Dermacentor

American dog tick Dermacentor variabilis, copyright Roy Cohutta Brown.

Belongs within: Ixodida.

Dermacentor, the wood ticks, is a cosmopolitan genus of ticks found on all continents except Australia and Antarctica. They include vectors of diseases such as Rocky Mountain spotted fever, Q fever and tularemia (Keirans 2009).

The Dermacentor ticks
Published 30 November 2021
Pacific Coast tick Dermacentor occidentalis, copyright Jerry Kirkhart.

Among the ticks of most concern to humans are species of the genus Dermacentor. This genus of about forty known species is widely distributed in Africa, Eurasia and the Americas. Examples include the meadow tick D. reticulatus in Europe, and the wood tick D. variabilis and Rocky Mountain wood tick D. andersoni in North America. They are parasites of mammals, including both generalist and more host-specific species; records of Dermacentor individuals from reptiles and even carpenter bees (Goddard & Bircham 2010) presumably represent incidental and/or accidental associations. Species of Dermacentor are responsible for the spread of bacteria causing diseases such as Rocky Mountain spotted fever (which, despite sounding like a 1950s dance craze, is presumably not much fun), Q fever and tularemia. The ticks can also be more directly hazardous, as their bites inject a toxin that can cause tick paralysis.

Distinguishing features of Dermacentor species relative to other ticks include a rectangular base to the capitulum, relatively short, broad palps, well-developed eyes and the presence of festoons (impressed divisions of the posterior margin of the body) (Keirans 2009). Most are ornate—that is, marked on the dorsum with contrasting pale patterns—with the notable exception of the tropical horse tick D. nitens of the Americas (until recently, often treated as forming its own genus Anocentor). The function of such markings is unknown though suggestions include environmental protection, warning predators of distastefulness, or sexual signalling.

Meadow tick Dermacentor reticulatus, copyright Ferran Turmo Gort.

The majority of Dermacentor species have a three-host life cycle, dropping off the host between each of the life stages of larva, nymph and adult, and seeking out a new host after moulting. However, at least two New World species, the aforementioned D. nitens and the winter tick D. albipictus (a parasite of deer), are one-host ticks that remain on their original host between instars. In general, Dermacentor species are more resilient to dry climates than many other tick species. Individual species can differ in their climate tolerance, however. In North America, the geographical divide between D. variabilis in the east of the continent and D. andersoni in the west seems to be driven by the need for the latter of drier conditions (Yoder et al. 2007). Older instars also tend to be hardier than younger. Females of the ornate sheep tick D. marginatus, a European species, leave their host after gorging at the beginning of winter and then wait for more amoenable spring conditions before laying their delicate eggs (Dörr & Gothe 2001).

Higher relationships within the genus do not appear to have been extensively studied. A preliminary molecular phylogeny of hard ticks has suggested the possibility of a basal division between Afrotropical, Eurasian and New World lineages (Barker & Murrell 2004). Comparison with related tick genera raises the possibility of an Afrotropical origin for Dermacentor, though the genus has only a relictual presence in that continent now. However, with only a handful of species subjected to broad phylogenetic analysis to date, further testing is demanded. Does the continental divide hold true? Do the one-host species form a single clade within the genus? Inquiring minds wish to know.

Systematics of Dermacentor

Characters (from Keirans 2009): Basis capituli quadrangular. Eyes present (rarely reduced). Palpi about as long as basis capituli, palpal segment II about as broad as long. Seven or eleven festoons present.

<==Dermacentor Koch 1844 [incl. Anocentor Schulze 1937]KDB02
    |--D. albipictus [incl. D. nigrolineatus]L01
    |--D. andersoni Stiles 1908SH91
    |--D. atrosignatus Neumann 1906H98
    |--D. auratus Supino 1897R72
    |--D. marginatus Sulzer 1776VR91 [incl. D. daghestanicusE-PE-P91, D. marginatus lacteolusE-PE-P91]
    |--D. nitensB91
    |--D. niveus Neumann 1897A56
    |--D. nuttalliLC96
    |--D. occidentalisL01
    |--D. parumapertusF91
    |--D. (Dermacentor) reticulatus (Neumann 1897)F91, BG-P02
    |--D. silvarumLC96
    |--D. sinicusJLW91
    |--D. ushakovaeE-PE-P91
    `--D. variabilis (Say 1821) [=Ixodes variabilis]H98

*Type species of generic name indicated

References

Barker, S. C., & A. Murrell. 2004. Systematics and evolution of ticks with a list of valid genus and species names. Parasitology 129: S15–S36.

[BG-P02] Barral, M., A. L. García-Pérez, R. A. Juste, A. Hurtado, R. Escudero, R. E. Sellek & P. Anda. 2002. Distribution of Borrelia burgdorferi sensu lato in Ixodes ricinus (Acari: Ixodidae) ticks from the Basque Country, Spain. Journal of Medical Entomology 39 (1): 177–184.

[B91] Belozerov, V. N. 1991. Evolution of life cycles in ticks (Ixodidae) due to climate seasonality. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 2 pp. 135–139. SPB Academic Publishing: The Hague.

Dörr, B., & R. Gothe. 2001. Cold-hardiness of Dermacentor marginatus (Acari: Ixodidae). Experimental and Applied Acarology 25: 151–169.

[E-PE-P91] Estrada-Peña, A., & R. Estrada-Peña. 1991. Phenotypic variation of Dermacentor marginatus (Ixodidae) in the Palaearctic region. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 2 pp. 155–162. SPB Academic Publishing: The Hague.

[F91] Filippova, N. A. 1991. A hypothesis for the palaeogenesis of the distribution of the main vectors for Lyme disease. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 1 pp. 109–118. SPB Academic Publishing: The Hague.

Goddard, J., & L. Bircham. 2010. Parasitism of the carpenter bee, Xylocopa virginica (L.) (Hymenoptera: Apidae), by larval Dermacentor variabilis (Say) (Acari: Ixodidae). Systematic and Applied Acarology 15: 195–196.

[H98] Halliday, R. B. 1998. Mites of Australia: A checklist and bibliography. CSIRO Publishing: Collingwood.

[JLW91] Jiang Z.-J., Li F. & Wang W.-L. 1991. Study on diapause of adult ticks of the genus Dermacentor. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 2 pp. 571–579. SPB Academic Publishing: The Hague.

Keirans, J. E. 2009. Order Ixodida. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 111–123. Texas Tech University Press.

[KDB02] Klompen, H., S. J. Dobson & S. C. Barker. 2002. A new subfamily, Bothriocrotoninae n. subfam., for the genus Bothriocroton Keirans, King & Sharrad, 1994 status amend. (Ixodida: Ixodidae), and the synonymy of Aponomma Neumann, 1899 with Amblyomma Koch, 1844. Systematic Parasitology 53: 101–107.

[LC96] Li, D., & Q. Chen. 1996. Studies on piroplasmoses and the tick (Ixodidae) vectors in China. In: Mitchell, R., D. J. Horn, G. R. Needham & W. C. Welbourn (eds) Acarology IX vol. 1. Proceedings pp. 469–471. Ohio Biological Survey: Columbus (Ohio).

[L01] Lindquist, E. E. 2001. Poising for a new century: diversification in acarology. In: Halliday, R. B., D. E. Walter, H. C. Proctor, R. A. Norton & M. J. Colloff (eds) Acarology: Proceedings of the 10th International Congress pp. 17–34. CSIRO Publishing: Melbourne.

[R72] Rajagopalan, P. K. 1972. Ixodid ticks (Acarina: Ixodidae) parasitizing wild birds in the Kyasanur Forest disease area of Shimoga District, Mysore State, India. Journal of the Bombay Natural History Society 69 (1): 55–78.

[SH91] Sonenshine, D. E., J. G. Hamilton, J. S. Phillips & W. R. Lusby. 1991. Mounting sex pheromone: its role in regulation of mate recognition in the Ixodidae. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 1 pp. 69–78. SPB Academic Publishing: The Hague.

[VR91] Výrosteková, V., J. Řeháček, D. Guryčová & E. Kocianová. 1991. Prevalence of Francisella tularensis in ticks of Slovakia. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 2 pp. 55–59. SPB Academic Publishing: The Hague.

Yoder, J. A., D. R. Buchan, N. F. Ferrari & J. L. Tank. 2007. Dehydration tolerance of the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae), matches preference for a dry environment. International Journal of Acarology 33 (2): 173–180.

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