Pheromones and other semiochemicals of ticks and their use in tick control

Tick chemosensation and implications for novel control strategies

Ticks pose a major threat to the health of humans and animals. The use of synthetic acaricides and repellents has raised the concerns of potential health and environmental risks and increasing resistance in ticks. This article highlights the importance of the research on tick chemosensation in developing novel control agents. It provides a review on our current understanding of tick chemosensory system and proposes using chemosensory receptor (CR) genes as molecular targets to discover novel tick control agents. The releases of high-quality tick genomes provide unprecedented opportunities to explore CR gene repertoires. Further functional characterization is necessary to identify the receptors for key chemical cues and signals and unravel whether tick chemosensation involves ionotropic and/or metabotropic mechanisms.

Responses of juvenile blacklegged ticks (Acari: Ixodidae) to hosts of varying quality

Blacklegged ticks (Ixodes scapularis) are the most medically and economically important vectors in North America. Each of their 3 life stages requires a blood meal from one of many potential host species, during which they can acquire or transmit pathogens. Host species, however, vary tremendously in their quality for ticks, as measured by differences in feeding and molting success. There should be clear fitness benefits for ticks that preferentially feed upon high-quality hosts (e.g., white-footed mice, Peromyscus leucopus), or at least avoid feeding on very low-quality hosts (e.g., Virginia opossums, Didelphis virginiana). Indeed, laboratory experiments have found some evidence of host preferences in I. scapularis; but these involve presenting ticks with hosts simultaneously and measuring movement towards hosts on a horizontal plane. In nature, however, host-seeking ticks encounter hosts sequentially and their movements are principally in a vertical plane. Here, we present the results of a study in which we measured the vertical movements of host-seeking juvenile blacklegged ticks before and after a host (P. leucopus, Tamias striatus, Sciurus carolinensis, or D. virginiana) was present, and whether the strength of their responses varies with host quality. We found ticks did not measurably alter the speed of their vertical movement in the presence of any hosts, regardless of host quality. Both larvae and nymphs quested slightly higher in the presence of hosts, but this did not vary by host species. These results call into question the existence of active host preferences, at least in this stage of the host-seeking process.

Attractant and repellent properties of Senna didymobotrya plant extracts to Amblyomma variegatum and Rhipicephalus appendiculatus

The growing challenge of acaricide resistance and geographical range expansion of invasive tick species demands other interventions, like plant-based alternatives, for sustainable tick control. Leaves, flowers, seedpods, and twig branch extracts of Senna didymobotrya were analyzed using coupled gas chromatography mass spectrometry (GC-MS). Response of adult Amblyomma variegatum and Rhipicephalus appendiculatus to extracts was evaluated. The most attractive plant extract was fractionated and ticks' responses to its fractions assessed. Potential tick attractants in the attractive plant part extract and its fractions were identified by GC-MS analysis. Non- significant qualitative and quantitative differences were observed in the plant parts' extract composition (R = 0.6178). Flower extracts attracted both species, with a 0.1-fold higher attraction in A. variegatum compared to the standard attraction aggregation attachment pheromone (AAAP). Leaf and seedpod extracts repelled ticks at various concentrations. Bioassays after fractionating flower extracts identified hexane and ethyl acetate fractions as most attractive to A. variegatum (P < 0.001) and R. appendiculatus (P < 0.001), respectively. Chemical analysis of the most attractive extracts and fractions identified compounds, including documented acarine attractants, squalene and linoleic acid. A squalene and linoleic acid blend (1:1) at 1 mg/mL significantly attracted adult A. variegatum (P < 0.01) and R. appendiculatus (P < 0.001). The results of this study broaden comprehension of how ticks respond to plants in nature, and showcase the promising potential for integrating these insights into effective tick management programs.

Developing attractants and repellents for ticks: promises and challenges

Historically, some of the most effective tools to counter vector-borne diseases have been those directed against the vectors. Ticks are undergoing a population explosion as evidenced by the recent expansion of their distribution range. Tick control has traditionally relied heavily on pesticides. However, sustained use of acaricides is resulting in resistant tick populations. Multipronged management strategies that build and expand upon innovative control methods are sorely needed. Behavior-modifying chemicals, referred to as semiochemicals, such as pheromones and repellents, offer a first line of personal protection against ticks. We review the current understanding of tick semiochemicals, and how such understanding is leading to the identification of novel chemistries that are effective and safe.

Density and behavior of capybara (Hydrochoerus hydrochaeris) ticks (Acari: Ixodidae) Amblyomma sculptum and Amblyomma dubitatum with notes on Rickettsia bellii infection: Assessing human exposure risk

In several urban and peri‑urban areas of Brazil, populations of Amblyomma sculptum and Amblyomma dubitatum ticks are maintained by capybaras (Hydrochoerus hydrochaeris). In some of these areas, this host and these tick species are associated with Brazilian spotted fever (BSF), a lethal human disease caused by the bacterium Rickettsia rickettsii. In this work, we evaluated the risk of human exposure to these tick species using four collection techniques to discern host-seeking behavior. The study was carried out in 10 urban sites inhabited by capybaras in Uberlândia, a BSF-free municipality in southeastern Brazil. Ticks were collected in areas of 400 m2 at each site and at three seasons. Within the same municipality, the distance and speed of A. sculptum nymphs moving towards the CO2 traps were evaluated. In a sample of ticks Rickettsia DNA was investigated. During the study period, 52,953 ticks were collected. Among these, 83.4 % were A. sculptum (1,523 adults, 10,545 nymphs and 32,104 larvae) and 16.6 % were A. dubitatum (464 adults, 2,153 nymphs and 6,164 larvae). An average annual questing tick density of 4.4/m² was observed, with the highest density recorded at one site in autumn (31.8/m²) and the lowest in summer at another site (0.03/m²). The visual search yielded the highest proportion of A. sculptum larvae, constituting 47 % of the total and 63.6 % of all A. sculptum larvae. In contrast, CO2 traps collected a greater proportion of nymphs and adults of A. sculptum ticks. In the case of A. dubitatum, the CO2 trap was the most efficient technique with 57.7 % of captures of this species, especially of nymphs (94.5 % of captures) and adults (97.8 % of captures). Ticks' ambush height on vegetation (9 to 77 cm), observed by visual search 30 times, yielded a total of 20,771 ticks. Of these, 28 (93 %) were A. sculptum ticks, with only two (7 %) identified as A. dubitatum ticks. Among A. sculptum ticks, the nymph was the most attracted stage to humans and larva in the case of A. dubitatum. Amblyomma sculptum adults and nymphs were significantly more attracted to humans than those of A. dubitatum, but A. dubitatum larvae were significantly more attracted than the same stage of A. sculptum. The maximum distance and speed of horizontal displacement for A. sculptum nymphs were five meters and 2.0 m/h, respectively. The only species of Rickettsia detected in ticks, exclusively in A. dubitatum, was R. bellii. Importantly, it was observed that the higher the proportion of A. sculptum in the community of ticks, the lower the rate of infection of A. dubitatum by R. bellii. In conclusion, host-seeking behavior differed between the two tick species, as well as between stages of the same species. A greater restriction of A. dubitatum ticks to the soil was observed, while larvae and nymphs of A. sculptum dispersed higher in the vegetation. The behavior presented by A. sculptum provides greater opportunities for contact with the hosts, while A. dubitatum depends more on an active search for a host, the hunter behavior. Taken together, these observations show that a human being crossing an area infested with A. sculptum and A. dubitatum ticks will have almost exclusive contact with A. sculptum larvae and/or nymphs. Humans in a stationary position (sitting, lying or immobile) are exposed to both tick species, but they are more attractive to adults and mainly nymphs of A. sculptum compared to the corresponding stages of the tick A. dubitatum. The negative effect of A. sculptum on A. dubitatum infection by R. bellii deserves further studies.

Prevalence and associated risk factors of ixodid tick species infesting cattle and sheep in Balochistan, Pakistan

Tick infestation poses a serious threat to animal health, leading to significant losses in terms of vector-borne disease transmission, reduced live weight, lower quality hides, decreased milk production, and impaired reproduction in tropical and subtropical regions worldwide. This study aimed to determine the prevalence, seasonal variation, distribution pattern, and associated risk factors of Ixodid family tick species in the cattle and sheep population of three different districts in Balochistan, Pakistan. This study employed a convenient sampling method, collecting 4080 adult ticks from 816 cattle and sheep of various breeds, ages, and sexes. Specific morphological keys were used to identify the ticks up to the genus and species level. Among cattle, the highest prevalence was recorded for R. (B) annulatus (27.01%), followed by R. (B) microplus (24.02%), and H. anatolicum (20.54%). H. dromedarii (5.29%) was the least prevalent species observed in cattle. In the sheep population, H. anatolicum (30.34%) showed the highest prevalence, followed by H. marginatium (22.99%), and R. (B) annulatus (20.88%). H. dromedarii (6.96%) was the least prevalent species observed in sheep. The prevalence of R. (B) decoloratus, H. anatolicum and H. dromedarii was found to be significantly associated (P < 0.05) with the breed, age, and sex of both cattle and sheep. However, the presence of R. (B) annulatus, R. (B) microplus and H. marginatium tick species showed no significant association (P > 0.05) with these factors. In addition, the prevalence of ticks was higher in younger, female, and crossbred Friesian cattle compared to adults, males, and other breeds. Conversely, the prevalence of ticks was higher in adult, female and Hernai breed of sheep in the studied area. In conclusion, R. (B) annulatus and H. anatolicum are the dominant tick species infesting the cattle and sheep population in Balochistan. Consequently, this study provides valuable insights for developing practical and effective control measures against ticks and tick-borne diseases in the sheep and cattle population of Balochistan, Pakistan.

Mixed-sex clusters on grass blades: breeding strategy of the ornate dog tick, Dermacentor reticulatus

BACKGROUND

The ornate dog tick Dermacentor reticulatus is second only to the hard tick Ixodes ricinus in terms of importance as a vector of infectious organisms, especially of Babesia canis, the agent of canine babesiosis. Both the geographical range and local densities of D. reticulatus are steadily increasing in many regions of Europe. In the present study, we tested the hypothesis that D. reticulatus possesses an efficient breeding strategy that allows for a rapid increase in tick numbers and densities through the formation of mixed-sex clusters/aggregations while questing in the environment.

METHODS

An observational study was carried out in the spring of 2023, at three sites in two regions in Central and North-Eastern Poland, both characterised by high tick densities. At each site, a 400-m-long transect was inspected for questing ticks. All noted ticks were collected, and tick numbers and sexes per stem were recorded. Differences in tick distribution by site and sex were analysed statistically.

RESULTS

A total of 371 D. reticulatus (219 females, 152 males) ticks were collected from 270 grass stems over a combined 1200 m of transect. The majority of grass stems (74.4%) were occupied by just a single individual, with two-tick clusters the second most common category. The maximum number of D. reticulatus individuals observed on a single grass stem was six. Mixed-sex clusters were significantly more common than single-sex clusters at all three sites. With study sites combined, mixed-sex clusters accounted for 17.4% (95% confidence limit [95% CL] 13.9-21.6%) of observations, while for multiple males and multiple females, the values were 2.6% (95% CL: 1.4-4.7%) and 5.6% (95% CL: 3.7-8.3%), respectively.

CONCLUSIONS

Mixed-sex clusters of D. reticulatus ticks were significantly more common than single-sex clusters, which we hypothesise reflects an efficient, likely pheromone-mediated breeding strategy of this expansive tick species.

Semiochemical based integrated livestock pest control

The role of arthropods as livestock pests has been well established. Besides their biting habits causing nuisance in animals; they are important vectors for transmission of economically important livestock diseases worldwide. Various pests and vector control managemental programs that also make use of chemicals have variable success rates. Consequently, insecticide/acaricide resistance has been reported against most of the commonly used chemicals along with increased concern for environment and demand for clean and green, residue-free animal products. This calls for an urgent need to develop novel, alternate, effective strategies/technologies. This lays the foundation for the use of semiochemicals as alternatives along with other biological control agents. Current knowledge on semiochemical use in livestock is refined and limited; however, it has been widely exploited in the agricultural sector to control plant and food crop pests, surveillance, and monitoring. Semiochemicals have an added advantage of being natural and safe; however, knowledge of extraction and quantification by using assays needs to be explicit. Expertise is required in behavioral and electrophysiological studies of arthropods and their interactions with the host and environment targeting specific semiochemicals for promising results. A thorough prior understanding on aspects such as mechanism of action, the stimulus for the release, the effecter/target species, response produced, application methods, dose and concentration is required to develop any successful pest/vector control program. The current review provides essential and frontline information on semiochemicals and their potential applications in the livestock sector along with future challenges and interventions.

In vitro feeding of Hyalomma excavatum and Hyalomma marginatum tick species

The rearing of ticks is an important technique for studies aiming to elucidate the course and pathogenesis of tick-borne diseases (TBDs). TBDs caused by protozoans (Theileria, Babesia) and bacteria (Anaplasma/Ehrlichia) impose a serious constraint upon livestock health and production in tropical and sub-tropical regions where the distributions of host, pathogen, and vector overlap. This study focuses on Hyalomma marginatum, one of the most important Hyalomma species in the Mediterranean region, being a vector of the virus that causes Crimean-Congo haemorrhagic fever in humans, together with H. excavatum, a vector of Theileria annulata, an important protozoan of cattle. The adaptation of ticks to feeding on artificial membranes allows the creation of model systems that can be put to use examining the underlying mechanisms of pathogen transmission by ticks. Silicone membranes, in particular, offer researchers the flexibility to adjust membrane thickness and content during artificial feeding. The aim of the present study was to develop an artificial feeding technique using silicone-based membranes for all developmental stages of H. excavatum and H. marginatum ticks. Attachment rates after feeding on silicone membranes for females H. marginatum and H. excavatum were 8.33% (8/96) and 7.95% (7/88), respectively. The use of cow hair as a stimulant increased the attachment rate of H. marginatum adults in comparison to other stimulants. The engorgement of H. marginatum and H. excavatum females took 20.5 and 23 days with average weights of 307.85 and 260.64 mg, respectively. Although both tick species could complete egg-laying, and this was followed by hatching of larvae; their larvae and nymphs could not be fed artificially. Taken together, the results of the present study clearly indicate that silicone membranes are suitable for feeding of H. excavatum and H. marginatum adult ticks, supporting engorgement, laying of eggs, and hatching of the larvae. They thus represent a versatile tool for studying transmission mechanisms of tick-borne pathogens. Further studies are warranted to examine attachment and feeding behaviours in order to increase the success of artificial feeding of larvae and nymphal stages.

Synergistic attraction of Western black-legged ticks, Ixodes pacificus, to CO2 and odorant emissions from deer-associated microbes

Foraging ticks reportedly exploit diverse cues to locate their hosts. Here, we tested the hypothesis that host-seeking Western black-legged ticks, Ixodes pacificus, and black-legged ticks, I. scapularis, respond to microbes dwelling in sebaceous gland secretions of white-tailed deer, Odocoileus virginianus, the ticks' preferred host. Using sterile wet cotton swabs, microbes were collected from the pelage of a sedated deer near forehead, preorbital, tarsal, metatarsal and interdigital glands. Swabs were plated on agar, and isolated microbes were identified by 16S rRNA amplicon sequencing. Of 31 microbial isolates tested in still-air olfactometers, 10 microbes induced positive arrestment responses by ticks, whereas 10 others were deterrent. Of the 10 microbes prompting arrestment by ticks, four microbes-including Bacillus aryabhattai (isolates A4)-also attracted ticks in moving-air Y-tube olfactometers. All four of these microbes emitted carbon dioxide and ammonia as well as volatile blends with overlapping blend constituents. The headspace volatile extract (HVE) of B. aryabhattai (HVE-A4) synergistically enhanced the attraction of I. pacificus to CO2. A synthetic blend of HVE-A4 headspace volatiles in combination with CO2 synergistically attracted more ticks than CO2 alone. Future research should aim to develop a least complex host volatile blend that is attractive to diverse tick taxa.

Current Knowledge on Chemosensory-Related Candidate Molecules Potentially Involved in Tick Olfaction via Haller's Organ

Ticks are obligatory hematophagous ectoparasites and vectors of many animal and human pathogens. Chemosensation plays a significant role in tick communication with their environment, including seeking out blood meal hosts. Studies on the structure and function of Haller's organ and its components have improved our understanding regarding tick olfaction and its chemical ecology. Compared with the knowledge on insect olfaction, less is known about the molecular basis of olfaction in ticks. This review focused on the chemosensory-related candidate molecules likely involved in tick olfaction. Members of the ionotropic receptor family and a new class of odorant-binding proteins are now known to be involved in tick olfaction, which appear to differ from that of insects. These candidate molecules are more closely related to those of mites and spiders than to other arthropods. The amino acid sequences of candidate niemann-pick type C2 and microplusin-like proteins in ticks exhibit features indicating their potential role as binding proteins. In the future, more comprehensive pertinent research considering the existing shortcomings will be required to fully understand the molecular basis of tick olfactory chemoreception. This information may contribute to the development of new molecular-based control mechanisms to reduce tick populations and related disease transmission.

Attractant Activity of Host-Related Chemical Blends on the Poultry Red Mite at Different Spatial Scales

Many blood-feeding arthropods use volatile organic compounds (VOCs) to detect their vertebrate hosts. The role of chemical interactions in mediating the behavior of hematophagous insects and ticks has been investigated before but remains poorly understood in hematophagous mesostigmatic mites. The poultry red mite Dermanyssus gallinae is an obligatory blood-sucking mesostigmatic mite that feeds on birds and causes damage in poultry farms. We characterized the attractive response of D. gallinae to candidate VOCs previously reported from the odor emitted by living hens. We performed in-vitro choice-test bioassays as well as semi-field and field trials using baited and unbaited traps, in the presence and absence of hens. Among different tested combinations of VOCs, a blend of 5 VOCs (mix1.0) was significantly attractive to our reference population of D. gallinae in vitro, whereas the same individual compounds tested alone were not attractive. Ammonia was attractive on its own and increased the mix1.0 attractiveness. The attractiveness of mix1.0 was confirmed at 'natural' spatial scales in the absence of hens both at the lab and on the farm that provided the reference population. The presence of hens inhibited the mix1.0 attractiveness. The attractive power of mix1.0 was not found in other farms. This research is an important step to advance our understanding of host-parasite interactions in hematophagous mesostigmatic mites and paves the way for developing alternative control tools against D. gallinae by interfering with chemical interactions. Moreover, it underlines the importance of assessing kairomonal activity on different pest populations when developing attract-and-kill systems.

Male mating preference in an ixodid tick

Background

Mate choice is a fundamental element of sexual selection and has the potential to shape the evolution of traits. Mate choice based on body size has been shown to be a common trait in several arthropod species. In hard ticks, a taxon of medical and veterinary importance, engorgement weight is positively correlated with reproductive output but it is unknown whether adult males show mate choice. Here, we experimentally investigated whether males (i) use chemical cues to choose their mating partner, (ii) consistently choose for the same female individual and (iii) prefer females with highest weight after feeding.

Methods

We used two experimental setups which allowed chemical communication between ticks: (i) a horizontal tube preventing physical contact with the female and (ii) an arena where tactile cues were allowed. In total, we tested 62 different triads in 124 tests (66 tests in the horizontal tube and 58 in the arena) composed of one male that could choose between two engorged females. Specifically, we tested 42 triads in the tube and 46 in the arena; 24 triads were repeatedly tested in the tube while 38 triads were tested in both setups.

Results

We found no preference for individual or heavier females in either setup. However, in the horizontal tube setup, males significantly preferred females that were not visited by them in the previous test.

Conclusions

Our results suggest a lack of male mate choice despite heavier females having higher fecundity. However, future studies should take into account that males may recognize the potential mating partners they previously met.

Graphical Abstract

Identification and expression of potential olfactory-related genes related to Niemann-Pick C2 protein and ionotropic receptors in Haemaphysalis longicornis

Studies have shown that the main pathway for tick host localization and perception of mating information may be chemosensory. However, chemical communication in ticks is poorly understood, especially in those other than the Ixodes ticks. Niemann-Pick C2 (NPC2) protein and ionotropic receptors (IRs) are considered to be closely related to the perception of infochemicals in arthropods. Through bioinformatic analysis, eight NPC2 and four IR candidate genes were identified through screening and identification of the transcriptome sequencing database of Haemaphysalis longicornis. Phylogenetic tree analysis indicated that H. longicornis possesses similar homology to the genus Ixodes. A comparison of the expression of NPC2 and IR in tick forelegs (first pair of legs), hind legs (fourth pair of legs), and capitula using RT-PCR revealed that, barring HlonNPC2-8, 11 candidate genes were highly expressed in the foreleg and capitulum, which are the main sensory organs of ticks. They were also expressed in the hind legs, except for six genes that were not expressed in the males. RT-qPCR analysis showed upregulation and higher relative expression of HlonNPC2-1, HlonNPC2-3, HlonNPC2-6, and HlonNPC2-8 when stimulated by ammonium hydroxide, whereas the others were downregulated and demonstrated lower relative expression. These results further support the putative role of NPC2s as a new odorant carrier in ticks and present 12 promising candidate genes for understanding tick olfactory communication, enriching the data on these genes, especially outside the genus Ixodes.

Quantitative proteomics analysis reveals core and variable tick salivary proteins at the tick-vertebrate host interface

Few studies have examined tick proteomes, how they adapt to their environment, and their roles in the parasite-host interactions that drive tick infestation and pathogen transmission. Here we used a proteomics approach to screen for biologically and immunologically relevant proteins acting at the tick-host interface during tick feeding and, as proof of principle, measured host antibody responses to some of the discovered candidates. We used a label-free quantitative proteomic workflow to study salivary proteomes of (i) wild Ixodes ricinus ticks fed on different hosts; (ii) wild or laboratory ticks fed on the same host; and (iii) adult ticks co-fed with nymphs. Our results reveal high and stable expression of several protease inhibitors and other tick-specific proteins under different feeding conditions. Most pathways functionally enriched in sialoproteomes were related to proteolysis, endopeptidase, and amine-binding activities. The generated catalog of tick salivary proteins enabled the selection of six candidate secreted immunogenic peptides for rabbit immunizations, three of which induced strong and durable antigen-specific antibody responses in rabbits. Furthermore, rabbits exposed to ticks mounted immune responses against the candidate peptides/proteins, confirming their expression at the tick-vertebrate interface. Our approach provides insights into tick adaptation strategies to different feeding conditions and promising candidates for developing anti-tick vaccines or markers of exposure of vertebrate hosts to tick bites.

De novo transcriptome sequencing of the northern fowl mite, Ornithonyssus sylviarum, shed light on parasitiform poultry mites evolution and its chemoreceptor repertoires

The northern fowl mite (NFM), Ornithonyssus sylviarum, and the poultry red mite (PRM), Dermanyssus gallinae, are the most serious pests of poultry, both of which have an expanding global prevalence. Research on NFM has been constrained by a lack of genomic and transcriptomic data. Here, we report and analyze the first global transcriptome data across all mite live stages and sexes. A total of 28,999 unigenes were assembled, of which 19,750 (68.10%) were annotated using seven functional databases. The biological function of these unigenes was classified using the GO, KOG, and KEGG databases. To gain insight into the chemosensory receptor-based system of parasitiform mites, we furthermore assessed the gene repertoire of gustatory receptors (GRs) and ionotropic receptors (IRs), both of which encode putative ligand-gated ion channel proteins. While these receptors are well characterized in insect model species, our understanding of chemosensory detection in mites and ticks is in its infancy. To address this paucity of data, we identified 9 IR/iGluRs and 2 GRs genes by analyzing transcriptome data in the NFM, while 9 GRs and 41 IR/iGluRs genes were annotated in the PRM genome. Taken together, the transcriptomic and genomic annotation of these two species provide a valuable reference for studies of parasitiform mites and also help to understand how chemosensory gene family expansion/contraction events may have been reshaped by an obligate parasitic lifestyle compared with their free-living closest relatives. Future studies should include additional species to validate this observation and functional characterization of the identified proteins as a step forward in identifying tools for controlling these poultry pests.

Isolation and evaluation of South African isolates of Beauveria bassiana (Hypocreales: Cordycipitaceae) on Rhipicephalus microplus (Acari: Ixodidae)

Beauveria bassiana (Hypocreales: Cordycipitaceae) is an entomopathogenic fungus that has shown promising results as a biocontrol agent of ticks. Locally isolated B. bassiana are better acclimatised to the natural conditions of their geographical origin; therefore, they are essential in developing effective biocontrol agents for ticks. The current study aimed to isolate native strains of B. bassiana that are pathogenic to Rhipicephalus microplus ticks. The virulence of the isolates was tested against R. microplus larvae using a formulation containing 15% avocado oil, 0.05% adjuvant and 10⁸ conidia mL^-1. The two best strains were further evaluated for various biological parameters on adult engorged female ticks. Breakthru® or Ballista® (adjuvant) was mixed with the formulation to compare their effect on the isolates' virulence. In total 61 entomopathogenic fungi were isolated from the 360 greater wax moth larvae, Galleria mellonella (Lepidoptera: Pyralidae) used. The virulence test identified Bb-40 and Bb-41 to be the most virulent isolates against R. microplus larvae with mortalities of 91 and 93% and LT₅₀ values of 5.8 and 6.2 days, respectively. Compared to the control, both strains significantly affected all the measured biological parameters. The type of adjuvant also considerably affected the susceptibility of ticks to the fungi. In conclusion, the two isolates combined with adjuvants can be used as a biocontrol agent to control R. microplus.

Tonic Immobility Is Influenced by Starvation, Life Stage, and Body Mass in Ixodid Ticks

The ability to escape predation modulates predator-prey interactions and represents a crucial aspect of organismal life history, influencing feeding, mating success, and survival. Thanatosis, also known as death feigning or tonic immobility (TI), is taxonomically widespread, but understudied in blood-feeding vectors. Hematophagous arthropods, such as ticks, are unique among animals as their predators (birds, mice, lizards, frogs, and other invertebrates) may also be their source of food. Therefore, the trade-off between predator avoidance and host-seeking may shift as the time since the last bloodmeal increases. Because ticks are slow-moving and unable to fly, or otherwise escape, we predicted that they may use TI to avoid predation, but that TI would be influenced by time since the last bloodmeal (starvation). We therefore aimed to quantify this relationship, examining the effect of starvation, body mass, and ontogeny on TI for two tick species: Dermacentor variabilis (Say) (Acari: Ixodidae) and Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae). As we predicted, the duration and use of TI decreased with time since feeding and emergence across species and life stages. Therefore, ticks may become more aggressive in their search for a bloodmeal as they continue to starve, opting to treat potential predators as hosts, rather than avoiding predation by feigning death. Antipredator behaviors such as TI may influence the intensity and amount of time ticks spend searching for hosts, driving patterns of tick-borne pathogen transmission. This identification and quantification of a novel antipredation strategy add a new component to our understanding of tick life history.

Applications of artificial membrane feeding for ixodid ticks

Ticks are obligatory hematophagous ectoparasites that feed on a large variety of vertebrates. In the laboratory, animals (mainly mice and rabbits) are used to maintain tick colonies. However, the use of animals to rear ticks can be expensive and requires dedicated animal facilities. In addition, research institutions are committed to the principle of 3Rs (Replacement, Reduction and Refinement), which encourages the use of alternatives to animals when possible. The development of artificial membrane systems has provided an alternative to animals, at least for some tick species. Over the years, different modifications in artificial feeding systems have led to new applications, including acaricide testing, tick-pathogen interaction, and novel approaches to study tick physiology. Although artificial membrane feeding still has some limitations, the method can provide numerous advantages, including the standardization of acaricide treatments under controlled conditions, an alternative to animals for tick rearing, and reduction of cost associated with animals and animal housing facilities. In this review, we summarized the evolution of tick feeding membranes and their applications over time, explaining the modifications incorporated to study tick physiology, tick-pathogen interactions, and acaricide testing.

Solar tick trap with a pheromone lure - A stand-in approach for off-host control of Rhipicephalus sanguineus sensu lato ticks

Rhipicephalus sanguineus sensu lato (s.l.), the brown dog tick, transmits several important haemo-protozoan and rickettsial pathogens to dogs. Effective control of these ticks is entirely by the use of acaricidal preparations both on and off the host. Indiscriminate use of acaricides can cause environmental pollution and toxicity to humans as well as development of acaricidal resistance in ticks. As an alternative control strategy, a novel, eco-friendly and economical solar tick trap, which attracts ticks using pheromones and kills them by electrocution, was fabricated for use in kennels to control different stages of ticks. All stages of ticks were found to be lured to sex pheromone (SP), assembly pheromone (AP) and a combination of SP + AP impregnated vapour patches and electrocuted. There was a highly significant (p < 0.01) difference in the level of attraction between engorged and questing stages of ticks to the pheromones in the trap. AP lured a higher number of ticks, both engorged and questing, in comparison to other pheromones. The solar tick trap bearing vapour patch impregnated with AP was considered most suitable for use in integrated pest management (IPM) of ticks in heavily infested kennels. The solar trap remained effective for a month after which, replacement of pheromone impregnated vapour patch was necessary for continued and effective attraction of the ticks. This solar tick trap device, which uses pheromone without any acaricide, could prove to be an ideal green alternative for use in IPM of ticks in kennels.

Chemosensory and Behavioural Responses of Ixodes scapularis to Natural Products: Role of Chemosensory Organs in Volatile Detection

Simple Summary

Ticks are responsible of transmitting serious disease agents of importance to human and veterinary health. Despite the importance of repellents, deterrents and acaricides in tick management, little is understood about the types of chemicals recognized and the mechanism behind chemoreception. Being almost totally blind, ticks rely on chemosensation to identify and locate hosts for a successful blood meal and to detect chemical signals in the environment. We explored the neurophysiology of tick chemosensory system in the context of behaviourally-relevant volatile stimuli, including essential oil components, to evaluate how the combination of attractants and plant volatile compounds is detected and processed. The observed inhibition (or deterrent effect) in tick electrophysiological response and behavioural activity, after the tick has been exposed to a binary mixture of attractant and volatile compound, represents an important advancement in understanding how tick olfaction works and what may be the mechanism behind detecting unpleasant odor stimuli and consequently been deterred. These information will provide more insights in developing new natural product-based deterrents for self-protection.

Abstract

Blacklegged ticks, Ixodes scapularis, represent a significant public health concern due to their vectoring of tick-borne disease. Despite their medical importance, there is still limited knowledge of the chemosensory system of this species, and thus a poor understanding of host-seeking behaviour and chemical ecology. We investigated the electrophysiological sensitivity of adult female blacklegged ticks to attractants and plant-derived compounds via an electrode inserted into the scutum. The response of female ticks to binary mixtures with a constant concentration of a selected attractant (butyric acid) and increasing concentration of volatile organic compounds (VOCs) (geraniol, phenethyl alcohol, β-citronellol, and citral) was recorded. A strict relationship between increasing volatile concentration and a decreasing response was observed for each VOC. Y-tube bioassays confirmed that tick attraction towards butyric acid decreased with the presence of a VOC, which exerted a deterrent effect. To determine the specific role of sensory appendages involved in the detection of attractant chemical stimuli, we tested tick electrophysiological response after removing appendages that house chemosensory sensilla (foretarsi, pedipalps, or both). The chemosensory response was related to the molecular structure of attractant odorant, and the lack of pedipalps significantly reduced olfactory responses, suggesting they play an important role in detecting attractants. This study provides new insight into the neurophysiological mechanisms underlying tick olfaction and the potential for interactions between attractant and deterrent chemical detection.

Free-living ticks (Acari: Ixodidae) in the Iguaçu National Park, Brazil: Temporal dynamics and questing behavior on vegetation

Basic knowledge of species, ecological preferences and behavior of ticks in preserved rainforests are scanty. We herein describe species richness, seasonal activity, altitude influence and questing height of ticks along 3375 m of animal trails within the largest remain of inland Atlantic rainforest in Brazil, the Iguaçu National Park (INP). Altogether, 2954 ticks from nine tick species were collected; Amblyomma brasiliense Aragão (49.09% of the specimens), Amblyomma coelebs Neumann (29.08%), Amblyomma incisum Neumann (12.49%), Haemaphysalis juxtakochi Cooley (5.21%), Amblyomma ovale Koch (2.64%), Amblyomma longirostre Koch (0.20%), Ixodes fuscipes Fonseca (0.17%), Ixodes loricatus Neumann (0.07%) and Amblyomma dubitatum Neumann (0.03%) (Ixodida: Ixodidae). There was an evident seasonal influence on tick host-questing activity, with each tick stage prevailing in a season before the following one, and a general trend of one tick generation per year. Adult tick questing height mode on vegetation showed a correspondence between tick species and preferred host size and height. Adult ticks quested higher than immatures, but several larval clusters were found high enough to seek for large-sized hosts as well. Nymphal and adult tick questing height increased significantly at higher altitudes within the park. Amblyomma incisum and A. coelebs were more abundant at higher and lower altitudes, respectively. The knowledge on tick species richness, ecological preferences and behavior herein obtained provides baseline information to understand tick-borne disease epidemiology occurring at landscapes under a strong anthropogenic impact.

Density of Dermacentor reticulatus Ticks in Eastern Poland

Dermacentor reticulatus, the ornate cow tick, is second only to Ixodes ricinus as the most important reservoir and vector of infectious diseases in Europe. In recent years, the distribution of D. reticulatus ticks has expanded into new territories, including increased population densities in areas of their previous occurrence. Our investigations around this consisted of two stages. In the first stage, we monitored the seasonal activity of D. reticulatus ticks in Polesie National Park in 2014-2019. The second stage, which was carried out in 2019 at the peak of the spring (March) and autumn (October) activity of this species, included assessment of the density of D. reticulatus ticks in the entire province. To this end, the study area was divided into 101 equal plots that were surveyed for ticks. The seasonal activity of D. reticulatus in Polesie National Park showed peaks of activity in autumn in 2014-2018 and in spring in 2019. A total of 19,559 adult D. reticulatus specimens were collected, with a mean of 96.8 specimens/100 m² in Lublin Province. The area of Lublin Province is characterized by a high density of the ornate cow tick. An increase in the surface area of meadows and fallow land has contributed to a rise in the number of local populations of D. reticulatus ticks.

Attract or repel Amblyomma sculptum ticks: Screening of semiochemicals

Amblyomma sculptum is a tick of medical-veterinary importance. Areas with high infestations need to be monitored, and parasitized hosts treated accordingly. Carbon dioxide (CO₂) traps and acaricides are commonly deployed as control measures, although with some disadvantages such as high costs, challenging logistics and vertebrate intoxication. Semiochemicals have the potential to improve tick attraction to traps and monitoring devices and alleviate the burden of A. sculptum infestations. Four concentrations (10, 5, 2.5 and 1.25 %) of 13 semiochemical candidates (CO₂ only at 5 % as the standard, benzaldehyde, benzoic acid, salicylic acid, 2,6 diclorophenol, R-limonene, S-limonene, methyl salicylate, 1-octen-3-ol, acetone, ammonium hydroxide, isobutyric acid and lactic acid) were tested on unfed A. sculptum nymphs and adults using a Y-tube olfactometer to evaluated repellence and attraction behaviors. All stages tested were attracted to CO₂, whereas nymphs were repelled by benzaldehyde and R-limonene, both at 10 %, and isobutyric acid at 5 and 10 %. Nymphs were attracted by methyl salicylate, benzoic acid and salicylic acid, all at 1.25 %, and by ammonium hydroxide at 2.5 %. Males were attracted by benzoic acid at 2.5 %, while females were repelled by benzaldehyde at 5 %. Mixtures with the attractive compounds achieved no attraction response. The compounds that caused attractiveness in the olfactometer assay (CO₂, methyl salicylate, benzoic acid, salicylic acid and ammonium hydroxide) were placed randomly in traps in a grassland plot naturally infested with A. sculptum in triplicate. Notably, dry ice (CO₂) remained the best at luring ticks in the field (P < 0.001). Benzoic acid should be further investigated since attractant activity was strongly confirmed in both laboratory and field tests. On the other hand, isobutyric acid and R-limonene could be better exploited due to their repellent role revealed by the lab assay, which makes them worthwhile molecules as natural repellents for the management of this tick.

Innovative way to dispense pheromones for off-host control of Rhipicephalus sanguineus sensu lato ticks

Vapour patches dispensing pheromones were evaluated as lures to increase the attractiveness of sticky tick traps for Rhipicephalus sanguineus sensu lato (s.l.). Sex pheromone (SP), assembly pheromone (AP) and a combination of SP + AP at optimal concentrations were impregnated in vapour patches. The responses of the different stages of R. sanguineus s.l. (i.e. larvae, nymphs and adults) to the pheromones were evaluated using a Petri dish bioassay. The impregnated vapour patches were retained as such for a period of two mo and their efficacy was reassessed. In a subsequent field trial, pheromone impregnated vapour patches were placed as lures in bamboo (Bambusa vulgaris) sticky traps designed for the control of ticks in dog kennels. In vitro AP impregnated vapour patches were effective in attracting the different life stages of R. sanguineus s.l. whereas SP was effective in attracting the unfed and fed male stages of R. sanguineus s.l. The field trial revealed that questing and engorged larvae, nymphs and females of R. sanguineus s.l. were attracted more towards AP impregnated vapour patches than SP and AP + SP impregnated vapour patches. Fed and unfed male ticks were lured effectively by SP alone. The combination of SP + AP revealed no potent additive or synergistic effect.

Chemical Equilibrium at the Tick-Host Feeding Interface:A Critical Examination of Biological Relevance in Hematophagous Behavior

Ticks secrete hundreds to thousands of proteins into the feeding site, that presumably all play important functions in the modulation of host defense mechanisms. The current review considers the assumption that tick proteins have functional relevance during feeding. The feeding site may be described as a closed system and could be treated as an ideal equilibrium system, thereby allowing modeling of tick-host interactions in an equilibrium state. In this equilibrium state, the concentration of host and tick proteins and their affinities will determine functional relevance at the tick-host interface. Using this approach, many characterized tick proteins may have functional relevant concentrations and affinities at the feeding site. Conversely, the feeding site is not an ideal closed system, but is dynamic and changing, leading to possible overestimation of tick protein concentration at the feeding site and consequently an overestimation of functional relevance. Ticks have evolved different possible strategies to deal with this dynamic environment and overcome the barrier that equilibrium kinetics poses to tick feeding. Even so, cognisance of the limitations that equilibrium binding place on deductions of functional relevance should serve as an important incentive to determine both the concentration and affinity of tick proteins proposed to be functional at the feeding site.

Comparison of in-vitro bioassays for evaluation of the response of different stages of Rhipicephalus sanguineus sensu lato to calcium alginate encapsulated pheromone beads

Tick sex pheromone (SP), assembly pheromone (AP) and their combination (SP + AP) were encapsulated in calcium alginate beads. In vitro bioassays, namely Petri dish and olfactometer assays, were employed to estimate the level of attraction of the various stages of Rhipicephalus sanguineus sensu lato, namely unfed and engorged (fed) larvae, nymphs, females, and males to the different pheromones. The study revealed that only the Petri dish assay was suitable to evaluate the response of larval stages whereas the olfactometer bioassay could also be used for evaluating the response of all other stages. Attraction to pheromone encapsulated calcium alginate beads of all tick stage was higher in the Petri dish assay than in the olfactometer assay.

Fatal attraction: lone star ticks (Amblyomma americanum) exhibit preference for human female breath over male breath

Ticks use a variety of chemical cues to locate hosts, the main cue being carbon dioxide, which is exhaled by hosts. This study sought to experimentally determine whether ticks exhibit preference among human hosts based on host sex, as the chemical components of human male and female breath have been shown to differ. We focused on the lone star tick, Amblyomma americanum, due to its importance as a disease vector in the United States and its active host-seeking behavior. To test the hypothesis that ticks exhibit preference based upon host sex, we conducted a binary choice behavioral bioassay. Male and female human volunteers (n = 20 pairs) breathed into opposite sides of a secured polycarbonate tube containing 10 adult A. americanum and the proportion of ticks that exhibited a host preference was recorded. We found that under controlled conditions, human females attract a significantly larger proportion of ticks than males. Possible mechanisms to explain these results include that (1) female breath contains components that ticks find attractive, and/or (2) male breath contains a repellent chemical component.

Surface lipidome of the lone star tick, Amblyomma americanum, provides leads on semiochemicals and lipid metabolism

Lipids extracted from the surface of the lone star tick, Amblyomma americanum, were analyzed by high resolution mass spectrometry. Prior to lipid extraction, the adult ticks were either unfed or fed on cattle, and the fed ticks were in groups either containing males and females together, or containing only males or females. Cholesteryl esters were found on the surfaces of fed females, and they may provide a more complete description of the composition of the mounting sex pheromone. Dihydrocholesteryl esters were detected on the surfaces of unfed males and females, suggesting a possible role in survival during host-seeking. Dehydrodeoxyecdysone, found on fed females, could be a component of the genital sex pheromone. The most abundant polar surface lipids detected were acylglycerides. High levels of sphingolipids and glycerophospholipids on males fed separately might be derived, in part, from sperm development. A high level of a 20:4 fatty acid, presumably arachidonic acid, was found on the surface of fed females, indicating that it may be a component of the genital sex pheromone. A high level of docosenamide was found on the surface of fed females. Wax esters were found on the surfaces of fed ticks but not on unfed ticks. These esters could be involved in elasticity of the cuticle of engorged females or in wax coating of eggs. N-acylethanolamines were found on the surfaces of male and female ticks fed together, and on male ticks fed separately, but were absent or at low levels on females fed separately and on unfed ticks. This pattern suggests a possible role as a metabolic coordination primer pheromone.

Towards a new phenotype for tick resistance in beef and dairy cattle: a review

About 80% of the world’s cattle are affected by ticks and tick-borne diseases, both of which cause significant production losses. Cattle host resistance to ticks is the most important factor affecting the economics of tick control, but it is largely neglected in tick-control programs due to technical difficulties and costs associated with identifying individual-animal variation in resistance. The present paper reviews the scientific literature to identify factors affecting resistance of cattle to ticks and the biological mechanisms of host tick resistance, to develop alternative phenotype(s) for tick resistance. If new cost-effective phenotype(s) can be developed and validated, then tick resistance of cattle could be genetically improved using genomic selection, and incorporated into breeding objectives to simultaneously improve cattle productive attributes and tick resistance. The phenotype(s) could also be used to improve tick control by using cattle management. On the basis of the present review, it is recommended that three possible phenotypes (haemolytic analysis; measures of skin hypersensitivity reactions; simplified artificial tick infestations) be further developed to determine their practical feasibility for consistently, cost-effectively and reliably measuring cattle tick resistance in thousands of individual animals in commercial and smallholder farmer herds in tropical and subtropical areas globally. During evaluation of these potential new phenotypes, additional measurements should be included to determine the possibility of developing a volatile-based resistance phenotype, to simultaneously improve cattle resistance to both ticks and biting flies. Because the current measurements of volatile chemistry do not satisfy the requirements of a simple, cost-effective phenotype for use in commercial cattle herds, consideration should also be given to inclusion of potentially simpler measures to enable indirect genetic selection for volatile-based resistance to ticks.

A foreleg transcriptome for Ixodes scapularis ticks: Candidates for chemoreceptors and binding proteins that might be expressed in the sensory Haller's organ

Little is known about the molecular basis for the olfactory capabilities of the sensory Haller's organ on the forelegs of ticks. We first expanded the known repertoire of Ionotropic Receptors (IRs), a variant lineage of the ionotropic glutamate receptors, encoded by the black-legged Ixodes scapularis genome from 15 to 125. We then undertook a transcriptome study of fore- and hind-legs of this tick in an effort to identify candidate chemoreceptors differentially expressed in forelegs as likely to be involved in Haller's organ functions. We primarily identified members of the IR family, specifically Ir25a and Ir93a, as highly and differentially expressed in forelegs. Several other IRs, as well as a few members of the gustatory receptor family, were expressed at low levels in forelegs and might contribute to the sensory function of Haller's organ. In addition, we identified eight small families of secreted proteins, with sets of conserved cysteines, which might function as binding proteins. The genes encoding these Microplusin-Like proteins and two previously described Odorant Binding Protein-Like proteins share a common exon-intron structure, suggesting that they all evolved from a common ancestor and represent an independent origin of binding proteins with potential roles comparable to the ChemoSensory Proteins and Odorant Binding Proteins of insects. We also found two Niemann-Pick Type C2 proteins with foreleg-biased expression, however we were unable to detect foreleg-biased expression of a G-Protein-Coupled pathway previously proposed to mediate olfaction in the tick Haller's organ.

Phylogenetic studies of bacteria (Rickettsia, Coxiella, and Anaplasma) in Amblyomma and Dermacentor ticks in Thailand and their co-infection

In this study, we attempted to detect Rickettsia, Coxiella and Anaplasma bacteria in one hundred and fourteen-Dermacentor and thirty three-Amblyomma unfed adult ticks that were collected from under leaves along animal trails at different places across Thailand. PCR amplification was used to identify bacterial infection with general conserved sequences of bacteria. The results revealed single infection in Amblyomma testudinarium ticks with Rickettsia (24%) and Coxiella (6%). Anaplasma bacteria were often detected in Dermacentor auratus ticks (32%). Coxiella spp. were detected in Dermacentor atrosignatus (6%) and D. auratus ticks (3%) in this study. Moreover, we found co-infection by Coxiella and Rickettsia bacteria (39%) in Am. testudinarium. In contrast, D. atrosignatus ticks were co-infected with Coxiella and Anaplasma bacteria (3%) and Dermacentor compactus ticks were co-infected with Rickettsia and Anaplasma spp. (25%). Interestingly, Am. testudinarium ticks (12%) were found for the first time to exhibit triple infection by these three bacteria. Phylogenetic studies showed the rickettsiae from ticks causing both single and multiple infections had sequence similarity with spotted fever group rickettsial strains, including Rickettsia massilliae, R. raoultii and R. tamurae. In addition, the phylogenetic analysis of the 16S rRNA gene of Coxiella bacteria showed that they were closely grouped with Coxiella endosymbionts in both Dermacentor and Amblyomma. Moreover, the Anaplasma identified in a D. auratus tick was grouped in the same clade with the pathogenic bacterium Anaplasma phagocytophilum. Bacterial co-infections in Dermacentor and Amblyomma ticks may cause co-transmission of some tick-borne microorganisms (pathogen and endosymbiont, whether enhance or reduce) in humans and animals and they could affect medical and veterinary health.

In-vitro trials to ascertain sustained release efficacy of assembly pheromone micro particles for the control of brown dog tick, Rhipicephalus sanguineus

Sustained release micro particles were prepared incorporating assembly pheromone and deltamethrin. Two natural polymers, namely, chitosan and calcium alginate and a synthetic polymer, poly-ε-caprolactone were used for encapsulating the assembly pheromone-acaricide combination. The micro particles were subjected to in vitro evaluation freshly after preparation and then at monthly intervals to assess their sustained release efficacy. The response of the unfed stages of dog tick, Rhipicephalus sanguineus to fresh and aged micro particles was assessed and results were recorded. The micro particles were found to release assembly pheromone in a sustained manner up to 2 months of study period.

The chemosensory appendage proteome of Amblyomma americanum (Acari: Ixodidae) reveals putative odorant-binding and other chemoreception-related proteins

Proteomic analyses were done on 2 chemosensory appendages of the lone star tick, Amblyomma americanum. Proteins in the fore tarsi, which contain the olfactory Haller's organ, and in the palps, that include gustatory sensilla, were compared with proteins in the third tarsi. Also, male and female ticks were compared. Proteins were identified by sequence similarity to known proteins, and by 3-dimensional homology modeling. Proteomic data were also compared with organ-specific transcriptomes from the tick Rhipicephalus microplus. The fore tarsi express a lipocalin not found in the third tarsi or palps. The fore tarsi and palps abundantly express 2 proteins, which are similar to insect odorant-binding proteins (OBPs). Compared with insect OBPs, the tick OBP-like sequences lacked the cysteine absent in C-minus OBPs, and 1 tick OBP-like sequence had additional cysteines that were similar to C-plus OBPs. Four proteins similar to the antibiotic protein microplusin were found: 2 exclusively expressed in the fore tarsi and 1 exclusively expressed in the palps. These proteins lack the microplusin copper-binding site, but they are modeled to have a significant internal cavity, potentially a ligand-binding site. Proteins similar to the dust mite allergens Der p7 and Der f 7 were found differentially expressed in female fore tarsi. A protein exclusively expressed in the fore tarsi has similarities to Neto, which is known to be involved in clustering of ionotropic glutamate receptors. These results constitute the first report of OBP-like protein sequences in ticks and point to several research avenues on tick chemosensory reception.

Behavioural responses of Ixodes ricinus nymphs to carbon dioxide and rodent odour

Many haematophagous ectoparasites use carbon dioxide (CO₂ ) and host odour to detect and locate their hosts. The tick Ixodes ricinus (Linnaeus) (Ixodida: Ixodidae) walks only small distances and quests in vegetation until it encounters a host. The differential effects of CO₂ and host odour on the host-finding behaviour of I. ricinus have, however, never been clarified and hence represent the subject of this study. The effects of CO₂ and odour from bank voles on the activation and attraction of I. ricinus nymphs were analysed in a Y-tube olfactometer. Carbon dioxide evoked a response in the absence and presence of host odour, but did not attract nymphs. Host odour, however, did not evoke a response but did attract nymphs in the absence and presence of CO₂ . The current results show that CO₂ is an activator, but not an attractant, and that host odour is an attractant, but not an activator, of I. ricinus nymphs, and provide ecological insights into the host-finding behaviour of I. ricinus.

A novel assembly pheromone trap for tick control in dog kennels

A novel ecofriendly sticky tick trap device for the control of dog tick Rhipicephalus sanguineus using gold nanoparticle assembly pheromone complex as a bait was developed. Assembly pheromones comprising of guanine, xanthine and adenine in the ratio of 25:1:1 was encapsulated in gold nanoparticle. The response of the different stages of unfed R. sanguineus ticks was evaluated using petridish bioassay. Statistical analysis was done using chi-square test. Petridish bioassay with unfed stages of R. sanguineus revealed that 100% of the larvae, nymph and adults were attracted to assembly pheromone nanogold complex within 24h. Of the 952 ticks trapped, ticks of different stages trapped in total by the baited sticky trap device, 543 (57%) were engorged and 409 (43%) were unfed ticks. The study revealed that assembly pheromone baited traps has the potential to control tick infestations in dog kennels.

Sarcoptes scabiei: genomics to proteomics to biology

BACKGROUND

The common scabies mite, Sarcoptes scabiei is a cosmopolitan parasite of humans and other mammals. An annotated genome of Sarcoptes scabiei var. canis has been deposited in the National Center for Biotechnology Information (NCBI) and VectorBase and a proteomic analysis of proteins in extracts of mite bodies and eggs from this strain has been reported. Here we mined the data to identify predicted proteins that are known to be involved in specific biological processes in other animals.

RESULTS

We identified predicted proteins that are associated with immunomodulation of the host defense system, and biological processes of the mite including oxygen procurement and aerobic respiration, oxidative metabolism, sensory reception and locating a host, neuronal transmission, stressors (heat shock proteins), molting, movement, nutrient procurement and digestion, and excretion and water balance. We used these data to speculate that certain biological processes may occur in scabies mites.

CONCLUSION

This analysis helps understand the biology of Sarcoptes scabiei var. canis and adds to the data already available in NCBI and VectorBase.

Amblyomma maculatum Feeding Augments Rickettsia parkeri Infection in a Rhesus Macaque Model: A Pilot Study

Rickettsia parkeri is an emerging eschar-causing human pathogen in the spotted fever group of Rickettsia and is transmitted by the Gulf coast tick, Amblyomma maculatum. Tick saliva has been shown to alter both the cellular and humoral components of the innate and adaptive immune systems. However, the effect of this immunomodulation on Rickettsia transmission and pathology in an immunocompetent vertebrate host has not been fully examined. We hypothesize that, by modifying the host immune response, tick feeding enhances infection and pathology of pathogenic spotted fever group Rickettsia sp. In order to assess this interaction in vivo, a pilot study was conducted using five rhesus macaques that were divided into three groups. One group was intradermally inoculated with low passage R. parkeri (Portsmouth strain) alone (n = 2) and another group was inoculated during infestation by adult, R. parkeri-free A. maculatum (n = 2). The final macaque was infested with ticks alone (tick feeding control group). Blood, lymph node and skin biopsies were collected at several time points post-inoculation/infestation to assess pathology and quantify rickettsial DNA. As opposed to the tick-only animal, all Rickettsia-inoculated macaques developed inflammatory leukograms, elevated C-reactive protein concentrations, and elevated TH1 (interferon-γ, interleukin-15) and acute phase inflammatory cytokines (interleukin-6) post-inoculation, with greater neutrophilia and interleukin-6 concentrations in the tick plus R. parkeri group. While eschars formed at all R. parkeri inoculation sites, larger and slower healing eschars were observed in the tick feeding plus R. parkeri group. Furthermore, dissemination of R. parkeri to draining lymph nodes early in infection and increased persistence at the inoculation site were observed in the tick plus R. parkeri group. This study indicates that rhesus macaques can be used to model R. parkeri rickettsiosis, and suggests that immunomodulatory factors introduced during tick feeding may enhance the pathogenicity of spotted fever group Rickettsia.

Response of unfed stages of Rhipicephalussanguineus to subtle variations in the composition of assembly pheromone

Two combinations of assembly pheromone (AP), with and without hematin were utilized as a lure for the unfed larvae, nymph and adults of Rhipicephalussanguineus ticks. In-vitro trials were carried out with the AP encapsulated in calcium alginate beads and the response of different stages of ticks were recorded. Analysis of results revealed that rapid attraction was evident in unfed larvae exposed to beads containing AP without hematin. In case of unfed nymphal and adult stages, the presence or absence of hematin did not have any impact on arrestment.

Co-feeding transmission in Lyme disease pathogens

This review examines the phenomenon of co-feeding transmission in tick-borne pathogens. This mode of transmission is critical for the epidemiology of several tick-borne viruses but its importance for Borrelia burgdorferi sensu lato, the causative agents of Lyme borreliosis, is still controversial. The molecular mechanisms and ecological factors that facilitate co-feeding transmission are therefore examined with particular emphasis on Borrelia pathogens. Comparison of climate, tick ecology and experimental infection work suggests that co-feeding transmission is more important in European than North American systems of Lyme borreliosis, which potentially explains why this topic has gained more traction in the former continent than the latter. While new theory shows that co-feeding transmission makes a modest contribution to Borrelia fitness, recent experimental work has revealed new ecological contexts where natural selection might favour co-feeding transmission. In particular, co-feeding transmission might confer a fitness advantage in the Darwinian competition among strains in mixed infections. Future studies should investigate the ecological conditions that favour the evolution of this fascinating mode of transmission in tick-borne pathogens.

Control of brown dog tick, Rhipicephalus sanguineus using assembly pheromone encapsulated in natural polymer, chitosan

In the current study, an attempt was made to encapsulate assembly pheromone using natural polymer, chitosan. Chitosan beads were prepared by incorporating assembly pheromone in conjunction with an acaricide, namely, deltamethrin. In the in vitro bioassay, the test beads attracted and killed 79 % of unfed larvae, 88 % of unfed nymphs and 61 % of unfed adults of the brown dog tick, Rhipicephalus sanguineus, in 24 h of exposure. Field trials were carried out to attract and kill the pre-parasitic environmental stages. The beads were dispersed onto specially designed devices and they were placed in infested kennels. The devices were observed after 10 days.

Seasonal feeding activity of the tree-hole tick, Ixodes arboricola

Bird-specific ticks do not infest humans and livestock, but these ticks often share their avian hosts with generalist ticks that do. Therefore, their feeding activity may have an impact on the transmission of pathogens outside bird-tick transmission cycles. Here we examined the seasonal feeding activity of the tree-hole tick (Ixodes arboricola) in relation to the activity of its hole-breeding hosts (Parus major and Cyanistes caeruleus). We analysed data on ticks derived from birds, on the abundance of engorged ticks inside nest boxes, and on bird nests that were experimentally exposed to ticks. We observed a non-random pattern of feeding associated with the tick instar and host age. The majority of adult ticks fed on nestlings, while nymphs and larvae fed on both free-flying birds and nestlings. Due to their fast development, some ticks were able to feed twice within the same breeding season. The highest infestation rates in free-flying birds were found during the pre-breeding period and during autumn and winter when birds roost inside cavities. Except during winter, feeding of I. arboricola overlapped in time with the generalist Ixodes ricinus, implying that tick-borne microorganisms that are maintained by I. arboricola and birds could be bridged by I. ricinus to other hosts.

A novel approach to control brown dog tick, Rhipicephalus sanguineus using sustained release poly-ɛ-caprolactone-pheromone microspheres

Control of brown dog tick, Rhipicephalus sanguineus was attempted by utilizing sustained release preparations of synthetic analogues of assembly pheromones. The assembly pheromone, in defined ratio, was encapsulated using poly-ɛ-caprolactone by water-in-oil-in-water double emulsion solvent evaporation technique. In the in vitro bioassay, percent mortality with test microspheres was 95.6, 64 and 44 among the unfed larvae, unfed nymph and unfed adults respectively, 24 hours post-exposure. Field trials were carried out to evaluate the efficacy of microspheres in luring and killing environmental stages of R. sanguineus in dog houses/kennels. Engorged and unfed stages in the environment were found adhered and dead on the specially designed lure.

Field trials to attract questing stages of brown dog tick, Rhipicephalus sanguineus using tick pheromone-acaricide complex

Evaluations were made to assess the efficacy of assembly pheromone, attractant sex pheromone and the kairomone carbon dioxide in attracting the questing larval nymphal and adult stages of the brown ear dog tick, Rhipicephalus sanguineus. Ticks attracted to one location were killed using the acaricide deltamethrin. Initially, simulated field trials were conducted to observe the percentage of attraction of ticks from different distances. Tick lure comprising of carbon dioxide as kairomone and 2,6-dichlorophenol in combination with assembly pheromone and deltamethrin on a thermocol platform was prepared and field trials were conducted in the kennels of Blue Cross Society of India, Velachery, Chennai. The tick lure attracted larval, nymphal and adult stages of R. sanguineus ticks in and around the kennels. Observations were made after 24 h of placing the tick lure. In simulated field out of the 50 ticks used for each distance trials, positive response was exhibited by a total number of 20 (40 %), 17 (34 %) and 14 (28 %) ticks from 0.5, 1 and 1.5 m, respectively. Field trials conducted revealed considerable attraction of larvae and nymph to the tick lure. Few adult ticks (2-5) were also lured to the pheromone impregnated filter paper disc.

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

Carbon dioxide (CO(2) ), 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 CO(2) , acetone, 1-octen-3-ol and ammonium hydroxide elicited significant preferences from adult A. americanum, and only CO(2) was attractive to adult D. variabilis. Acetone, 1-octen-3-ol and ammonium hydroxide were separately evaluated at three doses against CO(2) (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.