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Amblyomma tuberculatum on Gopherus polyphemus (Gopher tortoise) Photo by Dirk Stevenson. Image subject to copyright.
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Amblyomma tuberculatum Marx, 1894

Gopher tortoise tick

Federal Protection: No US federal protection

State Protection: No Georgia state protection

Global Rank: G2G3

State Rank: S2

SWAP High Priority Species (SGCN): Yes

Element Occurrences (EOs) in Georgia: 13

Habitat Summary for element in Georgia: Sandhills, longleaf pine woodlands, other sandy open habitats


Description

A large tick (the largest tick species in North America) especially in the adult stage. Members of the genus Amblyomma have an ornate (patterned) dorsal scutum. Adult females of A. tuberculatum have a cream colored scutum laterally with a wide brownish central line, whereas males have a cream colored scutum (which covers most of the dorsal surface) with numerous brown marks. Nymphs and larvae are progressively smaller and have an almost entirely brown scutum. Blood-engorged females can be the size of a large marble.

Similar Species

In Georgia, the only other congeneric ticks are theGulf Coast tick (Amblyomma maculatum), and the Lone Star Tick (Amblyomma americanum). Adult females of the Gulf Coast tick have a white scutum with a narrow, dark central line whereas adult males have a brownish scutum distinctly marked with several pale straight lines lines across the whole scutum. Females of the lone star tick have a dark scutum with a distinct pale posterior spot whereas males have a reddish brown scutum with a few marginal, pale, small wavy lines. In Florida, A. tuberculatum may co-occur with other congeneric ticks, namely Amblyomma rotundatum and Amblyomma dissimile. Adults of these ticks, and of the other species of Amblyomma mentioned here can be identified using the key of Keirans and Litwak (1989). Nymphs and larvae of all of these species can be identified using Keirans and Durden (1998) and Clifford et al. (1961), respectively

Habitat

Open-canopied longleaf pine–wiregrass sandhills and similar savanna-like habitats underlain by deep, well-drained sandy soils. Gopher tortoise burrows (adult burrows are on average about 2.4 m [8 feet deep] and 4.6-6.1 m [15-20 feet] long, provide A. tuberculatum with humid, shaded conditions needed for oviposition, egg development and escape from droughty conditions. Notably, not all gopher tortoise sites support populations of A. tuberculatum. Tortoise populations present on deep, well-drained sand soils (mean sand depth > 100 cm) are more likely to support A. tuberculatum (as compared to shallower or loamier sands and other less well-drained, soil types). Other habitat variables, (e.g., biomass of small mammals and occurrence of other reptile species on-site, potential food sources for larvae) as of yet not quantified, may be important to the presence of A. tuberculatum.

Diet

The adults and nymphs are obligate parasites of gopher tortoises. Occasionally, feeding on other vertebrate species occurs by nymphs. The larval stage is less host specific and parasitizes numerous species of ectotherms and endotherms, including mammals and reptiles. Although larval A. tuberculatum have been documented to attach to and feed on humans, this behavior is rare and there are not any tick-borne disease issues associated with such events.

Life History

Sequentially, the life stages of A. tuberculatum are: egg, larva, nymph, adult. Adult female specimens of A. tuberculatum maintained in the laboratory engorged on gopher tortoises, ingesting at least 2,100 mg of blood and producing up to 9,300 eggs each. Eggs incubated at constant temperatures hatched at 21.1 - 32.2 °C. Larvae engorged in 9–13 days on rabbits and molted to the nymph in a minimum of 20 days. Larvae exposed to subfreezing temperatures survived for 1.5 months. Nymphs, after feeding for 10–37 days on rabbits, molted into adults in a minimum of 19 days. The life cycle required a minimum of 207 days. When parasitizing tortoises, ticks may attach on the softer body tissues of the neck and beneath the forelimbs or hindlimbs but may also penetrate sutures between scutes of the carapace and plastron. Up to several dozens ticks have been observed feeding on the same gopher tortoise.

Survey Recommendations

A fine-scale understanding of the current distribution of this tick, both range-wide and for Georgia, is sorely needed. Gopher tortoise ticks (feeding on tortoises) are noticed by observant naturalists and field herpetologists when they encounter or examine tortoises, thus increased reporting of tick occurrences by these groups will greatly augment our knowledge.

Range

The distribution of A. tuberculatum, an obligate parasite, is intimately linked to the distribution of its primary host, the gopher tortoise. The range of this tick includes portions of the Coastal Plain (inhabited by tortoises) from extreme southeastern South Carolina to southeastern Mississippi. It is widespread in the Coastal Plain region of Georgia.

Threats

Population size and distribution of host-specific tick species has been shown to be sensitive to host declines. Continuing declines of gopher tortoise populations in Georgia, due chiefly to habitat loss and/or lack of habitat management, will in turn adversely affect tick populations.

Georgia Conservation Status

The conservation status of this tick closely mirrors that of the gopher tortoise.Considering that some to many tortoise sites do not support tick populations, it is accurate to classify this species as more imperiled than its host.

Conservation Management Recommendations

Increased tick surveys at tortoise populations throughout the species range in Georgia are needed to better determine this tick’s distribution. Active management of gopher tortoise habitats, including the use of regular prescribed fire, is of paramount importance not just to tortoises but also to commensal species like A. tuberculatum. As part of gopher tortoise translocations, standard protocols for tortoise ticks (present on such tortoises) need to be developed and followed.

References

Bishop, F.C., and H.L. Trembley. 1945. Distribution and hosts of certain North American ticks. Journal of Parasitology 31:1−54.

Budachetri, K., D. Gaillard, J. Williams, N. Mukherjee, and S. Karim. 2016. A snapshot of the microbiome of Amblyomma tuberculatum ticks infesting the gopher tortoise, and endangered species. Ticks and Tick-Borne Diseases 7:1225−1229.

Clifford, C. M., G. Anastos, and A. Elbl. 1961. The larval ixodid ticks of the eastern United States. Miscellaneous Publications of the Entomological Society of America 2: 213-237.

Cooney, J.C., and K. L. Hays. 1972. Bionomics of the Gopher Tortoise Tick, Amblyomma tuberculatum Marx. Journal of Medical Entomology 9:239-245.

Ennen, J.R., and C.P. Qualls. 2011. Distribution and habitat utilization of the gopher tortoise tick (Amblyomma tuberculatum) in southern Mississippi. Journal of Parasitology 97:202−206.

Felz, M.W., L.A. Durden, and J.H. Oliver, Jr. 1996. Ticks parasitizing humans in Georgia and South Carolina. Journal of Parasitology 82:505−508.

Jackson, D.R., and E.G. Milstrey. 1989. The fauna of gopher tortoise burrows. Pages 86-98 in J.E. Diemer, D.R. Jackson, J.L. Landers, J.N. Lane, and D.A. Wood, editors. Gopher Tortoise Relocation Symposium Proceedings, Nongame Wildlife Program Technical Report #5. Florida Game and Fresh Water Fish Commission, Tallahassee, Florida.

Keirans, J.E., and L.A. Durden. 1998. Illustrated key to nymphs of the genus Amblyomma (Acari: Ixodidae) found in the United States. Journal of Medical Entomology 35:489−495.

Authors of Account

Dirk Stevenson

Date Compiled or Updated

1 December, 2018

Gopher tortoise tick. Photo by Dave Almquist. Image subject to copyright.