Ticks (Acari: Ixodidae) of the state of Amazonas,Brazil

The tick fauna of Brazil is currently composed by 72 species. The state of Amazonas is the largest of Brazil, with an area of ≈ 19% of the Brazilian land. Besides its vast geographic area, only 19 tick species have been reported for Amazonas. Herein, lots containing ticks from the state of Amazonas were examined in three major tick collections from Brazil. A total of 5933 tick specimens were examined and recorded, comprising 2693 males, 1247 females, 1509 nymphs, and 484 larvae. These ticks were identified into the following 22 species: Amblyomma cajennense sensu lato, Amblyomma calcaratum, Amblyomma coelebs, Amblyomma dissimile, Amblyomma dubitatum, Amblyomma geayi, Amblyomma goeldii, Amblyomma humerale, Amblyomma latepunctatun, Amblyomma longirostre, Amblyomma naponense, Amblyomma oblongoguttatum, Amblyomma ovale, Amblyomma rotundatum, Amblyomma scalpturatum, Amblyomma varium, Dermacentor nitens, Haemaphysalis juxtakochi, Ixodes cf. Ixodes fuscipes, Ixodes luciae, Rhipicephalus microplus, Rhipicephalus sanguineus sensu lato. Ticks were collected from 17 (27.4%) out of the 62 municipalities that currently compose the state of Amazonas. The following four species are reported for the first time in the state of Amazonas: A. coelebs, A. dubitatum, H. juxtakochi, and Ixodes cf. I. fuscipes. The only tick species previously reported for Amazonas and not found in the present study is Amblyomma parvum. This study provides a great expansion of geographical and host records of ticks for the state of Amazonas, which is now considered to have a tick fauna composed by 23 species. It is noteworthy that we report 1391 Amblyomma nymphs that were identified to 13 different species.     

Redescription of Amblyomma fuscum Neumann, 1907 (Acari: Ixodidae), a rare South America tick confirmed in Brazil

The species Amblyomma fuscum Neumann, 1907 is a rare tick found on the Neotropical Region, but it has not been recorded as a valid taxon in some lists proposed by current taxonomists. After a comparison between the Brazilian material of A. fuscum deposited in the Acari Collection of the Butantan Institute, São Paulo, Brazil, and the male type deposited in Leiden Museum of Natural History, The Netherlands, we confirm the taxonomic validity of A. fuscum and redescribe the adult specimens based on light and scanning electron microscope studies.     

Anteroposterior gradient during nymphal-adult moulting cycle of the tropical bont tick,Amblyomma variegatum (Acarina: Ixodidae)

Summary The structure of the extensible (alloscutum) and inextensible (scutum) integument of the nymph, Amblyomma variegatum was examined during the whole bloodmeal and the nymphal-adult moulting cycle. Integumental events were tentatively correlated with the ecdysteroid levels measured by radioimmunoassay. We observed that all the integumental events were realised along an anteroposterior gradient. During the 5 days corresponding to the bloodmeal, although the hormone concentration was low, a new endocuticle was deposited on both the alloscutum and scutum. Furthermore, mitoses were initiated in the capitulum. On days 1–2 after the meal, ecdysteroid titres began to increase and reached a first peak corresponding to 4.1 ng 20-hydroxyecdysone equivalents/tick on the 4th day after the ticks dropped off their host. At this time the epidermis of the capitulum was detached and the outline of the adult capitulum was already visible. Mitotic activity in the alloscutum was initiated. On day 6 post-drop, the frontal apolysis was achieved and the ecdysteroid titres declined to basal values. A second peak much higher than the first one (maximum value of 33.7 ng/tick) and identified principally as 20-hydroxyecdysone by HPLC/RIA was noted on the 13th day post-drop. During the period of increase in the ecdysteroid levels (days 9–10 post-drop), the mitotic phase ended in the alloscutum and the apolysis began. Epicuticle was deposited after day 12 postdrop. Then, while the titre fell to low values (about 1.6 ng/tick, days 16–20 post-drop), the exocuticle was deposited and the nymphal cuticle was digested. All adult structures were functional 3 days before ecdysis. In young male as in female adults the mean value of the ecdysteroid levels corresponded to about 2.5 ng/tick. Finally, hydrolysis of tick whole extracts with esterase demonstrated a low increase of RIA-positive material, demonstrating the probable presence of natural ecdysteroid fatty-acid conjugates in this species.     

Optimal sampling and spatial distribution of Ixodes pacificus, Dermacentor occidentalis and Dermacentor variabilis ticks (Acari: Ixodidae)

A common method for sampling tick populations is flagging, which is a method of dragging a white cloth over a plant substrate for a fixed distance along a transect. Flagging over rough physical surfaces or using long subtransect lengths could lead to the underestimation of tick densities. Using estimates of the drop-off rates of adult Ixodes pacificus in flag sampling, optimal sampling schemes (the length and number of subtransects) were examined using the relationships between the tick drop-off rates (c), the tick density and distribution patterns and the roughness of the sampled plant substrate. It was found that the optimal number of subtransects and Lmax, the longest subtransect length which did not significantly underestimate the tick density from c, were affected by the tick density, substrate roughness and tick distribution pattern. This study also showed that the density and distribution of I. pacificus and Dermacentor occidentalis varied greatly over time in the populations sampled, while the Dermacentor variabilis densities were low and showed no significant changes over time. Both I. pacificus and D. occidentalis had clumped distributions along trails and these clumps were aggregated. However, the clump sizes (or individual clump areas) changed significantly over time because of density fluctuation or the movement of ticks. Finally, a positive association between the number of I. pacificus and D. occidentalis adults was observed from 2 m subtransect flag collections in March 1995; no relationship was found in 1994. © Rapid Science Ltd. 1998     

Ticks (Acari: Ixodidae) parasitizing humans in an Atlantic rainforest reserve of Southeastern Brazil with notes on host suitability

While conducting projects on ticks from deer and on tick ecology in animal trails in an Atlantic rainforest reserve in Southeastern Brazil, researchers of our group were bitten by ticks several times. Some of these episodes were recorded. Three species of adult ticks attached to humans: Amblyomma brasiliense Aragão, Amblyomma incisum Neumann, and Amblyomma ovale Koch. Eight nymphal attachments with engorgement on humans were recorded. From these, six molted to adults of A. incisum, one to an adult of A. brasiliense, and one had an anomalous molting, therefore the adult tick could not be properly identified. Local reactions to tick attachment varied among individual hosts from almost imperceptible to intense. Especially itching, but hyperemia and swelling as well, were prominent features of the reaction. Overall it can be affirmed that human beings can be a physiologically suitable host species for ticks in the Atlantic rainforest and that itching was an important if not the major component of the resistance to tick bite.     

Natural and experimental infection of the lizard Ameiva ameiva with Hemolivia stellata (Adeleina: Haemogregarinidae) of the toad Bufo marinus

Developmental stages of a haemogregarine in erythrocytes of the lizard Ameiva ameiva (Teiidae), from Pará State, north Brazil, were shown to be those of Hemolivia by the nature of the parasite's sporogonic cycle in the tick Amblyomma rotondatum. The type species, Hemolivia stellata Petit et al., 1990 was described in the giant toad Bufo marinus and the tick Amblyomma rotondatum, also from Pará State, and in view of the fact that A. ameiva and Bufo marinus share the same habitat and are both commonly infested by A. rotondatum, the possibility that the parasite of A. ameiva is H. stellata had to be considered. Uninfected lizards fed with material from infected ticks taken from B. marinus, and others fed with liver of toads containing tissue-cysts of H. stellata, were shown to subsequently develop typical Hemolivia infections, with all stages of the development similar to those seen in the naturally infected lizards. Conversely, a juvenile, uninfected toad became infected when fed with sporocysts of Hemolivia in a macerated tick that had fed on an infected A. ameiva and pieces of liver containing tissuecysts from the same lizard. The remarkable lack of host specificity shown by H. stellata, in hosts so widely separated as an amphibian and a reptile, is discussed.     

Redescription of Dekeyseria picta (Siluriformes; Loricariidae), a poorly known ancistrin from the Amazon and Orinoco Basins

A re‐evaluation of Dekeyseria brachyura and D. pulchra found them to be junior synonyms of D. picta, the oldest species among these congeners, based on continuous intraspecific variation in morphometrics and colour pattern. Examination of material deposited at Brazilian and Venezuelan collections, including the original type specimens of Ancistrus brachyurus and A. pictus, plus samples recently collected in the Rio Negro, Amazonas, Brazil, allowed re‐evaluation of the taxonomic status of D. picta and provides additional information on its distribution, habitats and reproductive strategies.     

Biology and life cycle of <Emphasis Type="Italic">Amblyomma incisum</Emphasis> (Acari: Ixodidae)

Amblyomma incisum Neumann is a major tick species in the Atlantic Forest of Brazil. Tapir is the main host for adult ticks and a high aggressiveness of nymphs to humans has been reported. In this work data on the biology and life cycle of this tick species is presented for the first time. It was shown that horse is a suitable host for A. incisum adults and rabbit for larvae and nymphs. It was also shown that A. incisum is a big tick species (mean engorged female weight of 1.96 g) with a long life cycle which lasts 262.3 days when maintained at 27°C and 85% RH. These laboratory conditions were, however, inappropriate and egg hatching rate (1.2%) was very low. Nevertheless egg hatching of ticks in a forest patch increased considerably (72.2%) indicating that this A. incisum population is highly dependent on a forest-like environment.     

Distribution, host range, and climatic constraints on Centistes gasseni (Hymenoptera: Braconidae), a South American parasitoid of cucumber beetles, Diabrotica spp. (Coleoptera: Chrysomelidae)

The genus Diabrotica includes a large number of pest species, including some of the most important crop pests of the Americas. The parasitoid Centistes gasseni Shaw is the first braconid to be described parasitizing Diabrotica in South America, and high natural infestations are reported. Field and experimental observations on the host range, distribution and biology of this parasitoid are described. Centistes gasseniwas collected in southern Brazil, eastern Paraguay and northeastern Argentina, in a region comprising humid lowlands and highlands, and cool temperate to warm subtropical climates, with regular rainfall in excess of 1300 mm. Three Diabroticaspecies, D. limitata (Sahlberg), D. speciosa (Germar) and D. viridula (Fabricius) were found to host the parasitoid, with mean percent parasitism of 5.4, 2.0 and 1.0%, respectively. Diabrotica speciosa and D. viridula are the two most important pest Diabroticaspecies in South America. Laboratory experiments with field-collected beetles and parasitoid cocoons indicated that C. gasseni overwinters in adult host beetles, remaining dormant in its live host below developmental temperatures. A potential distribution of C. gasseni in North America is proposed based on its known climatic range and the distribution of the main pest species of adult overwintering North American Diabrotica.     

The Distribution and Ecological Preferences of Boophilus microplus (Acari: Ixodidae) in Mexico

This paper focuses on the distribution of the cattle tick, Boophilus microplus, in Mexico. The study is aimed to understand the climate factors responsible of the recorded distribution that can statistically define the suitable habitat for the tick. Sites where the tick is recorded display significantly higher values of some climate variables in comparison with those where the tick is absent, namely mean monthly temperature (T) and atmospheric water vapour (W), yearly accumulated T, W and rainfall (R) (p < 0.001 for every variable), with smaller significance for the yearly sum of T/R and T/W ratios (p < 0.05). Interestingly, variables involving the Normalized Derived Vegetation Index (NDVI) do not shown statistical differences between the sites where the tick is present or absent. The best set of habitat-defining variables was integrated into a framework to assess the habitat suitability for the tick in Mexico. We used a point-to-point similarity metric to assign a classification value to a candidate site based on the proximity in environmental space of the most similar record site. A combination of 7 yearly and monthly values for temperature, rainfall and water vapour variables captured the tick distribution. Model performance, as tested with a separate set of distribution tests and defined by the AUC value, was 0.89. Causes of errors as detected with a visual comparison of both known and predicted distribution of the tick may be attributed to the use of a medium resolution, unable to capture locally important features of tick distribution, and to incomplete collections in some parts of the country.     

Capybaras and ticks in the urban areas of Uberlândia,Minas Gerais,Brazil: ecological aspects for the epidemiology of tick-borne diseases

In Brazil capybara, the biggest existing rodent species, and associated tick species, Amblyomma cajennense and Amblyomma dubitatum, are undergoing an unplanned host and parasite population expansion in both urban and rural areas. However, scientific information about such issue, particularly in urban areas, is scanty. Such rodent and ticks are associated in some municipalities, particularly in southeastern Brazil, with the transmission of the highly lethal Rickettsia rickettsia caused spotted-fever. In this study ecological aspects related to the establishment and expansion of capybaras and ticks in urban areas of Uberlandia, Minas Gerais State, Brazil were evaluated. For this purpose, capybara and tick abundance in four urban areas and an ecological reserve was determined. Abundance of capybaras varied between areas and over the sampling period and these differences were related to human activities. A positive correlation was found between capybara and tick abundance, however, the tick species had an uneven distribution within the municipality and environmental factors rather than host availability were blamed for such. On the whole these observations show that capybara populations in urban areas are associated to high environmental infestation of ticks and the increased risk of bites and of pathogen transmission to humans. At the same time the uneven distribution of tick species might implicate in an unequal risk of tick-borne diseases within the same urban area.