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Many argasid tick species are known only through their larval descriptions, in which the chaetotaxy, together with other external morphological characteristics, has been used to separate genera and species. However, the illustrations of these features are based on optical microscopy alone and many of these features are not clearly defined. Because of the difficulties in determining the larval and nymph stages of some genera, we have prepared illustrated keys for the immature stages of argasids, including an up-to-date list of the known species of the Neotropical region. We have also included an illustrated key for larvae of the Ornithodoros species from Brazil, based on scanning electron microscopy.Keywords: Argasidae, Ornithodoros, immature, identification, key, Brazil. ResumoMuitos carrapatos argasídeos são conhecidos somente por descrições larvais, nas quais a quetotaxia associada a outros caracteres morfológicos tem sido usada para separar gêneros e espécies. No entanto, as ilustrações sobre esses caracteres são baseadas somente em microscopia óptica e muitos deles não estão claramente definidos. Devido às dificuldades em determinar estágios larvais e ninfais de alguns gêneros, elaboramos chaves ilustradas para os estágios imaturos de argasídeos, incluindo uma lista atualizada de espécies conhecidas da região Neotropical. Incluímos também uma chave ilustrada para larvas das espécies de Ornithodoros do Brasil baseada em microscopia eletrônica de varredura.

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The tick Ixodes luciae occurs in many countries within the Neotropical region but only adult ticks have been morphologically described. Larvae and nymphs parasitize marsupials and rodents while adults are common on marsupials. A colony of I. luciae was obtained from females collected on marsupials from the State of Rondônia, Northern Brazil. After being fed on rabbits, the specimens were maintained under controlled conditions of temperature and humidity. Unfed larvae, nymphs, males and females of the first generation were cleaned and prepared for both optical and scanning electron microscopy. Ixodes luciae is closely related to Ixodes loricatus, Ixodes schulzei, and Ixodes amarali, although each species has its own array of distinctive characters. The larva of I. luciae differs from those of both I. schulzei and I. amarali in the length of the capitulum and from I. schulzei in the number of posthalleral setae in the Haller’s organ. Nymphs differ from I. amarali, I. loricatus and I. schulzei by the length of the external spur on coxae I, and from I. schulzei and I. amarali in having slender and shorter capitulum and hypostome. Males and females of I. luciae differ from the other three species by the length of the external spur on coxae I and by the scutal punctations, which are much longer and larger, respectively, in I. luciae. However, except for a few features, the chaetotaxy is the same for larvae of the four species, not only on the idiosoma (e.g. scutum with four pairs of setae), palpi and tarsus I, but also the number of porose setae within the capsule of Haller’s organ and the prehalleral setae.

The species Ixodes aragaoi Fonseca was described as Ixodes ricinus aragaoi, and later placed in synonymy with Ixodes affinis. However, this synonymy was rejected and the subspecies was elevated to species, and named as I. aragaoi. Some researchers did not consider the validity of I. aragaoi and maintained the synonymy proposed until 1998 when I. aragaoi was revalidated, and it was suggested that Ixodes pararicinus could be a synonym. The aim of this study was to confirm the taxonomic validity of I. aragaoi by means of redescription of adults and molecular analysis. Morphological studies were performed by optical and scanning electron microscopy; types of I. aragaoi were compared with those of I. pararicinus from Argentina, and also with material of I. pararicinus from Uruguay and I. affinis from the United States. Mitochondrial 16S rDNA sequences were obtained for determining phylogenetic relationships based on maximum parsimony. Morphological and molecular differences between I. aragaoi, I. pararicinus from Argentina, and I. affinis confirm the validity of the first each of these species. The morphological similarities of I. pararicinus from Uruguay with I. aragaoi, and the small distance of nucleotide sequences between them, confirm that the Uruguayan ticks are in fact I. aragaoi and expand the geographical distribution of this species. Based on the specimens of Ixodes examined in the present study, from the same locality of the types of I. ricinus rochensis in Uruguay, we agree with the synonymy of this subspecies with I. aragaoi as previously reported. Finally, our analyses indicate that both I. aragaoi and Ixodes fuscipes, another South American tick species, belong to the I. ricinus complex, currently composed of 19 species.

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Ornithodoros brasiliensis is an endemic tick from Brazil and is very aggressive to humans, resulting in pain, fever andintense inflammatory response. After more than 50 years without report, this species was recently found in rural areas ofSão Francisco de Paula municipality, State of Rio Grande do Sul, southern Brazil, from where it was originally described.Herein, we describe the larva and redescribe the adults of O. brasiliensis based on scanning electron microscopy. Sincethe type was lost we designate the neotype specimen under the number IBSP 10409. In addition, the relationship betweenO. brasiliensis and other species from the Neotropical region that share the morphological characteristics of Ornithodoroswith dorsal humps on tarsi, and also live under the soil and feed on hosts other than bats, are discussed. Molecular analysisinferred from a portion of the 16S rRNA mitochondrial gene is also provided and it placed O. brasiliensis in a cluster sup-ported by a maximal bootstrap value (100%) with Ornithodoros parkeri, Ornithodoros rostratus, and Ornithodoros turicata.