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New Neotropical records are presented for ticks belonging to the Ixodes auritulus Neumann, 1904, species group, together with a review of hosts and localities from which members of this complex have previously been collected. The range of the I. auritulus species group is now understood to include Colombia, and 15 bird species are listed as new hosts. From Guatemala to southern Argentina and Chile, specimens of the I. auritulus group have been found on birds belonging to the orders Ciconiiformes, Columbiformes, Falconiformes, Galliformes, Passeriformes, Piciformes, Procellariiformes and Tinamiformes. Passeriform birds are probably the principal hosts, sustaining tick populations throughout the Neotropics. Collection data have yielded four areas--southern South America (from 56 degrees S to 51 degrees S), southern Brazil (25 degrees S-22 degrees S), south-central Peru (14 degrees S-10 degrees S) and Central America (10 degrees N-15 degrees N)--where the I. auritulus group appears to commonly parasitize birds, but additional collections may show that the range of this complex is less discontinuous than currently perceived. Several morphological differences are described for ticks within and among these areas, but it is still unclear whether the I. auritulus group comprises more than one species.

Collections of Amblyomma auricularium (Conil 1878) and A. pseudoconcolor Aragão, 1908 are discussed in relation to distribution and hosts. Three tick collections (two from Argentina and a third from the USA) house a total of 574 A. auricularium (307 males, 162 females, 73 nymphs and 32 larvae) and 179 A. pseudoconcolor (96 males, 74 females, 4 nymphs and 5 larvae). Apart from an adult A. pseudoconcolor found on a bird, Nothura maculosa Temminck, 1815, all ticks were found on mammals. The great majority of specimens of both ticks species were removed from the family Dasypodidae Gray, 1821 (84.9% and 93.8% of A. auricularium and A. pseudoconcolor, respectively). Amblyomma auricularium has also been found on wild hosts of the families Myrmecophagidae and occasionally Didelphidae, Caviidae, Chinchillidae, Hydrochaeridae, Muridae, Canidae, Mustelidae, Procyonidae and domestic animals (cattle, dogs, horses), while A. pseudoconcolor has also been found occasionally on wild hosts of the family Didelphidae and on domestic animals (cattle, dogs). Amblyomma pseudoconcolor appears to be restricted to the Neotropical region, covering northern Argentina and the eastern region of South America from Uruguay to Surinam, including south-eastern Paraguay, eastern Brazil and French Guiana. Amblyomma auricularium is distributed from northern Patagonia in Argentina throughout the Neotropics into the Nearctic region up to the southern USA (Texas, Florida), with collection localities also in Belize, Bolivia, Brazil, Colombia, Costa Rica, French Guiana, Honduras, Mexico, Nicaragua, Panama, Paraguay, Trinidad & Tobago, Uruguay and Venezuela. It is not known whether A. auricularium is an established resident of the USA.