Jerome A. Klun

Benzoquinones from millipedes deter mosquitoes and elicit self-anointing in capuchin monkeys ( Cebus spp.)

Neotropical monkeys of the genus Cebus anoint themselves by rubbing arthropods and plants against their pelage. A recent study has shown that free-ranging wedge-capped capuchin monkeys (C. olivaceus) in Venezuela self-anoint with a benzoquinone-secreting millipede, an activity by which they are hypothesized to appropriate chemical deterrents of mosquitoes. To evaluate the plausibility of this hypothesis, female yellow fever mosquitoes (Aedes aegypti) were presented with two millipede secretory compounds, 2-methyl-1,4-benzoquinone and 2-methoxy-3-methyl-1,4-benzoquinone, on nylon-reinforced silicone membranes placed over wells filled with human blood, a highly preferred food. Mosquitoes exhibited fewer landings, fed less frequently, and flew more frequently (a possible indication of repellency) in the presence of membranes treated with benzoquinones than with controls. These compounds also elicit self-anointing in captive male and female tufted (C. apella) and white-faced (C. capucinus) capuchin monkeys.

A New Module for Quantitative Evaluation of Repellent Efficacy Using Human Subjects

Abstract A new module for quantitative evaluation of arthropod repellents in human subjects was designed, constructed, and protocols for use of the module were developed. Doses of 3 arthropod repellents, 1-[3-cyclohexen-1-ylcarbonyl] piperidine (AI3-35765), 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine (AI3-37220), and N, N-diethyl-3-methylbenzamide (deet), were evaluated using the mosquito, Anopheles stephensi Liston. Biting responses to varied doses of the repellents on human skin were quantified, and the effectiveness of the 3 repellents was compared. The new module consists of 6 test cells and permits the simultaneous comparison of up to 5 repellent doses or chemical types and a control using a complete randomized block design with minimal treatment interaction and with ≥6 replicates per human subject.

Repellent and deterrent effects of SS220, Picaridin, and Deet suppress human blood feeding by Aedes aegypti, Anopheles stephensi, and Phlebotomus papatasi.

Abstract A series of behavioral tests with Aedes aegypti (L.), Anopheles stephensi Liston, mosquitoes, and the sand fly Phlebotomus papatasi Scopoli in the presence of Deet, SS220, and Picaridin topically applied to the skin of human volunteers showed that the insects were deterred from feeding on and repelled from surfaces emanating the compounds. When offered a 12- or 24-cm2 area of skin, one-half treated with compound and one-half untreated, the insects fed almost exclusively on untreated skin. The sand flies and mosquitoes did not at any time physically contact chemically treated surfaces. When treated and untreated skin areas were covered with cloth, insects contacted, landed, and bit only through cloth covering untreated skin. These observations provided evidence that the compounds deterred feeding and repelled insects from treated surfaces primarily as a result of olfactory sensing. When cloth, one-half untreated and one-half treated with chemical, was placed over untreated skin, insects only touched and specifically bit through the untreated cloth. This showed that the activity of the chemicals does not involve a chemical × skin interaction. In the presence of any of the three chemicals, no matter how they were presented to the insects, overall population biting activity was reduced by about one-half relative to controls. This reduction showed a true repellent effect for the compounds. Results clearly showed that Deet, SS220, and Picaridin exert repellent and deterrent effects upon the behavior of mosquitoes and sand flies. Heretofore, the combined behavioral effects of these compounds upon mosquito and sand fly behavior were unknown. Moreover, protection afforded by Deet, SS220, and Picaridin against the feeding of these three disease vectors on humans is mechanistically a consequence of the two chemical effects.

Repellency of deet and SS220 applied to skin involves olfactory sensing by two species of ticks

Abstract.  Responses of host‐seeking nymphs of the blacklegged tick, Ixodes scapularis Say and lone star tick, Amblyomma americanum (Linnaeus) (Acari: Ixodidae) to the repellents N,N‐diethyl‐3‐methylbenzamide (deet) and (1S, 2′S)‐2‐methylpiperidinyl‐3‐cyclohexene‐1‐carboxamide (SS220) were studied using fingertip laboratory bioassays. Ethanol solutions of both compounds applied to the skin strongly repelled both species of ticks at 0.8 and 1.6 µmole of compound/cm2 skin. The ticks were also repelled when two layers of organdie cloth covered the portion of a finger treated with either deet or SS220. Gas chromatographic analyses of the outer layer of cloth that had covered skin treated with 1.6 µmole compound/cm2 skin revealed only 0.1 nmole SS220/cm2 cloth and 2.8 nmole deet/cm2 cloth. However, in bioassays in which a single layer of cloth was treated with a dose of deet or SS220 equivalent to the amount found in the outer layer of cloth, ticks were not repelled. Results unequivocally demonstrated that these ticks responded to the repellents in the vapour phase when repellent treated skin was covered with cloth to obviate tactile contact with them, and made it clear that the ticks detect the repellents by olfactory sensing. Heretofore, the mode of action of deet and SS220 was unclear.

Synthesis and Repellent Efficacy of a New Chiral Piperidine Analog: Comparison with Deet and Bayrepel Activity in Human-Volunteer Laboratory Assays Against Aedes aegypti and Anopheles stephensi

Abstract Optically active (1S, 2′S)-2-methylpiperidinyl-3-cyclohexen-1-carboxamide (SS220) is a new synthetic arthropod repellent. A three-step synthesis based on a chiral Diels-Alder reaction and diastereomeric resolution of 2-methylpiperidine was developed to prepare the compound. Quantitative laboratory assays using human volunteers compared the effectiveness of SS220 with the commonly used repellents Deet and Bayrepel against Aedes aegypti (Linnaeus) and Anopheles stephensi Liston mosquitoes. In two experiments using Aedes aegypti, one using a single identical dose and one with varying doses used to develop a dose–response curve, SS220 was as effective as Deet and both compounds were more effective than Bayrepel. The three compounds were equally effective against An. stephensi. Based on the ease of its synthetic preparation and its repellent efficacy, we surmise that SS220 is a candidate to serve as a new and effective alternate repellent for protection against arthropod disease vectors.

Isolongifolenone: A Novel Sesquiterpene Repellent of Ticks and Mosquitoes

ABSTRACT A naturally occurring sesquiterpene, isolongifolenone, derivatives of which have been used extensively as ingredients in the cosmetics industry, was discovered to effectively repel blood-feeding arthropods that are important disease vectors. We show that (—)-isolongifolenone deters the biting of the mosquitoes, Aedes aegypti (L.) and Anopheles stephensi Liston, more effectively than the widely used synthetic chemical repellent, N,N-diethyl-3-methyl benzamide (DEET), in laboratory bioassays. The compound also repelled blacklegged ticks, Ixodes scapularis Say, and lone star ticks, Amblyomma americanum (L.), as effectively as DEET. Isolongifolenone is easily synthesized from inexpensive turpentine oil feedstock. We are therefore confident that the compound has significant potential as an inexpensive and safe repellent for protection of large human populations against blood-feeding arthropods.

Comparative Resistance of Anopheles albimanus and Aedes aegypti to N,N-Diethyl-3-methylbenzamide (Deet) and 2-Methylpiperidinyl-3-cyclohexen-1-carboxamide (AI3-37220) in Laboratory Human-Volunteer Repellent Assays

Abstract The insect repellents N,N-diethyl-3-methylbenzamide (Deet) and the racemate and 1S,2′S stereoisomer of 2-methylpiperidinyl-3-cyclohexene-1-carboxamide (AI3-37220) were tested against Anopheles albimanus Wiedemann and Aedes aegypti (L.) in laboratory human-volunteer assays. Estimated skin doses of Deet or racemic AI3–37220 required to reduce biting by 95% in Ae. aegypti were 2.3 and 3.5 × 10–2 μmol/cm2 skin, respectively, whereas estimated doses for 95% bite reduction of An. albimanus in an ≈40-yr-old laboratory colony established from El Salvador were 5 times higher at 12 × 10–2 μmol Deet/cm2 skin and >20 × 10–2 μmol/cm2 skin for AI3-37220. In tests with the 1S,2′S stereoisomer of AI3-37220, a newly established colony of An. albimanus from Belize bit less aggressively than El Salvador An. albimanus. However, the Belize-derived mosquitoes were as resistant as the old El Salvador colony to repellent effects of 1S,2′S stereoisomer of 2-methylpiperidinyl-3-cyclohexene-1-carboxamide. Earlier workers surmised that usual skin doses of Deet would offer only limited protection against An. albimanus in the field. Our findings support this speculation, but they also indicate that doses of Deet higher than those needed for protection against Ae. aegypti might offer reasonable protection against An. albimanus. Results indicate that neither racemate nor 1S,2′S stereoisomer of 2-methylpiperidinyl-3-cyclohexene-1-carboxamide offer as much protection as Deet against An. Albimanus, despite being highly effective against Ae. aegypti.

Feeding Deterrent Effects of Catnip Oil Components Compared with Two Synthetic Amides Against Aedes aegypti

Abstract Recently, catnip, Nepeta cataria L. (Lamiaceae), essential oil has been formulated and marketed as an alternative repellent for protection against biting arthropods by several vendors. We isolated the major active components of catnip oil, E,Z- and Z,E-nepetalactone, and quantitatively measured their antibiting efficacy compared with the repellents N,N-diethyl-3-methylbenzamide (deet) and chiral (1S,2′S)-2-methylpiperidinyl-3-cyclohexene-1-carboxamide (SS220) against the yellowfever mosquito, Aedes aegypti (L.), by using an in vitro assay and human volunteers at 24 nmol compound/cm2 (cloth or skin). Of all compounds tested in an in vitro assay, SS220 ranked as the most effective, whereas catnip oil and the nepetalactone compounds did not differ significantly from each other or from deet. However, in human volunteer bioassays, neither E,Z and Z,E-nepetalactone nor racemic nepetalactone deterred mosquito biting as effectively as SS220 or deet. All compounds differed significantly from the control. We conclude that catnip oil and nepetalactone isomers are significantly less effective than deet or SS220 in deterring the biting of Ae. aegypti.

Sex Pheromone of the Soybean Aphid, Aphis glycines Matsumura, and Its Potential Use in Semiochemical-Based Control

Abstract The newly invasive soybean aphid, Aphis glycines Matsumura, has seriously threatened soybean production in North America, after having spread to >20 states in the United States and several southern provinces of Canada. Control of A. glycines has focused on applications of insecticides, which are not a long-term solution to soybean aphid pest management. In autumn, soybean aphids start producing alate females (gynoparae) that search for their overwintering host plants, the common buckthorn, Rhamnus cathartica. The gynoparae then produce pheromone-emitting wingless female offspring (oviparae) that attract male aphids. In this study, we report the chemical identification of the soybean aphid sex pheromone using gas chromatography–electroantennogram, gas chromatography–mass spectrometry, and nuclear magnetic resonance spectroscopy. Behavioral activities of males and gynoparous females in the field were also characterized. The potential applications using formulations containing specific soybean aphid pheromone compositions for reducing overwintering populations are discussed.

Stereochemical Effects in an Insect Repellent

Abstract Racemic 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine repels blood-feeding arthropods such as mosquitoes, chiggers, and ticks. The compound contains two asymmetric carbon atoms and the racemate consists of four stereoisomers. Quantitative mosquito bioassays using Aedes aegypti (L.) showed that (1S,2′S) and (1R,2′S) configurations were 2.8–3.1 and 1.6–1.8 times more effective, respectively, than the other two stereoisomers in reducing mosquito bites. (1S,2′S) was 2.5 more repellent than the racemate. Biological data show that an interaction of the (2′S)-2-methylpiperidine configuration with a repellent receptor system in A. aegypti is apparently important to repellent activity. Nuclear magnetic resonance spectra and molecular mechanics calculations for the stereoisomers provided insight into the conformation of the (2′S)-group. Results indicate that enhanced repellent effects can be realized through formulation of the most active stereoisomers of the compound.