Geographic distribution of the hard ticks (Acari: Ixodida: Ixodidae) of the world by countries and territories.

The hard tick family Ixodidae currently comprises 762 species worldwide, but an analysis of the occurrence of these species in the world´s countries, territories, zoogeographic regions (Afrotropical, Australasian, Nearctic, Neotropical, Oriental, Palearctic) and remote islands has not been attempted since 2009. Here, we present and critically discuss distributional data for all currently accepted ixodid species known from 226 countries and territories in six zoogeographic realms. This summary of ixodid tick biogeography should prove to be a valuable reference for biologists interested in ticks as organisms as well as specialists focusing on tick-borne diseases. Data for all species treated here were derived from a literature search that ended on March 31, 2022.

Do parapatric populations of the ticks Amblyomma tonelliae Nava, Beati & Labruna, 2014 and Amblyomma sculptum Berlese, 1888 (Acari: Ixodidae) hybridize?

This work aimed to determine if the tick species, Amblyomma sculptum and Amblyomma tonelliae, hybridize along their contact zones in Argentina. Free-living adults and nymphs of A. sculptum and A. tonelliae were collected in seven sampling locations of northern Argentina. In four of them, the two species occur in parapatry (possible hybrid zone) whereas in the other three sites, only one species is known to occur. A total of 65 A. sculptum and 65 A. tonelliae from both, allopatric and parapatric populations, were analysed. The nuclear (ITS2) and mitochondrial (COI and 12SrDNA) gene sequences of each tick were amplified and analysed to verify whether or not they could reveal the presence of hybrids among the parapatric samples. No morphological and molecular evidence was found to support the hypothesis of ongoing natural hybridization. Intrinsic postzygotic barriers may be the cause of lack of gene flow between the two species in areas of co-ocurrence. The results can be explained by the length of time the two lineages spent in allopatry since the middle of the Miocene and before their respective distribution range expanded again reaching a narrow secondary contact zone.

Worldwide host associations of the tick genus Ixodes suggest relationships based on environmental sharing rather than on co-phylogenetic events.

BACKGROUND: This study aims to capture how ticks of the genus Ixodes gained their hosts using network constructs. We propose two alternative hypotheses, namely, an ecological background (ticks and hosts sharing environmentally available conditions) and a phylogenetic one, in which both partners co-evolved, adapting to existing environmental conditions after the association took place. METHODS: We used network constructs linking all the known pairs of associations between each species and stage of ticks with families and orders of hosts. Faith's phylogenetic diversity was used to evaluate the phylogenetic distance of the hosts of each species and changes occurring in the ontogenetic switch between consecutive stages of each species (or the extent of the changes in phylogenetic diversity of hosts for consecutive stages of the same species). RESULTS: We report highly clustered associations among Ixodes ticks and hosts, supporting the influence of the ecological adaptation and coexistence, demonstrating a lack of strict tick-host coevolution in most cases, except for a few species. Keystone hosts do not exist in the relationships between Ixodes and vertebrates because of the high redundancy of the networks, further supporting an ecological relationship between both types of partners. The ontogenetic switch of hosts is high for species with enough data, which is another potential clue supporting the ecological hypothesis. Other results suggest that the networks displaying tick-host associations are different according to the biogeographical realms. Data for the Afrotropical region reveal a lack of extensive surveys, while results for the Australasian region are suggestive of a mass extinction of vertebrates. The Palearctic network is well developed, with many links demonstrating a highly modular set of relationships. CONCLUSIONS: With the obvious exceptions of Ixodes species restricted to one or a few hosts, the results point to an ecological adaptation. Even results on species linked to groups of ticks (such as Ixodes uriae and the pelagic birds or the bat-tick species) are suggestive of a previous action of environmental forces.

Description of two new species in the Ixodes ricinus complex from the New World (Acari: Ixodidae), and redescription of Ixodes affinis Neumann, 1899.

Ixodes chacoensis n. sp. is described based on males, females, nymphs and larvae collected from vegetation, ungulates and passerine birds in northeastern Argentina. Ixodes affinis Neumann, 1899 is redescribed based on the original type specimens (females) from Leopardus pardalis, and from recently collected specimens from Costa Rica. Ixodes keiransi n. sp., previously treated as North American populations of Ixodes affinis, is described based on males and females from carnivores and ungulates from the southeastern United States. Concatenated total evidence phylogenetics based on combined DNA sequence analyses from mitochondrial genes (12SrDNA, 16SrDNA and COI) and a nuclear gene (ITS2) corroborate the recognition of these species.

Assessment of habitat suitability for the cattle tick Rhipicephalus (Boophilus) microplus in temperate areas.

The aim of this research was to analyze and model the aptitude of temperate areas to support permanent populations of the cattle tick Rhipicephalus microplus, which is principally distributed in tropical and subtropical areas. This work integrated field-derived data of tick development with temperature and land-based models of tick spread in Argentina. The integrated analysis of the results suggest that approximately 31°S is the southern limit where R. microplus finds appropriate climatic conditions to be established permanently. The establishment of permanent populations of R. microplus south of this latitudinal threshold is currently restricted because the low temperatures in autumn and winter inhibit the development of its eggs, but the introduction of cattle infested with R. microplus from early spring to late summer in temperate areas could produce engorged females laying eggs that would originate viable larvae from late spring to winter. The comparison of the temperature-based maps of habitat suitability with those obtained considering the lands suitable for livestock grazing, clearly shows that the models based only on climatic variables overestimate the potential dispersal of the cattle tick. The outcomes of this study suggest that an increase of temperature in the months of autumn and winter around 2°-2.75 °C should be necessary for the establishment of permanent populations of R. micoplus in the region belonging to temperate areas. This would allow that a tick generation emerged in early spring due to the overwintering of eggs and larvae originated from females detached from cattle during autumn or early winter.

Resistance of the cattle tick Rhipicephalus (Boophilus) microplus to fluazuron in Argentina.

The aim of this work is to report the presence of resistance to fluazuron in a population of Rhipicephalus microplus in Argentina. The evidence was obtained from field and in vitro trials. In the field trial, cattle infested with ticks was treated with two commercial formulations of fluazuron. The in vitro trial (adult immersion test, AIT) was performed by using technical grade fluazuron. In the field trial, there were no significant differences between the treated and control groups between days 2 and 34 post-treatment. The only exceptions (treated group I in day 14 post-treatment, treated group II in days 23 and 29 post-treatment) had a significantly lower tick load than the untreated group, but the efficacy was not higher than 70%. Viable engorged females were collected on both groups of treated bovines in all counts, and the production of viable larvae was not precluded with the application of the two commercial formulations of fluazuron evaluated in this study. The results obtained with the in vitro assay (AIT) also indicate that the R. microplus population tested in this work has a higher level of resistance to fluazuron than another susceptible field strain. The integrated analysis of the field and in vitro trials clearly reveals the emergence of resistance to fluazuron in a R. microplus population from Argentina. This diagnosis of resistance does not imply that the fluazuron has lost its functionality at a regional scale, but it highlights the need to establish control strategies that minimize the use of this drug in order to preserve its functionality as an acaricide.

Reestablishment of Rhipicephalus secundus Feldman-Muhsam, 1952 (Acari: Ixodidae).

Rhipicephalus secundus is reestablished as a valid tick name within the Rhipicephalus sanguineus group and removed from the synonymy list of Rhipicephalus turanicus. Morphological re-description of both male and female of R. secundus and the analysis of its phylogenetic position based on mitochondrial DNA sequences are presented. The morphological re-description was made with tick specimens collected on goat in Israel. The phylogenetic analyses showed that R. secundus belong to a different clade from those formed by R. turanicus sensu stricto (s.s.) and R sanguineus s.s., and by other taxa from the R. sanguineus group. Rhipicephalus secundus is morphologically related to R. turanicus, but the scutal punctation pattern of both male and female allows the morphological differentiation between R. secundus and R. turanicus, punctations being clearly more numerous and larger in the latter. Both male and female of R. secundus can be differentiated from those of R. sanguineus s.s. by the shape of the spiracular plate. In males, the dorsal prolongation of the spiracular plate is equal to the breadth of the adjacent festoon in R. secundus, while it is narrower than the breadth of the adjacent festoon in R. sanguineus s.s. The dorsal prolongation of the spiracular plate in the female of R. secundus is wider than in the female of R. sanguineus s.s. The genital apertures of the females of R. secundus and R. sanguineus are both U-shaped, but in R. sanguineus s.s. it is broader than in R. secundus. Considering the results obtained in this study, it can be stated that R. secundus is present at least in Israel, Palestinian Territories, Turkey, Albania and southern Italy, but it is necessary to carry out additional studies to determine the geographical range and host usage of this species.

Exotic tick detected in Argentina on a tourist returning from South Africa.

The aim of this study was to report the finding of a nymph attached to an Argentinean tourist returning from South Africa. The nymph specimen was morphologically analysed, submitted to DNA extraction and amplifying the 16S rRNA mitochondrial gene. Additionally, the nymph DNA was screened for Rickettsia, Ehrlichia and Anaplasma infection. The nymph was determined to belong to Amblyomma marmoreum species complex. No specific diagnosis was achieved because the comparative descriptions of species in this complex contain important discordances, and the DNA sequence obtained in the present study is positioned within the same clade with sequences of A. marmoreum see above, but the genetic divergence with them (4.96 and 5.76%) indicate that they belong to different species. No DNA of the Rickettsiales order bacterial was detected in the A. marmoreum species complex nymph.

Ixodes silvanus n. sp. (Acari: Ixodidae), a new member of the subgenus Trichotoixodes Reznik, 1961 from northwestern Argentina.

Females, nymphs, and larvae of Ixodes silvanus n. sp. collected from birds and from the vegetation in northwestern Argentina (Yungas Phytogeographic Province) are described herein. The new species belongs to the subgenus Trichotoixodes (Acari: Ixodidae). The female is diagnosed by a combination of the following characters: scutum with setae moderately long and more numerous in central field, fewer and moderately long setae on lateral fields, and inconspicuous setae in anterior field; basis capituli subtriangular dorsally; porose areas large and irregular in shape, lacking distinct margins; auriculae with straight edges diverging posterolaterally and ending with small blunt processes; hypostome narrow and pointed with dental formula 4/4 in the anterior third, then 3/3 and 2/2 near the base; coxae I with two spurs, sub-equal in size, internal slightly slimmer than external. The nymph is diagnosed by notum with numerous and long setae, ventral surface covered by numerous whitish setae, scutum with short scapulae and few and shallow punctations, setae on scutum few, short and irregularly distributed, basis capituli sub-triangular dorsally with posterior margin straight, cornua large and directed postero-laterally, auriculae large and projected laterally, lateral margin of basis capituli above auriculae with a lateral and triangular projection, hypostome pointed with dental formula 3/3 in the anterior third and then 2/2, and coxa I with two short, sub-equal, triangular spurs. The diagnostic characters of the larva are: basis capituli dorsally sub-triangular with lateral angles acute and posterior margin straight, auriculae as large triangular lateral projections, hypostome with apex bluntly pointed and dental formula 3/3 in the anterior third and then 2/2, coxa I with two short, sub-equal, triangular spurs, and pattern of dorsal and ventral body setae. This new species is phylogenetically related to Ixodes brunneus, Ixodes turdus and Ixodes frontalis, and the principal hosts for all its parasitic stages are birds.

Ixodidae (Acari: Ixodoidea): descriptions and redescriptions of all known species from 1758 to December 31, 2019.

References to the descriptions and redescriptions of the 742 species of Ixodidae published from 1758 to December 31, 2019 are compiled, with the goal of enabling tick taxonomists to readily access this diffuse and often confusing literature. Additionally, data resulting from this effort are critically analyzed to demonstrate the problems attending correct identification of several tick species that are of medical, veterinary and/or evolutionary importance, and to highlight the need for new or enhanced diagnostic techniques. Recent morphological and molecular studies indicate that some ixodid species names represent more than one taxon; therefore, it is expected that new species will be described in the near future, based partly on material already deposited in museums around the world.

Resistance of the cattle tick Rhipicephalus (Boophilus) microplus to ivermectin in Argentina.

Resistance to ivermectin in populations of the cattle tick Rhipicephalus microplus in Argentina was diagnosed in this work. The in vitro larval immersion test (LIT) was used to determine quantitatively the levels of resistance to ivermectin in different populations of R. microplus. Additionally, field trials to control natural infestations of R. microplus on cattle with a commercial formulation of ivermectin 3.15% were carried and jointly analyzed with the in vitro assays. The phenotypic response of the populations analyzed was not uniform. Five of them were classified as susceptible, four populations as resistant, and one in the category "incipient resistance". Regarding the field trials, the therapeutic efficacy in a population classified with LIT as susceptible achieved values higher than 94% two weeks after treatment, and no reproductively viable females were observed after the second day post-treatment. Conversely, the values of efficacy percentage in a population (named as "San Martín") classified with LIT in the category "incipient resistance" never exceeded the 70.8%, and engorged females were collected in practically all counts. The population "San Martín" was classified in the category "incipient resistant" with LIT analysis, but the field trial unambiguously shows that this tick population is resistant. The comparison of the results obtained with LIT in vitro assays and through field trials shows that biased estimations of resistance levels may occur when resistance ratios (RR) values are ≤2, and additional field efficacy trials could be needed to know with precision the status of the tick populations evaluated.

A community approach to the Neotropical ticks-hosts interactions.

The relationships between ticks and hosts are relevant to capture the ecological background driving the evolution of these parasites. We used a set of 4,764 records of ticks of the genera Amblyomma, Ixodes, and Haemaphysalis and their hosts in the Neotropics to approach the tick-host relationships using a network-based construct. The network identified 9 clusters of interacting hosts and ticks partially connected by 22 tick species that switch their host range according to their life cycle stage. These links among clusters do not confer an extra resilience to the network following removal of hosts and subsequent cascade extinctions of ticks: the robustness of the network slightly changed when these inter-clusters links are considered. Phylogenetic clustering of ticks to hosts at cluster level was not significant (p > 0.15) but if examined individually 63 tick species/stages (59%) displayed such clustering, suggesting that their hosts have a related phylogenetic background. We interpreted these results under an ecological perspective in which ticks could track its environmental niche associating to vertebrates that would maximize tick survival under the range of abiotic traits. We encourage these integrated analyses to capture the patterns of circulation of tick-transmitted pathogens, a topic still unaddressed in the Neotropical region.

Description of a new species of Ixodes (Acari: Ixodidae) and first report of Ixodes lasallei and Ixodes bocatorensis in Brazil.

In a recent study, we relegated the taxon Ixodes aragaoi Fonseca, 1935 to a junior synonym of Ixodes fuscipes Koch, 1844, and reinstated Ixodes spinosusNeumann, 1899 (a former synonym of I. fuscipes) to a valid species. We examined all lots of ticks formerly identified as I. fuscipes or I. aragaoi in three tick collections of Brazil. Through morphological analysis, some of the examined specimens could not be assigned to either I. fuscipes or I. spinosus based on the examination of the type specimens of these two species. Herein, we report these ticks to represent three different species: Ixodes catarinensis n. sp. Onofrio & Labruna, Ixodes lasalleiMéndez Arocha and Ortiz, 1958, and Ixodes bocatorensisApanaskevich and Bermúdez, 2017. The latter two species are reported for the first time in Brazil. Phylogenetic analysis inferred from the tick 16S rRNA gene partial sequences corroborated our morphological analysis, indicating that I. spinosus, I. lasallei, I. bocatorensis, and I. catarinensis n. sp. form a natural group of neotropical ticks. With the present study, the number of Ixodes species in Brazil increases from 9 to 12. We propose a new identification key for females and males of Ixodes species currently recognized in Brazil.

Synonymy of Ixodes aragaoi with Ixodes fuscipes, and reinstatement of Ixodes spinosus (Acari: Ixodidae).

Ixodes fuscipes Koch, 1844, described from Brazil, has been considered a valid species with records from Brazil and Peru. Ixodes spinosus Neumann, 1899, also described from Brazil, has been considered a synonym of I. fuscipes. In 2014, Ixodes aragaoi Fonseca, 1935 was redescribed as a valid species for Brazil and Uruguay. Until the present study, one major difference between the females of I. fuscipes and I. aragaoi was the horn-like auriculae in the former versus the ridge-like auriculae in the later, but this morphological difference was not supported after examination of the holotype of I. fuscipes and a syntype female of I. spinosus. Surprisingly, we found the type of I. fuscipes to have ridge-like auriculae, in contrast to the horn-like auriculae of I. spinosus. Comparisons of the I. fuscipes holotype with the syntypes of I. aragaoi revealed that they correspond to the same species. Therefore, we redescribe I. fuscipes, relegate I. aragaoi to a junior synonym of I. fuscipes, and reinstate I. spinosus as a valid species. After examining all lots of I. fuscipes in four tick collections, no specimen was recognized as I. fuscipes when compared with the type specimen of this taxon. On the other hand, specimens previously identified as I. aragaoi are now confirmed as I. fuscipes, with bona fide records for Brazil and Uruguay. Some of the specimens previously reported as I. fuscipes are now confirmed as I. spinosus, with records in two Brazilian biomes, Amazon and Atlantic rainforest. We present lists of the ticks examined in this study, with their current taxonomic status.

The Ixodes ricinus complex (Acari: Ixodidae) in the Southern Cone of America: Ixodes pararicinus, Ixodes aragaoi, and Ixodes sp. cf. I. affinis.

The goal of this study was to clarify the taxonomic status of the Ixodes ricinus complex in the Southern Cone of America, by using morphological characters and molecular markers (mitochondrial 16SrDNA and cox1 genes). The morphological analysis indicates that three different taxa of the I. ricinus complex occur in this region: Ixodes pararicinus, Ixodes aragaoi, and Ixodes sp. cf. I. affinis. The most prominent diagnostic character among them is the size of scutal punctations in both male and female ticks. In the males of Ixodes sp. cf. I. affinis, the punctations on the central field and along the median marginal groove of the scutum are clearly larger than in the males of I. aragaoi and I. pararicinus, while the punctations of I. aragaoi are larger but less numerous than in I. pararicinus. The punctations in Ixodes sp. cf. I. affinis females are larger and deeper than in females of I. aragaoi and I. pararicinus, and those of I. aragaoi are slightly larger than in I. pararicinus. The length of the lateral posterior denticles of the male hypostome is comparatively longer in I. aragaoi than in the other two species, and longer in Ixodes sp. cf. I. affinis than in I. pararicinus. In the 16S analysis, I. pararicinus and I. aragaoi are monophyletic (99% and 98% bootstrap support, respectively), while Ixodes cf. I. affinis does not represent a single lineage. In the cox1 analysis, both I. pararicinus and I. aragaoi are well-defined taxa, but the bootstrap support for Ixodes sp. cf. I. affinis is low (67%). In general, there are considerable 16SrRNA differences among lineages of Ixodes sp. cf. I. affinis from different geographical areas. These results may be indicative of the existence of different species. The populations morphologically compatible with I. affinis from Argentina, Colombia, Panama, Belize, and USA should be provisionally named as Ixodes sp. cf. I. affinis until an integrative taxonomic work with further evidence redefines whether or not this taxon actually represents a species complex.

Description of a new species of Ixodes (Acari: Ixodidae) and first report of Ixodes lasallei and Ixodes bocatorensis in Brazil

In a recent study, we relegated the taxon Ixodes aragaoi Fonseca, 1935 to a junior synonym of Ixodes fuscipes Koch, 1844, and reinstated Ixodes spinosus Neumann, 1899 (a former synonym of I. fuscipes) to a valid species. We examined all lots of ticks formerly identified as I. fuscipes or I. aragaoi in three tick collections of Brazil. Through morphological analysis, some of the examined specimens could not be assigned to either I. fuscipes or I. spinosus based on the examination of the type specimens of these two species. Herein, we report these ticks to represent three different species: Ixodes catarinensis n. sp. Onofrio & Labruna, Ixodes lasallei Méndez Arocha and Ortiz, 1958, and Ixodes bocatorensis Apanaskevich and Bermúdez, 2017. The latter two species are reported for the first time in Brazil. Phylogenetic analysis inferred from the tick 16S rRNA gene partial sequences corroborated our morphological analysis, indicating that I. spinosus, I. lasallei, I. bocatorensis, and I. catarinensis n. sp. form a natural group of neotropical ticks. With the present study, the number of Ixodes species in Brazil increases from 9 to 12. We propose a new identification key for females and males of Ixodes species currently recognized in Brazil.

Synonymy of Ixodes aragaoi with Ixodes fuscipes, and reinstatement of Ixodes spinosus (Acari: Ixodidae)

Ixodes fuscipes Koch, 1844, described from Brazil, has been considered a valid species with records from Brazil and Peru. Ixodes spinosus Neumann, 1899, also described from Brazil, has been considered a synonym of I. fuscipes. In 2014, Ixodes aragaoi Fonseca, 1935 was redescribed as a valid species for Brazil and Uruguay. Until the present study, one major difference between the females of I. fuscipes and I. aragaoi was the horn-like auriculae in the former versus the ridge-like auriculae in the later, but this morphological difference was not supported after examination of the holotype of I. fuscipes and a syntype female of I. spinosus. Surprisingly, we found the type of I. fuscipes to have ridge-like auriculae, in contrast to the horn-like auriculae of I. spinosus. Comparisons of the I. fuscipes holotype with the syntypes of I. aragaoi revealed that they correspond to the same species. Therefore, we redescribe I. fuscipes, relegate I. aragaoi to a junior synonym of I. fuscipes, and reinstate I. spinosus as a valid species. After examining all lots of I. fuscipes in four tick collections, no specimen was recognized as I. fuscipes when compared with the type specimen of this taxon. On the other hand, specimens previously identified as I. aragaoi are now confirmed as I. fuscipes, with bona fide records for Brazil and Uruguay. Some of the specimens previously reported as I. fuscipes are now confirmed as I. spinosus, with records in two Brazilian biomes, Amazon and Atlantic rainforest. We present lists of the ticks examined in this study, with their current taxonomic status.

Description of a new species of Ixodes (Acari: Ixodidae) and first report of Ixodes lasallei and Ixodes bocatorensis in Brazil

In a recent study, we relegated the taxon Ixodes aragaoi Fonseca, 1935 to a junior synonym of Ixodes fuscipes Koch, 1844, and reinstated Ixodes spinosus Neumann, 1899 (a former synonym of I. fuscipes) to a valid species. We examined all lots of ticks formerly identified as I. fuscipes or I. aragaoi in three tick collections of Brazil. Through morphological analysis, some of the examined specimens could not be assigned to either I. fuscipes or I. spinosus based on the examination of the type specimens of these two species. Herein, we report these ticks to represent three different species: Ixodes catarinensis n. sp. Onofrio & Labruna, Ixodes lasallei Méndez Arocha and Ortiz, 1958, and Ixodes bocatorensis Apanaskevich and Bermúdez, 2017. The latter two species are reported for the first time in Brazil. Phylogenetic analysis inferred from the tick 16S rRNA gene partial sequences corroborated our morphological analysis, indicating that I. spinosus, I. lasallei, I. bocatorensis, and I. catarinensis n. sp. form a natural group of neotropical ticks. With the present study, the number of Ixodes species in Brazil increases from 9 to 12. We propose a new identification key for females and males of Ixodes species currently recognized in Brazil.

Synonymy of Ixodes aragaoi with Ixodes fuscipes, and reinstatement of Ixodes spinosus (Acari: Ixodidae)

Ixodes fuscipes Koch, 1844, described from Brazil, has been considered a valid species with records from Brazil and Peru. Ixodes spinosus Neumann, 1899, also described from Brazil, has been considered a synonym of I. fuscipes. In 2014, Ixodes aragaoi Fonseca, 1935 was redescribed as a valid species for Brazil and Uruguay. Until the present study, one major difference between the females of I. fuscipes and I. aragaoi was the horn-like auriculae in the former versus the ridge-like auriculae in the later, but this morphological difference was not supported after examination of the holotype of I. fuscipes and a syntype female of I. spinosus. Surprisingly, we found the type of I. fuscipes to have ridge-like auriculae, in contrast to the horn-like auriculae of I. spinosus. Comparisons of the I. fuscipes holotype with the syntypes of I. aragaoi revealed that they correspond to the same species. Therefore, we redescribe I. fuscipes, relegate I. aragaoi to a junior synonym of I. fuscipes, and reinstate I. spinosus as a valid species. After examining all lots of I. fuscipes in four tick collections, no specimen was recognized as I. fuscipes when compared with the type specimen of this taxon. On the other hand, specimens previously identified as I. aragaoi are now confirmed as I. fuscipes, with bona fide records for Brazil and Uruguay. Some of the specimens previously reported as I. fuscipes are now confirmed as I. spinosus, with records in two Brazilian biomes, Amazon and Atlantic rainforest. We present lists of the ticks examined in this study, with their current taxonomic status.