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.     

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     

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.     

Attractivity of cattle infested by Amblyomma variegatum (Acari: Ixodidae) for conspecific adult ticks from the field in Guadeloupe

Four field experiments were conducted with creole cattle in Guadeloupe to study the attractivity for adult ticks of animals previously infested with males of Amblyomma variegatum producing aggregation attachment pheromones (AAPs). In each experiment, two groups of cattle were used; the first group was infested with adult A. variegatum and the second group was kept free of ticks and pheromones by acaricidal treatment and by washing the hair and skin of previously infested sites. Both groups were then exposed to natural infestation by ticks present in the environment or by ticks bred in the laboratory and released on the pasture. The number of additional ticks infesting animals were compared between the treated and control groups. There were no significant differences between both groups in the numbers of new male ticks infesting the animals during the first days following the beginning of the experiment. Thereafter, comparison of the slopes of infestation indicated that infested cattle were no more attractive for male ticks than uninfested hosts. Uninfested cattle were spontaneously and rapidly infested by male ticks. It is concluded that carbon dioxide or another host component was a major attractant for A. variegatum males. Female ticks attached on predilection sites exclusively in the presence of AAP-producing males, i.e. 5–10 days after the attachment of the first males. Based on these results we postulate that slow-release devices impregnated with pheromones have no additional attractive effect on A. variegatum males under Caribbean conditions. However, they may be useful in inducing the attachment of females, but only in the first days preceding the arrival of pioneer AAP-producing males. © Rapid Science Ltd. 1998     

Performance of a Prototype Baited-trap in Attracting and Infecting the Tick Amblyomma variegatum (Acari: Ixodidae) in Field Experiments

Investigations were commenced to study the potential use of the fungi, Beauveria bassiana, Metarhizium anisopliae, and the attraction-aggregation-attachment pheromone (AAAP) for the control of Ambloyomma variegatum as an environmentally friendly technology. The objective of the study was to develop and test a device, which could be used for pheromone and carbon dioxide delivery and infection of ticks with the fungi in an attempt to control the tick populations in the vegetation. Using a pheromone-baited device treated with the fungi mixture, 79% of the ticks released were attracted and exposed to the fungi and of these, 78% died during incubation in the laboratory. In another set of experiments, of the released ticks that were similarly exposed to fungi using the pheromone-baited device and left in the vegetation, 33.8% were recovered compared to recoveries of between 76 and 84% in the controls. These results were significantly different at the 5% level, an indication that the pheromone/fungi mixtures had significant effect in reducing the tick population in the field.     

Detection of Babesia caballi in Amblyomma variegatum ticks (Acari: Ixodidae) collected from cattle in the Republic of Guinea

A reverse line blot hybridisation (RLB) assay was applied to screen Amblyomma variegatum adult ticks (n = 504) collected from N'Dama cattle in the Republic of Guinea. In a PCR, the V1 hypervariable region of the 16S ribosomal RNA (rRNA) gene was amplified with a set of primers unique for species of the genera Anaplasma and Ehrlichia, and the V4 hypervariable region of the 18S rRNA gene was amplified with primers specific for members of the genera Theileria and Babesia. Amplified PCR products from A. variegatum ticks were hybridised onto a membrane, to which oligonucleotide probes species-specific for Ehrlichia/Anaplasma and Theileria/Babesia parasites were covalently linked. No pathogens belonging to Ehrlichia/Anaplasma species were found, while 10 DNA samples resulted positive for Babesia caballi and 5 samples for Theileria velifera. This is the first report of B. caballi in A. variegatum ticks. One of the B. caballi positive samples was sequenced. This new strain (BcabGuinea) showed a 97% similarity to the Z15104 B. caballi GenBank sequence.     

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.     

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.     

Integrated Management Strategies for Amblyomma Americanum (Acari: Ixodidae) in Non-Agricultural Areas

The simulation model LSTSIM was revised and adapted to estimate the effects of different management strategies on populations of the lone star tick, Amblyomma americanum (Linnaeus), in non-agricultural areas. The control technologies evaluated were area-wide acaricide application, acaricide self-treatment of white-tailed deer, vegetation reduction and reductions in the density of white-tailed deer. Estimated changes in tick populations using these technologies compared favorably with results from actual integrated tick management studies at five different geographic locations. Area-wide acaricide application and vegetation reduction, as well as combinations of the two technologies proved to be useful for short-term, seasonal management of ticks in small non-agricultural areas and residential sites. Self-treatment of deer with acaricide, applied topically or as a systemic, appears to be the most cost-effective technology for use in area-wide, long-term programs for tick control. The results of simulations suggest that reductions in deer density should be considered as a component of any tick management program.     

An Inhibitor of Thrombin-Stimulated Blood Platelet Aggregation from the Salivary Glands of the Hard Tick Amblyomma variegatum (Acari: Ixodidae)

The tropical bont tick, Amblyomma variegatum can cause intense skin irritation and inflammation and bites that often develop into septic wounds or abscess in their host. Crude salivary gland extract (SGE) of partially engorged A. variegatum females as well as SGE protein fractions purified by three-step reverse phase HPLC procedure were tested for their anti-aggregatory effect on isolated human blood platelets stimulated with thrombin and compared with the effect of recombinant hirudin. At concentrations 10⁻³ and 5 × 10⁻³ μg protein/ml the following rank order of antiplatelet activity was detected: AV 16/3 (inhibitor purified from AV-III, third purification) > SGE > AV-II (fraction from first purification) > AV-III (fraction from first purification) > hirudin. The effect of all fractions tested was dose-dependent. For fraction AV 16/3, the inhibitory effect was 49 and 61% for 10⁻³ and 5 × 10⁻³ μg protein/ml, respectively. The results suggest that protein fractions from A. variegatum SGE possess an antithrombin effect on human blood platelets with hirudin-like activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Acaricide susceptibility ofAmblyomma variegatum (Acari: Ixodidae) from Puerto Rico and Guadeloupe

Base-line data on acaricide susceptibility of larvae and of larvae and nymphs of the tropical bont tick,Amblyomma variegatum (Fabricius), from Puerto Rico and Guadeloupe were collected on 14 and six compounds, respectively. Nymphs 7–8 weeks old from Puerto Rico and Guadeloupe, and larvae 3–4 weeks old from Guadeloupe, were exposed for 24 or 48 h to residues of acetone dilutions of technical-grade or commercial formulations of acaricides on disposable glass pipettes. Effectiveness of the acaricides in killing nymphs (lc ₅₀) from Guadeloupe and Puerto Rico ranged from 0.0001% for deltamethrin to 0.269% for malathion. For Puerto Rico, the susceptibility to toxaphene and amitraz, but not to dioxathion, increased with increasing age of nymphs. Nymphs from Guadeloupe were 9.5 times more susceptible to chlorpyrifos than nymphs from Puerto Rico. The susceptibility of larvae from Guadeloupe to acaricides tested ranged fromlc ₅₀ 0.000012% for deltamethrin to 0.0141% for ethion. There was no evidence of development of acaricide resistance in ticks from Guadeloupe or Puerto Rico.     

Secretory process of salivary glands of female Amblyomma cajennense (Acari: Ixodidae) ticks fed on resistant rabbits

Ticks have great economic and health importance since infested animals have reduced milk and meat production, and, besides that, they are expensive ectoparasites to control. While feeding, ticks can transmit to their hosts a large amount of pathogens, including Rickettsia rickettsii responsible for the ??spotted fever?? or ??fever of the mountains.?? It is known that animals infested with ticks or artificially immunized with their salivary gland extracts develop resistance, which is related to a decrease in engorged female weight, in egg-laying by adults, in egg viability and, in some cases, in the capacity of pathogens transmission. The present study aimed to examine morpho-histochemically the female salivary glands of semi and engorged Amblyomma cajennense fed on resistant rabbits. The results revealed that acinus I had no changes when compared to that of females fed on naive rabbits. The c cells of acinus II showed signs of early degeneration, which may result in feeding efficiency decrease. In acinus III d cells, activity time was longer. Such occurrence was associated with the time of female fixation, which increased in females fed on resistant hosts.     

Underwater survival of Rhipicephalus sanguineus (Acari: Ixodidae)

Rhipicephalus sanguineus (Acari: Ixodidae) is a worldwide distributed tick, also due to its adaptability to different environmental conditions. In order to assess its ability to survive and to lay eggs after water immersion, 150 engorged females from southern Italy were water immersed for 1-15 days whereas eggs were flooded for 1-5 days. All females survived water immersion for 48 h, some of them up to 72 h, but egg hatch rate was negatively correlated with female submersion period. All eggs flooded for up to 120 h hatched successfully. These findings suggest that R. sanguineus is able to survive underwater for some days without loosing any biological activity. This feature should be considered in relation to its potential to spread to new areas and to its role as a vector of pathogens also in consideration of changes in climate the Earth is currently experiencing.     

Evaluation of the eradication program forAmblyomma variegatum (Acari: Ixodidae) on Puerto Rico

A cooperative effort between the United States Department of Agriculture, Animal and Plant Health Inspection Service, Veterinary Services, the Agricultural Research Service, and the Department of Agriculture, Commonwealth Government of Puerto Rico has been successful in eardicatingAmblyomma variegatum (Fabricius) from the islands of Puerto Rico and Vieques (an island municipality of Puerto Rico). Application of acaricides to livestock and dogs at 14-day intervals for an 18-month period eliminated foci of tick infestation on 188 farms in four different locations without additional aerial or ground treatment. Reasons for the success and some of the costs associated with the eradication program on Puerto Rico are presented.     

Antiviral effect of the egg wax of Amblyomma cajennense (Acari: Ixodidae)

The control of viral infections, especially those caused by influenza viruses, is of great interest in Public Health. Bio prospection has shown the presence of active principles in the hemolymph of arthropods, and in the salivary gland of ticks, and some of these are of interest for the development of new pharmacological drugs. Ticks lay their eggs in the environment, and to protect them from desiccation and microbial attack they involve the eggs in a waxy layer produced by an organ known as Gené’s Organ. In this study, the eggs wax from tick Amblyomma cajennense (Fabricius) was extracted using ice cold phosphate buffer. The antiviral activity was evaluated with picornavirus and influenza virus. In both cases egg wax was able to inhibit virus replication. For influenza virus, an amount as small as 12 μg/mL of crude egg wax suspension neutralized 128 UHA (hemaglutinant unit) of H₁N₁ influenza virus. With picornavirus, egg wax led to a 256-fold reduction in virus production by L929 cells. Egg wax was not cytotoxic to VERO, MDCK and L929 cell, being observed that the cell morphology was preserved with concentration as high as 2 mg/mL. In addition no genotoxic effect was observed for Vero cells, suggesting a very interesting potential antiviral activity.     

Studies on survival and water balance of unfed adult Dermacentor marginatus and D. reticulatus ticks (Acari: Ixodidae)

The water content, the survival time at various relative humidities(r.h.) and the critical equilibrium activity of unfed adultDermacentor marginatus and D.reticulatus ticks were investigated at a constant temperature of20 °C. It was also examined whether these ticks use liquidwaterto compensate water loss. Both Dermacentor spp. showed nosignificant differences in water content in relation to body mass. The meanwater content of D. marginatus and D.reticulatus was 54.6% and 54.7%, respectively, in females and 56.3%and 57.0%, respectively, in males. The survival time of unfed adults prolongedwith decreasing saturation deficits. On average, males survived longer thanfemales and D. marginatus ticks survived mostly longerthanD. reticulatus ticks. The 50% mortality period rangedbetween 40 d at 33% r.h. and 420 d at 95% r.h. in D.marginatus, and between 43 d at 33 r.h. and 366 d at 95% r.h. inD. reticulatus. The critical equilibrium activity of unfedadults was estimated to be 0.84 for both species and was independent of sex.When dehydrated adult D. marginatus and D.reticulatus ticks were offered liquid water, only a few slightlygained weight while most further lost weight. Liquid water was not attractivefor dehydrated or non-dehydrated ticks and drinking was not observed. Aftersubmerging in water for 2 d, most of the dehydrated ticks had gained weight.