the potential of NEs to enhance the toxicity of geranium EO against larvae of Culex pipiens pipiens (EO LC₅₀ = 80.97 ppm, NEs LC₅₀ = 48.27 ppm) and Plodia interpunctella (EO + β-cypermethrin LD₅₀ = 0.16 μg larvae^-1, NEs + β-cypermethrin LD₅₀ = 0.07 μg larvae^-1). Overall, our findings pointed out that NEs can increase twofold the insecticidal efficacy of EO, and thus, they can be considered further for the development of botanical insecticides.

The Octopamine Receptor Is a Possible Target for Eugenol-Induced Hyperactivity in the Blood-Sucking Bug Triatoma infestans (Hemiptera: Reduviidae)

Eugenol is a major component of the essential oils in cloves and other aromatic plants. In insects, it produces toxic effects and repellency, and there is evidence that its site of action is the octopamine receptor. The objective of the present study was to explore whether the octopamine receptor is involved in the hyperactivity produced by eugenol in the blood-sucking bug Triatoma infestans (Klug). This insect is the main vector of Chagas disease in Latin America. Four treatments were topically applied on third instar nymphs: 1) octopamine, 2) eugenol, 3) phentolamine hydrochloride (an antagonist of the octopamine receptor) followed by octopamine, and 4) phentolamine hydrochloride followed by eugenol. Both octopamine and eugenol hyperactivated the nymphs. However, pretreatment with phentolamine hydrochloride inhibited the hyperactivating effect of both compounds. These results are in agreement with previous works on Drosophila melanogaster (Meigen) (Diptera: Drosophilidae) and the American cockroach. They suggest that the octopamine receptor is a possible site of action for eugenol.

In vitro acaricidal activity of essential oil and alcoholic extract of Trachyspermum ammi against Dermanyssus gallinae

This study aimed to assess in vitro acaricidal activity of essential oil (EO) and alcoholic extracts (AE) of Ajowan against D. gallinae. Using contact and spraying bioassays, different doses of EO and AE were tested. Cypermethrin and thymol (positive controls), and ethanol and distilled water (negative controls) were also tested. The results indicated that effects were method and dose dependent. Statistical analysis showed a highly significant difference for contact and spraying bioassays and various doses of EO and AE (p < 0.0001) as, the spraying method was more effective than the contact method for acaricidal activity at 24 h post treatment (PT). In this method, Cypermethrin, EO and thymol caused over 90 % mite mortality at 50 μgcm^-2, while AE caused this rate at 150 μgcm^-2. In the contact bioassay, all tests produced low mortality rates except for Cypermethrin. Thymol was the main constituent of EO (Area = 42.26 %) and AE (Area = 45.8 %). Results of the present study indicated that Ajowan had a satisfactory acaricidal effect against D. gallinae in vitro. It was also found that the spraying method could be used to control the D. gallinae as the most appropriate method.

An Overview of Micro- and Nanoemulsions as Vehicles for Essential Oils: Formulation, Preparation and Stability

The interest around essential oils is constantly increasing thanks to their biological properties exploitable in several fields, from pharmaceuticals to food and agriculture. However, their widespread use and marketing are still restricted due to their poor physico-chemical properties; i.e., high volatility, thermal decomposition, low water solubility, and stability issues. At the moment, the most suitable approach to overcome such limitations is based on the development of proper formulation strategies. One of the approaches suggested to achieve this goal is the so-called encapsulation process through the preparation of aqueous nano-dispersions. Among them, micro- and nanoemulsions are the most studied thanks to the ease of formulation, handling and to their manufacturing costs. In this direction, this review intends to offer an overview of the formulation, preparation and stability parameters of micro- and nanoemulsions. Specifically, recent literature has been examined in order to define the most common practices adopted (materials and fabrication methods), highlighting their suitability and effectiveness. Finally, relevant points related to formulations, such as optimization, characterization, stability and safety, not deeply studied or clarified yet, were discussed.

Essential oil from Negramina (Siparuna guianensis) plants controls aphids without impairing survival and predatory abilities of non-target ladybeetles

Plant essential oils are regarded as interesting alternative tools to be integrated into the management of pest insects. However, as they generally consist of mixtures of numerous molecules, the physiological basis for their action is unresolved. Here, we evaluated the effects of essential oil of the Neotropical plant Siparuna guianensis Aubl., commonly known as Negramina, against an important pest insect: the green peach aphid Myzus persicae (Sulzer), and also in two non-target natural enemies: the ladybeetle predators Coleomegilla maculata (DeGeer) and Eriopis connexa (Germar). In addition, we conducted a computational docking analysis for predicting the physical interactions between the two Negramina essential oil major constituents: β-myrcene and 2-undocanone, and the transient receptor potential (TRP) channels as potential binding receptors in the aphid and ladybeetles. As the most important results, Negramina essential oil caused mortality in M. persicae aphids with an LC₉₅ = 1.08 mg/cm², and also significantly repelled the aphids at concentrations as low as 0.14 mg/cm². Our computational docking analysis reinforced such selectivity actions as the Negramina essential oil major compounds (i.e., β-myrcene and 2-undocanone) bound to the TRP channels of M. persicae but not to ladybeetle-related TRP channels. Interestingly, the exposure to the Negramina essential oil did not affect the predatory abilities of C. maculata but increased the abilities of E. connexa to prey upon M. persicae. Collectively, our findings provided a physiological basis for the insecticidal and selectivity potential of Negramina essential oil, reinforcing its potential as a tool to be used in integrated pest control programs.

Insecticidal Activity of Compounds of Plant Origin on Mahanarva spectabilis (Hemiptera: Cercopidae)

The damage caused by spittlebugs varies according to the species of grass, and the losses can reach alarming levels. Measures for population control are currently restricted to the use of resistant grasses and the diversification of pastures. Therefore, alternative control measures are necessary, such as the use of botanical insecticides. The aim of this study was to evaluate the insecticidal activities of thymol, carvacrol, eugenol, cinnamaldehyde, and trans-anethole on Mahanarva spectabilis eggs, nymphs, and adults under laboratory conditions. In the egg tests, treatments with eugenol, carvacrol, and thymol showed the highest mortalities, presenting efficiencies higher than 85% after 48 h of application. In the nymph tests, the treatments with thymol and carvacrol at 2.5% and eugenol at 2.0% and 2.5% showed intermediate efficiencies, with values above 61%. The highest mortality was observed in the treatment with trans-anethole at 2.5%, with an efficiency of 95%. In the tests with adults, only treatment with trans-anethole at 2.5% obtained an efficiency reaching 90%; in the other treatments, the efficiency did not exceed 51%. These results showed that, at these concentrations, trans-anethole presents a high rate of insecticidal activity on M. spectabilis nymphs and adults and, therefore, is recommended as a potential natural insecticide for the control of this pest.

Climatic Conditions: Conventional and Nanotechnology-Based Methods for the Control of Mosquito Vectors Causing Human Health Issues

Climate variability is highly impacting on mosquito-borne diseases causing malaria and dengue fever across the globe. Seasonal variability change in temperature and rainfall patterns are impacting on human health. Mosquitoes cause diseases like dengue fever, yellow fever, malaria, Chikungunya, West Nile and Japanese encephalitis. According to estimations by health organizations, annually one million human deaths are caused by vector-borne diseases, and dengue fever has increased about 30-fold over the past 50 years. Similarly, over 200 million cases of malaria are being reported annually. Mosquito-borne diseases are sensitive to temperature, humidity and seasonal variability. Both conventional (environmental, chemical, mechanical, biological etc.) and nanotechnology-based (Liposomes, nano-suspensions and polymer-based nanoparticles) approaches are used for the eradication of Malaria and dengue fever. Now green approaches are used to eradicate mosquitoes to save human health without harming the environment. In this review, the impact of climatic conditions on mosquito-borne diseases along with conventional and nanotechnology-based approaches used for controlling malaria and dengue fever have been discussed. Important recommendations have been made for people to stay healthy.

Essential oils disrupt steroidogenesis in a feto-placental co-culture model

We determined whether 5 common essential oils (basil, fennel seed, orange, black pepper and sage) interfered with feto-placental steroidogenesis in a co-culture model composed of fetal-like adrenocortical (H295R) and placental trophoblast-like (BeWo) cells. After a 24 h exposure, only basil and fennel seed oil significantly increased hormone concentrations of estradiol, estrone, dehydroepiandrosterone (DHEA), androstenedione, progesterone, and estriol. Basil and fennel seed oil were shown to significantly alter the expression of steroidogenic enzymes involved in cholesterol transport and steroid hormone biosynthesis, including StAR, CYP11A1, 3β-HSD1/2, SULT2A1, and HSD17β1, -4, and -5. Also, basil and fennel seed oil stimulated placental-specific promoter I.1 and pII-derived CYP19 mRNA in BeWo and H295R cells, respectively, as well as, increased CYP19 enzyme activity. Our results indicate that further study is necessary to determine the potential risks of using basil and fennel seed oils during pregnancy considering their potential to disrupt steroidogenic enzyme activity and expression in vitro.

Prolonged mosquitocidal activity of Siparuna guianensis essential oil encapsulated in chitosan nanoparticles

Background

The use of synthetic insecticides is one of the most common strategies for controlling disease vectors such as mosquitos. However, their overuse can result in serious risks to human health, to the environment, as well as to the selection of insecticidal resistant insect strains. The development of efficient and eco-friendly insect control is urgent, and essential oils have been presented as potential alternatives to synthetic insecticides. Moreover, nanoencapsulation techniques can enhance their efficiency by protecting from degradation and providing a controlled release rate.

Results

We assessed the potential of chitosan nanoparticles in encapsulating Siparuna guianensis essential oil, and maintaining its efficiency and prolonging its activity for the control of Aedes aegypti larvae. The encapsulation was characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), with an encapsulation efficiency ranging from 84.8% to 88.0%. Toxicity studies have demonstrated efficacy against mosquito larvae over 50% for 19 days with 100% mortality during the first week. This persistent action is presumably due to the enhanced contact and slow and maintained release conferred by chitosan nanoparticles. Furthermore, the exposure of aquatic non-target organisms (e.g. embryos and small adult fishes) revealed adequate selectivity of these nanoparticles.

Conclusions

The encapsulation of S. guianensis essential oil in chitosan nanoparticles showed promising potential as a larvicide control alternative and should be considered within strategies for fighting Ae. aegypti.

Numerous outbreaks of infectious diseases such as dengue, zika, and chikungunya in tropical countries have occurred where the mosquito Aedes aegypti is the transmitting vector. In Brazil, these infections are responsible for deaths and severe sequelae. Thus, many efforts have been made by governmental and research groups to control these outbreaks. However, complete success in this control has so far remained unachieved. Parallel to the need to develop new technologies that contribute to the control of insects that transmit diseases, there is a growing societal awareness regarding the risks associated with the use of synthetic insecticides, which has led to a search for natural alternatives such as essential oils from plants. Thus, our group conducted experiments to evaluate the application of nanotechnology in obtaining an efficient prolonged release system to combat Ae. aegypti larvae using the essential oil of a plant native to the Cerrado and Amazonian forests. These results demonstrate that using a simple and easily scalable encapsulation technique; it is possible to keep the low toxicity against non-target organism and prolong the activity of an essential oil in water and maintain larval mortality at a significant level for more than a week with a single application.

The unusual action of essential oil component, menthol, in potentiating the effect of the carbamate insecticide, bendiocarb

Standard chemical insecticides present mainly neurotoxic effects and are becoming less and less effective due to insects developing resistance to them. One of the innovative strategies to control insects pests is to find a way to increase the sensitivity of the target sites in the insect nervous system to the applied insecticides. In the presented research, we proposed menthol, a component of essential oils, as a factor increasing the effectiveness of bendiocarb, a carbamate insecticide. The aim of our study was to evaluate the potentiation of the bendiocarb effect by menthol. In toxicity tests performed on Periplaneta americana, menthol (0.1 μM) accelerated the lethal effect of bendiocarb, primarily in its low concentrations (lower than 0.05 mM). In the presence of menthol (1 and 0.1 μM), the ability of insects to turn back from its dorsal to the normal ventral side was significantly lower than with bendiocarb (1 μM) alone. We also evaluated the effectiveness of chemicals on the activity of the ventral nerve cord of the cockroach. In this preparation, bendiocarb (1 μM and higher concentrations) caused an irregular, spontaneous bursts of action potentials. The total nerve activity (including the response to stimulation and spontaneous firing) was much higher when bendiocarb was applied in the presence of menthol (1 μM). The effect of menthol was similar to the octopamine effect and was abolished by phentolamine, the octopamine receptor antagonist. Our results clearly indicated a strengthening effect of menthol on bendiocarb effectiveness; potentiation occurred through octopamine receptors activation.

Insecticidal Properties of Ocimum basilicum and Cymbopogon winterianus against Acanthoscelides obtectus, Insect Pest of the Common Bean (Phaseolus vulgaris, L.)

The bean weevil, Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae), causes severe post-harvest losses in the common bean, Phaseolus vulgaris L. The control of this insect is still poor and involves the use of conventional insecticides. There is an increasing demand in the search for new active substances and products for pest control towards reduction of adverse effects on human health and the environment. The protection of grains with alternative products, such as essential oils, is a possible alternative to meet the needs described above. Therefore, this investigation evaluated the applications of basil, Ocimum basilicum, and citronella, Cymbopogon winterianus, essential oils for A. obtectus control. These essential oils significantly reduced the bean weight losses and the number of beans damaged by A. obtectus at higher doses than 60 or 120 μL/sample. The number of holes per bean did not differ between the doses of basil essential oil, not even at the dose of 60 μL, while it was higher at 120 μL, probably due to a lower capacity of movement of the insects treated with this dose and/or the oil's direct or indirect effects on the insects. Basil and citronella oils exhibited similar patterns of insecticidal activity over the insect, both directly in adult insects or indirectly over bean seeds. These essential oils affected the development of A. obtectus since the greatest doses applied on beans decreased the emergence of the bean weevil. The results prove the insecticidal capacity of the tested essential oils and hence their potential as active substances against A. obtectus in environmentally low risk pest control strategies. Supplementary trials should be conducted under real storage conditions.

Efficacy of Two Monoterpenoids, Carvacrol and Thymol, and Their Combinations against Eggs and Larvae of the West Nile Vector Culex pipiens

Background: Insect vector control is facing the challenges of resistance development and environmental hazards caused by synthetic pesticides. This has led to a considerable market opportunity for botanical insecticides. In this scenario, our study investigated the potential of selected bioactive monoterpenoids, carvacrol and thymol, as safe and effective tools to control the West Nile vector Culex pipiens. Furthermore, the combined effect of thymol-carvacrol mixtures and their possible interactions were assessed. Methods: For determining larvicidal and ovicidal 50% lethal concentration (LC₅₀), each monoterpenoid was tested at different concentrations (5–500 mg/L). Then, the fixed ratio method was used for evaluating their combinational efficacy. Results: Carvacrol was more toxic against larvae of Cx. pipiens, with a LC₅₀ value of 14 mg/L, whereas thymol exhibited a LC₅₀ value of 49 mg/L. Comparable trends of efficacy were observed when toxicity on Cx. pipiens eggs was investigated, with LC₅₀ values of 7 and 13 mg/L for carvacrol and thymol, respectively. In combinational toxicity assays, the mixture thymol-carvacrol at 1:4 ratio achieved a synergistic effect against larvae of Cx. pipiens, whereas an additive effect was observed on eggs. Other ratios showed antagonistic effects. Conclusions: Overall, our findings pointed out that the 1:4 ratio of thymol-carvacrol blend can enhance the insecticidal efficacy on Cx. pipiens young instars and can be considered further as active ingredient for developing botanical insecticides to be used in mosquito control operations.

Morphological and immunohistochemical study of the midgut and fat body of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: noctuidae) treated with essential oils of the genus Piper

Essential oils are a promising alternative to insecticides. We investigated the LD₅₀ of oils extracted from Piper corcovadensis, P. marginatum, and P. arboreum after 48 h topical contact with Spodoptera frugiperda larvae using morphometry, histochemistry and immunohistochemistry of the midgut and fat body. Chromatography revealed that E-caryophyllene was the principal compound common to the Piper species. The essential oils of P. corcovadensis, P. marginatum and P. arboreum caused deleterious changes in the midgut of S. frugiperda larvae. P. corcovadensis oil produced the lowest LD₅₀ and significant histopathological alterations including elongation of the columnar cells, formation of cytoplasmic protrusions, reduction in carbohydrate, increased apoptotic index and decreased cell proliferation. P. arboreum oil caused histopathological alterations similar to P. corcovadensis, but caused the highest rate of cell proliferation and increased regenerative cells, which indicated rapid regeneration of the epithelium. Our findings demonstrated the insecticidal potential of P. corcovadensis for control of S. frugiperda owing to the significant damage it inflicted on S. frugiperda midgut.

Plant extracts for developing mosquito larvicides: From laboratory to the field, with insights on the modes of action

In the last decades, major research efforts have been done to investigate the insecticidal activity of plant-based products against mosquitoes. This is a modern and timely challenge in parasitology, aimed to reduce the frequent overuse of synthetic pesticides boosting resistance development in mosquitoes and causing serious threats to human health and environment. This review covers the huge amount of literature available on plant extracts tested as mosquito larvicides, particularly aqueous and alcoholic ones, due to their easy formulation in water without using surfactants. We analysed results obtained on more than 400 plant species, outlining that 29 of them have outstanding larvicidal activity (i.e., LC₅₀ values below 10 ppm) against major vectors belonging to the genera Anopheles, Aedes and Culex, among others. Furthermore, synergistic and antagonistic effects between plant extracts and conventional pesticides, as well as among selected plant extracts are discussed. The efficacy of pure compounds isolated from the most effective plant extracts and - when available - their mechanism of action, as well as the impact on non-target species, is also covered. These belong to the following class of secondary metabolites: alkaloids, alkamides, sesquiterpenes, triterpenes, sterols, flavonoids, coumarins, anthraquinones, xanthones, acetogenonins and aliphatics. Their mode of action on mosquito larvae ranges from neurotoxic effects to inhibition of detoxificant enzymes and larval development and/or midugut damages. In the final section, current drawbacks as well as key challenges for future research, including technologies to synergize efficacy and improve stability - thus field performances - of the selected plant extracts, are outlined. Unfortunately, despite the huge amount of laboratory evidences about their efficacy, only a limited number of studies was aimed to validate their efficacy in the field, nor the epidemiological impact potentially arising from these vector control operations has been assessed. This strongly limits the development of commercial mosquito larvicides of botanical origin, at variance with plant-borne products developed in the latest decades to kill or repel other key arthropod species of medical and veterinary importance (e.g., ticks and lice), as well as mosquito adults. Further research on these issues is urgently needed.

Commercially Available Essential Oil Formulas as Repellents Against the Stored-Product Pest Alphitobius diaperinus

The main aim of the presented paper is to assess the potential repellent effect of selected essential oils (EOs) against the lesser mealworm (Alphitobius diaperinus), which can cause economic losses in storage and in the poultry industry. Due to the development of pesticide resistance in A. diaperinus populations, as well as an attempt to limit extensive use of potentially harmful pesticides in food-related industries, there is a strong need for the development of alternative methods of dealing with A. diaperinus infestations. Because of their cost-effectiveness, availability and low vertebrate toxicity, EOs are promising agents in pest management. In the presented paper four off-the-shelf EOs: mint, vanilla, lemon and citronella (and mixtures of them) were tested as potential repellents. Moreover, a novel preference assay, providing an extended analysis of the preference and the locomotor response, was used. The most effective EOs were: citronella and lemon. EOs mixtures were generally more repellent than individual EOs, with the lemon and vanilla 1:1 mixture acting as the strongest repellent. A few of the tested EOs caused significant alterations to the locomotor activity, although no direct relation was observed. In conclusion, EOs can be potentially used as repellent agents in A. diaperinus management. Additionally, data on the locomotor activity may lead to designing better push-pull strategies in pest management.

Chemical composition, Aedes mosquito larvicidal activity, and repellent activity against Triatoma rubrofasciata of Severinia monophylla leaf essential oil

Aedes aegypti and Ae. albopictus are key vectors in the spread of arboviruses such as dengue, chikungunya, yellow fever, and Zika. Triatoma rubrofasciata is an "assassin bug" whose populations and association with humans have dramatically increased and may represent a serious health concern. Control of insect vectors is a logical course of action to prevent the spread of these insect-borne infections. This work presents the leaf essential oil composition, mosquito larvicidal activities, and insect-repellent activity of Severinia monophylla. The essential oil of S. monophylla from Vietnam was obtained by hydrodistillation and analyzed by gas chromatography and mass spectrometry. The major components were sabinene, β-caryophyllene, bicyclogermacrene, germacrene D, (E)-nerolidol, globulol, and linalool. The leaf essential oil showed remarkable larvicidal activity against Ae. aegypti with LC₅₀ (48 h) of 7.1 μg/mL and Ae. albopictus with LC₅₀ (48 h) of 36 μg/mL. The essential oil also showed repellent activity on T. rubrofasciata at a concentration of 0.5%.

Menthol acts as a positive allosteric modulator on nematode levamisole sensitive nicotinic acetylcholine receptors

The ongoing and widespread emergence of resistance to the existing anti-nematodal pharmacopeia has made it imperative to develop new anthelminthic agents. Historically, plants have been important sources of therapeutic compounds and offer an alternative to synthetic drugs. Monoterpenoids are phytochemicals that have been shown to produce acute toxic effects in insects and nematodes. Previous studies have shown nicotinic acetylcholine receptors (nAChRs) to be possible targets for naturally occurring plant metabolites such as carvacrol and carveol. In this study we examined the effects of monoterpenoid compounds on a levamisole sensitive nAChR from Oesophagostomum dentatum and a nicotine sensitive nAChR from Ascaris suum. We expressed the receptors in Xenopus laevis oocytes and used two-electrode voltage-clamp to characterize the effect of various compounds on these cys-loop receptors. At 100 μM the majority of these compounds acted as antagonists. Interestingly, further experiments revealed that both 0.1 μM and 10 μM menthol potentiated acetylcholine and levamisole responses in the levamisole sensitive receptor but not the nicotine sensitive receptor. We also investigated the effects of 0.1 μM menthol on the contractility of A. suum somatic muscle strips. Menthol produced significant potentiation of peak contractions at each concentration of acetylcholine. The positive allosteric modulatory effects of menthol in both in vivo and in vitro experiments suggests menthol as a promising candidate for combination therapy with cholinergic anthelmintics.

•

We screened 12 monoterpenoid compounds to search for a potential anthelmintic.

•

Menthol acted as a PAM on levamisole sensitive nematode nAChRs in vitro & in vivo.

•

Carvacrol produced antagonism on both levamisole and nicotine sensitive nAChRs.

•

Monoterpenoid compounds can be used as an adjunct with cholinergic anthelmintics.

Toxicity to, oviposition and population growth impairments of Callosobruchus maculatus exposed to clove and cinnamon essential oils

The use of plant essential oils has been shown to efficiently control insect pests of stored beans, significantly reducing the threats associated with synthetic insecticides. Here, we evaluated the potential of applications of essential oils of clove, Syzygium aromaticum L., and cinnamon, Cinnamomum zeylanicum L., to control Callosobruchus maculatus, considered as one of the most cosmopolitan pests of stored beans. Using four combinations of couples (i.e., unexposed couples, exposed females, exposed males, and exposed couples), we also evaluated how sublethal exposure to these essential oils impacted C. maculatus oviposition. Bioassays results revealed that both essential oils exhibited insecticidal activities similar to the synthetic pyrethroid insecticide deltamethrin. Furthermore, oil dosage increments proportionately decreased the growth rate and reduced the losses in bean weight caused by cowpea weevils, and offspring emergence was almost abolished when parents were exposed to the LD₂₀ of each essential oil. Finally, significant oviposition impairments were perceived only in couples where females were exposed (i.e., females exposed and exposed couples) to the LD₂₀ of cinnamon and clove essential oils. Thus, by exhibiting similar insecticidal activities as synthetic insecticides and by significantly affecting the oviposition of sublethally exposed C. maculatus females, the cinnamon and clove essential oils represent valuable tools with potential of integration into the management of C. maculatus infestations.

Essential oil of Siparuna guianensis as an alternative tool for improved lepidopteran control and resistance management practices

Although the cultivation of transgenic plants expressing toxins of Bacillus thuringiensis (Bt) represents a successful pest management strategy, the rapid evolution of resistance to Bt plants in several lepidopteran pests has threatened the sustainability of this practice. By exhibiting a favorable safety profile and allowing integration with pest management initiatives, plant essential oils have become relevant pest control alternatives. Here, we assessed the potential of essential oils extracted from a Neotropical plant, Siparuna guianensis Aublet, for improving the control and resistance management of key lepidopteran pests (i.e., Spodoptera frugiperda and Anticarsia gemmatalis). The essential oil exhibited high toxicity against both lepidopteran pest species (including an S. frugiperda strain resistant to Cry1A.105 and Cry2Ab Bt toxins). This high insecticidal activity was associated with necrotic and apoptotic effects revealed by in vitro assays with lepidopteran (but not human) cell lines. Furthermore, deficits in reproduction (e.g., egg-laying deterrence and decreased egg viability), larval development (e.g., feeding inhibition) and locomotion (e.g., individual and grouped larvae walking activities) were recorded for lepidopterans sublethally exposed to the essential oil. Thus, by similarly and efficiently controlling lepidopteran strains susceptible and resistant to Bt toxins, the S. guianensis essential oil represents a promising management tool against key lepidopteran pests.