J. F. Carroll

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.

Essential oils of Cupressus funebris, Juniperus communis, and J. chinensis (Cupressaceae) as repellents against ticks (Acari: Ixodidae) and mosquitoes (Diptera: Culicidae) and as toxicants against mosquitoes

ABSTRACT: Juniperus communis leaf oil, J. chinensis wood oil, and Cupressus funebris wood oil (Cupressaceae) from China were analyzed by gas chromatography and gas chromatography-mass spectrometry We identified 104 compounds, representing 66.8–95.5% of the oils. The major components were: &agr;-pinene (27.0%), &agr;-terpinene (14.0%), and linalool (10.9%) for J. communis; cuparene (11.3%) and &dgr;-cadinene (7.8%) for J. chinensis; and &agr;-cedrene (16.9%), cedrol (7.6%), and &bgr;-cedrene (5.7%) for C. funebris. The essential oils of C. funebris, J. chinensis, and J. communis were evaluated for repellency against adult yellow fever mosquitoes, Aedes aegypti (L.), host-seeking nymphs of the lone star tick, Amblyomma americanum (L.), and the blacklegged tick, Ixodes scapularis Say, and for toxicity against Ae. aegypti larvae and adults, all in laboratory bioassays. All the oils were repellent to both species of ticks. The EC95 values of C. funebris, J. communis, and J. chinensis against A. americanum were 0.426, 0.508, and 0.917 mg oil/cm2 filter paper, respectively, compared to 0.683 mg deet/cm2 filter paper. All I. scapularis nymphs were repelled by 0.103 mg oil/cm2 filter paper of C. funebris oil. At 4 h after application, 0.827 mg oil/cm2 filter paper, C. funebris and J. chinensis oils repelled ≥80% of A. americanum nymphs. The oils of C. funebris and J. chinensis did not prevent female Ae. aegypti from biting at the highest dosage tested (1.500 mg/cm2). However, the oil of J. communis had a Minimum Effective Dosage (estimate of ED99) for repellency of 0.029 ± 0.018 mg/cm2; this oil was nearly as potent as deet. The oil of J. chinensis showed a mild ability to kill Ae. aegypti larvae, at 80 and 100% at 125 and 250 ppm, respectively.

Different Activities and Footwear Influence Exposure to Host-Seeking Nymphs of Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae)

Abstract The relative potential for a person accidentally acquiring host-seeking nymphs of the blacklegged tick, Ixodes scapularis Say, and lone star tick, Amblyomma americanum (L.), while wearing either of two types of footwear, walking, crawling on hands and knees, and sitting on large fallen logs in deciduous woods, was evaluated. Although flag samples indicated substantial populations of I. scapularis nymphs and low to moderate numbers of A. americanum at the study sites, relatively few I. scapularis and fewer still A. americanum nymphs were acquired during 30-s and 5-min walks. Significantly fewer I. scapularis were picked up when boots were worn with ankles taped (an anti-tick precaution) than when sneakers were worn with socks exposed during 5-min walks, but when thus attired, there was no significant difference between the number of nymphs acquired during 30-s walks. Nymphs of I. scapularis did not appear to accumulate incrementally on footwear or clothing during walks when boots were worn and ankles taped. Crawling for 30 s (≈3 m distance) yielded significantly more I. scapularis nymphs than walking for 30 s. During crawling, I. scapularis nymphs were picked up on 58% of the 30-s samples. Most ticks picked up during crawls were on pant legs. When a flannel flag cloth (0.5 by 0.5 m) was appressed to the upper surface of logs suitable to be sat upon by tired hikers, I. scapularis nymphs were found on 87% of the logs and in 36% of the samples. These data indicate that the potential for contact with host-seeking nymphs of I. scapularis occurring at these densities is greatly elevated by engaging in activities that involve contact with fallen logs and close contact of hands and knees with leaf litter.

Natural product studies of U.S. endangered plants: Volatile components of Lindera melissifolia (Lauraceae) repel mosquitoes and ticks

The number of endangered plant species in the U.S. is significant, yet studies aimed towards utilizing these plants are limited. Ticks and mosquitoes are vectors of significant pathogenic diseases of humans. Repellents are critical means of personal protection against biting arthropods and disease transmission. The essential oil and solvent extracts from Lindera melissifolia (Walt.) Blume (Lauraceae) (pondberry) drupes were gathered and analyzed by GC and GC-MS. The essential oil obtained from this endangered plant showed a significant dose dependent repellency of ticks and a moderate mosquito repellent effect while the subsequent hexanes extract was completely ineffective. Fractional freezing enriched the tick repellent components of the essential oil. Several known tick repellent components were recognized by the GC-MS comparison of the resulting fractions and β-caryophyllene, α-humulene, germacrene D and β-elemene warrant evaluations for tick repellency. Identifying pondberry as a potential renewable source for a broad spectrum repellent supports efforts to conserve similar U.S. endangered or threatened plant species.

How specific are host-produced kairomones to host-seeking ixodid ticks?

Ixodid ticks respond to host-produced substances (kairomones) that influence the ticks’ host-finding behavior. In the laboratory adult blacklegged ticks, Ixodes scapularis Say, lone star ticks, Amblyomma americanum L., and American dog ticks, Dermacentor variabilis (Say) became akinetic on residues rubbed from their principal hosts (deer for the former two species and dogs for the latter). However, arrestment also occurred when adults of these species were tested using the same method bioassay, but with host substances reversed (i.e., I. scapularis and A. americanum against canine substances, and D. variabilis against deer gland substances). Although adult D. variabilis exhibited arrestant responses to deer substances and are often found along trails used by deer, they apparently make little use of deer as hosts. It is unclear whether responding to deer-produced kairomones may have disadvantages for D. variabilis. Until the active components of host-produced arrestment kairomones are isolated, identified and evaluated in behavioral tests, this host-finding strategy remains only partially understood.

Interdigital Gland Substances of White-Tailed Deer and the Response of Host-Seeking Ticks (Acari: Ixodidae)

Abstract Host-seeking male and female blacklegged ticks, Ixodes scapularis Say, exhibited an arrestant response when contacting substances from front and rear interdigital glands of male and female white-tailed deer, Odocoileus virginianus (Zimmermann). Female I. scapularis responded positively to substances from interdigital glands on the fore legs and hind legs of female deer, whereas male I. scapularis responded only to samples from the fore legs of does. These results showed that previously reported responses of I. scapularis to residues from interdigital glands of hind legs of deer were independent of tarsal gland substances, which may contaminate interdigital gland substances on hind legs. Nymphs of I. scapularis and female lone star ticks, Amblyomma americanum (L.), did not show an arrestant response to substances from hind legs of does, but male A. americanum did.

Responses of adult Ixodes scapularis (Acari: Ixodidae) to urine produced by white-tailed deer of various reproductive conditions.

Abstract The responses of adult female blacklegged ticks,Ixodes scapularis Say, to urine from white-tailed deer,Odocoileus virginianus (Zimmermann), belonging to 4 reproductive categories (doe in estrous, doe out of season, reproductive [dominant] buck, young buck) and to a mixture of urine from nondominant bucks in rut, young bucks out of rut, and nonestrous does were studied in laboratory behavioral bioassays. In high humidity (≈95% RH) in a glove box there were no statistically significant arrestment responses to any of the 5 types of urine, but an avoidance response was observed to urine from dominant reproductive bucks. When ticks were tested at ≈50% RH, with samples of all 5 types of urine in the glove box, significant arrestant responses by the ticks were elicited by urine from does in estrous and by dominant reproductive bucks. When tested without other types of urine in the glove box, the urine mixture elicited an arrestant response at 50% RH. In some circumstances, adultI. scapularis may possibly use deer urine as a chemical cue in selecting host-ambush sites.

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

Abstract The oregano, Origanum onites L., essential oil (EO) was tested in laboratory behavioural bioassays for repellent activity against Amblyomma americanum (L.) and Aedes aegypti (L.). The O. onites EO was characterised using GC-FID and GC-MS. Carvacrol (75.70%), linalool (9.0%), p-cymene (4.33%) and thymol (1.9%) were the most abundant compounds. At a concentration of 0.413 mg oil/cm2 of filter paper, O. onites 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 Ae. aegypti, O. onites 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, N,N-dimethyl-3-methylbenzamide (DEET) with a MED = 0.007 ± (0.003) mg/cm2.

Solvent, Drying Time, and Substrate Affect the Responses of Lone Star Ticks (Acari: Ixodidae) to the Repellents Deet and Picaridin

ABSTRACT Behavioral bioassays remain a standard tool in the discovery, development, and registration of arthropod repellents. Tick repellent bioassays are generally uncomplicated, but their results can be affected by basic variables (e.g., dimensions of testing materials, substrate, timing, temperature) of the assay. Using lone star tick, Amblyomma americanum (L.), nymphs in climbing bioassays, we tested for the effects of substrate, solvent, and drying time on tick responses. In dose-response tests, the widely used repellents N,N-diethyl-3-methyl benzamide (deet) and 1-methylpropyl-2-(hydroxyethyl)-l-piperidinecarboxylate (picaridin) were applied to filter paper strips and challenged by ticks at 10, 20, 30, 40, and 120 min after application. At 10-min drying time, repellency at the intermediate concentration 500 nmol repellent/cm2 filter paper was significantly lower for ethanol solutions of deet and picaridin (0 and 10% ticks repelled, respectively) than for solutions of deet and picaridin in acetone (96.7 and 76.7% ticks repelled, respectively). Repellency was greatest for both the acetone and ethanol solutions of deet and picaridin when challenged 120 min after application, and at shorter drying times at the highest concentration tested (2,000 nmol compound/cm2). The repellency of picaridin relative to deet differed at some combinations of solvent and drying time but not others. In dose-response tests using different paper substrates and a drying time of 10 min, both ethanol and acetone solutions of deet differed in repellency, depending on both the paper substrate and the solvent. However, there were no differences in repellency between ethanol and acetone solutions of deet applied to nylon organdy in an in vitro and in an in vivo (fingertip) bioassay. When deet in solution with various proportions of ethanol:water was applied at 2,000 nmol deet/cm2 filter paper, the proportion of ticks repelled decreased as the proportion of water in the test solutions increased. Somewhat similar results were seen for solutions of deet in an acetone solvent. Water absorbed from the atmosphere may affect the efficacy of repellents in solution with anhydrous ethanol. Overall, results obtained from bioassays that differ in seemingly minor ways can be surprisingly different, diminishing the value of comparing studies that used similar, but not identical, methods. Nylon organdy or another similar thin cloth may be preferable to filter papers and copier paper for minimizing solvent-related differences. When a paper substrate is used, acetone may be the more suitable solvent if the solubility of the test compound and other factors allow.

Composition of Cyclotrichium niveum Essential Oil: Enantiomeric Separation of Pulegone and Repellent Activity Against the Lone Star Tick, and Yellow Fever Mosquito

Ticks and mosquitoes transmit pathogens that can cause serious and sometimes fatal diseases to humans and other animals. Chemical repellents are an important personal protection tool to protect humans and livestock from arthropod bites. Our research programs focuses on the discovery of naturally occurring insecticides and repellents that can be used to further reduce disease transmission risk to animals. The most widely used topical repellent is a synthetic compound, DEET (N,N-diethyl-m-toluamide). However, concerns over the safety of DEET lead to some user acceptability issues among repellent users. Consequently, there has been an increase in focus on alternative repellents from the natural sources. As part of our efforts to identify natural repellents, we investigated the essential oil of Cyclotrichium niveum (Boiss.) Manden. (Labiatae) as a repellent against the lone star tick, Amblyomma americanum nymphs, and against adult yellow fever mosquitoes, Aedes aegypti. Cyclotrichium niveum essential oil showed good repellent activity against both species and pulegone was more effective against A. americanum and Ae. aegypti. The enantiomeric distribution of (R)-(+)-pulegone was determined by using Rt-βDEXse fused silica chiral capillary column using multidimensional GC-MS system.Acknowledgements: This study was supported by USDA, ARS grant No. 56 – 6402 – 1-612 and Deployed War-Fighter Protection (DWFP) Research Program and the U.S. Department of Defense through the Armed Forces Pest Management Board (AFPMB).