Amblyomma triste

Koch, 1844

Amblyomma triste is a hard first described by Koch in 1844. It is the primary of parkeri, the causative agent of a spotted fever group rickettsiosis with resembling . The species is the sole tick responsible for human tick-borne in Uruguay and a significant vector in Argentina and Brazil. Though historically considered restricted to South America, specimens have been documented in the United States (Arizona and Texas) and Mexico, where they were long misidentified as the morphologically similar Amblyomma maculatum.

Amblyomma triste by (c) Lucas Rubio, some rights reserved (CC BY), uploaded by Lucas Rubio. Used under a CC-BY license.

Amblyomma triste by (c) Katja Schulz, some rights reserved (CC BY). Used under a CC-BY license.

Pronunciation

How to pronounce Amblyomma triste: /æmˈblaɪəmə ˈtrɪsteɪ/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Morphologically similar to Amblyomma maculatum and Amblyomma tigrinum, forming a cryptic . Accurate identification requires molecular analysis; the mitochondrial of A. triste shows 4.2% from A. maculatum. Specimens in North America were historically misidentified as A. maculatum due to this morphological convergence.

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Distribution

Native to South America: Venezuela, Argentina, Brazil, Colombia, Peru, and Uruguay. Documented in North America from Cochise and Santa Cruz Counties, Arizona, and Brewster and Jeff Davis Counties, Texas; also detected in import cattle from Mexican states of Coahuila, Durango, and Sonora.

Diet

Obligate blood-feeder on vertebrate . Larvae and nymphs feed on guinea pigs, chickens, rats, rabbits, wild mice, dogs, and capybaras. feed on dogs, capybaras, and rabbits. In natural settings, has been documented parasitizing marsh deer (Blastocerus dichotomus).

Host Associations

Cavia porcellus - Most suitable for larvae and nymphs in laboratory conditions
Gallus gallus - Secondary for stages
Hydrochaeris hydrochaeris - Most suitable for stage; produces more and heavier engorged females than other hosts
Canis familiaris - for and stages
Blastocerus dichotomus - Wild documented in Argentina; associated with Ehrlichia chaffeensis transmission cycle
Rattus norvegicus - Larval and nymphal
Oryctolagus cuniculus - Larval, nymphal, and
Calomys callosus - Wild mouse for stages

Life Cycle

Under laboratory conditions at 27°C and 90% relative humidity, the from to averages 155 days. Larval feeding period: 3.8–4.7 days; larval premolt period: 8.9–10.4 days. Nymphal feeding period: 4.2–6.2 days. Male nymph premolt period (15.4 days) is significantly longer than female nymph premolt period (14.7 days). Female nymphs are significantly heavier than male nymphs. Adult sex ratio is 0.9:1 (male:female).

Behavior

Exhibits questing typical of hard ticks, climbing vegetation and extending forelegs to encounter . Repeated of hosts induces acquired resistance; in guinea pigs, this manifests as reduced engorgement weight, prolonged feeding time, decreased nymph recovery rate, and marked cutaneous basophilia at bite sites.

Ecological Role

of zoonotic . Primary vector of parkeri in South America. Documented carrier of Ehrlichia chaffeensis in Argentina, with evidence of active in salivary glands indicating potential for transmission. Links wild mammal (marsh deer, small mammals) to human risk.

Human Relevance

Significant public health . Transmits parkeri, causing spotted fever group rickettsiosis. The sole responsible for human tick-borne in Uruguay; significant vector in Argentina and Brazil. Misidentification as A. maculatum in North America complicates surveillance and risk assessment. Laboratory studies show guinea pigs develop resistance after repeated exposure, with cutaneous basophilia playing a key role in this immune response.

Similar Taxa

Amblyomma maculatumCryptic with overlapping ; historically confused with A. triste in North America where specimens were misidentified for at least 67 years. of 4.2% in mitochondrial distinguishes them.
Amblyomma tigrinumThird member of the A. maculatum group; all three species are morphologically similar and share parkeri competence.