The natural hosts for larvae and nymphs of Amblyomma neumanni and Amblyomma parvum (Acari: Ixodidae)

Based on the hypothesis that birds and rodents are important hosts for subadults of the Neotropical Amblyomma neumanni and Amblyomma parvum ticks, a survey of these type of hosts was carried out from July 2004 to March 2006, in Quilino (A. parvum) and Dean Funes (A. neumanni), Córdoba province, Argentina. Additionally, monthly tick counts were performed on cattle and goats with occasional tick search in other domestic hosts. Records of questing height of subadult ticks on vegetation were also carried out monthly. Rodents (n = 123) and birds (n = 122) captured in Dean Funes showed no infestation with A. neumanni. Apart of few nymphs found on horses, all larvae and nymphs of A. neumanni were on cattle with a larval prevalence and mean number of 22.2%, and 7.7 ± 22.52, respectively, and a prevalence of nymphs of 47.8% with a mean of 7.9 ± 18.49. The average questing height of larvae and nymphs of A. neumanni was 23.5 ± 17.1 cm and 30.7 ± 26.7 cm, respectively. A total of 138 rodents and 130 birds were captured in Quilino but the Caviidae rodent Galea musteloides carried 99.3% of larvae and 99.8% of nymphs of A. parvum, and no immature stages were detected on cattle, goat or vegetation. Tick counts on G. musteloides (n = 74) showed a prevalence of 42% and a mean number of 9.9 ± 24.83 for larvae, while nymphal infestation had a prevalence of 56.5% and a mean of 8.7 ± 11.31. Cattle appear to be suitable hosts to sustain the complete cycle of A. neumanni in nature (adult ticks infest cattle too) and questing height of subadults indicates that they are expecting to feed on medium and large-sized mammals, such as cattle and other ungulates. At least in the study site, G. musteloides is the principal host for the survival strategy of A. parvum subadults; adult ticks are common on cattle and goats. These hosts are introduced in the Neotropics but A. neumanni was able to develop a surrogate cycle independent of native hosts while A. parvum still depends on probably primeval hosts to sustain their larvae and nymphs.     

Biology of Amblyomma aureolatum (Pallas, 1772) (Acari: Ixodidae) on some laboratory hosts in Brazil

The ixodid Amblyomma aureolatum is suspected to play a role in the epidemiology of wild life-cycle hemoparasites, which frequently infect dogs in rural and hunting areas in Brazil. Little is known about its bionomics. The objective of the present study was to evaluate some bionomic aspects of A. aureolatum ticks in Brazil. One engorged female, collected from a dog (Canis familiaris) in S?o Sebasti?o das Aguas Claras, State of Minas Gerais, was used to establish a colony in the laboratory. Subsequently its parasitic stage progeny were fed on domestic dogs and laboratory animals. The free-living stages were incubated at 27 degrees C +/- 2 degrees C and minimum 70% relative humidity in a BOD incubator. The egg incubation period ranged from 31 to 34 days; the parasitic period of larvae ranged from 4 to 6 days and ecdysis to nymphs occurred from day 19 up to day 22. The parasitic period of nymphs ranged from 5 to 8 days and the period of ecdysis to adults from 31 to 33 days. The parasitic period of adults ranged from 11 to 15 days, the pre-oviposition period from 6 to 12 days, and the oviposition period from 9 to 38 days. The total duration of the life cycle ranged from 116 to 168 days.     

The life cycle of Amblyomma pseudoparvum (Acari: Ixodidae) in the laboratory

A colony of Amblyomma pseudoparvum was started with male and female ticks collected from the cavy-like rodent Dolichotis salinicola, in the Province of Salta, Argentina. These ticks and their progenies were fed on rabbits and the non-parasitic stages maintained in darkness at 27±1°C, 83–86% RH. The life cycle (pre-feeding and oviposition periods not tested) of A. pseudoparvum had a mean duration of 90.9 days. The mean time (days) for the different periods of the cycle were as follows: Feeding of females, 12.3; pre-oviposition, 5.1; minimum egg incubation, 33.4; feeding of larvae, 5.6; pre-moult to nymphs, 11.5; feeding of nymphs, 6.9; pre-moult to adults, 16.1. The mean recovery rates of larvae, nymphs and females were 16.0%, 18.7% and 53.0%, respectively.     

Hyperparasitism in Amblyomma rotundatum (Acari: Ixodidae)

In the present study, we report a case of hyperparasitism in Amblyomma rotundatum. During examination of live ticks immediately after collecting them from Boa constrictor snakes held in a reptile facility in Mossoró, RN, northeastern Brazil, 1 unengorged tick female was seen attached to the venter of a partially engorged female. The hypostome and chelicerae of the unengorged female had penetrated the integument of the partially engorged female to the level of the basis capitulli and the palps were splayed outward. To our knowledge, we present the second report of hyperparasitism for the genus Amblyomma.     

Wild birds as hosts of Amblyomma cajennense (Fabricius, 1787) (Acari: Ixodidae).

We evaluated the prevalence, mean intensity and relative density of ticks in 467 wild birds of 67 species (12 families) from forest and cerrado habitats at two protected areas of Minas Gerais, between March and September 1997. Ticks collected (n=177) were identified as larvae and nymphs of Amblyomma cajennense and four other species of Amblyomma. We report for the first time 28 bird species as hosts of the immature stages of A. cajennense, demonstrating the lack of host specificity of the larvae and nymphs. A. cajennense had 15% prevalence on birds, with a mean infestation intensity of 0.37 ticks per host sampled, and 2.5 ticks per infested bird. Prevalence varied in relation to host species, diet and between birds from forests at two successional stages. There were no differences in relation to host forest dependence, participation in mixed flocks of birds, and nest type constructed. A. cajennense is a species of medical and veterinary importance, occurring on domestic animals but is known little of its occurrence on wildlife.     

Life cycle of Amblyomma cooperi (Acari: Ixodidae) using capybaras (Hydrochaeris hydrochaeris) as hosts

The life cycle of Amblyomma cooperi was evaluated under laboratory conditions testing different host species. Larval infestations were performed on chickens (Gallus gallus) and capybaras (Hydrochaeris hydrochaeris). Nymphal infestations were performed on G. gallus, H. hydrochaeris, guinea pigs (Cavia porcellus) and wild mice (Calomys callosus). Infestations by adult ticks were performed only on capybaras. All free-living stages were observed in darkness at 27 degrees C and RH 85%. Capybaras were significantly (p < 0.05) the most suitable hosts for immature ticks, with the highest larval (63.6%) and nymphal (48%) recovery. Larval and nymphal feeding and premolt periods were significantly different (p < 0.05) between ticks fed on different host species. Male nymphs showed premolt period significantly shorter (p < 0.05) than female nymphs. The overall sex ratio of adult ticks was 0.92:1 (M:F). Infestations by adult ticks on capybaras yielded more than 76% of engorged female recovery. Only three out of 33 engorged females fed on capybaras did not lay fertile eggs. The life cycle of A. cooperi in laboratory, reported for the first time, was completed in an average period of 189.4 days. During the premolt period, all A. cooperi engorged nymphs secreted distinct blackish drops, which seem to be inherent to this species. Our results, associated data in the literature, confirm the high suitability of capybaras for the adult stage of A. cooperi and also indicate this animal species as a primary host for immature stages of A. cooperi in nature. On the other hand, the results of larval and nymphal infestation on chickens and guinea pigs suggest that birds and wild guinea pigs, which are also present in the distribution area of A. cooperi in South America, could be potentially infested by A. cooperi immature stages in nature.     

Life-cycle and host specificity of Amblyomma tigrinum (Acari: Ixodidae) under laboratory conditions

Biological data of three generations of Amblyomma tigrinum in the laboratory are reported and the suitability of different host species for immature ticks are compared. Grouping the three generations, infestations by both the larval and nymphal stages were performed on chickens (Gallus gallus), wistar rats (Rattus norvegicus), rabbits (Oryctolagus cuniculus),wild mice (Calomys callosus), dogs (Canis familiaris) and opossums (Didelphis albiventris). Only dogs were used for infestations by adult ticks. Tick developmental periods were observed in an incubator at 27°C and RH 90%. The proportion of engorged larvae recovered from chickens (21.7% of the exposed larvae) was significantly larger (p<0.001) than those from the five mammal species used in the infestations (maximum of 3.1%). A significant larger (p<0.01) proportion of engorged larvae successfully molted after being fed on chickens than on mammal hosts. The proportion of engorged nymphs recovered from chickens (28.8% of the exposed nymphs) was significantly larger (p<0.001) than those from mammal hosts (range: 0–2.1%). Larvae showed similar feeding periods on exposure to different host species, except for those larvae fed on C. callosus, which showed significantly longer (p<0.001) feeding periods. Engorged larvae detachment peaked on the 5^th feeding day, followed by the 6^th day, on all hosts except for C. callosus. Larval premolt periods were similar for engorged ticks exposed to different host species, except for larvae fed on dogs, which showed significantly longer (p<0.001) premolt periods. Host detachment of engorged nymphs peaked on the 6^th feeding day on chickens. Although nymphal detachment on rats peaked on the 8^th day, only 15 nymphs were recovered from this host species. In a sample of 144 F₃ nymphs fed on chickens no significant difference (p>0.10) was found between the feeding or premolt periods of 82 males and 62 females, but female nymphs were significantly heavier (p<0.005) than male nymphs. Sixteen engorged females (61.5% of the exposed ticks) were recovered after being fed on dogs, and all these females laid viable eggs. Chickens, the only avian host, were the most suitable host when compared with the five mammal species. Dogs were demonstrated to be a suitable host for adults of A. tigrinum, which is consistent with, several reports of adult A. tigrinum ticks parasitizing dogs in different areas of South America. Our results reinforce that in these same areas avian species are the major hosts for immature stages of this tick species. This revised version was published online in July 2006 with corrections to the Cover Date.     

The life cycle of Amblyomma neumanni Ribaga, 1902 (Acari: Ixodidae) in the laboratory

A colony of Amblyomma neumanni was started with engorged females collected from cattle in the province of Salta (24° 51S, 65° 33W), Argentina. The larvae and nymphs were fed on rabbits and the adults on calves. The non-parasitic stages were maintained in darkness at 27 ± 1°C and 83–86% RH. The life cycle (pre-feeding period not tested) had a mean duration of 205.7 days. The mean time (days) for the different phases of the cycle were as follows: feeding of females 8.8, pre-oviposition 23.8, oviposition 41.4, minimum egg incubation 76.1, feeding of larvae 8.5, pre-moult to nymphs 16.4, feeding of nymphs 7.9 and pre-moult to adults 22.8. The mean recovery rates of larvae, nymphs and females were 83.8, 85.6 and 89.3%, respectively. The nymphs moulting to females were heavier (8.1 ± 2.34 mg) than those moulting to males (6.0 ± 2.34 mg; p < 0.01), but their range of engorgement weight showed overlap (2.3–16.2 versus 2.2–12.8 mg, respectively). Two gynandromorphs were detected between the nymphs. A comparison of biological parameters of A. neumanni with other American Amblyomma species from mammals is presented. © Rapid Science Ltd. 1998     

Morphogenetic diapause in Amblyomma variegatum (Acari: Ixodidae)

In southern Africa, Amblyomma variegatum Fabricius is characterized by a strict seasonal activity. Experiments were carried out to determine whether a diapause mechanism regulates this seasonality. Engorged A.variegatum females were exposed to controlled laboratory conditions or natural field conditions at different times of the year. Females exposed in a natural environment in September-October (short day) had significantly longer pre-oviposition periods than females exposed from November to March. The season in which the previous instar fed had no apparent effect on the engorgement or pre-oviposition periods of the females. Furthermore, artificial changes in photoperiod during and after female engorgement had no significant effects on pre-oviposition periods. It is tentatively concluded that the unfed female is the responsive stage to photoperiodic changes which induce diapause. Diapause could be terminated and oviposition induced by exposing females to a short period of chilling (18 degrees C for 48 h). It is concluded that a morphogenetic diapause mechanism exists in A.variegatum, which is probably induced by short day responses and terminated following rainfall and a concomitant decrease in soil temperature. The diapause, which occurs in females which fed early in the season, causes a delay in oviposition and therefore effectively synchronizes the life-cycle to ensure that eggs and larvae occur at a climatically favourable period.     

Amblyomma triste (Koch, 1844) (Acari: Ixodidae): morphological description of the ovary and of vitellogenesis

The present study presents the morphology, histology, and the dynamics of vitellogenesis in females of the tick Amblyomma triste. The ovary in this species is of the panoistic type, therefore it lacks nurse cells. It is composed of a layer of epithelial cells that outwardly form the wall of the ovary, but also originate the pedicel, the structure that attaches the oocytes to its external margin, as well the oocytes themselves. In Amblyomma triste, the oocytes develop in four synchronic stages, which differs from the process in other tick species. The classification of the stages of the oocytes was carried out based on the presence of four morphologic characteristics: cytoplasm appearance; site of the germ vesicle; presence, quantity, and constitution of the yolk granules and presence of chorium.     

Life cycle and host specificity of Amblyomma triste (Acari: Ixodidae) under laboratory conditions

We report biological data of two generations of Amblyomma triste in laboratory and compared the suitability of different host species. Infestations by larval and nymphal stages were performed on guinea pigs (Cavia porcellus), chickens (Gallus gallus), rats (Rattus norvegicus), rabbits (Oryctolagus cuniculus), wild mice (Calomys callosus), dogs (Canis familiaris) and capybaras (Hydrochaeris hydrochaeris). Infestations by adult ticks were performed on dogs, capybaras and rabbits. Tick developmental periods were observed in an incubator at 27 degrees C and RH 90%. Guinea pigs were the most suitable hosts for larvae and nymphs, followed by chickens. The remaining host species were less suitable for immature ticks as fewer engorged ticks were recovered from them. Mean larval feeding periods varied from 3.8 to 4.7 d between different host species. Mean larval premolt periods ranged from 8.9 to 10.4 d. Nymphal mean feeding periods varied from 4.2 to 6.2 d for ticks fed on different host species. Premolt period of male nymphs (mean: 15.4 d) was significantly longer than that of female nymphs (14.7 d). Female nymphs were significantly heavier than male nymphs. The overall sex ratio of the adult ticks emerged from nymphs was 0.9:1 (M:F). Capybaras were the most suitable host for the tick adult stage as significantly more engorged females were recovered from them and these females were significantly heavier than those recovered from dogs or rabbits. The life cycle of A. triste in laboratory could be completed in an average period of 155 d. The potential role of guinea pigs, birds and capybaras, as hosts for A. triste in nature, is discussed.     

Lack of parthenogenesis by Amblyomma cajennense (Acari: Ixodidae)

Some reproductive parameters of adult stages of Amblyomma cajennense ticks were studied. The capacity of virgin females to reproduce by parthenogenesis was evaluated, during an experimental infestation, in absence of males, on a horse (Equus cabalus). Ticks were spread either completely free or in limited sites on the body of the animal. The engorged virgin females showed longer feeding periods and lighter body weights than those that had been fertilized. Some of these unmated females produced smaller egg masses, which had no embryonary development. On the other hand, females that had been inseminated produced larger egg masses, with normal embryonary development that led to viable larvae. Under the studied conditions, A. cajennense females did not reproduce by parthenogenesis.     

Identification of two genes essential for sperm development in the male tick Amblyomma hebraeum Koch (Acari: Ixodidae)

In most ticks of the family Ixodidae, gonad maturation and spermatogenesis are stimulated by the taking of a blood meal. Previous work from this laboratory identified 35 genes that are up-regulated by feeding [Weiss, B.L., Stepczynski, J.M., Wong, P., Kaufman, W.R., 2002. Identification and characterization of genes differentially expressed in the testis/vas deferens of the fed male tick, Amblyomma hebraeum. Insect Biochemistry and Molecular Biology 32, 785-793]. The functions of most of these genes remain unknown. We used RNA interference technology to investigate the consequences of blocking the function of 13 of these genes. Attenuation of the expression of two of these in particular, AhT/VD 8 and AhT/VD 10, correlated with deformities in the testis and abnormalities in spermiogenesis. Furthermore, most females fed in the company of these males did not engorge properly and laid many fewer eggs, most of which were infertile.     

Gynandromorphism in Amblyomma cajennense and Rhipicephalus sanguineus (Acari: Ixodidae)

During a survey of ticks on horses in November 2000, at the University of S?o Paulo farm in Pirassununga county, S?o Paulo, Brazil, 1 gynandromorph of Amblyomma cajennense was collected from a naturally infested horse. In another survey on dogs in March 2001, in the urban area of Monte Negro, Rond?nia, Brazil, a gynandromorph of Rhipicephalus sanguineus was collected from a naturally infested dog. Both specimens are described and classified as perfect bipartite protogynanders.     

Brazilian distribution of Amblyomma varium Koch, 1844 (Acari: Ixodidae), a common parasite of sloths (Mammalia: Xenarthra)

Amblyomma varium, commonly known in Brazil as the "carrapato-gigante-da-pregui a" (sloth's giant tick) is found from southern Central America to Argentina. The present study adds information on the geographical distribution of A. varium, as well as on their hosts, based on material deposited in the main Brazilian collections and on the available literature. Eighty-two vials, containing 191 adult specimens, deposited in five Acari collections between 1930 and 2001, were examined. These vials included data on the host and collection localities. The biology of A. varium is unknown. However it is known that, during the adult stage, the tick presents a high host specificity and is found almost exclusively on the sloths Bradypus tridactylus, B. variegatus, B.torquatus (Bradypodidae), Choloepus hoffmanni and C. didactylus (Megalonychidae). Based on the material examined, the states of Rond nia, Amazonas, Bahia and Alagoas are newly assigned to geographic distribution of A. varium in Brazil.     

Study of the life cycle of Amblyomma dubitatum (Acari: Ixodidae) based on field and laboratory data

The life cycle of Amblyomma dubitatum was described based on the seasonal distribution of all parasitic stages and the development periods of engorged ticks under different conditions of photoperiod and temperature. All stages were found active along the entire year in the study area. Larvae peaked from May to July, nymphs peaked from July to October, and females peaked from November to March. This pattern represents a life cycle with one generation per year with most of the ticks reaching adulthood during the warmest months. The analysis of the effect of the photoperiod on the development of A. dubitatum showed no indication of morphogenetic diapause. Exposure of ticks to field conditions indicates a delay in metamorphosis of immature stages, in the oviposition of females and in the incubation of eggs, which were associated with low winter temperatures. The results indicate that though A. dubitatum has a one year life cycle, more than one cohort can co-exist within the same population in a certain interval of time. Finally, the potential role of small rodents as hosts for larvae and nymphs of A. dubitatum is confirmed.