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.     

Studies on the ecology of Amblyomma marmoreum Koch 1844 (Acarnia: Ixodidae).

In the Eastern Cape Province of South Africa, larvae and nymphs of Ablyomma marmoreum Koch occur in habitats in which there is tree cover and herbaceous ground cover. Immatures of A. marmoreum are parasitic on reptiles, birds, and mammals. Adults occur only on reptiles. The major host for all stages is the moutain tortoise (Geochelone pardalis), and in the home areas of tortoises the density of ticks is high. Larvae are active in late summer and autumn. The rate of feeding is temperature-dependent, and some larvae which attach on tortoises in late autumn do not complete feeding until the following spring. Nymphs which occur in the home area of a tortoise become active in response to CO2 in early spring. Adults, and nymphs which occur outside the home area of a tortoise, become active in summer in response to rising temperatures. In nymphs which feed in spring, and hence develop into adults in midsummer, the life cycle is completed in 1 year. In nymphs which fed in midsummer, the life cycle is completed in 2 years.     

Description of a new species of Dermacentor Koch, 1844 (Acari: Ixodidae) from Laos and Thailand

Systematic Parasitology - Dermacentor laothaiensis n. sp. (Acari: Ixodidae) is described based on adults ex wild boar and vegetation from Laos and Thailand. Adults of D. laothaiensis n. sp. are...     

Ultrastructural detection of proteins, lipids and carbohydrates in oocytes of Amblyomma triste (Koch, 1844) (Acari; Ixodidae) during the vitellogenesis process

The ovary of the tick Amblyomma triste is classified as panoistic, which is characterized by the presence of oogonia without nurse and follicular cells. The present study has demonstrated that the oocytes in all developmental stages (I-IV) are attached to the ovary through a pedicel, a cellular structure that synthesizes and provides carbohydrate, lipids and proteins supplies for the oocytes during the vitellogenesis process. The lipids are deposited during all oocyte stages; they are freely distributed as observed in stages II, III and IV or they form complexes with other elements. The proteins are also deposited in all stages of the oocytes, however, in lower concentration in the stage IV. There is carbohydrate deposition from oocytes in the stage II as well as in stages III and IV. In addition, the present work has demonstrated that the oocyte yolk of A. triste has a glycolipoprotein nature and the elements are deposited in the following sequence: firstly the lipids and proteins, and finally the carbohydrates.     

The drop-off rhythm of Amblyomma triguttatum triguttatum Koch (Acari: Ixodidae) from laboratory hosts

The pattern of drop-off of Amblyomma triguttatum triguttatum Koch was studied by infesting rabbits and rats with larvae and nymphs, and calves with adult ticks maintained at a daily photoperiodic regime of 12 h light 12 h dark. Additional information was obtained by infesting rabbits with nymphs in or out of phase with the photoperiodic regime experienced by the host.The great majority of ticks detached during the photophase: only 9.7% of larvae and 11.3% of nymphs fed on rats, 12.0% of larvae and 15.8% of nymphs fed on rabbits, respectively, and 10.0% of female ticks detached during the scotophase. The rhythm was not substantially altered by feeding nymphs in or out of phase with the photoperiodic regime of the host. The drop-off rhythm seemed to be coupled with endogenous rhythms of the host.     

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.     

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.     

Responses of the tick, Amblyomma hebraeum (Acari: Ixodidae), to carbon dioxide

We investigated the effect of physiological state of adult ticks (Amblyomma hebraeum Koch; Acari: Ixodidae) on their responses to a CO2-enriched atmosphere. Ticks were exposed to CO2 or air in an experimental chamber; we measured the effects on questing, movement and latency (the time after exposure to CO2 or air when ticks began questing or moving). This study confirmed the hypothesis that responsiveness to CO2 is enhanced during host-seeking periods of the life cycle and reduced at other times. Thus, whereas newly moulted ticks quested infrequently when exposed to CO2, questing increased over the 6 week period following moulting. Likewise, in 6 week old ticks, movement in CO2 was significantly greater than in air. When a partially fed female below approximately ten times its unfed weight is removed from a host, it reattaches if subsequently presented to another host. Such females quested vigorously in CO2 but not in air. When a partially fed female above approximately ten times its unfed weight is removed from a host, it usually does not subsequently reattach. Such females quested infrequently, there being no significant difference between air and CO2. Males removed from a host at any stage of feeding reattach readily when given the opportunity. They quested frequently, moved readily and the latency was very low in air or CO2. Exp Appl Acarol 22: 667–681 © 1998 Kluwer Academic Publishers     

Distributions of the vectors of heartwater, Amblyomma hebraeum and Amblyomma variegatum (Acari: Ixodidae), in Zimbabwe

The tick vectors of heartwater (Cowdria ruminantium infection) in Zimbabwe, Amblyomma hebraeum and Amblyomma variegatum, historically were believed to be confined to the low-lying regions of the south and north-west of the country. However, country-wide surveys performed in 19751980 and 19881991 demonstrated that both species were also established in western parts of the highveld plateau and had started to encroach on the predominantly heartwater-free central and eastern highveld regions. To determine the current distributions of both the vectors and evaluate the potential threat of heartwater to animals in the highveld, a survey of ticks infesting cattle was performed in 1996 at 2994 locations in small-holder and large-scale commercial farming areas throughout Zimbabwe. Amblyomma hebraeum was collected at 1329 locations, A. variegatum at 72 locations and both A. hebraeum and A. variegatum at 13 locations. The results demonstrated that A. hebraeum was present, as previously recorded, throughout the southern half of the country and appeared to have undergone further limited spread into the central and eastern highveld regions. Only the northern-most region of the country appeared to be free of this species. Amblyomma variegatum was collected mainly in the north-west, as previously recorded, but was also found at isolated locations across the central highveld region and along the eastern border with Mozambique. This species was, however, still absent from the southern half and the northern-most regions of the country. An overlap of the distributions of the two species existed within a zone along the southern and eastern regions of the distribution of A. variegatum. These results suggest that the vectors of heartwater are spreading and threaten to introduce heartwater into intensive livestock-producing regions of the country.Exp Appl Acarol 22: 725740 © 1998 Kluwer Academic Publishers     

Host-parasite relationships of the genus Hyalomma Koch, 1844 (Acari, Ixodidae) and their connection with microevolutionary process

Host-parasite relationships of Hyalomma species of the world fauna are analyzed. The majority of species infests predominately various mammals. Birds and reptiles are used as preferred hosts by several Hyalomma species, and only on certain stage: adults of H. aegyptium parasitize tortoises; immature stages of H. marginatum parasitize birds. It is hypothesized that relationships of H. aegyptium adults (subgenus Hyalomma s. str.) with reptiles are secondarily in origin. Immature stages of H. aegyptium retain the primary wide diapason of hosts, which are various small mammals, birds and reptiles. The life cycle of this species is the three-host type that is considered as a primary type in ixodid ticks. A typical scheme of relationships with their hosts in all well-examined Hyalommina species has following features: the adult stage parasitize large and medium sized mammals, immature stages parasitize small mammals, three-host life cycle. A variety of preferred hosts and types of life cycle is observed in the subgenus Euhyalomma. All species of this subgenus can be arranged into two groups. In the first group, the immature stages infest only small mammals and birds, and the adults parasitize large mammals; this type of host preferences is probably primary host-parasite relationships of Hyalomma. This group includes: H. albiparmatum, H. asiaticum, H. excavatum, H. franchinii, H. impeltatum, H. impressum, H. lusitanicum, H. marginatum, H. nitidum, H. schulzei, and H. truncatum. Hyalomma marginatum and H. schulzei are two-host species; H. excavatum is two- or three-host tick. All the remaining species (except H. albiparmatum, which life cycle is unknown) are three-host ticks. In the second group, the immature stages as well as the adult stage parasitize large mammals. This group includes: H. dromedarii, H. anatolicum, and H. scupense. These species are two- or one-host ticks.     

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.     

Description of a new species of Haemaphysalis Koch, 1844 (Acari: Ixodidae) from the H. (Rhipistoma) asiatica subgroup,parasite of an endemic Malagasy carnivoran (Carnivora: Eupleridae)

Systematic Parasitology - Haemaphysalis (Rhipistoma) galidiae n. sp. (Acari: Ixodidae) is described herein based on males and a single female. Adults of H. galidiae n. sp. were collected from the...     

Estimation of hearing capabilities of Early Miocene sloths (Mammalia,Xenarthra, Folivora) and palaeobiological implications

The Miocene Santacrucian sloths are a very important assemblage because they represent the first major radiation among sloths and, therefore, they could provide many insights about sloth evolution and diversity. Based on other studies, the hearing capabilities of Pleistocene sloths were identified. For a deeper understanding of these capabilities from an evolutionary point of view, in this article we study the hearing capabilities of Santacrucian sloths. We estimate the frequency range and the best frequency of hearing of six species of stem-megatherines and one species of mylodont. In most cases, the best frequency of hearing is much lower than the expected value for the estimated body mass of the species. This general shift towards low values of frequency is different than the pattern observed in mammals where sound localisation is improved by an increased sensitivity to high frequencies. In this article, we also propose some palaeobiological inferences of the low-frequency shift of hearing range in Miocene Santacrucian sloths.     

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.     

Amblyomma vikirri n. sp. (Acari: Ixodida: Ixodidae), a parasite of the gidgee skinkEgernia stokesii (Reptilia: Scincidae) from South Australia

All active stages of the tickAmblyomma vikirri n. sp. (Acari: Ixodidae) are described from the gidgee skinkEgernia stokesii, a widely distributed lizard in South Australia, western New South Wales, western Queensland, Northern Territory and Western Australia. Thus far, the tick has been collected from this host only in the Flinders and Gawler Ranges of South Australia, plus a single record from Mt Dare in the far north of South Australia. Adults attach primarily on the tail and hind-back ofE. stokesii, while the larvae and nymphs prefer the ears and between the toes.