The Amblyomma maculatum Koch, 1844 (Acari: Ixodidae ...

Systematic Parasitology (2005) 60: 99–112

© Springer 2005

The Amblyomma maculatum Koch, 1844 (Acari: Ixodidae: Amblyomminae) tick group: diagnostic characters, description of the larva of A. parvitarsum Neumann, 1901, 16S rDNA sequences, distribution and hosts Agust´ın Estrada-Peña1 , Jos´e M. Venzal2 , Atilio J. Mangold3 , Mar´ıa M. Cafrune4 & Alberto A. Guglielmone3 1 Unidad

de Parasitolog´ıa, Facultad de Veterinaria, Miguel Servet 177, 50013-Zaragoza, Spain de Parasitolog´ıa, Facultad de Veterinaria, Montevideo, Uruguay 3 Instituto Nacional de Tecnolog´ıa Agropecuaria, Rafaela, CC 22, 2300 Santa Fe, Argentina 4 Instituto Nacional de Tecnolog´ıa Agropecuaria, CC 228, 4400 Salta, Argentina 2 Departamento

Accepted for publication 7th June 2004

Abstract A review of the largely confused Amblyomma maculatum Koch, 1844 tick group of the subgenus Anastosiella Santos Dias, 1963 (A. neumanni Ribaga, 1902, A. maculatum, A. parvitarsum Neumann, 1901, A. tigrinum Koch, 1844 and A. triste Koch, 1844) is presented together with a discussion of the diagnostic characters used for the determination of adults, nymphs and, to a lesser extent, larvae. A key for this tick group is produced, including the description of the larva of A. parvitarsum, 1901. Sequences of 16S rDNA are obtained and compared with other Amblyomma spp., including two other species currently in Anastosiella but in the ovale tick group, A. ovale Koch, 1844 and A. aureolatum (Pallas, 1772). According to the morphology and the rDNA sequences, the maculatum group is reduced to A. maculatum (Neotropical-Nearctic), A. tigrinum (Neotropical) and A. triste (Neotropical) A. neumanni and A. parvitarsum are excluded from the subgenus. The distribution is sympatric in northern South America from where A. maculatum reaches the southern Nearctic and the range of A. tigrinum extends to the southern Neotropics. These species have been found on several domestic and wild vertebrates. A. triste and A. tigrinum have been also found on man. Their role as vectors of pathogens deserves further investigation.

Introduction The Amblyomma maculatum Koch, 1844, tick group currently includes A. neumanni Ribaga, 1902, A. parvitarsum Neumann, 1901, A. maculatum, A. tigrinum Koch, 1844 and A. triste Koch, 1844 (Camicas et al., 1998). Adults of these tick species share the presence of a 3/3 hypostome, two spurs on coxa I with the external spur being much longer than the internal, spines (strong conical modified setae) on tibiae II to IV and a similar scutal ornamentation pattern. These species, along with 10 additional taxa, were included by Santos Dias (1993) in the subgenus Anastosiella Santos Dias, 1963. This assemblage was modified by Camicas et al. (1998), who considered that Anastosiella was composed of two groups: maculatum and

ovale, the last group containing A. aureolatum (Pallas, 1772) and A. ovale Koch, 1844, but these authors did not define the morphological features supporting this classification. Furthermore, the systematic of the subgenera of Amblyomma Koch, 1844, as outlined by Santos Dias (1963, 1993), is questionable because it is not supported by any taxonomic or species relationship analysis. Adults of the species included in the A. maculatum group have largely been misdetermined or have outdated descriptions. Both A. tigrinum and A. triste were considered synonyms of A. maculatum until Kohls (1956) redefined and resurrected these valid species. However, this confusion continued because Aragao & Fonseca (1961) published figures of A. triste under the

100 name A. tigrinum. One of the critical characters of the female of A. maculatum are the small chitinous tubercles at the posterior body margin, as shown by Walker & Olwage (1987). The male of this species only has an indication of chitinous tubercles on the festoons. Cooley & Kohls (1944) do not depict these tubercles when redescribing A. maculatum, Kohls (1956) stated that A. maculatum has no tubercles, and Jones et al. (1972) were unaware of their presence. Adults of A. neumanni bear one spine on tibiae II to IV as shown by Robinson (1926) under the name A. furcula Donitz, 1909, and the male has an interrupted marginal groove on the paracentral festoons (Boero, 1957). A less controversial species of the group is A. parvitarsum, the only representative with beady, orbited eyes and with two spines on tibiae II to IV. Guglielmone & Hadani (1985) presented a key for the diagnosis of males and females of A. maculatum group tick species, stressing the importance of marginal grooves and spines on the tibia for their identification. The presence of tubercles at the posterior body margin of the females of A. maculatum was again ignored. The immature stages of A. maculatum were described by Cooley & Kohls (1944) and Keirans & Durden (1998), and those of A. neumanni, A. tigrinum and A. triste were described by Estrada-Peña et al. (1993, 2002). The latter authors observed that the morphology of the immature stages of A. neumanni differs substantially from that of A. tigrinum and A. triste, and considered that A. neumanni belonged to a different taxonomic assemblage. Herein we attempt a revision of the five species of the A. maculatum tick group. This includes the redescription of the major diagnostic characters of the adults and immature stages, the description of the larva of A. parvitarsum, 16S rDNA sequences and a comparison with the sequences of other species of Amblyomma in order to demonstrate that species of this group belong to a different subgenus. Information on the distribution and hosts is also included. Materials and methods Specimens studied Material of the following tick species were used for scanning electron microscopy, following the technique of Corwin et al. (1979): A. maculatum (Oklahoma State University, Stillwater, USA), A. neumanni, A. parvitarsum and A. tigrinum (Instituto Nacional de Tecnología Agropecuaria, Estaciones Experimentales

Agropecuarias Rafaela and Salta, Rafaela and Cerrilles Argentina) and A. triste (Veterinary Faculty, Montevideo, Uruguay). The material used for the description of the larva of A. parvitarsum was derived from a female tick collected on Lama glama (Linnaeus) (Mammalia: Artiodactyla: Camelidae), December 1999 (Biviano Luzco Coll.), Huancar, Jujuy, Argentina (23◦ 45 S, 66◦ 30 W). Specimens of these five species were preserved in 96% ethanol and stored at −20 ◦ C until used to sequence mitochondrial 16S rDNA. Extraction of DNA was carried out from a single male tick of each species and polymerase chain reaction (PCR) amplification was set up as described by Mangold et al. (1998). Multiple alignments were done by using Clustal W (Thompson et al., 1994). For all data-sets, to ensure that they would begin and end at the same position, all sequences were truncated. Aligned sequences were examined using the computer program MEGA 2.1 (Kumar et al., 2001) and a divergence matrix was constructed. Sites containing alignment gaps were excluding in the pairwise distance estimation. The following mithocondrial 16S rDNA sequences of Amblyomma species available in GenBank were also used for pairwise comparisons: A. americanum (Linnaeus, 1758) (GenBank accesion number: L34313), A. aureolatum (AF541254), A. cajennense (Fabricius, 1787) (L34312), A. glauerti Keirans, King & Sharrad, 1994 (U95853), A. hebraeum Koch, 1844 (L34316), A. ovale (AF541255), A. tuberculatum Marx, 1894 (U95856) and A. variegatum (Fabricius, 1794) (L34312). A. hebraeum and A. variegatum are of African origin, A. glauerti is Australian and all the others are either North or South American species. Phylogenetic relationships were analysed using distance measure and a neighbour-joining (NJ) tree was generated from Kimura two-parameters method. Support for the NJ topology was tested by boot-strapping over 1,000 replications. Two 16S rDNA sequences of Ixodes species were also used as outgroups: Ixodes persulcatus Schulze, 1930 (L34295) and I. scapularis Say, 1821 (L34293). Additionally, maximum parsimony (MP) analyses were performed using MEGA 2.1 software. The heuristic search procedure was used to find trees of minimal length, and relative support for internal nodes was assessed using a heuristic bootstrap analysis with 1,000 replications. Distribution and hosts Information on the different species was obtained from two databases constructed as a part of the International

101 Consortium on Ticks and Tick-Borne Diseases-2. One database contains the localities and hosts of ticks species in the A. maculatum group derived from tick collections in Argentina (curator AAG), Brazil and Uruguay (curator JMV) compiled by one of the authors (AE-P). Brazilian collections were from the Instituto Butantan and the University of Sao Paulo, both in Sao Paulo, and the Centro de Pesquisas Veterinárias ‘Desiderio Finamor’, Eldorado do Sul. The second database contains literature information on the localities and hosts from Mexico to Argentina compiled by one of the authors (AAG). Biogeographical data were obtained from Cabrera & Willink (1973) for Central and South America and from Kuchler (1964) for North America. These are widely used herein to delineate the habitats to which species are commonly linked. Those Neotropical records containing known hosts and tick stages were used to obtain a gross estimation of the frequency of records on different types of hosts.

The Amblyomma maculatum Koch, 1844 Group Morphological remarks A. neumanni Ribaga, 1902. Males with palpal article II (femur) slightly longer than palpal article III (genu). Marginal groove incomplete because of interruption at level of paracentral festoons. Eyes flat. External spur on coxa I 2-3 times larger than internal spur. With very long spur on coxa IV reaching level of anus. Females with several rows of white setae on notum. Spur on coxa IV short. Both sexes with small but evident internal spur on coxa I. One spine on tibiae II to IV. Chitinous tubercles on posterior side of festoons absent. Nymphs with palpal femur only slightly longer than palpal genu. Lateral margins of basis capituli broadly rounded, lacking auriculae and ventral processes. With 2 spurs on coxa I and well-defined spur on coxa IV. A. parvitarsum Neumann, 1901. Males with palpal femur almost same length as palpal genu. Marginal groove incomplete. Eyes orbited. Well-developed internal spur on coxa I. External spur on coxa I twice as large as internal spur. Very long spur on coxa IV, almost reaching anus. Females with glabrous notum. Spur on coxa IV well defined. Both sexes with 2 spines on tibiae II to IV. Chitinous tubercles on ventral side of festoons absent. Nymphs not known.

A. maculatum Koch, 1844. Males with complete marginal groove. Eyes flat. Spur on coxa IV not reaching level of anus. Spiracular plate comma-shaped; caudal process of spiracular plate half size of last festoon. Females with glabrous notum. Both sexes with palpal femur almost twice length of palpal genu. Internal spur on coxa I indistinct. Chitinous tubercles on posterior side of festoons present but minute, lacking on central festoon. Two spines on tibiae II to IV. Nymphs with palpal femur 2-3 times longer than palpal genu. Basis capituli with laterally produced auriculae and ventral processes. Dorsal margin of basis capituli essentially straight, with convex margins in postero-lateral region. Single evident external spur and indistinct internal spur on coxa I. No spur on coxa IV. A. tigrinum Koch, 1844. Males with complete marginal groove. Eyes flat. External spur on coxa I very long. Spur on coxa IV not reaching level of anus. Spiracular plate comma-shaped; caudal process half size of last festoon. Females with glabrous notum. External spur on coxa I reaching half of coxa II. Both sexes with palpal femur almost twice length of palpal genu. Internal spur in coxa I indistinct. One spine on tibiae II to IV. Tubercles lacking on posterior side of festoons. Nymphs with palpal femur 2-3 times longer palpal genu. Basis capituli with laterally produced auriculae and ventral processes. Dorsal margin of basis capituli with small concavity and clearly concave in postero-lateral region. External spur and small internal spur on coxa I. No spur on coxa IV. A. triste Koch, 1844. Males with complete marginal groove. Eyes flat. Internal spur on coxa I indistinct. External spur on coxa I very long. Spur on coxa IV not reaching anus. Spiracular plate oval; caudal process as wide as last festoon. Females with glabrous notum. Both sexes with palpal femur almost twice length of palpal genu. Chitinous tubercles on posterior side of festoons present. Single spine and 1 strong seta on tibiae II to IV. Nymphs with palpal femur 2-3 times longer than palpal genu. Basis capituli with laterally produced auriculae and ventral processes. Dorsal margin of basis capituli with small concavity, clearly concave in postero-lateral region. Single spur on coxa I. No spur on coxa IV. Key to males (Figure 1) 1. Two spines on tibiae II to IV (Figure 1A) . . . . . . . 2 - One spine on tibiae II to IV (Figure 1B) . . . . . . . . 3

102

Figure 1. Morphological details of males of the former A. maculatum tick group according to Camicas et al. (1980). A. Presence of two spines on the tibia. B. Presence of one spine on the tibia (note the strong seta accompanying the spine). C,D. Dorsal and ventral view, respectively, of the capituli of males with the palpal femur almost the same length as the palpal genu, as in A. neumanni and A. parvitarsum. E,F. Dorsal and ventral view, respectively, of capituli of males with the palpal femur almost the same length as the palpal genu, as in A. maculatum, A. triste and A. tigrinum. G. Tubercles on the ventral side of the festoons, as in A. triste. H. Absence of tubercles on the ventral side of the festoons. I. Marginal groove incomplete, as in A. neumanni. J. Marginal groove complete, as in A. tigrinum. K. Differences in the length of the spur on coxa IV.

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Figure 2. Additional morphological details of females of the former A. maculatum tick group according to Camicas et al. (1980). A. Basis capituli rectangular, wider than long. Porose areas separated by one diameter, as in A. parvitarsum. B. Basis capituli almost triangular, with widely rounded margins. Porose areas separated by more than one diameter, as in A. maculatum, A. tigrinum and A. triste. C. Small tubercles on the posterior margin of the body, as in A. triste. D. Comparative length of the external spur on coxa I.

2. Palpal femur almost same length as palpal genu (Figures 1C,D). Eyes orbited . . . . . A. parvitarsum - Palpal femur almost twice length of palpal article III (Figures 1E, 1F). Eyes flat . . . . . . A. maculatum 3. With tubercles on ventral side of festoons. Spiracular plate oval. Caudal process of spiracular plate as wide as last festoon (Figure 1G) . . . . . . . . . A. triste - Tubercles on ventral side of festoons, absent. Spiracular plate comma-shaped. Caudal process of spiracular plate half width of last festoon (Figure 1H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Marginal groove incomplete (Figure 1I). With long spur on coxa IV reaching anus. External spur on

coxa I 2-3 times length of internal spur (Figure 1K) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. neumanni - Marginal groove complete (Figure 1J). Spur on coxa IV not reaching anus. External spur on coxa I more than 7-8 times length of internal spur (Figure 1K) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. tigrinum Key to females (Figures 1, 2) 1. Two spines on tibiae II to IV (Figure 1A) . . . . . . . 2 - One spine on tibiae II to IV (Figure 1B) . . . . . . . . . 3 2. Eyes orbited. Basis capituli clearly rectangular, wider than long. Palpi inserted apically into basis

104

Figure 3. Morphological details of nymphs of the former A. maculatum group, showing, from left to right, the capitulum ventral, the capitulum dorsal and the venter with the coxal armature. From top to bottom, A. neumanni (A, B, C), A. tigrinum (D, E, F), A. triste (G, H, I) and A. maculatum (J, K, L). The nymph of A. parvitarsum is unknown.

105 capituli. Porose areas large, separated by 1 diameter (Figure 2A). Without tubercles on posterior side of festoons. . . . . . . . . . . . . . . . . . . . . . . . . A. parvitarsum - Eyes flat. Basis capituli almost triangular, with widely rounded margins. Palpi inserted laterally into basis capituli. Porose areas relatively small, separated by >1 diameter (Figure 2B). With tubercles on posterior side of festoons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. maculatum 3. With small tubercles on posterior margin of body (Figure 2C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. triste - No tubercles on posterior margin of body . . . . . . . 4 4. External spur of coxa I almost 2-3 times length of internal spur. Both spurs broadly rounded (Figure 2D). With several rows of white hairs on notum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. neumanni - External spur of coxa I 6-8 times as long as internal spur. Internal spur broadly rounded and external spur clearly pointed (Figure 2D). Notum glabrous. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. tigrinum Key to nymphs (Figure 3) (the nymph of A. parvitarsum is not known) 1. Without processes on ventral side of basis capituli and auriculae (Figure 3A,B). Coxa I with external and internal spurs (Figure 3C). . . . . . . . A. neumanni - Processes on ventral side of basis capituli and auriculae both present. Coxa I with external spur only, but may have internal thickening. . . . . . . . . . . . . . . . 2 2. Auriculaepostero-laterallyproduced. Postero-lateral margins of ventral basis capituli with clear concavity (Figure 3D,G, arrows). Posterior margin Of dorsal basis capituli produced into more or less marked lateral concavities (Figure 3E,H, arrows) . . . . . . . . 3 - Auriculae produced laterally, essentially straight (Figure 3J). Posterior margin of dorsal basis capituli straight and convex postero-laterally (Figure 3K, arrows). . . . . . . . . . . . . . . . . . . . . . . . . . . A. maculatum 3. Coxa I with narrow external spur and small internal thickening, not fused at their base (Figure 3F, arrow). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. tigrinum - Coxa I with triangular external spur, its base reaching to internal margin of coxa (Figure 3I, arrow). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. triste Key to larvae (the larvae of A. maculatum, A. triste and A. tigrinum cannot be adequately determined by morphological characters) (Figure 4) 1. Palpal femur almost same length as palpal genu (Figure 4A,D). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

- Palpal femur very much longer than palpal genu (Figure 4G,J,M). . . . A. maculatum-tigrinum-triste group (additional details in Figure 4H-O). . . . . . . . . 2. With 2 small (external and internal spurs) on coxa I (Figure 4C). Total body length (from tip of hypostome to posterior margin) always 900 µm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. parvitarsum (Figure 4E,F) Amblyomma parvitarsum Neumann, 1901. Description of larva (Figure 4D,E,F) [Measurements (in micrometres) from 26 unengorged specimens mounted in Hoyer’s medium.] Body outline widely rounded, very large. Total length, from apex of hypostome to posterior body margin, 974 (962-993); total length of idiosoma 805 (774-836); total width at maximum point 711 (690-732). Scutum with posterior margin widely rounded, not sinuous, with very short setae. Scutum 360 (345-376) long, 541 (502-575) wide. Eyes positioned at point of maximum width of scutum. Capitulum essentially rectangular (Figure 4D,E). Length of capitulum 200 (171-215). Basis capituli 174 (171-179) wide, broad triangular dorsally, with straight posterior margin. Cornua not well developed. Palpi long, wide. Palpal trochanter in form of short stripe, 34 (26-40) long; palpal femur 61 (58-66) long; palpal genu 54 (42-60) long; palpal tibiotarsus 27 (23-31) long, inserted almost apically into genu; small cuticular ridge present in ventral side of palpal genu posteriorly to insertion of palpal tibiotarsus. Hypostome (Figure 4E) with dental formula 2/2, in 6 files of denticles and with corona at apex. Hypostome 131 (124-136) long, 43 (42-45) wide. Single pair of post-hypostomal setae. Ventral surface as illustrated (Figure 4F). Coxa I with transverse cuticular ridge; coxae II and III with spurs which are more stout on coxa III. Anus oval to round. Species relationships The larva of A. parvitarsum is closely related to that of A. neumanni, sharing a similar general apperance and capitulum morphology. The most important feature for separating both species is the size of unengorged specimens. A. parvitarsum is a very large species of well over 900 µm, while specimens of A. neumanni are smaller than 600 µm in size Furthermore, A. neumanni

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Figure 4. Morphological details of larvae of the former A. maculatum group, showing, from left to right, the capitulum ventral, the capitulum dorsal and the venter with the coxal armature. From top to bottom, A. neumanni (A, B, C), A. parvitarsum (D, E, F), A. maculatum (G, H, I), A. tigrinum (J, K, L) and A. triste (M, N, O).

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Figure 5. Neighbour-joining tree using Kimura two-parameters distance. Numbers below the lines represent the percentages of bootstrap support.

has two small cuticular internal and external ridges on coxa I, whereas A. parvitarsum has a single transverse one. DNA sequences The length of the sequenced mitochondrial 16S rDNA gene fragment for the five species of the A. maculatum group was 393 bp for A. maculatum (GenBank accesion number AY498559), 392 for A. neumanni (AY498560), 399 bp for A. parvitarsum (AY498561), 393 bp for A. tigrinum (AY498562) and 393 bp for A. triste (AY498563). The DNA sequence analysis showed that A. maculatum, A. tigrinum and A. triste are closely related species and the difference between sequences was 3.0–4.7% (Table 1). On the other hand, A. neumanni and A. parvitarsum exhibited 11% difference between them and 11.4-12.7% with other representatives of the A. maculatum group. Pairwise comparison with eight other species of Amblyomma are also presented in Table 1. There were ample differences (8.6–17.0%) between species of the A. maculatum tick group and other Amblyomma species.

The NJ tree is shown in Figure 5. A high bootstrap value (99%) supported the close relationship between A. maculatum, A. tigrinum and A. triste. However, A. neumanni and A. parvitarsum were associated with A. cajennense and A. americanum, but with weak support in bootstrap analysis. The results provide support for the cluster containing A. aureolatum and A. ovale (76%) and the African species A. hebraeum and A. variegatum (83%). The topology and support for the interior branches of MP tree were similar to those found in the NJ analyses (data not shown), reinforcing the close relationship of A. maculatum, A. tigrinum and A. triste. Distribution Collection sites for all species are shown in Figure 6. The A. maculatum distribution comprises USA, Mexico, Guatemala, Belize, Nicaragua, Honduras, Costa Rica, Colombia, Venezuela, Ecuador and Peru (Guglielmone et al., 2003), but coordinates were unavailable for some localities in Belize, Ecuador, Honduras, Nicaragua and Peru. There is a lack of precise records in Mexico, but the tick has a patchy distrib-

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Figure 6. Recorded distribution of A. maculatum, A. neumanni, A. parvitarsum, A. tigrinum and A. triste.

Table 1. Matrix of sequence divergence (% of nucleotide differences) on pairwise comparison (gaps excluded) of the mitochondrial 16S rDNA sequences for the species of the Amblyomma maculatum group according to Camicas et al. (1998) (A. maculatum, A. neumanni, A. parvitarsum, A. tigrinum and A. triste) and eight other species of Amblyomma 1 1 A. maculatum 2 A. triste 3 A. tigrinum 4 A. neumanni 5 A. parvitarsum 6 A. americanum 7 A. cajennense 8 A. glauerti 9 A. tuberculatum 10 A. aureolatum 11 A. ovale 12 A. hebraeum 13 A. variegatum

– 3.0 4.7 11.4 12.4 15.7 14.6 8.6 13.6 14.0 14.8 12.3 12.3

2

3

4

5

6

7

8

9

10

11

12

13

– 12.7 12.1 14.8 15.2 8.9 13.5 13.7 14.2 12.9 11.7

– 11.0 14.5 13.0 10.3 12.9 17.0 14.8 15.3 13.1

– 15.0 14.2 9.6 14.1 15.3 13.9 14.5 12.8

– 13.1 12.5 16.9 18.4 16.3 16.7 16.6

– 12.5 16.4 16.4 15.4 17.6 16.3

– 10.0 10.3 12.9 10.9 11.6

– 14.5 13.5 14.1 13.8

– 12.9 15.5 15.8

– 15.2 13.7

– 10.0

–

– 4.1 12.2 11.8 16.0 15.5 8.9 15.0 14.5 15.0 13.7 11.5

109 ution in the north-eastern area of the country (Texas border) and along some areas in the Gulf of Mexico, reaching the Yucatan Peninsula, and along the western coast. Squire (1972) mentioned its presence in Bolivia, but we regard this record as doubtful. Morel (1966) considered the only Caribbean record of A. maculatum in Jamaica as an accidental import on cattle and we excluded Jamaica from its distribution. A. maculatum is widely distributed in USA, especially in the southern states (Cooley & Kohls, 1944), with several records along the Mississippi River and in parts of the Atlantic states. There is also a record of this tick in California. In the USA, it is associated with the vegetation of Juniper/Oak savanna, the Oak/Hickory/Pine series and the Oak/Hickory series (Kuchler, 1964) Records from the Neotropical region are associated with the biogeographical Pacific and Savannah provinces. A. maculatum has been confused with A. tigrinum and/or A. triste in Argentina, Chile, Uruguay and Brazil (Guglielmone et al., 2003). Many records of A. maculatum in southern South America, previous to the work by Kohls (1956), should be regarded as doubtful. As reviewed by Guglielmone et al. (2003), A. maculatum is wrongly listed as ranging from the USA to Argentina, even in recent papers. The records of A. maculatum for Argentina, as reported by Keirans (1982), are printing errors (Guglielmone et al., 2003). However, some records of A. maculatum or A. triste may be in error because the morphological similarities between the two species. This is further reinforced by the sympatric distribution of both species. A. tigrinum has been collected in Venezuela, French Guiana, Peru, Brazil, Paraguay, Bolivia, Argentina, Chile and Uruguay. Graham et al. (1975) mentioned its presence in Mexico, but this has not been confirmed by Hoffmann & López-Campos (2000) and we exclude Mexico from its range (see also distribution of A. maculatum and the problems derived from morphological affinities). The ecological preferences of A. tigrinum in Argentina have been studied by Guglielmone et al. (2000) and are not repeated here. In the rest of its range, this tick prefers biotopes related to the Amazonian and Pampeana biogeographical provinces, with a high prevalence in Chaco and Espinal provinces. A. triste is known from records in Colombia, Venezuela, Ecuador, Peru, Brazil, Argentina and Uruguay (Guglielmone et al., 2003). Graham et al. (1975) and Woodham et al. (1983) mentioned its presence in Mexico, but this record was not confirmed by Hoffmann & López-Campos (2000). See also notes above on the distribution of A. maculatum

and problems derived from morphological similarities and sympatry. Coordinates for several records in Colombia, Peru, Argentina (Buenos Aires Province) and Venezuela (Amazonian region) are not known. Collections of A. triste in Uruguay by one of the authors (JMV) show that this tick is common along the coastal areas in zones with a high relative humidity. Most records of A. neumanni are from Argentina and there is at least one confirmed record from Colombia (López & Parra, 1985). Its presence in Uruguay has been mentioned but no further confirmation has been presented (Venzal et al., 2003). The distribution of this species is related to the Chaco biogeographical province. Localities for A. parvitarsum extend into the arid Andean High Plateau region of Argentina, Bolivia, Chile and Peru. This species has been also found in the arid Patagonian region (southern Argentina). There is also a record of A. parvitarsum from Brazil (Becker et al., 1997), but we consider it as accidental (see ‘Hosts’ below); therefore, Brazil is excluded from the area of distribution of A. parvitarsum. The distribution of this species is related to the High Andean biogeographical province. Hosts Records of immature stages and/or adults for the five species of ticks were derived from compilations of two tick databases in cases when host and tick stages were clearly defined. Fifteen (20.5%) of 73 records, 170 (74.6%) of 228, 25 (78.1%) of 32; 235 (74.0%) of 318 and 34 (72.3%) of 47 records of A. maculatum, A. neumanni, A. parvitarsum, A. tigrinum and A. triste, respectively, were used. No host records of larvae and nymphs of A. maculatum and A. parvitarsum were found. The few host records of A. maculatum adults indicated no infestations of man and a lack of obvious preference for any host (33%, 27% and 20% of records were from Equidae, Canidae and Bovidae, respectively). The same appears to be true for A. triste, with 23%, 20% and 10% of adult records from man, Cervidae , and Canidae, respectively. Nevertheless, one of us (JMV) found that most Uruguayan records of A. triste were from dogs, while Szabó et al. (2003) found that this species was prone to infest the deer Blastocerus dichotomus in Brazil. Larvae and nymphs of A. triste were found on Muridae but also on Dideplhidae and Vespertilionidae. The great majority of A. tigrinum adults have been found Canidae (78%). Larvae and nymphs of A. tigrinum were found on

110 Cervidae, Tayassuidae, Canidae, Leporidae, Muridae and several families of Aves. Two percent of records of A. tigrinum were from man. Forty-nine percent of A. neumanni records were from Bovidae (especially cattle, which also appear to be good hosts for immature stages). However, a relatively important proportion of A. neumanni adults, as well as immature stages, have been found on Equidae and Canidae. Man is frequently infested by A. neumanni (17% of all records). Most A. parvitarsum were collected from South American Camelidae (56%), but Bovidae also represented an important proportion of records (16%); this species has been also found on sheep and horses. We consider accidental the finding of A. parvitarsum on a migratory penguin (Becker et al., 1997) in Brazil, and this may also apply to its finding on a South American ostrich (Boero, 1957). A. parvitarsum has never been collected from man.

Discussion This study has presented detailed information on the morphology, taxonomic keys and 16S rDNA sequences, together with details and host preferences of five tick species currently included in the maculatum group of Amblyomma. However, this study shows that only three species should be included in this group. This conclusion is also supported by the work of Estrada-Peña et al. (1993), who regarded the larva and the nymph of A. neumanni well separated from A. tigrinum, because of the shape of the basis capituli and associated palpal structures. This finding is further supported by data presented herein. Although the adults of the five species studied share some morphological features, such as coxal armatures and spines on the tibiae, these cannot alone be used as a basis for the taxonomic arrangement of these taxa. This may be also true for the species of the ovale group. According to Camicas et al. (1998), the seven species should be included in the subgenus Anastosiella. Nevertheless, we postulate that Anastosiella is formed by A. maculatum, A. tigrinum and A. triste. A. neumanni and A. parvitarsum belong to another, yet undetermined, subgenus along with the species currently included in the A. ovale group. This might be further suported when the immature stages of A. aureolatum and A. ovale are described. The 16S rDNA sequences also support the notion that the subgenus Anastosiella is not a monophyletic group.

The determination of A. maculatum, A. tigrinum and A. triste adults can be achieved by a combination of spines on the tibiae, spurs on coxae I and IV and the presence/absence of tubercles on the posterior body margin. It is especially difficult to determine the males of both A. maculatum and A. triste. However, the relative size of the caudal process and the shape of the spiracular plate may be useful in this respect, together with the presence of one or two spines on tibiae II to IV. However, immature stages are very difficult to resolve and the larvae are almost identical. There are subtle differences in the nymphal stages, mainly at the level of the basis capituli and coxal spurs. These characters are constant for each species but may be difficult to use when applied to individual specimens. Adults of these tick species have commonly been confused in the past, and there is probably some degree of confusion in the regions of their sympatry in northern South America. It seems clear that A. maculatum is a Neotropical– Nearctic tick species, while A. tigrinum and A. triste are Neotropical species. A. tigrinum covers almost all South American territory, reaching 45◦ S in Patagonia (Argentina) (Ruiz et al., 2003). A. triste appears to be restricted to northern and central South America. It is possible that the speciation of these three tick species took place in northern South America, from where A. maculatum was able to radiate into the Nearctic region and A. triste and A. tigrinum into the central and southern parts of South America, respectively. The only species of the group whose adults are prone to infest a particular type of host is A. tigrinum, which is commonly found on canids (Hoogstraal & Aeschlimann, 1982; Guglielmone et al., 2000). These authors did not specify a host preference for either A. maculatum or A. triste. The records from the Neotropical region appear to show that adults of A. maculatum and A. triste have no particular host-specificity, but additional research is needed to confirm this. Immature stages of A. maculatum appears to prefer feeding on birds in the Nearctic region (Keirans & Durden, 1998). The same was found for the Neotropical A. tigrinum (González Acuña et al., 2003; Labruna et al., 2002). Nevertheless, Labruna et al. (2002) found that rodents are poor hosts for immature stages of a Brazilian colony of A. tigrinum, while D.H. Aguirre (personal communication) obtained excellent results using rodents to maintain a colony of the same tick species originating in Argentina. Reasons for this divergence are unclear. According to records from Uruguay, members of the Rodentia and the Didel-

111 phimorphia appear to be suitable hosts for larvae and nymphs of A. triste in nature (Venzal et al., 2003). A. neumanni and A. parvitarsum are easy to distinguish from the previously mentioned three species because of distinct differences in the shape of the capitulum and palpi in both adult and known immature stages. The distribution of A. neumanni is discontinuous, with confirmed records in northern Argentina and Colombia; however, this gap in distribution may be due to a lack of information rather than absence. A. parvitarsum appears to be restricted to the southwestern arid regions of South America, where its natural hosts are present. Hoogstraal & Aeschlimann (1982) considered the adults of A. parvitarsum as strict feeders on Neotropical camelids. Indeed, South American camelids are the preferred hosts of this species; however, our data appear to indicate that A. parvitarsum is only moderately specific to these hosts, because a relevant proportion of other herbivores were also found infested. Need et al. (1991) stated that lizards and birds may be hosts for the larvae and nymphs of A. parvitarsum, but additional studies are needed to confirm this. A. triste, A. neumanni and, to a lesser extent, A. tigrinum have been found on man. A. triste has been implicated in the transmission of Rickettsia to man (Conti, 2001), but the impact of these species on human health has been little investigated and their capacity to act as vectors is not known. Acknowledgements The authors thank C. Almazán and J. de la Fuente for specimens of A. maculatum. D. Barros-Batesti, J. Martins and M. Labruna kindly provided data on collections deposited in their laboratories. References Aragao, H. & Fonseca, F. da (1961) Notas de ixodología. VIII. Lista e chave para os representantes da fauna ixodológica brasileira. Memórias do Instituto Oswaldo Cruz, 59, 115–129. Becker, G.K., Silva-Filho, A.L., Sinkoc, A.L. & Brum, J.G.W. (1997) Amblyomma parvitarsum Neumann, 1901 (Acari: Ixodidae) em pingüim de Magalhães Spheniscus magellanicus (Sphenicidae) na Praia do Cassino, Rio Grande do Sul, Brasil. Arquivos do Instituto de Biología, 64, 81–82. Boero, J.J. (1957) Las garrapatas de la República Argentina (Acarina: Ixodoidea). Buenos Aires: Departamento Editorial de la Universidad de Buenos Aires, 113 pp. Cabrera, A.L. & Willink, A. (1973) Biogeografía de América Latina. Monografías Científicas de la Secretaría General de la Organización de los Estados Americanos, Serie de Biología, No. 13, 120 pp.

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