Better than DEET Repellent Compounds Derived from Coconut Oil

Hematophagous arthropods are capable of transmitting human and animal pathogens worldwide. Vector-borne diseases account for 17% of all infectious diseases resulting in 700,000 human deaths annually. Repellents are a primary tool for reducing the impact of biting arthropods on humans and animals. N,N-Diethyl-meta-toluamide (DEET), the most effective and long-lasting repellent currently available commercially, has long been considered the gold standard in insect repellents, but with reported human health issues, particularly for infants and pregnant women. In the present study, we report fatty acids derived from coconut oil which are novel, inexpensive and highly efficacious repellant compounds. These coconut fatty acids are active against a broad array of blood-sucking arthropods including biting flies, ticks, bed bugs and mosquitoes. The medium-chain length fatty acids from C8:0 to C12:0 were found to exhibit the predominant repellent activity. In laboratory bioassays, these fatty acids repelled biting flies and bed bugs for two weeks after application, and ticks for one week. Repellency was stronger and with longer residual activity than that of DEET. In addition, repellency was also found against mosquitoes. An aqueous starch-based formulation containing natural coconut fatty acids was also prepared and shown to protect pastured cattle from biting flies up to 96-hours in the hot summer, which, to our knowledge, is the longest protection provided by a natural repellent product studied to date

Pyrethroid resistance alters the blood-feeding behavior in Puerto Rican <i>Aedes aegypti</i> mosquitoes exposed to treated fabric

<div><p>Emerging insecticide resistance is a major issue for vector control. It decreases the effectiveness of insecticides, thereby requiring greater quantities for comparable control with a net increase in risk of disease resurgence, product cost, and damage risk to the ecosystem. Pyrethroid resistance has been documented in Puerto Rican populations of <i>Aedes aegypti</i> (L.) mosquitoes. In this study, topical toxicity of five insecticides (permethrin, etofenprox, deltamethrin, DDT, transfluthrin) was determined for susceptible (Orlando—ORL) and resistant (Puerto Rico—PR) strains of <i>Ae</i>. <i>aegypti</i>. Resistance ratios were calculated using LD₅₀ values, and high resistance ratios for permethrin (112) and etofenprox (228) were observed for the Puerto Rico strain. Behavioral differences in blood-feeding activity for pyrethroid-resistant and pyrethroid-susceptible strains of <i>Ae</i>. <i>aegypti</i> when exposed to pyrethroid-treated cloth were also explored. Strains were exposed for 15 min to a range of concentrations of pyrethroid-treated uniform fabric in a cage that contained 60 female <i>Ae</i>. <i>aegypti</i> mosquitoes. Interestingly, the resistance ratios for blood-feeding were similar for permethrin (61) and etofenprox (70), but were lower than their respective resistance ratios for topical toxicity, suggesting that knockdown resistance was the primary mechanism of resistance in the blood feeding assays. Results showed a rightward shift in the dose-response curves for blood-feeding that indicated higher concentrations of pyrethroids were necessary to deter blood-feeding behavior in the pyrethroid-resistant Puerto Rican strain of <i>Ae</i>. <i>aegypti</i>.</p></div

Example of blood-feeding assay with untreated control (A) and permethrin-treated uniforms (B) inserted into a stock cage filled with approximately 60 female <i>Ae</i>. <i>aegypti</i> mosquitoes.

<p>Photos by G. Allen.</p

Topical LD₅₀, blood-feeding ED₅₀, and resistance ratios (RR) for ORL and PR <i>Ae</i>. <i>aegypti</i> strains tested with five insecticides.

<p>Blood-feeding data for transfluthrin are omitted because it had slope factors not significantly different from zero.</p

Dose response curves for blood-feeding behavior on permethrin-, etofenprox-, deltamethrin-, and DDT-treated uniforms with <i>Ae</i>. <i>aegypti</i> mosquitoes of the susceptible Orlando (ORL) strain (A) and pyrethroid-resistant Puerto Rico (PR) strain (B).

<p>The axes indicate the relationship between percent bite protection (right y-axis) and the log of the concentration in milligram per centimeter squared (x-axis) of insecticide-treated fabric. The left y-axis has been converted to a probit scale for clearer presentation. Error bars indicate SEM.</p

Essential Oil Composition of Pimpinella cypria and its Insecticidal, Cytotoxic, and Antimicrobial Activity

WOS: 000384513900030PubMed ID: 30549615A water-distilled essential oil (EO) from the aerial parts of Pimpinella cypria Boiss. (Apiaceae), an endemic species in northern Cyprus, was analyzed by GC-FID and GC-MS. Forty-five compounds were identified in the oil, which comprised 81.7% of the total composition. The compound classes in the oil were oxygenated sesquiterpenes (33.9%), sesquiterpenes (22.0%), monoterpenes (11.4%), oxygenated monoterpenes (2.6%), and phenylpropanoids (7.5%). The main components of the oil were (Z)-beta-farnesene (6.0%), spathulenol (5.9%), ar-curcumene (4.3%), and 1,5-epoxy-salvial(4)14-ene (3.8%). The P. cypria EO deterred yellow fever mosquitoes (Aedes aegypti) from biting at a concentration of 10 mu g/cm(2) in in vitro bioassays. The oil was tested for repellency in assays using human volunteers. The oil had a minimum effective dosage (MED) for repellency of 47 +/- 41 mu g/cm(2) against Ae. aegypti, which was less efficacious than the positive control N,N-diethyl-3-methylbenzamide (DEET). In larval bioassays, P. cypria EO showed an LC50 value of 28.3 ppm against 1st instar Ae. aegypti larvae. P. cypria EO demonstrated dose dependent repellency against nymphs of the lone star tick, Amblyomma americanum. Between 45.0% and 85.0% repellency was observed at concentrations ranging from 26 to 208 mu g/cm(2). However, P. cypria EO was less effective compared with DEET in the tick bioassays. Cytotoxicity assays showed that the P. cypria EO did not exhibit significant effects up to the maximum treatment concentration of 50 mu g/mL on HEK293, PC3, U87MG, and MCF cells. P. cypria EO also demonstrated moderate antimicrobial activity against Gram-negative and-positive bacteria with MICs ranging from 15.6 to 62.5 mu g/mL, except for Candida albicans, which showed the same MIC value of 7.8 mu g/mL as the positive control, flucytosine. This is the first report on the chemical composition of P. cypria EO and its insecticidal, toxicant, cytotoxic, and antimicrobial activity.Deployed War-Fighter Protection Research Program Grant by the U.S. Department of Defense through the Armed Forces Pest Management BoardWe would like to thank AREL (Ege University School of Medicine Research and Education Laboratory) for carrying out the cell culture studies. This study was in part funded by a Deployed War-Fighter Protection Research Program Grant by the U.S. Department of Defense through the Armed Forces Pest Management Board. We thank Dr James J. Becnel (USDA-ARS, CMAVE, Gainesville FL) for supplying Ae. aegypti eggs, and Greg Allen (USDA-ARS, CMAVE, Gainesville FL) and James McCrary (USDA, ARS, IIBBL) for mosquito and tick repellency bioassays

Repellency of the <i>Origanum onites</i> L. essential oil and constituents to the lone star tick and yellow fever mosquito

<p>The oregano, <i>Origanum onites</i> L., essential oil (EO) was tested in laboratory behavioural bioassays for repellent activity against <i>Amblyomma americanum</i> (L.) and <i>Aedes aegypti</i> (L.). The <i>O. onites</i> EO was characterised using GC-FID and GC-MS. Carvacrol (75.70%), linalool (9.0%), <i>p</i>-cymene (4.33%) and thymol (1.9%) were the most abundant compounds. At a concentration of 0.413 mg oil/cm² of filter paper, <i>O. onites</i> EO repelled 100% of the ticks tested and at 0.103 mg oil/cm² of filter paper, 66.7% of the ticks were repelled. At 0.075 mg oil/cm² filter paper, thymol repelled 66.7% of the ticks compared to 28.7% by carvacrol at that same concentration. Against <i>Ae. aegypti</i>, <i>O. onites</i> EO was repellent at the minimum effective dosage (MED) of 0.011 (±0.00) mg/cm² in the cloth patch assay compared to the reference control, <i>N</i>,<i>N</i>-dimethyl-3-methylbenzamide (DEET) with a MED = 0.007 ± (0.003) mg/cm².</p

Rhanterium epapposum Oliv. essential oil: Chemical composition and antimicrobial, insect-repellent and anticholinesterase activities

The essential oil (EO) of the aerial parts of Rhanterium epapposum Oliv. (Asteraceae), was obtained by hydrodistillation. The oil was subsequently analyzed by both GC-FID and GC-MS, simultaneously. Forty-five components representing 99.2% of the oil composition were identified. The most abundant compounds were camphene (38.5%), myrcene (17.5%), limonene (10.1%) and α-pinene (8.7%). Referring to the ethnobotanical utilization, an insecticidal assay was performed, where the oil repelled the yellow fever mosquito Aedes aegypti L. at a minimum effective dose (MED of 0.035 ± 0.010 mg/cm2) compared to the positive control DEET (MED of 0.015 ± 0.004 mg/cm2). Additionally, the in vitro antimicrobial activity against a panel of pathogens was determined using a microdilution method. The acetyl- and butyrylcholine esterase inhibitory activities were measured using the colorimetric Ellman method. The bioassay results showed that the oil was rather moderate in antimicrobial and cholinesterase inhibitions when compared to the standard compounds