Ticks of Canada

• Introduction to Ticks of Canada

  Ticks are actually a highly distinctive group of relatively large mites (body length 1 to 5 mm as unfed adults but up to 20 mm when fully engorged), among which they are distinguished by a set of unique specializations of their mouthparts and body for seeking and feeding obligately on the blood of vertebrate animals, especially birds and mammals. All postembryonic instars - larva, nymph and adult - of most tick species are capable of harming their hosts through exsanguination or secondary infection at sites of attachment. Larval ticks have three pairs of legs, like other larval mites, and they lack lateroventral respiratory openings, the stigmata, on the body. Nymphal and adult ticks have four pairs of legs and a pair of stigmatal plates behind or lateral to their fourth pair of legs.

  Over 800 species of ticks have been described, and ticks occur with their hosts throughout the world. Although encountered most frequently in tropical and subtropical regions, ticks are also significant pests of wild and domesticated animals and humans in temperate and boreal forest and prairie habitats, and even in harsher tundra of the far north. In addition to exsanguination, ticks of some species serve as reservoirs and vectors for a surprising variety of pathogens, including viruses, rickettsias, bacteria, sporozoans and spirochaetes. In Canada, these pathogens include the causative agents of Lyme disease, relapsing fever, tularaemia, Rocky Mountain spotted fever, Q fever, Colorado Tick fever, Powassan encephalitis, babesiosis, and perhaps others. Ixodid ticks of the genus Dermacentor also can cause a motor paralysis in humans and mammals following extended periods of engorgement. Tick paralysis may result in death if the feeding ticks are allowed to remain attached to the host.

  Ticks are classified in their own order, Ixodida (also named Metastigmata), in the Acari, or mites, a subclass of Arachnida. Of the three families of Ixodida generally recognized, two, the Argasidae and Ixodidae, are represented in Canada , where 40 species in 10 genera are known to occur. Argasid ticks, known as 'soft ticks' in lacking a hard dorsal shield on their bodies, are generally nocturnal and are rapid feeders , resembling bed bugs in this respect. Only 8 species, in 4 genera, are known or thought to occur in Canada . Ixodid ticks, known as 'hard ticks' in having a hard dorsal shield, or scutum, that covers at least the anterior portion of the body, are mostly diurnal and slow feeders, remaining attached to their hosts for considerable lengths of time if undisturbed. Thirty-two species, in 6 genera are known or thought to occur in Canada , 23 of which belong to the genus Ixodes.

  Keys for identification and other information about Canadian ticks were last presented in a work by J.D. Gregson, published in 1956. Although that work has served well during the 45-year interval since its issue, it has become considerably out of date with regard to the species of ticks that are now known to occur in Canada , their distribution, their range of hosts, and the variety of pathogens that they carry. For example, Lyme disease has only been known as such since the mid-1970's, and human babesiosis is a more recently emerging disease in the northeastern United States and southeastern Canada . Moreover, there has been no publication, either for Canada or the continental United States , that has included keys to the larval instar of tick species. As a reservoir and vector of pathogens, the larva may be just as important as subsequent instars. An accurate identification of a feeding tick to species, whether it be larva, nymph, female or male, is the essential first step in leading to information as to whether there should be concern about the tick being a potential vector of a pathogen of one disease or another. Although certain species of ticks have been shown to be carriers and competent vectors of diseases, many others either do not harbor pathogens or do not serve as competent vectors of them. As users of other keys to species of ticks available for various regions of North America , we are aware of how difficult some sections of keys are for non-specialists. We have tried to make our keys as 'user-friendly' as possible, by selecting relatively easily visible attributes and by including a second attribute for most couplets, in case the first one is damaged or missing on a specimen.

  This web site is designed to present a general survey of available information on all species of ticks known or anticipated to occur in Canada , in such a way that viewers may become familiar with their identities and known biologies. This information will be equally useful in Alaska and the northern tier of contiguous states of the United States of America bordering Canada . Information on tick distributions and hosts, beyond that given in Gregson's work, is based on data with specimens accumulated in the Canadian National Collection (CNC) of ticks in the care of the Research Branch, Agriculture & Agri-Food Canada, Ottawa . Gregson's extensive collection, which is considerably concentrated on western and mid-western Canadian records, has been deposited in the CNC, and it is complemented by substantial numbers of ticks and records that have accumulated largely from mid-eastern and eastern Canadian sources since 1960. Data from other Canadian sources have also been included.

  Topics to be presented in this web site include:

  • General information on tick life history;
  • Medical and veterinary importance of ticks in Canada ;
  • External structures and terms used for identifying ticks;
  • Summary of classification of ticks;
  • Illustrated keys to larvae, nymphs, and adult females and males of genera and species of ticks in Canada ;
  • Diagnoses, summary life histories, host preferences, general distribution, disease vector potential, and computerized maps of Canadian distribution of ticks;
  • Methods of collecting, rearing and preserving ticks, and of analysing them for pathogens;
  • Control of ticks and prevention of their bites.

  Host-tick, tick-host, disease-vector, and vector-disease indices are also planned.

  There remain gaps in our knowledge of species of ticks in Canada , particularly their life histories, vector potentials, and methods of dispersal. We hope that this web site will serve to stimulate further investigations in these fields.

• List of Ticks Occuring in Canada 

  Amblyomma

  Amblyomma americanum (Linnaeus)

  Amblyomma maculatum Koch

  Argas

  Argas (Argas) cooleyi Kohls and Hoogstraal

  Argas (Persicargas) persicus (Oken)

  Carios

  Carios concanensis (Cooley and Kohls)

  Carios kelleyi (Cooley and Kohls)

  Dermacentor

  Dermacentor albipictus (Packard)

  Dermacentor variabilis (Say)

  Dermacentor andersoni Stiles

  Haemaphysalis

  Haemaphysalis leporispalustris (Packard)

  Haemaphysalis chordeilis (Packard)

  Ornithodoros

  Ornithodoros hermsi Wheeler, Herms and Meyer

  Ornithodoros parkeri Cooley

  Otobius

  Otobius megnini (Dugès)

  Otobius lagophilus Cooley and Kohls

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• External Structures and Terms for Describing and Identifying Ticks

  As with their relatives, the mites, the body of ticks consists of an anterior gnathosoma or capitulum , and a posterior idiosoma or "body"; these are separated by the circumcapitular suture , which is the only articulation of the body other than on the appendages. The capitulum is generally positioned to project apically , so as to be visible in dorsal aspect, in larval ticks, but it projects ventrally, and is usually concealed from above, in nymphal and adult argasid ticks, in contrast to maintaining its visible apical position and anterior projection in nymphal and adult ixodid ticks.

  Capitulum. The capitulum superficially resembles the head of insects, and it consists of a subcapitulum or basis capituli , a hypostome , and the paired chelicerae and palpi . The basis capituli (or, simply, basis ) is the basal portion of the capitulum to which the palpi and mouthparts ( hypostome and chelicerae) are attached. In nymphal and adult argasid ticks, the capitulum lies in a depression, the camerostome , which becomes less clearly defined in engorged specimens. Along its sides, the camerostome has a pair of flaps, the cheeks, which may be either fixed or movable. An anterior projection of the dorsal idiosomal wall, the hood, covers the camerostome . In ixodid ticks, the capitulum is fully exposed in all active instars, and a variety of its visible structures are useful diagnostically. The length of the capitulum is measured from the middle of the posterior dorsal margin of the basis to the apex of the hypostome , and excludes the length of the caudal projections, or cornua , that may arise from the posterolateral angles of the dorsal margin. Dorsally, the basis capituli commonly has a rectangular shape, with more or less parallel sides, but it is hexagonal, with angularly projecting sides, in adults and immatures of Rhipicephalus and in immatures of Haemaphysalis and some species of Dermacentor , and it is triangular, with posteriorly projecting angles, in adults and immatures of some species of Ixodes and in immatures of some other species of Dermacentor . The basis of ixodid adult females bears a pair of porose areas, which are somewhat depressed with pitted floors; these have characteristic shapes among species in some genera, as Ixodes ; they are absent in males, nymphs and larvae. Ventrally, the anterolateral margins of the basis capituli , which are sometimes called the "shoulders of the hypostome " ( Gregson 1956), are more or less characteristically flattened or humped or angled in leading to the base of the hypostome . Posterior to the attachment of the palpi , the lateral margins of the basis sometimes have a pair of projections, the auriculae , whose form varies among different species; they may be mild protuberances, or flattened ridges, or more strongly developed as hornlike processes or retrorse spurs. Near the posteroventral margin of the basis capituli , a transverse sutural line is evident in some species. Posteriorly , the basis may be constricted to a more or less typical degree among some species, or it may remain untapered . Two or three pairs of setae on the ventral face of the basis are notable diagnostically at the species level for larvae and nymphs. These include one or two pairs of posthypostomal setae, inserted near the base of the hypostome , and one pair of postpalpal setae , inserted more laterally behind the bases of the palpi . The former are equivalent to the hypostomal or subcapitular setae, and the latter, found only on some argasid ticks, are equivalent to the palpcoxal or capitular setae, of mesostigmatic mites.

  A singularly specialized characteristic of ticks, in contrast to the other acarines , the mites, is the hypostome , a forward extension from the anterior portion of the basis that is modified as a piercing organ and armed with retrorse teeth or denticles , or sharp-edged ridges, termed crenulations (or, more concisely, crenulae ),on its lateral and ventral surfaces. The denticles are usually arranged in parallel longitudinal rows, or files, and the dentition formula indicates the number of files on each side of the midline of the hypostome . For example, 2/2 indicates the presence of two files on each side, whereas "first 3/3 and then 2/2" indicates that, of three files beginning on the distal portion, one file does not continue to the base of the hypostome . The lateralmost row is designated as file 1. The relative size of denticles differs characteristically among species of ticks, such that the number of teeth in each file is a useful diagnostic attribute; the lateral file generally has denticles at least as large as any present elsewhere on the hypostome . Sexual dimorphism is commonly present in the hypostome among adult ticks of the same species. In males the denticles may be altered to transverse or diagonal rows of sharp or blunt elevations or ridges called crenulations or crenulae as noted above. The argasid genus Otobius is unusual in that its adults have a vestigial hypostome in contrast to a well developed one in the immature instars. The apex of the hypostome may be pointed or rounded or notched, and it is commonly armed with a crown, the corona, of more or less numerous small denticles that do not form readily recognizable files. In this guide, the length of the hypostome is measured from the apex to the base of the most proximal denticles or, in cases where the denticles are obviously limited to the distal half or two-thirds of the hypostome , to the approximate origin of the hypostome on the basis as indicated by a more or less clearly outward curvature of its lateral margins where they join the basis capituli .

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  Lying dorsal to the hypostome are the paired chelicerae, which are reduced to two segments in ticks and consist of an extrudable and retractable shaft that extends through the basis capituli and bears apical cutting digits of a uniquely modified form. These digits consist of a fixed inner digit to which a strongly dentate, outer digit is articulated on its external surface. A bifid or serrate dorsal process is also attached to the external side of the inner digit (see fig. 5.12E, p. 150 in Evans 1992). Only the cutting external teeth are generally exposed, and no emphasis is placed on the chelicerae in diagnoses.

  The palpi are movable, segmented, paired appendages attached to the basis capituli anteriorly on either side flanking the hypostome . They are hollowed along their inner faces, such that, when apposed, they more or less cover the hypostome and chelicerae; they are spread apart during feeding. The palpi generally consist of four, or rarely three, free segments and these are usually named and numbered articles 1 to 4 in a proximal to distal sequence in descriptive literature on ticks (e.g., Gregson 1956, Clifford et al. 1961, Edwards 1975). However, palpal setal numbers and setation patterns among larval ticks confirm that the four free segments in Ixodida are homologous with the segments termed trochanter , femur, genu , and fused tibiotarsus of other parasitiform Acari , and we follow Klompen (1992) in applying these terms to ticks. The proximal palpal trochanter is small, and sometimes immovably articulated; it may be visible only ventrally, or it is sometimes vestigial, as in the genus Boophilus . It sometimes bears one or two projections or flanges, directed diagonally anteriorly or posteriorly , or both, which may be of diagnostic value, especially among species of Ixodes ; these are designated as anterior and posterior "horns" or "spurs" in some treatments. Some members of this genus are characterized by having the basal palpal segment not only fused with the basis capituli but also enlarged and often provided with the spurlike processes noted above. This enlarged structure, termed the palpiger , has been used to some extent in the diagnosis of subgenera of Ixodes . The palpal femur and genu are large conspicuous segments that are often more or less fused, with or without a defined suture line between them; the lateral margin profile of these two segments, whether straight or convex, and their combined length relative to their width are of diagnostic use. In the genus Haemaphysalis , the bases of the palpal femora are strongly flared laterally, giving the palps a characteristically conical shape. Excepting some taxa of Argasidae , the palpal tibiotarsus is small, and it is sometimes reduced to an inconspicuous papilla lying in a ventral depression near the apex of the palpal genu .

  The number and arrangement of setae on the palpal femur, genu , and tibiotarsus of larval ticks are important diagnostic attributes. Palpal setation characters are not useful for nymphal and adult ticks because of increased numbers and intraspecific variability of setae during ontogeny, which render the homology of setae difficult and unreliable. The notation applied to the larval palpal setae is that proposed by Evans (1963b) for mesostigmatic mites and modified slightly by Klompen (1992) for ticks. Setae are distinguished and denoted by their position on the anterior (ad) and posterior (pd) dorsal faces, anterolateral (al) and posterolateral (pl) faces, and ventral (v) face of the palpal segments, except that the cluster of distal setae on the tibiotarsus are simply counted but not individually denoted. The palpal trochanter consistently lacks setae in larval ticks, as in other larval Parasitiformes . A maximum of six setae are present on the palpal femur of larval ticks; these are denoted al, ad, pd-1, pd-2, pl, and v. Larvae of all Argasidae lack seta v, those of some argasid genera also lack one of the two pd setae, and those of Otobius also lack seta al on the palp femur ( Klompen 1992). A maximum of seven setae are present on the palpal genu of larval ticks; these are denoted al, ad-1, ad-2, ad-3, pd-1, pd-2, pl. While larvae of Ixodidae have this full complement of setae or lack but one of the two pd setae, those of all Argasidae lack seta ad-3 and one of the two pd setae, and one or two other setae (commonly al, and sometimes ad-2) are absent in some argasid genera ( Klompen 1992). A porelike structure is often evident on the dorsal face in the palpal genual area; care should be taken to not mistake this for an alveolus of a detached seta. According to Klompen (1992), setation of the fused palpal tibiotarsus in larval ticks is maximally 12 (Lindquist et al. 1999 observed 15 in larvae of Ixodes gregsoni ), including a group of at most four (al, ad, pd, v) on the main body of the segment and a distal cluster of at most eight, which are not denoted as they are not readily homologized; setae al and pd are absent from the main body of the larval tibiotarsus , and one or two setae are absent from the distal cluster in some genera of Argasidae . All of the above reductions in setal numbers from the maximum complements on the palpal segments are considered to be derived character states within the Ixodida relative to more distantly related outgroups of parasitiform Acari ( Klompen 1992).

  Idiosoma . The idiosoma , often simply (and erroneously) called the "body", is the largest region of the body of ticks, and is analogous to the combined thorax and abdomen of insects. The idiosoma of larval ixodid ticks bears a moderately small but well developed anterior dorsal shield that is retained in relatively similar size on the nymph and adult female, and named the scutum ; the scutum is greatly expanded to cover most of the dorsal surface on the adult male. In contrast, the idiosoma of larval argasid ticks has at most a small mid-dorsal plate, or mesonotal shield , that is lost in postlarval instars. Argasids are commonly referred to as 'soft ticks' due to this lack of a well developed dorsal scutum . However, the dorsal surface of nymphal and adult argasids is typically leathery and wrinkled, granulated or covered with small elevations called mammillae , and the lateral margins of the dorsal surface are sometimes sharply delineated from those of the ventral surface by a definite sutural line . In addition, small, somewhat raised or depressed discs , or scutellae , of thickened cuticle may be visible as patterns on both dorsal and ventral surfaces of the idiosoma ; these represent muscle attachment sites, or sigillae . The shape of the idiosoma is sometimes diagnostic among argasid species; for example, in dorsal view it is abruptly constricted posteriorly in adults of Otobius megnini , in contrast to O. lagophilus , and in lateral view its anterior margin is turned up in adults of Argas reflexus , in contrast to A. persicus .

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  The scutum of adult Ixodidae bears a pair of anterolateral projections, the scapulae; these may be pointed, rounded, or reduced to small lobes. The scutum of nymphal ixodids bears more weakly developed scapulae, or these may be indicated only as more narrowly rounded anterolateral corners, as on the larvae. The transverse anterior excavation between the scapulae in adult ixodids , the scutal emargination , accommodates upward movement of the closely articulated capitulum ; it may be characteristically straight or somewhat sinuous. The scutum in all instars of Ixodidae often bears a pair of linear depressions, the cervical grooves, that begin closely behind the scapulae and extend posterolaterally to somewhat beyond the midlevel of the scutum . They are sometimes absent, and when present they are often shallow, so as to be seen best by reflected light on temporarily dried specimens. Lateral to the cervical grooves, there may be linear elevations, the lateral carinae , close to the margins of the scutum anterolaterally . When present, these are evident as more or less well developed ridges, but they are often difficult to discern and we prefer to avoid referring to their presence or absence as diagnostic characters. The region bearing soft, pliable dorsal cuticle lateral and posterior to the scutum in ixodid immatures and females is sometimes termed the alloscutum .

  The shape and ornamentation of the scutum are important diagnostic characters of all instars of ixodid ticks (though less so of adult males). The scutum may be inversely subtriangular versus oval, its greatest width may be lesser versus greater than its median length, and the greatest width may be located anterior to, versus about at, its midlength . The scutal surface may be partly or entirely marked with minute irregular fissures (crazed), or pitted with puncta of various size and density, or wrinkled (rugose). The nature of scutal ornamentation of ixodid adults and nymphs is visible under a good stereomicroscope, but that of ixodid larvae is often discernible only with a compound microscope, in which case temporary or permanent slide preparations of specimens need to be made. The scutum of some kinds of adult ixodid ticks is termed ornate when it has a pattern of enamel-like color superimposed over the base color of some shade of brown. Both color and color pattern or location may be useful diagnostically, particularly among species of Dermacentor , though considerable intraspecific variation of these attributes must be accounted for. Scutal setation , or its "hairiness", including the relative density and length of setae, is sometimes a useful attribute. As with scutal topography, setation is best seen by reflected light on temporarily dried specimens of nymphs and adults. On larvae of ixodid ticks, the nature of scutal setation may be of more critical diagnostic importance, and includes the number, length and position of setae, as well as porelike structures (see below) on the scutum when viewed in slide preparations under a compound microscope. In some genera of ixodid ticks, a pair of hyaline lenslike structures, the eyes, are present near the lateral margins of the scutum . Two pairs of such structures are present on the anterior submarginal region of the idiosoma of certain argasid ticks. However, eyes are absent among most taxa of Argasidae , all species of the genus Ixodes , and some other genera of Ixodidae . In species of Dermacentor the anterior region of the expansive scutum of males may be distinguished by a difference in color pattern and by the posterior limits of the cervical grooves. This region, which is homologous with the smaller scutum of the nymph and female, is called the pseudoscutum . In males of other ixodid genera, the scutum may have a pair of lateral grooves that extend along the sides of the shield, beginning near the scapulae and extending to its posterior extremity. These grooves correspond to the pair of marginal grooves found on soft cuticle behind the scutum on adult females. A pair of circular structures, the foveae, are sometimes present on the midregion of the male scutum ; these are on soft cuticle closely posterior to the scutum of conspecific females. Uniform, subrectangular areas separated by grooves, called festoons, may be present along the posterolateral margins of the idiosomal dorsum in adults of both sexes of some genera, including Dermacentor , Rhipicephalus and Haemaphysalis . Festoons are thought to represent external vestiges of ancestral segmental boundaries ( Klompen 1996). The unpaired caudal festoon is termed the parma . Located on the dorsal scutum in males, but on soft cuticle in females, the number of festoons may be a useful diagnostic attribute at the species or genus level.

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  The setation of the idiosomal dorsum of larval ixodid ticks is highly important in the diagnosis of larvae of genera and species. Diagnostic attributes include the number and position of homologous setae on the scutum and soft cuticle and their positional relationship to certain other structures such as gland pores and lyrifissures , as well as the shape and size of setae. The system of notation follows that of Lindquist and Evans (1965) for mesostigmatic mites, as applied by Klompen et al. (1996) for larval Ixodidae . Dorsal idiosomal setae are recognized to form three longitudinal series, named and denoted as the dorsal median j-J series, dorsal mediolateral z-Z series, and dorsal lateral s-S series (an earlier system of chaetotaxy for larval ixodid ticks, developed by Glashchinskaya-Babenko 1949 and used by Clifford and Anastos 1960, named and denoted the setae on soft cuticle as the central dorsals Cd , supplementaries S, and marginal dorsals Md ; see Table 1 for equivalents). Lower-case letters are applied to setae on the scutum and elsewhere on the podonotal region (e.g., j5), while upper-case letters are applied to setae on the opisthonotal region (e.g., J2). The numbering of setae is designed to arrange them in transverse rows that correspond with hypothesized segments, which lack external delineation in ticks. Thus setae j5 and s5 are thought to be elements of the fifth segment of the podonotal region, and J2 and S2 are elements of the second segment of the opisthonotal region. Klompen et al. (1996) also applied a notation to the lyrifissures and gland pores on the scutum and soft cuticle of ixodid larvae, which enables one to recognize hypothetical homologies among these structures and to use their absence or presence and position relative to adjacent structures as diagnostic attributes. In various works previous to Klompen's , the lyrifissures were referred to as "sensilla auriformia", the small glands and their pores as "sensilla hastiformia", and the large glands and their pores as "sensilla sagittiformia". Because of their prominence and apparently different function, the large glands have been designated as large wax glands (LWG). The absence or presence of a pair of large glands on the dorsolateral surface of the idiosoma , and their position relative to the marginal dorsal setae, are useful attributes in distinguishing larval ixodids to genus (Clifford and Anastos 1960, Klompen 1996). However, the use of lyrifissures and gland pores is only beginning to be applied diagnostically (e.g., Lindquist et al. 1999), and sufficient data from the diversity of ticks that occur in Canada are not available for their use as an aid in identifying larvae to species in the present guide.

  Ventrally, the idiosoma bears the genital aperture between the bases of legs II or III in adult females and between legs I, II or III in adult males, and, posteriorly , the anus in all instars. The genital aperture of the female is more obvious as a somewhat larger, transverse slit than that of the male. The anus is surrounded by a circular or oval sclerotized ring and is covered by a pair of eversible anal valves that bear one to several pairs of setae, the number of which is useful diagnostically among species of Ixodes . The anus is partly enclosed by an anal groove in the soft cuticle of most ixodid ticks; this groove embraces the anus as an anterior arch in the genus Ixodes , but is contoured posteriorly to the anus in other genera, though it is absent in a few, e.g., Boophilus . A set of ventral plates or shields distinguish males of Ixodes from females as well as from males of other genera of Ixodidae which, as found in Canada, either have only a partial set of these plates ( Rhipicephalus ) or lack them entirely ( Dermacentor , Haemaphysalis ). A small pregenital plate may be present between the bases of legs I and II, in front of the male genital aperture. A more expansive median plate covers the area behind the genital aperture between and somewhat behind the bases of legs III and IV; it abuts both the anal plate, which surrounds the anus, and the pair of adanal plates, which flank the anal plate. A pair of epimeral plates, sometimes less well delineated, may flank the adanal plates; these are designated accessory plates in genera such as Rhipicephalus and Boophilus . Although subject to some intraspecific variation, the relative size and shape of these plates are useful diagnostically among species of Ixodes . Nymphal and adult argasids often have a series of ventral grooves or folds, which become less obvious as the ticks engorge. The presence or absence of some of these, such as the paired dorsoventral grooves lateral to the bases of legs IV, and the unpaired preanal , transverse postanal , and median postanal grooves, are used descriptively, though usually not diagnostically, in keys to species of Ornithodoros . A pair of respiratory spiracular plates, also called stigmatal plates , is located just posterior to coxae IV in the nymphs and adults of all ticks; larval ticks lack these structures. The plate may be characteristically round , elliptical, oval, or inversely comma-shaped. In ixodid ticks, its periphery is bordered by one or several rings of pore-like chambers, which surround a field of goblets, small orifices whose relative size, number and arrangement may be useful diagnostically at the species level. Near the center of the spiracular plate of ixodid adults lies a larger and more heavily sclerotized hollow, the macula, which is the principal respiratory opening. In argasid ticks, the spiracular plate lacks pore-like chambers and goblets, and has a simple opening set in a hinged flap which passes directly into an atrial cavity (Hinton 1967).

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  As on the dorsum, the setation of the venter of the larval idiosoma has considerable diagnostic importance. A chaetotactic notation, developed like that for the dorsal setae, recognizes three longitudinal series, named and denoted as the ventral medial Jv series, ventral mediolateral Zv series, and ventral lateral Sv series (the earlier system of chaetotaxy , developed by Glashchinskaya-Babenko 1949 and used by Clifford and Anastos 1960, named and denoted these setae the preanals Pa, premarginals Pm, and marginal ventrals Mv ; see Table 1 for equivalents). Only upper-case letters are applied to the ventral setae that are useful diagnostically, as all are on the opisthogastric region. Klompen et al. (1996) also applied a notation to the lyrifissures and gland pores on the ventral soft cuticle of ixodid larvae, as was done for the dorsum. Again, however, the use of lyrifissures and gland pores is only beginning to be applied diagnostically, and sufficient data are not available for their use in the present guide.

  Legs. All the legs of ticks have six segments, named from base to apex coxa , trochanter , femur, genu , tibia, tarsus) plus a pretarsus which bears a pair of claws and, in ixodids , a well developed soft pad, the pulvillus , between the claws that enables ticks to walk on smooth surfaces. The coxae of ixodid ticks bear some of the most useful diagnostic attributes for identification, including their shape, presence or absence of spurs or flanges, and setation . When coxa I is denoted as 'bifid', as in the genus Dermacentor , it bears two spurs close together, with a deep incision between them. The absence or presence, shape and size of one or two well separated spurs on the ventral surface of coxa I is critically important in diagnosis of species of Ixodes . The internal spur is on the proximal region of the coxa , closest to the body midline, and the external spur is on the apical region, farthest from the body midline. The absence or presence of spurs or flanges on the ventral surfaces of coxae II to IV, and whether the posterior edge of the coxae are rounded or have a projected edge, or salience , are used descriptively, but usually not diagnostically, among ixodid species. The trochanter of legs I to IV of ixodids may bear a ventral spur of variable shape and size, and among species of Dermacentor a variably developed retrorse spur also occurs on the dorsal surface of trochanter I; the latter process is called the "dorsal horn" in some works. The coxae and trochanters are generally unarmed in argasid ticks. The tarsus of leg I of all ticks possesses a complex of sensory structures in a posterior capsule and an anterior pit or depression, which together form Haller's organ on the dorsal subapical surface of the segment. Details of the microanatomy and fine structure of Haller's organ, when viewed under a scanning electron microscope, have been used as an aid in distinguishing between species of Ixodes ( Homsher and Sonenshine 1975); however, these attributes are generally not visible when examining specimens under more limited magnifications of stereomicroscopes using incident light. In all ticks, tarsi II to IV consist of a shorter basal metatarsus, or basitarsus , which is delineated by a circumsegmental fissure from a longer apical telotarsus . The length and shape of these elements offer useful diagnostic attributes for some taxa of ticks. In lateral view, the telotarsus in some species tapers gradually and has an even profile to the apex; in others, the dorsal and ventral surfaces are parallel proximally but are humped or abruptly sloped dorsoapically . In some argasids , this subapical dorsal protuberance is distinguished from the presence or absence of one to several additional dorsal elevations, called dorsal humps, located more proximally on the telotarsus and sometimes on the basitarsus . In some adult ixodids , e.g., Rhipicephalus , the ventral surface of tarsi II to IV has one or two projections designated as the terminal and subterminal ventral tarsal spurs .

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  Even more so than on the palps , the number and arrangement of setae on some of the segments of the three pairs of legs of larval ticks are important diagnostic characters. The notation applied to the leg setae is that proposed by Evans (1963a, 1969) for mesostigmatic mites and applied to larval Ixodidae by Edwards and Evans (1967) and to larval Argasidae by Edwards (1975) and Klompen (1992). Setae are denoted by their position on the anterior (ad) and posterior (pd) dorsal faces, anterolateral (al) and posterolateral (pl) faces, and anteroventral ( av ) and posteroventral ( pv ) faces of the segments. This scheme of notation generally is not applied to the more complex complement of setae and clusters of sensilla of Haller's organ on tarsus I. It is also not applied to the leg setation of nymphal and adult ticks, as the complements of setae become much higher on segments and do not lend themselves to being readily assigned a notation that implies homologies of structures.

  Coxae I to III of argasid larvae consistently bear 2 setae ( av and pv ) each, but a third ventral seta is generally present on coxa I, and sometimes on coxae II and III, of ixodid larvae. The absence or presence of the third seta on coxae II and III is a useful diagnostic larval attribute among species of Ixodes . Specific setal complements for the coxae are given as simple formulas; for example, 3-2-3 for I. muris indicates 3 setae on coxa I, 2 on coxa II, 3 on coxa III. The larval setal patterns for trochanters I to III are constant among all Canadian species of Argasidae and Ixodidae , so they are not useful diagnostically: trochanter I bears 4 setae (ad, av , pv , pl), trochanter II bears 5 (al, ad, av , pv , pl), and trochanter III bears 4 (al, ad, av , pv ).

  The larval setal patterns for femora I to III are constant in most species of Ixodidae , and include 10 setae each on femora I and II (al, ad-1, ad-2, av-1, av-2, pd-1, pd-2, pv-1, pv-2, pl) and 9 on femur III (pl absent). In contrast, larval argasids do not have this full complement of femoral setae, and show a variety of losses which may be useful diagnostically. Larvae of Argas reflexus have the same full complement of 10 setae on femur I, but they have one less ventral seta (pv-2 absent) on femora II and III than in ixodids . Those of other argasid species deviate in a variety of ways from the ixodid pattern, as discussed by Edwards (1975) and Klompen (1992). For example, larval Ornithodoros kelleyi have 8 setae on femur I (av-2, pv-2 absent), 9 on femur II (pv-2 absent), and 7 on femur III (av-2, pv-2 absent).

  The larval setal patterns for genua I to III are constant in Ixodidae and some Argasidae , and include the same 8 setae (al, ad-1, ad-2, av , pd-1, pd-2, pv , pl). Larvae of some argasid taxa diverge from this pattern in having either a lower or rarely a higher number of genual setae than usually is common to all three legs. For examples (Edwards 1975), Otobius megnini and O. lagophilus have 6 setae on each of genua I to III (ad-2, pd-2 absent), and Ornithodoros kelleyi has 5 setae on each of genua I to III (ad-2, pd-2, pv-1 absent). The larva of Argas reflexus is unusual in having 10 setae on genu I (al-2, av-2 added) but 9 on genua II-III (al-2 added) ( Klompen 1992).

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  The larval setation of tibiae I to III offers perhaps the most interesting patterns for diagnosis of species and higher taxa in both Ixodidae and Argasidae . The maximum complement in Ixodidae occurs in the genus Ixodes , and includes the same 8 setae as for the genua of legs I to III (al, ad-1, ad-2, av , pd-1, pd-2, pv , pl). Larvae of the ixodid genus Haemaphysalus diverge from this pattern in having 7 setae on tibiae I-III (pd-2 absent), while those of the ixodid genera Dermacentor , Rhipicephalus , Amblyomma , Boophilus differ further from this pattern in having 7 setae on tibia I (pd-2 absent) and only 6 setae on tibiae II-III (ad-2 also absent) (Edwards and Evans 1967). The basic setal pattern of the tibiae in larval Argasidae , which occurs in some species of Argas , is the same as the 8 setae found on all legs in Ixodes . However, many argasids , including species of Ornithodoros and Otobius , have only 6 setae (ad-2, pd-2 absent) on tibiae I-III. Rarely, an addition of 1 or 2 setae to the basic complement of 8 may occur on the tibiae in scattered species of Argasidae ; these may involve any of setae ad-2, pd-2, al-2, pl-2, av-2, pv -2, as discussed by Klompen (1992).

  The larval setation of tarsus I is not readily used diagnostically for species of ticks, due to the number and complexity of structures present, to difficulties in discerning some of them readily, without access to scanning electron microscopy, and to lack of a reliable notation for structures, based on homologies. A comparative discussion of attributes of setae and other structures on tarsus I, which notes family and some genus level differences between larval ticks, is given by Klompen (1992). Surface features of Haller's organ, as viewed with scanning electron microscopy, have been useful as an aid in distinguishing between adults of species of Ixodes , and determining subgeneric levels of classification in this genus ( Homsher and Sonenshine 1975, Homsher et al. 1991).

  The larval setation of tarsus II is the same as that of tarsus III, and shows some diagnostic patterns that distinguish Ixodidae and Argasidae . Ancestrally, these patterns include three whorls, or verticils , of up to 6 setae each. The 6 setae in a given whorl are denoted al and pl laterally, ad and pd dorsally, and av and pv ventrally. The notation is applied such that the most distal whorl is the first one; thus, ad-2 denotes the anterodorsal seta of the second whorl, while pv-3 denotes the posteroventral seta of the most basal, third whorl. Larval Ixodidae display a full complement of three whorls, each with 6 setae, for a total of 18 setae, while the setal complement in larval Argasidae is generally reduced, variably so among genera ( Klompen 1992). The dorsal setation in Ixodidae presents 6 setae, including a distal pseudosymmetric "pair" ad-1, pd-1, a median "pair" ad-2, pd-2, and a proximal "pair" ad-3, pd-3. In some genera of Argasidae (e.g., Carios , Ornithodoros , Otobius ), an unpaired dorsomedial seta, dm, is present mid-dorsally. This seta is not added until the nymphal instar in genera of Ixodidae and others of Argasidae . Dorsal seta ad-2 is absent in larvae of some genera of Argasidae , e.g., Ornithodoros , while setae pd-2 and ad-3 are absent in larvae of Otobius ( Klompen 1992). The lateral and ventral patterns of larval setae in Ixodidae also present 6 setae each, but the proximal "pair" of ventrals , av-3, pv3, is inserted on a small intercalary sclerite in the region of the circumsegmental fissure, instead of on the basitarsus , which bears al-3, pl-3 as well as ad-3, pd-3. The lateral and ventral setation is reduced in most larval Argasidae , except for some species of Argas , because of the absence of setal "pairs" al-3, pl-3 and av-3, pv-3; however, in a few species (e.g., Argas persicus ), an additional ventral seta, denoted avx , is present on the basitarsus ( Klompen 1992). Absences of other setae among some taxa of Argasidae that are not found in Canada , as well as variation in relative positions of tarsal setae in Argasidae , are discussed by Klompen (1992). The position of setae ad-2, pd-2 relative to the dorsal lyrifissure on the telotarsus is another diagnostic larval attribute notable among Canadian ticks. This "pair" of setae is inserted proximal to the lyrifissure among all genera of Ixodidae , but only among some of Argasidae , such as Argas . In some other argasid genera, including Carios , these setae are inserted distal to the lyrifissure , while in yet others, including Ornithodoros , pd-2 is distal to the lyrifissure while ad-2, as noted above, is absent ( Klompen 1992).

  Table 1. Comparison of idiosomal setal notation systems for larval ticks. Notation in parentheses indicate setae infrequently expressed.

  Idiosomal dorsum		Odopsp,a; venter
  Klompen 1996	Clifford & Anastos 1960	Klompen 1996	Clifford & Anastos 1960
  j3	Sc3	st1, jv2	St1
  j5	Cd1	st2, jv3	St2
  J2	Cd2	st3, jv4	St3
  J3)	---	Jv3	Pa1
  J4)	---	Jv5	Pa2
  (J5)	---
  z2	Sc1	Zv1	Pm1
  z4	Sc5	Zv2	Pm2
  (z6)	---	Zv3	Pm3
  (Z1)	---	Zv4	---
  Z2	S1	Zv5	Pm4
  (Z3)	---
  (Z4)	---
  (Z5)	---
  s2	Sc2	Sv1	Mv1
  s3	Sc4, Md1	Sv2	Mv1, Mv2
  s4	Md1, Md2	Sv3	Mv2, Mv3
  s5	Md2	Sv4	Mv3, Mv4
  s6	Md3	Sv5	Mv4, Mv5
  S1	Md4
  S2	Md4, Md5
  S3	Md5, Md6
  S4	Md6, Md7
  S5	Md7, Md8

  
  

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  Literature Cited

  Clifford, C.M. and Anastos , G. 1960.

  The use of chaetotaxy in the identification of larval ticks ( Acarina : Ixodidae ). Journal of Parasitology 46: 567-578.

  Clifford, C.M., Anastos , G. and Elbl , A. 1961.

  The larval ixodid ticks of the Eastern United States ( Acarina : Ixodidae ). Miscellaneous Publications of Entomological Society of America 2(3): 213-237.

  Edwards, M.A. 1975.

  The chaetotaxy of the pedipalps and legs of some larval ticks ( Acari : Argasidae ). Transactions of the Zoological Society of London 33: 1-76.

  Edwards, M.A. and Evans, G.O. 1967.

  Some observations on the chaetotaxy of the legs of larval Ixodidae ( Acari : Metastigmata ). Journal of Natural History 4: 595-601.

  Evans, G.O. 1963a.

  Observations on the chaetotaxy of the legs in the free-living Gamasina ( Acari : Mesostigmata ). Bulletin of the British Museum (Natural History), Zoology, 10: 277-303.

  Evans, G.O. 1963b.

  Some observations on the chaetotaxy of the pedipalps in the Mesostigmata ( Acari ). Annals and Magazine of Natural History, Series 13, 6: 513-527.

  Evans, G.O. 1969.

  Observations on the ontogenetic development of the chaetotaxy of the tarsi of legs II-IV in the Mesostigmata ( Acari ). In: G.O. Evans (editor), Proceedings of the 2nd International Congress of Acarology , Sutton Bonington ( England ), 9th-25th July 1967. Akademiai Kiado, Budapest, pp. 195-200.

  Evans, G.O. 1992.

  Principles of acarology . C.A.B. International. University Press, Cambridge . xviii + 563 pp.

  Glashchinskaya-Babenko , L.V. 1949.

  Chetotaksiya tela lichinok kleshchei sem . Ixodidae i ee taksonomicheskoe znachenie [ Chaetotaxy of the body of larvae of ticks of the family Ixodidae and its taxonomic significance]. Doklady Akademii Nauk SSSR, new series, 65: 245-248 (in Russian).

  Gregson , J.D. 1956.

  The Ixodoidea of Canada. Entomology Division, Science Service , Canada Department of Agriculture, Publication 930. 92 pp.

  Hinton, H.E. 1967.

  The structure of the spiracles of the cattle tick, Boophilus microplus . Australian Journal of Zoology 15: 941-945.

  Homsher , P.J. and Sonenshine , D.E. 1975.

  Scanning electron microscopy of ticks for systematic studies. 2. Structure of Haller's organ in Ixodes brunneus and Ixodes frontalis . Journal of Medical Entomology 14: 93-97.

  Homsher , P.J., Robbins, R.G. and Keirans , J.E. 1991.

  Scanning electron microscopy of Haller's organ for subgeneric systematic studies in the genus Ixodes . In: F. Dusbabek and V. Bukva (editors), Modern Acarology , Academia, Prague and SPB Academic Publishing bv , The Hague, Vol. 2: 335-342.

  Klompen , J.S.H. 1992.

  Comparative morphology of argasid larvae ( Acari : Ixodida : Argasidae ), with notes on phylogenetic relationships. Annals of the Entomological Society of America 85: 541-560.

  Klompen , J.S.H., Keirans , J.E., Filippova , N.A. and Oliver, J.H., Jr. 1996.

  Idiosomal lyrifissures , setae, and small glands as taxonomic characters and potential indicators of ancestral segmentation patterns in larval Ixodidae ( Acari : Ixodida ). International Journal of Acarology 22: 113-134.

  Lindquist, E.E. and Evans, G.O. 1965.

  Taxonomic concepts in the Ascidae , with a modified setal nomenclature for the idiosoma of the Gamasina ( Acarina : Mesostigmata ). Memoirs of the Entomological Society of Canada 47. 64 pp.

  Lindquist, E.E., Wu, K.W. and Redner , J.H. 1999.

  A new species of the tick genus Ixodes ( Acari : Ixodidae ) parasitic on mustelids ( Mammalia : Carnivora ) in Canada. Canadian Entomologist 131: 151-170.

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