Synthetic Repellents Research Articles

Chemical Composition and In Vitro Evaluation of the Mosquito (Anopheles) Repellent Property of Neem (Azadirachta indica) Seed Oil

As one of the killer diseases in the world, malaria contributes to child mortality and global death annually. As a result, many reactive mechanisms have evolved to control and repel mosquitoes. The use of synthetic mosquito repellents with N,N-Diethyl-meta-toluamide (DEET) is one of the popular interventions despite its dermatological limitations such as skin irritations. Ethnobotanical reviews have identified that the adoption of natural repellents promises high repellence on mosquitoes with minimal side effects compared with synthetic ones. However, this has received little attention in modern pharmaceutical literature. This research is focused on the formulation of a natural mosquito repellent from the oil extracted from Azadirachta indica (A. Juss). The oil cream was formulated in concentrations of 10% v/w, 12.5% v/w, 15% v/w, 17.5% v/w, and 20% v/w using an in vitro evaluation approach. Pharmacopoeia characteristics of the cream such as pH, viscosity, spreadability, and organoleptic properties were carried out to verify acidity, permeation, and flow properties of the formulated cream. The spreadability rate was inversely proportional to the concentration of the cream in terms of oil content falling from 1.24 gm/s to 0.84 gm/s from concentrations 10% v/w to 20% v/w correspondingly. Skin irritation tests, however, indicated traces of irritation at 20% v/w. Repellency properties of the cream revealed a lasting effect on the mosquitoes, although this was dependent on concentration levels. Formulations of 17.5% v/w and 20% v/w neem seed oil cream had an equal repellency effect of 87.5%, whereas the synthetic repellent had a repellency of 75% within a justifiable time frame for all the formulations. This work shows that plant-based mosquito repellents promise a healthier approach in controlling mosquito bites, protecting the skin, and preventing malaria.

A dual-target molecular mechanism of pyrethrum repellency against mosquitoes

Pyrethrum extracts from flower heads of Chrysanthemum spp. have been used worldwide in insecticides and repellents. While the molecular mechanisms of its insecticidal action are known, the molecular basis of pyrethrum repellency remains a mystery. In this study, we find that the principal components of pyrethrum, pyrethrins, and a minor component, (E)-β-farnesene (EBF), each activate a specific type of olfactory receptor neurons in Aedes aegypti mosquitoes. We identify Ae. aegypti odorant receptor 31 (AaOr31) as a cognate Or for EBF and find that Or31-mediated repellency is significantly synergized by pyrethrin-induced activation of voltage-gated sodium channels. Thus, pyrethrum exerts spatial repellency through a novel, dual-target mechanism. Elucidation of this two-target mechanism may have potential implications in the design and development of a new generation of synthetic repellents against major mosquito vectors of infectious diseases.

Natural Anophelin mosquito repellents and phytochemical analysis of ethanol and hexane leaf extracts from four plant species

Currently mosquitoes control is the cornerstone to minimize the rising number of mosquito borne diseases. There is an urgent need looking for alternatives to the current reliance on synthetic insecticides for the vectors control. Application of active toxic agents from plant extracts as an alternative control strategy was available from ancient times. These are non-toxic, easily available at affordable prices, biodegradable and show broad-spectrum target-specific activities against different species of vectors. Natural products with repellency properties are urgently needed. An insect repellent works by masking human scent, and a number of natural and synthetic mosquito repellents were studied. The main aim of this study was to identify the phytochemicals and compare their potentials as mosquito repellents from the ethanol (Et. OH) and hexane (hex) leaf extracts (LEs) of Ocimum basilicum, Coleus forskohlii, Eucalyptus camaldulensis and Cymbopogon flexuosus under laboratory conditions at 50 and 100% concentrations. Phytochemical analysis showed that alkaloids, saponins, flavonoids, terpenes, tannins and terpenoids were present/or absent in the 4 plant-LEs. At 50% concentration of Et. OH extracts, C. forskohlii exhibited higher repellency potential on Anopheles gambiae with protection time of 137.3 min, while O. basilicum, E. camaldulensis and Cy. flexuosus registered protection time of 30.6, 15.3 and 19 min, respectively. At 100% concentration of ethanol- extracts, C. forskohlii caused the highest protection time against the vector with protection time of 182 min. O. basilicum, E. camaldulensis and Cy. flexuosus were equally less potent against the insect, with protection time 42.6, 32.6 and 28 min, respectively. Regarding hex-extract, at 50% concentration of C. forskohlii, the highest repellency potential , with protection time of 174 was registered, while O. basilicum, E. camaldulensis and Cy. flexuosus registered protection times of 44, 18 and 28.6 min, respectively. However, the 100% concentration of Et. OH-extracts of, C. forskohlii and O. basilicum exhibited the highest protection time, with protection times of 228 and 116min, respectively. E. camaldulensis and Cy. flexuosus were less potent, with protection times 28.6 and 54.6 min, respectively. The EOs of C. forskohlii and O. basilicum L EOs proved to have potentials as repellency agents against Anopheles. GC-MS analysis of the extracts identified the compounds of both solvents extracts and the terpens were the major compounds. According to the results, further studies are required, especially on the extracts of basil and coleus since they proved to be effective.

The irritant receptor TRPA1 mediates the mosquito repellent effect of catnip

SUMMARYCatnip (Nepeta cataria) is a common garden herb well known for its euphoric and hallucinogenic effects on domestic cats,1–3 for its medicinal properties,4,5 as well as for its powerful repellent action on insects.6,7 Catnip extracts have been proposed as a natural alternative to synthetic insect repellents, such as N,N-diethyl-3-methylbenzamide (DEET),8,9 but how catnip triggers aversion in insects is not known. Here, we show that, both in Drosophila melanogaster flies and Aedes aegypti mosquitoes, the major mediator of catnip repellency is the widely conserved chemical irritant receptor TRPA1. In vitro, both catnip extract and its active ingredient nepetalactone can directly activate fly and mosquito TRPA1. In vivo, D. melanogaster and Ae. aegypti TRPA1 mutants are no longer repelled by catnip and nepetalactone. Interestingly, our data show that some, but not all, fly and mosquito TRPA1 variants are catnip targets. Moreover, unlike the broad TRPA1 agonist allyl isothiocyanate (AITC) (an active ingredient of tear gas and wasabi), catnip does not activate human TRPA1. Our results support the use of catnip and nepetalactone as insect-selective irritants and suggest that, despite TRPA1’s broad conservation, insect TRPA1 can be targeted for the development of safe repellents.

Essential Oils as Green Repellents Against Mosquito Vectors

The mosquitoes are a serious threat to public health, since they are known vectors of many life-threatening diseases. Mosquito-borne diseases cause millions of deaths worldwide every year. While mosquitoes are important to maintain ecosystems, the aim is to keep them out of our personal space. People looking for alternatives to synthetic mosquito repellents may find that some natural repellents are effective in protecting them from bites. Natural insect repellents use natural ingredients such essential oils and other plant-based elements. Certain essential oils are effective and helpful in repelling mosquitoes, and are a natural alternative to the harsh chemicals in commercial bug sprays. These products are also likely to be less toxic to humans and the environment. Natural repellents and some essential oils may be effective in keeping mosquitoes away because they block their sense of smell. Many natural scents that are appealing to humans actually repel mosquitoes. Plant - based repellents are becoming more widely used as a protecting measure against mosquito bites, but more research is needed to develop natural repellents in terms of improving their repellent efficiency as well as in terms of their safety for use. This article presents a review about the best essential oils used as green repellents against mosquito bites, their efficiency, development and testing.

Functional assessment of biodegradable cotton nonwoven substrates permeated with spatial insect repellants for disposable applications

Arboviral diseases and malaria transmitted by mosquitoes are major health concerns worldwide responsible for millions of deaths annually. Spatial repellents have been used as preventative measures via direct application to the skin or disposable devices worn outside of clothing. Naturally derived, plant-based repellents are safe, effective alternatives to synthetic repellents and may be applied to disposable substrates including adhesive patches. Many disposables are composed of synthetic petrochemical-based polyester and polypropylene nonwoven fabrics, contributing to growing concern surrounding microplastic pollution. Sustainable and biodegradable substrates including those made from cotton are cost effective and environmentally friendly. Therefore, we explored the utilization of cotton-based substrates for the application of natural spatial and synthetic contact insect repellents. Cotton fibers used in the study were commercially available greige cotton, scoured and bleached greige cotton and reginned greige cotton motes, a value-added byproduct of the ginning process. Synthetic polyester and polypropylene were used for comparison. Thermogravimetric/derivative thermogravimetric analysis (TG/DTG) in combination with modulated differential scanning calorimetry (mDSC) were used to discern vaporization properties of repellents from the substrates. Retention times of repellents on the substrates were analyzed using a Fourier-transform infrared spectroscopy–focal plane array detector and compared with the TG/DTG and mDSC data. Mosquito landing assays confirmed the feasibility of using cotton-based substrates treated with plant-based spatial repellents as an effective and environmentally friendly alternative to synthetic materials.

Mosquito Repellency Effects of The Essential Oils from Cinnamomum iners Leaves and Barks

Synthetic mosquito repellents containing DEET (N, N-diethyl-3-methylbenzamide), DEPA (N, N-diethyl phenylacetamide), permethrin and deltamethrin as active components are known to be the most effective repellents. However, these types of repellents have contributed to numerous toxic effects on not only the environment, but also non-target organisms. The use of natural products such as essential oils is reported as a safe alternative. To date, the study on repellency activities against mosquitoes using Malaysian plants is rare. In the present study, essential oils from leaves and barks of Cinnamomum iners have been reported to show repellency activity, and the whole plant have been used by the local communities to repel mosquitoes and other blood-sucking insects. Repellency assay of the oils against Aedes aegypti was conducted using the percentage repellency bioassay method at three different concentrations: 1%, 5% and 10%. The results showed that the essential oils from barks had a significant percentage repellency (p<0.05) when compared to essential oils from leaves. Two main compounds were identified using the GC-MS: 1-isopropenyl-4-methyl-1,2-cyclohexanediol and 2-octen-1-ol,3,7-dimethyl (geraniol) from the bark and leaf essential oils, respectively. The essential oils demonstrated promising insect repellency activity which has the potential for further development into formulations that may serve as alternatives to DEET or be used as natural bioinsecticides to kill mosquitoes.

Salvia Spp. Essential Oils against the Arboviruses Vector Aedes albopictus (Diptera: Culicidae): Bioactivity, Composition, and Sensorial Profile-Stage 1.

Mosquito-borne arboviruses diseases cause a substantial public health burden within their expanding range. To date, their control relies on synthetic insecticides and repellents aimed to control the competent mosquito vectors. However, their use is hampered by their high economic, environmental, and human health impacts. Natural products may represent a valid eco-friendly alternative to chemical pesticides to control mosquitoes, and mosquito-borne parasitic diseases. The aim of this work was to combine the chemical and sensorial profiles with the bioactivity data of Salvia spp. essential oils (EOs) to select the most suitable EO to be used as a repellent and insecticide against the invasive mosquito Aedes albopictus (Diptera: Culicidae), vector of pathogens and parasites, and to describe the EOs smell profile. To do this, the EOs of four Salvia species, namely S. dolomitica, S. dorisiana, S. sclarea, and S. somalensis were extracted, chemically analyzed and tested for their bioactivity as larvicides and repellents against Ae. albopictus. Then, the smell profiles of the EOs were described by a panel of assessors. The LC50 of the EOs ranged from 71.08 to 559.77 μL L−1 for S. dorisiana and S. sclarea, respectively. S. sclarea EO showed the highest repellence among the tested EOs against Ae. albopictus females (RD95 = 12.65 nL cm−2), while the most long-lasting, at the dose of 20 nL cm−2, was S. dorisiana (Complete Protection Time = 43.28 ± 3.43 min). S. sclarea EO showed the best smell profile, while S. dolomitica EO the worst one with a high number of off-flavors. Overall, all the EOs, with the exception of the S. dolomitica one, were indicated as suitable for “environmental protection”, while S. dorisiana and S. sclarea were indicated as suitable also for “Body care”.

Terpenoids, DEET and short chain fatty acids as toxicants and repellents for Rhyzopertha dominica (coleoptera: Bostrichidae) and Lasioderma serricorne (Coleoptera: Ptinidae)

Plant-based products and common repellents have been suggested as promising alternatives for management of stored product insects. In this study, contact toxicity and repellent activity of the safe natural products carvacrol, citronella oil, geraniol, nootkatone, ocimene and R-(+)-pulegone, and the synthetic commercial repellents, N,N-Diethyl-3-methylbenzamide (DEET), and the fatty acid mixture of octanoic, nonanoic, and decanoic acids (C8910) were evaluated against the lesser grain borer, Rhyzopertha dominica and the cigarette beetle, Lasioderma serricorne under laboratory conditions. In contact toxicity assays the compounds were tested at concentrations ranging between 0.008 and 0.4 mg/cm2. Carvacrol and R-(+)-pulegone exhibited the highest contact toxicity with LC50 values of 0.019 and 0.023 mg/cm2 against L. serricorne and LC50 values of 0.012 and 0.019 mg/cm2 against R. dominica, respectively. Similarly, C8910, geraniol and citronella oil showed toxic effect against both insects. The repellent activity of compounds was tested using the preference method assay at concentrations ranging between 3.125 and 50.0 μg/cm2. The highest repellency percentage (RP) was achieved by C8910 against L. serricorne with a RP value of 76.0% at the lowest concentration (6.25 μg/cm2), while carvacrol showed the highest repellent activity against R. dominica with RP value of 88.0% at 3.125 μg/cm2 within 3 h of insect exposure. The tested compounds caused higher repellent activity to R. dominica than L. serricorne. In vitro inhibition studies of acetylcholinesterase (AChE) in adults of both species showed that R-(+) pulegone strongly inhibited AChE activity of R. dominica and L. serricorne with 69.0% and 88.0% inhibition at 40 mM, respectively. Carvacrol caused 41.8% inhibition in AChE activity of R. dominica compared to 66.7% of L. serricorne at 40 mM. The results indicated that the tested natural compounds may be useful alternatives for controlling R. dominica and L. serricorne.

Ecofriendly Ethyl Cellulose Microsponges of Citronella Oil: Preparation, Characterization and Evaluation of Cytotoxicity and Larvicidal assay.

Citronella Oil (CO) was used by the Indian army as mosquito repellant to repel mosquitoes at the beginning of the 20th century and later in 1948, it was registered in the USA for commercial purposes. Due to its ecofriendly nature, CO possesses immense potential as a mosquito repellent. Citronella oil is a valuable alternative to synthetic mosquito repellents commonly used nowadays. However, its volatile nature, poor stability in air and high temperature restrict its application. Its direct application on skin may lead to skin irritation. To surmount the above-mentioned issues, the present research aims to develop Microsponge (MS), a novel dosage form for enhancing the utility and safety of CO. Quasi emulsion solvent diffusion method was chosen for crafting MS using ethyl cellulose with various drug-polymer ratios and characterized. In vitro cytotoxicity evaluation was also carried out to check the dermal safety of COMS. The present results revealed that the size of all prepared formulation lies in the micro range (20 ± 3 to 41 ± 4 μm), with good payload (42.09± 3.24 to 67.08± 6.43%). The results of FE-SEM depicted that MS were spherical in shape with porous nature. Cytotoxicity results indicated that COMS were safe on skin cells, when compared to pure CO. The optimized MS were also assessed for larvicidal assay against larvae of Anopheles culicifacies. The CO micro-formulations were found to possess enhanced stability of this oil. Entrapment of CO in MS resulted in a better vehicle system in terms of safety, stability and handling benefits of this oil.

Reflexion on Bio-Sourced Mosquito Repellents: Nature, Activity, and Preparation

Over the last decades, the geographical distribution of certain mosquito species carrying vector-borne diseases has considerably expanded. They represent a major health concern as they transmit pathogens causing alarming epidemics. In the absence of vaccines for most of the mosquito-borne diseases, the use of topical mosquito repellents is one of the main measures to prevent human-mosquito contacts. Synthetic repellents are the most used mosquito repellents. However, several concerns about their safety for consumers have led to a growing demand of natural alternatives. Here we present an overview of the most commonly used natural-based mosquito repellents: repellent activity, biological action, composition, stereochemical structure (when appropriate) and syntheses, paradoxically far from being eco-friendly. We discuss on future prospective that would combine sustainable chemical processes and synergistic effects promising for the development of natural, safe and efficient topical repellents.

An investigation into the knowledge, perceptions and role of personal protective technologies in Zika prevention in Colombia

BackgroundArboviruses transmitted by day-biting Aedes mosquitoes are a major public health concern. With the challenges inherent in arbovirus vaccine and therapeutics development, vector control and bite prevention strategies are among the limited options available for immediate intervention. Bite prevention through personal protective technologies (PPT), such as topical mosquito repellents or repellent-impregnated clothing, may help to decrease biting rates and, therefore, the risk of disease in groups most susceptible to adverse outcomes from Zika virus. However, achieving high uptake and compliance with PPT can be challenging.Methodology/Principal findingsTo gain an insight into the knowledge and concerns of pregnant women surrounding Zika and their opinions regarding PPT, particularly repellent clothing, a focus group study was carried out with pregnant women, women of reproductive age, and semi-structured interviews with their male partners in two cities in Colombia. The discussions revealed shortfalls in basic knowledge of Zika virus, with several pregnant participants reporting being unaware of the potential for Zika-related congenital malformations. Although participants generally considered Zika to be a significant personal threat, most rated it as less of a concern than dengue or diarrheal diseases. Overall, repellent clothing and other forms of PPT were viewed as effective, although some participants expressed concerns over the high costs of repellents, and safety fears of regular contact with repellent chemicals, which they perceived as potentially harmful. Plant-derived repellents were considered to be safer than synthetic chemical repellents. Discussions also highlighted that health centers were the preferred source of information on bite-reduction.Conclusions/SignificanceAchieving high uptake and compliance with PPT in populations most at risk of adverse outcomes from Zika infection requires engaging key users in open dialogue to identify and address any practical issues regarding PPT use, and concerns over safety. The findings presented here suggest that educational campaigns should strongly emphasize the risks associated with Zika during pregnancy, and discuss safety profiles of approved synthetic repellents and the availability of EPA-approved plant-based repellents. In addition, the economic and political context should be a major consideration when evaluating personal mosquito-repellent strategies.

Efficacy of Plant-based Repellents Against Anopheles Mosquitoes: A Systematic Review

Mosquitoes are usually targeted using insecticides, insect growth regulators, and microbial agents. Indoor residual spraying and insecticide-treated bed nets. However, these strategies have negative effects on human health, the environment and induce resistance in a number of species. Eco-friendly tools have been recently implemented against mosquito vectors, including plant-based insecticides. To date few studies have adopted World Health Organization (WHO) Pesticide Evaluation Scheme guidelines for repellent testing against mosquitoes. This review presents a summary of recent information on development, and efficacy of plant-based repellents against Anopheles mosquitoes as well as promising new advances in the field. All eligible studies published up to April 2020 were systematically searched in several databases, namely PubMed/Medline, Scopus and Google scholar. The outcomes of interest were percentage repellency, protection time and additional properties identified in repellent compounds. A total of 27 trials met the inclusion criteria. The highest repellency effect against mosquitoes was conferred by citronella, followed by <i>Ligusticum sinense</i> extract, <i>pine</i>, <i>Dalbergia sissoo</i>, and <i>Rhizophora mucronata</i> oils with 100% protection for 8 to 14 hours. Furthermore, essential oils from plants such as lavender, camphor, catnip, geranium, jasmine, broad-leaved eucalyptus, lemongrass, lemon-scented eucalyptus, amyris, narrow-leaved eucalyptus, carotin, cedarwood, chamomile, cinnamon oil, juniper, cajeput, soya bean, rosemary, niaouli, olive, tagetes, violet, sandalwood, litsea, galbanum, and <i>C. longa</i> also showed >90% repellency within 8 hours against different species of Anopheles. Therefore, the review showed, essential oils and extracts of some plants could be formulated for the development of eco-friendly repellents against Anopheles species. Plant oils may serve as suitable alternatives to synthetic repellents in the future as they are relatively safe, inexpensive, and are readily available in many parts of the world.

Lemongrass (Cymbopogon Flexuosus Steud.) wats treated textile: A control measure against vector-borne diseases

Mosquito-borne diseases are one of the major threats to human health. The long-term use of synthetic repellents has made mosquitoes resistant to them leading to search for novel methods of mosquito control. In the present study, we have developed a low cost, safe and effective formulation to impart mosquito larvicidal and antibacterial effect using essential oils. Oil in water nanoemulsion of three different oils: Lemongrass (cymbopogon flexuosus steud.) wats (CF) oil, Eucalyptus oil (EO) and Chrysnathemum Indicum were prepared using high shear homogenization of the organic with the aqueous phase in presence of surfactant. The oil biocomponents were studied using GCMS. An experimental study of oil in water nanoemulsion preparation, process optimization and stability based on the required size distribution and accelerated stability was performed with surfactant oil ratio (SOR), stirring time and speed as the variables for nanoemulsion preparation. The storage stability of the nanoemulsion was also studied in terms of particle size, pH, viscosity and zeta potential at room temperature and refrigeration temperature for a period of 6 months. The optimized emulsion was also tested for its mosquito larvicidal effect against both the susceptible and resistant species of mosquitoes. The antimicrobial efficacy of the emulsion was also assessed.In the present study, nylon net fabric was treated with Cymbopogon flexuosus (CF) oil nanoemulsion by depositing polyelectrolyte multilayers through the layer by layer (LBL) technique. The nanoemulsion was characterized for particle size, zeta potential, viscosity, pH and Poly Dispersity Index. Mosquito antennal response to pure CF oil and its nanoemulsion was noted. The application technique was optimized for the concentration of nanoemulsion used and the number of polymeric layers applied. The treated samples were tested against mosquito bioassays, microbial growth and fragrance retention. Wash durability of the treated samples was also analysed. GCMS and SEM analysis of the treated and washed samples was done to ensure the presence of active ingredient and finish on the fabric. The fabrics showed good mosquito repellency, fragrance retention and antimicrobial efficacy even after 25 washes, though the percentage mortality dropped. The repellent and anti-microbial fabrics developed may provide a safe, environment-friendly and effective alternative to the chemical-based repellents for achieving protection against mosquito bites.

How DEET repels malaria mosquitoes

A group of scientists reports that DEET seems to keep malaria mosquitoes from smelling humans by preventing skin compounds from vaporizing and finding their way to the mosquitoes’ antennae. The lead researcher, Christopher Potter of the Johns Hopkins University School of Medicine, says understanding how mosquitoes’ olfactory systems interact with repellents could lead to a next generation of mosquito-fighting compounds that are less toxic than DEET but equally effective (Curr. Biol. 2019, DOI: 10.1016/j.cub.2019.09.007). The team developed a test that makes neurons in the mosquitoes’ antennae fluoresce when the odor receptors embedded in the cells turn on. After showing that the system responded to human odorants, the scientists tested several repellents, including synthetic ones (DEET, picaridin, and IR3535) and natural products (lemongrass oil and eugenol). The synthetic repellents had no effect on the mosquitoes’ olfactory system. The natural products did, suggesting that the natural repellents likely ...

Commonly Used Insect Repellents Hide Human Odors from Anopheles Mosquitoes.

The mode of action for most mosquito repellents is unknown. This is primarily due to the difficulty in monitoring how the mosquito olfactory system responds to repellent odors. Here, we used the Q-system of binary expression to enable activity-dependent Ca2+ imaging in olfactory neurons of the African malaria mosquito Anopheles coluzzii. This system allows neuronal responses to common insect repellents to be directly visualized in living mosquitoes from all olfactory organs, including the antenna. The synthetic repellents N,N-diethyl-meta-toluamide (DEET) and IR3535 did not activate Anopheles odorant receptor co-receptor (Orco)-expressing olfactory receptor neurons (ORNs) at any concentration, and picaridin weakly activated ORNs only at high concentrations. In contrast, natural repellents (i.e. lemongrass oil and eugenol) strongly activated small numbers of ORNs in the Anopheles mosquito antennae at low concentrations. We determined that DEET, IR3535, and picaridin decrease the response of Orco-expressing ORNs when these repellents are physically mixed with activating human-derived odorants. We present evidence that synthetic repellents may primarily exert their olfactory mode of action by decreasing the amount of volatile odorants reaching ORNs. These results suggest that synthetic repellents disruptively change the chemical profile of host scent signatures on the skin surface, rendering humans invisible to Anopheles mosquitoes.

Essential oils as tick repellents on clothing

Essential oils show promise as natural alternatives to synthetic tick repellents, but few studies have investigated their repellent efficacy in vivo or under field conditions. Here, blanket-drags and standardised walks were employed to evaluate tick acquisition by 1 m2 cotton blankets or cotton trousers, respectively, in woodland edge habitats of known high tick abundance. Blankets and trousers had been treated with one of 5% oregano, rosemary, spearmint or thyme oils, 20% DEET (N,N-diethyl-3-methylbenzamide) (positive control) or ethanol excipient-only (negative control). The number of ticks present on the blankets or trousers differed significantly between treatments: spearmint oil treatments resulted in significantly fewer ticks than the negative controls for both blankets and trousers and significantly fewer ticks were present on the oregano oil treated blankets. For ticks that did attach to the trousers, the rate of drop off within 3 min was significantly higher for trousers treated with spearmint oil or thyme oil than ethanol, oregano oil and rosemary oil. No reduction in repellence was detected over a 24 h period between treatment and testing. The results suggest that 5% oregano and spearmint oils exhibit potential as natural clothing repellents, with an effective equivalence to 20% DEET.

Chemical composition and repellent activity of native plants essential oils against dengue mosquito, Aedes aegypti

Aedes aegypti L. (Diptera: Culicidae) mosquito is an important vector of chikungunya, dengue and yellow fever. Plant based essential oils may serve as good alternatives to commercially available mosquito repellent, DEET. Steam distillation was used for the extraction of essential oils from fresh collected aerial parts of plants viz Chenopodium ambrosioides, Conyza sumatrensis, Erigeron canadensis, Eucalyptus camaldulensis, Mentha spicata, Parthenium hysterophorus, and Tagetes minuta. The essential oils were tested for mosquito repellent activity against laboratory reared female Ae. aegypti by human bait technique. Identification of chemical constituents of essential oils was carried out by gas chromatography-mass spectrometry (GC–MS). The essential oil of M. spicata, E. canadensis, P. hysterophorus, C. sumatrensis, T. minuta, C. ambrosioides, and E. camaldulensis exhibited 100%, 80%, 63.9%, 51.4%, 50.2%, 39.7%, and 13.7% mosquito repellent activity respectively, at the tested dose of 30 μg/cm2. The most abundant constituents of M. spicata, E. canadensis, P. hysterophorus, C. sumatrensis and T. minuta essential oils were piperitenone oxide (47.1%), limonene (41.3%), germacrene D (36.6%), cis-lachnophyllum ester (33.3%) and dihydrotagetone (20.9%) respectively. M. spicata essential oil completely inhibited the attractiveness of human hands toward female mosquitoes for more than 45 min thus showed bioactivity comparable to that of commercially used mosquito repellent, DEET. This study suggests that the dilute solution of M. spicata essential oil could be used as potent mosquito repellent against Ae. aegypti alternative to commercially available synthetic mosquito repellents.

Sensory Quality of Essential Oils and Their Synergistic Effect with Diatomaceous Earth, for the Control of Stored Grain Insects.

Essential oils (EOs) have gained increasing interest as a low-toxic, eco-friendly alternative to synthetic repellents and insecticides against insect pests. However, they have scarce practical application in the protection of stored grain because of their limited efficacy and their interference with the organoleptic properties of the grain. In this study, we evaluated the olfactory profile of the EOs of Foeniculum vulgare, Pistacia lentiscus, and Ocimum basilicum, and their toxicity against the main stored grain pest Sitophilus granarius. Trained assessors identified O. basilicum and F. vulgare, as more suitable than the P. lentiscus EO for the wheat treatment. In laboratory tests, the most toxic EO was the P. lentiscus (LC50 = 36.36 μL∙kg−1) while, the least toxic, was the F. vulgare one (LC50 = 77.59 μL∙kg−1). The EOs were also tested combined with diatomaceous earths (DEs) showing synergistic effects (co-toxicity coefficient values ranging from 1.36 to 3.35 for O. basilicum and F. vulgare EOs, respectively). Overall, O. basilicum resulted as the best EO for the wheat treatment, considering its insect toxicity and olfactory profile. In real storage conditions, the wheat co-treated with O. basilicum EO and DEs showed a significantly lower mean infestation (1.5 insect kg−1) than the non-treated wheat (7.0 insect kg−1).

Repellent Activity of Waste Extract from Two Local Medicinal Plant Against Rice Weevil (Sitophilus oryzae)

In order to find natural and inexpensive bioinsecticides, the active compound of waste extract from two medicinal plants were analyzed. Ethanolic extracts of Amomum cardamomum and Zingiber zerumbet were evaluated under laboratory conditions for their repellency against rice weevil (Sitophilus oryzae, L.). Four extracts concentration were tested in this research, i.e: 25, 50, 75 and 100%. Efficacy was measured based on the response of rice weevil in preference tests using Y Olfactometer Tube, then the results were converted into the Percentage Repellency (PR) and Preference Index (PI). The PR data were analyzed using ANOVA, whereas PI values were analyzed descriptively. The result showed that the PR were significantly (LSD test; α&gt; 0.05) and revealed that waste extracts repel the rice weevil at 100% solution. The highest PR was found at 100% solution in both extracts, however, statistically the repellency of A. cardamomum waste extract was higher than Z. zerumbet’s. Likewise, the PI of both extracts showed negative value at 75 and 100% concentration. This study concluded that extract of A. cardamomum and Z. zerumbet wastes have repellent effect against rice weevil and A. cardamomum repellency is better than Z. zerumbet. The findings of this study can provide a useful information for development of a rice weevil repellent extracted from waste product of medicinal plants that is more economically and environmentally friendly than synthetic insect repellents.