Repellents For Use Research Articles

Repellent Screening of Selected Plant Essential Oils Against Dengue Fever Mosquitoes Using Behavior Bioassays

Among the efforts to reduce mosquito-transmitted diseases, such as malaria and dengue fever, essential oils (EOs) have become increasingly popular as natural replacements for the repellant DEET. In this study, seven commercially available plant EOs against Aedes species mosquitoes were evaluated for their complete protection time (CPT, min) in vivo using human-hand in cage tests (GB2009/China and WHO2009). Among the EOs with the highest efficacy in repelling mosquitoes, Aedes albopictus (Skuse) were clove bud oil and patchouli oil. Both were further assessed according to the in vivo method recommended by the WHO, to determine their minimum effective dose and CPT. A comparison of the ED50 values (dose yielding a 50% repellent response) of these two EOs against Aedes aegypti(L.) showed that the ED50 (2.496 µg/cm2) of patchouli oil was 1248 times higher than that of clove bud oil (0.002 µg/cm2), thus demonstrating them greater efficacy of the latter in repelling Ae. aegypti mosquitoes. For the 2 EOs, eugenol was the major component with higher than 80% in relative amount of the clove bud oil. The patchouli oil had more than 30% of character chemical patchouli alcohol along with α-bulnesene (10.962%), α-guaiene (9.227%), and seychellene (7.566%). Clove bud oil was found to confer longer complete protection than patchouli oil against a common species of mosquito. These results suggest use of EOs as safe, highly potent repellents for use in daily life and against mosquito-transmitted diseases, such as malaria and dengue fever.

Three molecules found in rosemary or nutmeg essential oils repel ticks (Dermacentor variabilis) more effectively than DEET in a no-human assay.

Development of new personal repellents to prevent tick bites is progressing to keep up with the increasing threat of tick-borne diseases in humans. However, the market share of natural, plant-based repellents is still quite small. We tested all of the major (>1%) components found in the essential oils of rosemary (Spanish variety) and nutmeg. These were tested with Dermacentor variabilis ticks, a robust tick capable of vectoring human diseases, in a no-human horizontal Petri dish assay. For comparison, we also tested the active ingredients currently recommended by the CDC and EPA as personal repellents for use against ticks. Of the 16 oil components tested, three performed significantly better than N,N-diethyl-meta-toluamide (DEET) in our assay. These compounds were myristicin and safrole found in the nutmeg oil, and terpinolene found in nutmeg oil and as a minor (<1%) constituent of rosemary oil. The current market natural product, 2-undecanone, also performed strongly in our assay. Our assay focused on comparing active ingredients as potential repellents and found that many natural products can elicit a strong response from ticks. Terpinolene is the most promising active ingredient identified, owing to human health concerns regarding myristicin and safrole. Our results from examining individual terpenoids from two essential oils suggest that there remain unexploited natural compounds that could be further developed for new personal tick repellents. © 2020 Society of Chemical Industry.

Chemical Characterization of Lipophilic Constituents in the Skin of Migratory Adult Sea Lamprey from the Great Lakes Region.

The sea lamprey (Petromzons marinus) is an invasive ectoparasite of large-bodied fishes that adversely affects the fishing industry and ecology of the Laurentian Great Lakes. Lipid content in the whole sea lamprey and muscles, liver and kidney of metamorphosing larval stages has been reported. Similarly, the fatty acid profile of the rope tissues of sexually-mature male sea lampreys has also been reported. The average body weight of a sub-adult migratory sea lamprey is 250 g, which includes 14.4% skin (36 g). Our preliminary extraction data of an adult sea lamprey skin revealed that it contained approximately 8.5% of lipophilic compounds. Lamprey skin is home to a naturally aversive compound (an alarm cue) that is being developed into a repellent for use in pest management. As part of an ongoing investigation to identify the chemical structure of the sea lamprey alarm cue, we extracted the skin with water and methanol, respectively. The methanolic extract (1.55%) contained exclusively lipophilic compounds and did not include the alarm cue. We chemically characterized all compounds present in the methanolic extract as cholesterol esters (CE), tri- and di-glycerides (TG and DG), cholesterol, free fatty acids (FFA) and minor amounts of plasticizers. The free fatty acids fraction was composed of saturated (41.8%), monounsaturated (40.7%) and polyunsaturated (17.4%) fatty acids, respectively. The plasticizers characterized were phthalate and benzoate and found to be 0.95 mg and 2.54 mg, respectively, per adult sea lamprey skin. This is the first report of the chemical characterization of all the lipophilic constituents in the skin of sub-adult migratory sea lamprey. The CEs isolated and characterized from sea lamprey skin are also for the first time.

Gustatory receptor neuron responds to DEET and other insect repellents in the yellow-fever mosquito, Aedes aegypti

Three gustatory receptor neurons were characterized for contact chemoreceptive sensilla on the labella of female yellow-fever mosquitoes, Aedes aegypti. The neuron with the smallest amplitude spike responded to the feeding deterrent, quinine, as well as N,N-diethyl-3-methylbenzamide and other insect repellents. Two other neurons with differing spikes responded to salt (NaCl) and sucrose. This is the first report of a gustatory receptor neuron specific for insect repellents in mosquitoes and may provide a tool for screening chemicals to discover novel or improved feeding deterrents and repellents for use in the management of arthropod disease vectors.

Repellent activity of Nepeta grandiflora and Nepeta clarkei (Lamiaceae) against the cereal aphid, Sitobion avenae (Homoptera: Aphididae)

Nepeta spp. (Lamiaceae) contain principally the nepetalactone isomers (4a S,7 S,7a R) and (4a S,7 S,7a S)-nepetalactone, which are also known to comprise aphid sex pheromones and aphid parasitoid attractants. Previous studies have shown that Nepeta cataria can be grown as a non-food crop for the commercial-scale production of (4a S,7 S,7a R)-nepetalactone in high purity, thus removing requirement for highly demanding stereocontrolled synthesis. Furthermore, previous literature reports have suggested that Nepeta spp., other than the widely studied N. cataria, can produce a diverse range of natural products other than nepetalactones, including high value sesquiterpenes. Thus, with the aim of identifying alternative Nepeta spp. for production of high value semiochemicals, the essential oils of two readily available species, Nepeta grandiflora and N. clarkei, were collected by steam distillation and analysed using high resolution gas chromatography (GC) and coupled GC–mass spectrometry (GC–MS). Analysis of the oils surprisingly revealed a very low nepetalactone content, but instead the presence of predominantly sesquiterpene compounds, and, for N. clarkei, the major component, geranyl acetate. Amongst the compounds identified in both oils was ( S)-germacrene d, a previously reported potent arthropod repellent. To determine the potential crop protection value of these essential oils, the repellent activity of the oils was assessed using a four-way olfactometer assay, with both oils showing strong repellent effects. These findings illustrate that members of the Nepeta genus possess a diverse range of high value secondary metabolites, and also highlight their potential to be developed as renewable feedstocks for the production of repellents for use economically important crop pests, as well as for the production of sex pheromones and natural enemy attractants.

Evidence for inhibition of cholinesterases in insect and mammalian nervous systems by the insect repellent deet

BackgroundN,N-Diethyl-3-methylbenzamide (deet) remains the gold standard for insect repellents. About 200 million people use it every year and over 8 billion doses have been applied over the past 50 years. Despite the widespread and increased interest in the use of deet in public health programmes, controversies remain concerning both the identification of its target sites at the olfactory system and its mechanism of toxicity in insects, mammals and humans. Here, we investigated the molecular target site for deet and the consequences of its interactions with carbamate insecticides on the cholinergic system.ResultsBy using toxicological, biochemical and electrophysiological techniques, we show that deet is not simply a behaviour-modifying chemical but that it also inhibits cholinesterase activity, in both insect and mammalian neuronal preparations. Deet is commonly used in combination with insecticides and we show that deet has the capacity to strengthen the toxicity of carbamates, a class of insecticides known to block acetylcholinesterase.ConclusionThese findings question the safety of deet, particularly in combination with other chemicals, and they highlight the importance of a multidisciplinary approach to the development of safer insect repellents for use in public health.

Antiectoparasitic activity of the gum resin, gum haggar, from the East African plant, Commiphora holtziana

The mechanism of ixodid tick (Acari: Ixodidae) repellency by gum haggar, a resin produced by Commiphora holtziana (Burseraceae), was investigated by evaluating activity against the cattle tick, Boophilus microplus. In an arena bioassay, a hexane extract of the resin of C. holtziana exhibited a repellent effect lasting up to 5 h. The hydrocarbon fraction of the resin extract was shown to account for the repellent activity, and was analysed by coupled gas chromatography–mass spectrometry (GC–MS). Major sesquiterpene hydrocarbons were tentatively identified as germacrene-D, δ-elemene and β-bourbonene. The identity and stereochemistry of the former compound was confirmed as the (+)-isomer by peak enhancement using enantioselective GC, whereas the latter 2 compounds, which are most likely degradation products of germacrene-type precursors, were identified through isolation by preparative gas chromatography followed by microprobe-NMR spectroscopy. GC comparison of gum haggar with another resin, C. myrrha, which was inactive in the tick bioassay, showed that the latter contained much lower levels of these hydrocarbons. To assess the suitability of the gum haggar resin as a general acarine repellent, further tests were made on a major acarine pest of European and US animal husbandry systems, the red poultry mite, Dermanyssus gallinae (Acari: Dermanyssidae). Gum haggar extract, and the isolated hydrocarbon fraction, showed strong repellent effects in an olfactometer assay, and again gum myrrh showed no effect. These findings provide a scientific basis for the observed anti-tick properties of gum haggar, and demonstrate the potential for its development as a general acarine repellent for use in animal husbandry systems.

Crop diversifi cation leads to diverse bird problems in Hawaiian agriculture

Over the last 20 years, Hawaii’s agriculture has shifted from a focus on sugar cane (Saccharum offi cinarum) and pineapples (Ananas comosus) produced on large farms to a diverse array of products produced on a multitude of smaller farms. This dramatic shift in production, in addition to the introduction of many new avian species, has resulted in a concomitant change in the problems faced by agriculture. We surveyed farmers to determine the extent of bird damage to crops, the species responsible, the crops most vulnerable, and control methods employed. Bird problems varied by island, but cardinals (Cardinalis cardinalis, Paroaria coronata, and P. capitata) and pheasants (Phasianus colchicus and Lophura leucomelanos) were signifi cant problems on all islands. Seed corn (Zea mays), fruit, vegetables, rice (Oryza sativa), and orchids (Orchidaceae) all sustained notable damage to their crops by birds, and growers expressed much interest in gaining information on control measures. Most farmers incurred little damage, while a few reported losing 80 to 100% of their crops at certain times of the year. We recommend a multidimensional approach to control invasive bird species, including habitat alterations, scare tactics, cessation of game bird releases, prevention of the spread of known pests among islands, and the development of chemical repellents for use when other methods are not suffi cient.

Optically active arthropod repellents for use against disease vectors.

Optically inactive 1-[3-cyclohexen-1-ylcarbonyl] piperidine and 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine are repellents against blood-feeding arthropods. Pure stereoisomers of these compounds were synthesized and characterized for use in bioassays. Initial laboratory tests with the malaria vector Anopheles stephensi Liston showed that this species was repelled differentially by the stereoisomers of 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine. Two stereoisomers were twice as repellent as the other stereoisomers. These results indicate that stereoisomerism influences repellent efficacy in this class of compounds.

Deployed US Army soldiers' knowledge and use of personal protection measures to prevent arthropod-related casualties.

The recommendation to use personal protection measures (PPMs) to prevent arthropod-related diseases and nuisance bites is a common element of travel medicine consultation.1-3 Prevention of arthropod-related casualties is especially important to the military, given the often intense exposure of service members to biting arthropods and the threat of personnel losses to mission success. In the 1980s, 75% deet (N,N-diethyl-m-toluamide) was the US military-issue insect repellent for use on skin and clothing. Collaboration between military and civilian researchers led to the implementation in 1991 of the current US military system of PPMs which has three components: topical application of 33% extended-duration deet, treatment of field uniforms with permethrin, and proper wearing of field uniforms.4-6 Compared to military-issue 75% topical deet, 33% extended-duration deet prevents bites up to three times longer (as long as 12 hours), is less greasy, and has lower plasticizing properties. Field uniforms treated with the contact toxicant, permethrin, are also necessary to minimize bites from crawling arthropods such as ticks and chiggers. Implementation of all three components of this system is a safe and effective means of reducing the threat posed by biting arthropods.7 We conducted a questionnaire survey to assess the degree of deployed soldiers' knowledge of the US military's system of PPMs and use of PPMs in general. Survey results may promote the development of better ways to advise and teach military and civilian travelers about the proper use of PPMs given the multitude of available products and practices.

Thanaka (Limonia acidissima) and deet (di-methyl benzamide) mixture as a mosquito repellent for use by Karen women.

The prevention and treatment of drug-resistant malaria is becoming increasingly difficult. On the Thai-Myanmar border multi-drug resistant strains of falciparum malaria are increasing and, because the malaria vector Anopheles bite outdoors during early evening, insecticide house-spraying or impregnated bednets provide only limited protection. Therefore, the protective efficacy of repellent formulations containing di-methyl benzamide (deet) and permethrin against local vectors was estimated, when applied to the skin, and their acceptability amongst pregnant Karen women who are at relatively high risk from malaria was assessed. Human landing catches of mosquitoes showed that almost complete protection was achieved using different formulations of 20% deet and 0.5% permethrin for up to 6 h. All-night collections from human subjects indicated that this repellent combination reduced exposure to malaria parasites by at least 65 and 85% for those transmitted by Anopheles minimus and An. maculatus, respectively, the two principal vectors in this area. Pregnant women in the camps preferred repellents which were mixed with 'thanaka', a root paste made from pulp of the wood apple tree, Limonia acidissima, used locally as a cosmetic. Apart from a temporary warming sensation where repellent thanaka was applied to the skin, the repellents were well tolerated. An intervention trial is currently in progress to determine whether deet mixed with thanaka can protect pregnant women against malaria in this part of the world. Bioassays using a laboratory strain of Aedes aegypti demonstrated that thanaka is itself slightly repellent at high dosages and the mixture with deet provides protection for over 10 h. This treatment would therefore also provide some personal protection against dengue, which is increasing locally, transmitted by Ae. aegypti and Ae. albopictus biting during the daytime.

Effects of oil of cloves and citronellol, two commercially available repellents, against the webbing clothes mothTineola bisselliella Hum. (Lepidoptera: Tineidae)

Tineola bisselliella is a common pest on natural fabrics of economic importance. Two commercially available repellents for use against adult webbing clothes moths were tested for their efficacy in dual- and no-choice bioassays. Oil of cloves and citral in combination, as well as citronellol scented with oil of lavender showed promising repellent effects for 4 weeks when applied in small compartments of a wardrobe. Although the repellent efficacy was not 100% under the conditions tested, the usage of essential oils in combination with other infestation prevention techniques is discussed.

BIRD AVERSIVE PROPERTIES OF METHYL ANTHRANILATE, YUCCA, Xanthoxylum, AND THEIR MIXTURES

We tested the bird aversive properties of methyl anthranilate, yucca extracts, and Xanthoxylum spp. extracts in oneand two-bottle drinking assays that used European starlings (Sturnus vulgaris). In oneand two-bottle tests, methyl anthranilate proved to be the more potent stimulus in producing an avoidance response. Starlings avoided consuming Xanthoxylum and yucca only in the two-bottle tests. Previous studies showed that yucca was a good adjuvant in stabilizing lipophilic compounds in water. Starlings did not avoid binary mixtures of methyl anthranilate and yucca differently from what would be expected if they were only responding to the solution's methyl anthranilate content. However, yucca enhanced the aversive qualities of Xanthoxylum. The ability to identify mode of action for repellency and synergistic combinations of chemicals derived from natural products for use in repellent mixtures is an important aspect of the development of cost-effective, environmentally safe repellents for use in conflict resolution between humans and wildlife.

Progress Report of Investigations Relating to Repellents, Attractants and Larvicides for the Screw-Worm and Other Flies

Among many tests of baits for use against the screw worm fly,(Chrysomya macellaria) and its relatives dried egg was found to be one of the most satisfactory. Over two hundred chemicals were tested as repellents for use on live stock. Some of the most promising were furfural, safrol, salicylic aldebyde, several essential oils—namely cloves, cassia, citronella, fennel, sassafras and anise—pine tar oils and certain camphor oils. A very effective repellent for practical use is a mixture of one part furfural to four parts pine tar oil. As a larvicide for use on wounds benzol is satisfactory.