Novel field assays and the comparative repellency of BioUD(®) , DEET and permethrin against Amblyomma americanum

Two new field bioassay methods were developed to compare the repellent activity of BioUD^® (containing 7.75% 2‐undecanone), 98.1% DEET and 0.5% permethrin against natural populations of nymphal Amblyomma americanum (L.) (Acari: Ixodidae). In a cloth sheet assay, pieces of material measuring 41 × 58 cm, separately treated with one of the test materials or the appropriate solvent carrier, were placed at random on the ground and baited with dry ice for 1 h. Mean numbers of ticks on repellent‐treated sheets were significantly lower than on control sheets. There was no significant difference in the number of ticks collected between sheets treated with BioUD^® and those treated with DEET. However, significantly fewer ticks were found on sheets treated with BioUD^® or DEET than on permethrin‐treated sheets. In a sock test, over‐the‐calf tube socks were treated with one of the test materials or the appropriate solvent carrier. Human volunteers wore a repellent‐treated and a corresponding carrier‐treated sock on either leg and walked randomly over an area of approximately 4000 m² for 15 min. Significantly fewer ticks were collected from socks treated with BioUD^® or DEET than from socks treated with the carrier and there was no significant difference in repellency between these two agents. No difference in the mean number of ticks collected was found between permethrin‐treated and corresponding carrier‐treated socks. To examine the mechanism of repellency of BioUD^®, a four‐choice olfactometer was used to assess spatial repellency against adult A. americanum. As expected in the absence of a repellent, when all choices were represented by water‐treated filter paper, ticks were equally distributed among the choices. When one choice consisted of BioUD^®‐treated filter paper and the remaining choices of water‐treated paper, the distribution of ticks on the repellent‐treated paper was significantly lower than might be expected to occur by chance, suggesting that repellency is at least partly achieved by an olfactory mechanism.     

Sustained efficacy of the novel topical repellent TT‐4302 against mosquitoes and ticks

Mosquitoes and ticks are blood‐feeding pests of humans and animals that can vector many important aetiological agents of disease. Previous research demonstrated that TT‐4302 (Guardian^® Wilderness) containing 5% geraniol applied to human subjects gave 5–6 h of repellency against mosquitoes (depending on species) and was repellent to ticks in vitro. This study was conducted to obtain an independent third‐party evaluation of TT‐4302 against Stegomyia aegypti (= Aedes aegypti) (Diptera: Culicidae) mosquitoes and to test the efficacy of the product in the field against ticks. TT‐4302 provided an average of 6.5 h of repellency of ≥ 95% [Weibull mean protection time: 7.4 h, 95% confidence interval (CI) 5.8–11.3 h] for St. aegypti, whereas a 15% DEET formulation provided 4.7 h of repellency (Weibull mean protection time: 5.2 h, 95% CI 3.7–6.9 h). In tick field trials, the efficacy of TT‐4302 did not differ significantly from that of a 25% DEET formulation against Amblyomma americanum (Ixodida: Ixodidae). TT‐4302 was 81.3% repellent at 2.5 h after application, whereas DEET was 77.2% repellent at the same time‐point. Results at 3.5 h after application were 71.4% for TT‐4302 and 72.9% for DEET.     

Responses of Amblyomma americanum and Dermacentor variabilis to odorants that attract haematophagous insects

Carbon dioxide (CO₂), 1‐octen‐3‐ol, acetone, ammonium hydroxide, L‐lactic‐acid, dimethyl trisulphide and isobutyric acid were tested as attractants for two tick species, Amblyomma americanum and Dermacentor variabilis (Acari: Ixodidae), in dose–response bioassays using Y‐tube olfactometers. Only CO₂, acetone, 1‐octen‐3‐ol and ammonium hydroxide elicited significant preferences from adult A. americanum, and only CO₂ was attractive to adult D. variabilis. Acetone, 1‐octen‐3‐ol and ammonium hydroxide were separately evaluated at three doses against CO₂ (from dry ice) at a field site supporting a natural population of A. americanum nymphs and adults. Carbon dioxide consistently attracted the highest number of host‐seeking ticks. However, for the first time, acetone, 1‐octen‐3‐ol and ammonium hydroxide were shown to attract high numbers of A. americanum. Further research is needed to determine the utility of these semiochemicals as attractants in tick surveillance and area‐wide management programmes.     

Repellency and toxicity of a CO2-derived cedarwood oil on hard tick species (Ixodidae)

The repellency and toxicity of a CO₂-derived cedarwood oil (CWO) was evaluated against actively questing unfed nymphs of four species of hard ticks: Amblyomma americanum (L.), Dermacentor variabilis (Say), Ixodes scapularis Say, and Rhipicephalus sanguineus (Latreille). Using a vertical climb bioassay for repellency, nymphs of these species avoided a CWO-treated filter paper in proportional responses to treatment concentrations. At 60 min of exposure, I. scapularis nymphs were most sensitive with 50% repellency concentration (RC₅₀) of 19.8 µg cm^?2, compared with RC₅₀ of 30.8, 83.8 and 89.6 µg cm^?2 for R. sanguineus, D. variabilis and A. americanum, respectively. Bioassays determined the lethal concentration for 50% (LC₅₀) and 90% (LC₉₀) mortality of nymphs exposed to CWO in treated vials after 24- and 48-h exposure. After 24 h exposure, the LC₅₀ values were 1.25, 3.45 and 1.42 µg cm^?2 and LC₉₀ values were 2.39, 7.59 and 4.14 µg cm^?2 for D. variabilis, I. scapularis and R. sanguineus, respectively, but had minimal effect on A. americanum. After 48 h exposure, the LC₅₀ values were 4.14, 0.78, 0.79 and 0.52 µg cm^?2, and LC₉₀ values were 8.06, 1.48, 1.54 and 1.22 µg cm^?2 for A. americanum, D. variabilis, I. scapularis and R. sanguineus, respectively. The repellency of CWO on tick species decreased with time. The repellency and toxicity bioassays demonstrated concentration-dependent responses of tick nymphs to the oil, indicating the potential of the CO₂-derived cedarwood oil be developed as an eco-friendly repellent and/or acaricide.

     

Relationship between habitat type,fire frequency,and Amblyomma americanum populations in east‐central Alabama

Ticks were collected from 20 sites in the Calhoun, Cherokee, and Cleburne Counties in east‐central Alabama areas to determine the relationship between plant physiognomy, environmental variables, and tick populations. Sites investigated included various burning regimes, wildland‐urban–interface (WUI), a college campus, and an unmanaged area. Amblyomma americanum (L.) (Acari: Ixodidae) dominated the tick population while Ixodes scapularis Say was not encountered. There were complex differences in tick populations among site conditions. After prescribed burning, the tick population size was small but was larger in subsequent 2‐ and 5‐year post‐burn sites. An increase in Odocoileus virginianus foraging in recently burned sites is likely responsible for this phenomenon. WUI areas had the largest tick populations likely due to Odocoileus virginianus activity in an area that provides cover, forage, and a connection to a wildlife refuge. It is possible that the likelihood of humans coming in contact with ticks and tick‐borne diseases is greater in WUI areas than in unbroken contiguous forest. A. americanum showed a positive correlation with percent cover of grass and leaf litter mass and a negative relationship with pine sapling density. Variables expected to be strongly correlated with A. americanum populations such as soil moisture, canopy closure, and tree density were found to have weak correlations.     

Efficacy of chemical repellents against Otobius megnini (Acari: Argasidae) and three species of ixodid ticks

Otobius megnini (Dugès), often referred to as the ear tick or spinose ear tick, is a one-host tick native to the southwestern United States and Mexico. Infestations of this species can cause severe irritation and may affect breeding behavior in the host. Although chemical repellents are commonly used as an alternative approach to conventional arthropod vector control, information on repellency against O. megnini is lacking. This study compared repellency of ammonia, BioUD^®, 98.25 % DEET, garlic pepper tea, permanone, and pyrethrin with piperonyl butoxide, against larvae stages of O. megnini, Amblyomma americanum (L.), Dermacentor variabilis (Say), and Rhipicephalus sanguineus (Latreille). To test for repellency, tick movement was recorded at 30 s intervals for five min after introduction to a partially treated piece of filter paper. Results showed larvae of O. megnini exhibited less aversion to the chemicals tested when compared to the other tick species.     

An extract of Commiphora erythraea: a repellent and toxicant against ticks

A hexane extract of the gum of an African plant, Commiphora erythraea Engler (Burseraceae), has larvicidal and repellent activity against the lone star tick, Amblyomma americanum (L.) and the American dog tick, Dermacentor variabilis (Say). Adult deer ticks, Ixodes dammini Spielman, Clifford, Piesman and Corwin, were also repelled by the extract. Concentrations of 0.02 mg/cm² of the extract impregnated onto filter paper killed 96.15 (±3.56)% of A. americanum larvae exposed to it for 24h. A concentration of 0.16 mg/cm² was needed to kill 80.3% of D. variabilis larvae. The extract was less effective as a larvicide against A. americanum and D. variabilis than permethrin. Less than 15.5% of A. americanum larvae and adults and D. variabilis and I. dammini adults entered and remained for 2 or 3 min on areas of cloth strips treated with the extract at the rate of 0.2 mg/cm². However, 73.3 to 83.3% of the ticks tested entered and remained in areas treated with hexane. Permethrin was about 1 or 2 orders of magnitude more effective against A. americanum larvae as a repellent than the extract.

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Résumé Un extrait à l'hexane de la gomme de la plante africaine, C. erythraea Engler (Burseraceae) a des effets larvicides et répulsifs contre les tiques, Amblyomma americanum L. et Dermacentor variabilis Say; les adultes de Ixodes dammini Spielman, Clifford, Piesman & Corwin, ont été aussi éloignés par l'extrait. Une concentration de 0,02 mg/cm² de l'extrait imprégnant du papier filtre a tué 96,15% (±3,56) larves de A. americanum exposées pendant 24 h. Une concentration de 0,16 mg/cm² a été nécessaire pour tuer 80,3% des larves de D. variabilis. L'extrait a été moins efficace que la perméthrine comme larvicide contre A. americanum et D. variabilis. Moins de 15,5% des larves et des adultes de A. americanum et des adultes de D. variabilis et de I. dammini pénétrèrent et séjournèrent 2 à 3 minutes dans des morceaux de tissu traités avec l'extrait à raison de 0,2 mg/cm², contre 73,3 et 83,3% qui pénétrèrent et restèrent lors de traitement avec de l'hexane. Contre A. americanum, la perméthrine est un répulsif d'un ordre de grandeur une à deux fois supérieur à l'extrait de C. erythraea.

     

Efficacy of the new repellent BioUD<Superscript>®</Superscript> against three species of ixodid ticks

BioUD ^® with the active ingredient 2-undecanone originally derived from wild tomato plants is a new repellent recently registered by the US EPA. Repellent efficacy of BioUD ^® (7.75% 2-undecanone) and DEET (98.11%) was examined in the laboratory using a choice test between repellent-treated and control filter paper surfaces for Amblyomma americanum, Dermacentor variabilis, and Ixodes scapularis. BioUD ^® provided greater repellency against A. americanum and I. scapularis than DEET. No difference was found between BioUD ^® and DEET against D. variabilis. In head-to-head assays between BioUD ^® and DEET, undiluted and 50% dilutions of BioUD^® were more repellent than undiluted DEET against all three species tested. Similarly, a 25% dilution of BioUD^® was more repellent than DEET against A. americanum while no difference in mean percentage repellency was found between a 25% dilution of BioUD^® and DEET against I. scapularis. Based on regression analysis, the concentration of BioUD^® required for equivalent repellency to 98.11% DEET was 39.5% for D. variabilis and 29.7% for I. scapularis. A log-probit model could not be constructed for A. americanum from the dosages tested. Based on filter paper head-to-head assays, BioUD^® is at least 2–4 times more active as a repellent than DEET against three species of ixodid ticks under the conditions of our laboratory bioassays.     

Repellency of two terpenoid compounds isolated from <Emphasis Type="Italic">Callicarpa americana</Emphasis> (Lamiaceae) against <Emphasis Type="Italic">Ixodes scapularis</Emphasis> and <Emphasis Type="Italic">Amblyomma americanum</Emphasis> ticks

Callicarpenal (13, 14, 15, 16-tetranor-3-cleroden-12-al) and intermedeol [(4S,5S,7R,10S)-eudesm-11-en-4-ol], isolated from American beautyberry, Callicarpa americana (Lamiaceae), were evaluated in laboratory bioassays for repellent activity against host-seeking nymphs of the blacklegged tick, Ixodes scapularis, and lone star tick, Amblyomma americanum. A strip of organdy cloth treated with test solution was doubly wrapped (treatment on outer layer) around the middle phalanx of a forefinger and ticks released on the fingertip. Callicarpenal and intermedeol, at 155 nmole/cm² cloth repelled 98 and 96% of I. scapularis nymphs, respectively. Dose response tests with I. scapularis nymphs showed no difference in repellency among callicarpenal, intermedeol and Deet (N,N-diethyl-3-methylbenzamide), however, SS220 ((1S,2′S)-2-methylpiperidinyl-3-cyclohexene-1-carboxamide) was significantly more repellent than the other compounds. Callicarpenal, at 155 nmole/cm² cloth, repelled 100 and 53.3% of I. scapularis nymphs at 3 and 4 h, respectively, after the cloth was treated, whereas intermedeol repelled 72.5% of I. scapularis nymphs 3 h after treatment. In comparison with the results obtained with I. scapularis, callicarpenal, intermedeol, Deet and SS220 were less effective against A. americanum. Only intermedeol and SS220 repelled significantly more A. americanum than ethanol controls at 155 nmole compound/cm² cloth. At 1,240 nmole/cm² cloth, callicarpenal and intermedeol repelled 20 and 40% of A. americanum nymphs.     

Cleome monophylla essential oil and its constituents as tick (Rhipicephalus appendiculatus) and maize weevil (Sitophilus zeamais) repellents

The repellency of the essential oil of the shrubCleome monophylla (Family: Capparidaceae) and identified constituents of the oil were evaluated against the livestock tick,Rhipicephalus appendiculatus and the maize weevil,Sitophillus zeamais. In a tick climbing repellency bioassay, the oil ofC. monophylla exhibited repellency which, at the highest dose, was comparable to that of the commercial arthropod repellent N,N-diethyl toluamide (DEET). In a Y-tube olfactometer bioassay,C. monophylla oil showed higher or comparable repellency againstS. zeamais relative to DEET at all the doses tested. 14 Compounds were identified in theC. monophylla oil by GC, GC-MS and coinjection with authentic samples. Terpenolene was found to occur in largest quantity (14%) followed by 1-α-terpeneol (10%), pentacosane (9%), (α+β)-humulene (8%), phytol (5%) and 2-dodecanone (4%). The most repellent components againstR. appendiculatus andS. zeamais were 1-α-terpeneol and 2-dodecanone. The overall pattern of repellency activity of theC. monophylla constituents with respect to the two arthropods was, however, different. The potential ofC. monophylla in tick and maize weevil control is discussed.     

Simulating tick distributions over sub-Saharan Africa: the use of observed and simulated climate surfaces

Aim A broad suit of climate data sets is becoming available for use in predictive species modelling. We compare the efficacy of using interpolated climate surfaces [Center for Resource and Environmental Studies (CRES) and Climate Research Unit (CRU)] or high‐resolution model‐derived climate data [Division of Atmospheric Research limited‐area model (DARLAM)] for predictive species modelling, using tick distributions from sub‐Saharan Africa. Location The analysis is restricted to sub‐Saharan Africa. The study area was subdivided into 3000 grids cells with a resolution of 60 × 60 km. Methods Species distributions were predicted using an established multivariate climate envelope modelling approach and three very different climate data sets. The recorded variance in the climate data sets was quantified by employing omnidirectional variograms. To further compare the interpolated tick distributions that flowed from using three climate data sets, we calculated true positive (TP) predictions, false negative (FN) predictions as well as the proportional overlaps between observed and modelled tick distributions. In addition, the effect of tick data set size on the performance of the climate data sets was evaluated by performing random draws of known tick distribution records without replacement. Results The predicted distributions were consistently wider ranging than the known records when using any of the three climate data sets. However, the proportional overlap between predicted and known distributions varied as follows: for Rhipicephalus appendiculatus Neumann (Acari: Ixodidae), these were 60%, 60% and 70%; for Rhipicephalus longus Neumann (Acari: Ixodidae) 60%, 57% and 75%; for Rhipicephalus zambeziensis Walker, Norval & Corwin (Acari: Ixodidae) 57%, 51% and 62%, and for Rhipicephalus capensis Koch (Acari: Ixodidae) 70%, 60% and 60% using the CRES, CRU and DARLAM climate data sets, respectively. All data sets were sensitive to data size but DARLAM performed better when using smaller species data sets. At a 20% data subsample level, DARLAM was able to capture more than 50% of the known records and captured more than 60% of known records at higher subsample levels. Main conclusions The use of data derived from high‐resolution nested climate models (e.g. DARLAM) provided equal or even better species distribution modelling performance. As the model is dynamic and process based, the output data are available at the modelled resolution, and are not hamstrung by the sampling intensity of observed climate data sets (c. one sample per 30,000 km² for Africa). In addition, when exploring the biodiversity consequences of climate change, these modelled outputs form a more useful basis for comparison with modelled future climate scenarios.     

Tick species establishment in Oklahoma County,Oklahoma, U.S.A., identified by seasonal sampling in residential and non‐residential sites

In recent years, human tick‐borne disease occurrence has risen in Oklahoma, U.S.A., but year‐round data on tick presence in frequently used recreational areas is not widely available. In this study, ticks were collected monthly for one year at residential and non‐residential sites in a suburban area of Oklahoma County, OK, U.S.A. At each trapping site, dry ice traps were used in both woodland and grassland areas and fabric tick drags were used in grassland areas. Four species were collected from each park: Amblyomma americanum, Amblyomma maculatum, Dermacentor variabilis, and Ixodes scapularis. Prior to this study, A. americanum was the only species with an established population in Oklahoma County. Consistent with this, A. americanum was collected in all months of the year and accounted for over 90% of ticks collected at each site. Based on our tick survey, we report that A. maculatum, D. variabilis, and I. scapularis, which were each collected in numbers greater than six within a single sampling occasion, are now each confirmed as established populations in Oklahoma County.     

Assessment of the repellent effect of Lippia alba essential oil and major monoterpenes on the cattle tick Rhipicephalus microplus

The control of Rhipicephalus microplus (Ixodida: Ixodidae) is achieved using synthetic acaricides. However, resistant tick populations are widespread around the world. Plant essential oils can act as repellents, keeping ticks away from hosts and decreasing the selection pressure on synthetic acaricides. The aim of this study was to evaluate the in vitro repellent effect of Lippia alba essential oil on R. microplus larvae. Leaves from two L. alba genotypes maintained under the same agronomic and environmental conditions were collected. Essential oil was extracted by hydrodistillation and analysed by gas chromatography–mass spectrometry (GC‐MS). The major monoterpenes detected in the chemical analysis were commercially acquired and tested. For the repellency test, a glass rod was vertically fixed to measure active climbing of approximately 30 R. microplus larvae aged 14–21 days in response to essential oils and monoterpenes. Repellency was evaluated at 1 h, 3 h and 5 h after treatment. Variation in repellent action was detected between the genotypes. The major monoterpenes identified in the essential oils (limonene and carvone) showed low repellent effects in comparison with intact essential oils. Thus, the present results showed that L. alba essential oil contains bioactive compounds with great repellent activity against ticks that varies according to the plant genotype.     

High‐throughput screening method for evaluating spatial repellency and vapour toxicity to mosquitoes

Spatial repellents are an essential tool for personal protection against mosquitoes that bite and transmit disease pathogens to humans. Current repellent screening methods, such as olfactometers and alternative choice tests, are complex systems that require a relatively large quantity of compound (mg). The present study validates a high‐throughput spatial repellent screening method using a glass tube that has the ends covered with netting, in addition to treated filters and plastic end caps. The apparatus occupies relatively little space, is easy to decontaminate, and requires small amounts of compound (μg). In a horizontal tube orientation, DEET (N,N‐diethyl‐meta‐toluamide), citronella oil and IR3535 had 1 h half repellent concentration (EC₅₀) values of 32, 32 and 298 μg/cm², respectively, against the Orlando strain of Aedes aegypti (L.) (Diptera: Culicidae). Vertical tube orientation increased EC₅₀ values by approximately two‐fold, except IR3535, which remained essentially unchanged. Transfluthrin showed concentration‐dependent spatial repellency (1 h EC₅₀ = 0.5 μg/cm²) without any knockdown, although only in vertical tubes. Transfluthrin showed 50% knockdown in 1 h at 0.5 μg/cm² and 50% mortality at 0.15 μg/cm² in horizontal tubes. In conclusion, this high‐throughput screening method is useful for assessing vapour toxicity and the spatial repellency of candidate molecules prior to semi‐field and field studies.     

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.     

A polypeptide from male accessory glands which triggers maturation of tick spermatozoa

The maturation of tick (Acari: Ixodoidea) spermatozoa, after their transfer to the female, is induced by secretions of the male accessory gland which are added to the prospermia during ejaculation. Analysis of the secretions from male Ornithodoros moubata (Argasidae) and Dermacentor variabilis (Ixodidae) indicates that the factor responsible for inducing maturation is a polypeptide with a molecular weight of about 12,500. Although the polypeptides from the two species are similar in most respects, each will not activate the prospermia of the other species. The mode of action of the factor is hormone-like, inasmuch as a few minutes of exposure of the sperm to the factor are sufficient to trigger the entire maturation sequence, which takes 12–24 h in vitro.     

The geographic distribution and ecological preferences of the American dog tick,Dermacentor variabilis (Say), in the U.S.A.

Equine piroplasmosis (EP), caused by two parasitic organisms, Theileria equi and Babesia caballi, is a tick‐borne disease of recent concern in horses in the U.S.A. Outbreaks of EP have been detected in Florida, Missouri, Kansas and Texas. In 2009, EP transmission in Texas occurred through the adults of two tick species, Amblyomma mixtum [formerly known as Amblyomma cajennense (Fabricius, 1787)] Koch (Ixodida: Ixodidae) and Dermacentor variabilis (Say) (Ixodida: Ixodidae), the American dog tick (ADT). In this study, we developed a continent‐scale map for the distribution of the EP vector species D. variabilis, using a presence‐only modelling approach to assess the habitat preferences of this tick. We used identification records from our tick geodatabase of locations in which the presence of the ADT had been noted. The potential distribution of the ADT in the U.S.A. was estimated from environmental factors using the maximum entropy approach based on localities in which there is a high probability of occurrence according to habitat suitability. Elevation and temperature were found to be biologically significant environmental variables influencing the presence of this tick species. Properly designed and constructed probability surfaces using maximum entropy offer one useful approach to the mapping of distribution ranges of tick species based on suitable habitat in the U.S.A.     

Comparative analysis of hemocyte phagocytosis between six species of arthropods as measured by flow cytometry

Phagocytosis of pathogens by hemocytes is a rapid-acting immune response and represents a primary means of limiting microbial infection in some species of arthropods. To survey the relative capacity of hemocyte phagocytosis as a function of the arthropod immune response, we examined the extent of phagocytosis among a wide taxonomic range of arthropod species including a decapod crustacean (Litopenaeus vannamei), three ixodid tick species (Amblyomma americanum, Dermacentor variabilis, and Ixodes scapularis), a mosquito species (Aedes aegypti), and a larval moth (Manduca sexta). Injected fluorescent beads were used as a model to elicit phagocytosis and were measured by flow cytometry, a technique provided in detail that may be adapted for use with any species of arthropod. The data indicated that smaller arthropods generally had a higher proportion of phagocytic cells than larger arthropods.     

Evaluating levels of PCR efficiency and genotyping error in DNA extracted from engorged and non‐engorged female Dermacentor variabilis ticks

Polymerase chain reaction (PCR)‐based methods are increasingly used to elucidate tick biology. However, DNA extracted from ticks may provide poor PCR templates as a result of PCR inhibition by mammalian blood or contamination by male DNA (in fertilized females). In this study, the effects of removing the bloodmeal and reproductive organs were evaluated through paired DNA extractions in engorged and non‐engorged Dermacentor variabilis (Say) (Acari: Ixodidae), prior to PCR amplification at 12 microsatellites. The first extraction utilized only mouthparts and legs (‘mouthpart’ samples) and the second utilized tick bodies (‘body’ samples). The results indicated that contamination by male DNA was an unlikely source of genotyping error in mouthpart and body samples. Engorged females showed higher levels of PCR inhibition in body vs. mouthpart samples, with a 29% decrease in amplification success rates per PCR and a 10‐fold increase in levels of missing genotypes in body samples. By contrast, non‐engorged females showed little difference in amplification success rates or numbers of missing genotypes in body vs. mouthpart samples. We discuss analytical concerns related to this systematic bias in PCR problems and recommend the removal of the bloodmeal and reproductive organs prior to DNA extraction, especially in engorged female ticks.     

Repellencies and toxicities of five ant-derived defensive compounds against the lone star tick, <Emphasis Type="Italic">Amblyomma americanum</Emphasis> (Acari: Ixodidae)

The lone star tick, Amblyomma americanum, is a vector of several important human and animal diseases. This tick species has rapidly expanded in its geographic distribution, and its aggressive behavior has increased the risk of tick-borne diseases in these new areas. Repellents are recommended by the Centers for Disease Control and Prevention (CDC) for protection against tick bites. DEET is the most common repellent, but public concerns over its safety have increased the need for alternative safe and efficacious tick repellents. Several naturally derived animal compounds have been tested against other species of ticks or other arthropod pests, but not against A. americanum. Based on EC₅₀ values obtained using a vertical paper bioassay, decylamine and MT-710 (a 2-tridecanone formulation) were found to be as repellent as DEET. Those two substances along with 2-tridecanone were also found to be as repellent as DEET when their EC₉₅ values were compared. Lone star ticks were more susceptible to the toxic effects of DEET in glass vial assays than all of the ant-derived defensive compounds/formulations. These results suggest that the ant-derived defensive compounds are likely more effective lone star tick repellents than DEET, but they are not as toxic as DEET towards the ticks. The suitability of these compounds for use as personal repellents, as well as at the landscape scale, should be explored.