Vertical migration of adult Ixodes rubicundus,the Karoo paralysis tick (Acari: Ixodidae)

Mortality due to Karoo paralysis amongst livestock is of considerable economic importance in South Africa. Indications are that the extent of vertical migration of adult ticks, to reach questing positions on grasses, is influenced by sudden climatic chages. Such influences as well as selection of questing substrates were investigated under controlled conditions. Vertical migration of adult Ixodes rubicundus on copper rods was determined in a square metal arena within a closed glass container in a room in which temperature and light could be controlled. Significantly more female and male ticks migrated vertically on 1.5 mm diameter rods than on 4.0 mm rods and on 450 mm long rods than on 100 mm rods. More ticks of both sexes migrated vertically at RH>80% than at RH<50% and at 12°C than at 21°C. More female than male and more older than younger ticks migrated vertically in all experiments. The results of this study contribute towards an understanding of the epidemiology of Karoo paralysis.     

Sex ratio characteristics in Ixodes rubicundus (Acari: Ixodidae), the Karoo paralysis tick

The sex ratio is an important parameter which characterizes the state and dynamics of natural populations of animals. Although ixodid ticks are specialized ectoparasites, most species are bisexual and are characterized by a 1:1 sex ratio for their progeny. In natural populations and even in laboratory colonies, biased sex ratios are often observed. Ixodes rubicundus, the Karoo paralysis tick, parasitizes domestic stock and wild ungulates in South Africa. Adults quest from vegetation, can mate off or on the host and males are seldom parasitic. We hypothesized that the sex ratio for I. rubicundus would be 1:1 when observed directly in the progeny but that it would be strongly biased towards females in samples of parasitic adults. The results mostly supported the hypothesis but it was also shown that unexplained and unpredictable variations can occur. On hosts, females dominated strongly, except on adult angora goats where the sex ratio was biased in favour of the males. This disparity may be related to a greater retention of males in the coarse, curly hair of angora goats compared to the other hosts. Monthly variations in the sex ratios of the tick on hosts are believed to be related to the large fluctuations in sex ratios of questing ticks.     

The effect of feeding immature Karoo paralysis ticksIxodes rubicundus (Acari: Ixodidae) on the metabolic rate of the rock elephant shrew

The effect of feeding immature Karoo paralysis ticks (Ixodes rubicundus) on the resting metabolic rate (RMR) of their principal natural host, the rock elephant shrew (Elephantulus myurus), was investigated under laboratory conditions. The elephant shrews were artificially infested with numbers of ticks simulating natural burdens. The RMR of the elephant shrews was quantified by measuring the oxygen consumption in an open through-flow system. The RMR of hosts infested only with larvae did not differ from that of the control group. Those infested with nymphs, or nymphs and larvae, had significantly lower RMR's compared to the control animals. There were no signs of paralysis in any of the infested hosts.     

An evaluation of strategic and threshold control measures against the Karoo paralysis tick,Ixodes rubicundus (Acari: Ixodidae) in South Africa

Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.     

Improvement of field sampling methods for adult Karoo paralysis ticks,Ixodes rubicundus (Acari: Ixodidae), through addition of host odour

The responsiveness of Ixodes rubicundus ticks on questing substrates and the success of their attachment to non-living substrates were investigated. The purpose of this study was to relate responsiveness to conditions of temperature and humidity, to compare the efficacy of flagging and dragging methods to estimate the size of populations of adult I. rubicundus in the field, and to determine the possible influence of host odour on the efficacy of these methods. Responsiveness was tested under varying conditions of temperature and humidity under field conditions, and the same ticks were used to determine the duration of attachment to a flannel cloth, either impregnated with host odour from sheep wool or without it. Flagging and dragging methods were compared under laboratory conditions with cloths either treated with host odour or not. Within the range of ambient temperatures recorded during this study (7–25°C) most of the ticks (86%) were responsive. No obvious relationship between temperature, relative humidity and responsiveness of ticks was evident. Ticks remained on average 32.9 seconds (n=64) on cloth treated with host odour compared to 9.1 seconds (n=54) on untreated cloth. Flagging was 1.5–1.7 times as effective as dragging and treatment of the cloths with host odour increased the efficacy 2.4 (dragging) to 2.8 (flagging) times. The reactions of ticks to external stimuli should, therefore, be taken into account to maximize field sampling success.     

Regeneration of Haller's sensory organ in the tick, Ixodes rubicundus (Acari: Ixodidae)

A study of regeneration in nymphs and adults of the South African tick Ixodes (Afrixodes) rubicundus, from which the forelegs had been amputated during the previous instar, revealed that the structural changes in regenerated Haller's sensory organs resemble those observed in other ixodid ticks, in particular in another prostriate tick, Ixodes (Ixodes) ricinus. The adult regenerates re-establish their atavistic features in terms of the increased number of different sensilla on the distal knoll, in the anterior pit and the capsule. The nymphal regenerates, in contrast, re-establish the features of the previous instar through a reduction in the number of some sensilla on the distal knoll and in the post-capsular area. The structural changes in different compartments of the organ appear independent. The phenomenon of regenerative induction through the appearance of specific changes in Haller's organ of the contralateral non-treated foreleg is probably characteristic only of prostriate ticks. A unique modification in the regenerated Haller's organ as revealed by duplication of the Haller's organ capsule was discovered in both I. rubicundus nymphs and adult ticks.     

The life cycle of Ixodes rubicundus (Acari: Ixodidae) and its adaptation to a hot,dry environment

The life cycle of Ixodes rubicundus, the Karoo paralysis tick, was studied under field conditions in the south-western Orange Free State, South Africa, by placing freshly engorged ticks in small containers. The life cycle extends over 2 years. The two regulating phases in the life cycle, which undergo a morphogenetic diapause during the hot and dry summer months, are the egg and engorged nymph. Possible behavioural diapause in adults which suppresses questing activity before the end of March. can also serve as a third regulating phase. Temperature affects the duration of the pre-oviposition period of engorged females and the period between detachment of engorged larvae from hosts and ecdysis. Commencement of larval hatch is reasonably synchronized, irrespective of the month during which oviposition occurred. Peak activity periods of larvae (April or May) occur during a period of high rainfall and decreasing daily maximum temperatures. The period between detachment of engorged nymphs from hosts and ecdysis is highly variable (8–36 weeks). All developmental stages of the tick occur mainly during autumn and winter and no ticks are active during the hot summer months of December to February. Larvae, nymphs and adults each survive for only one season.     

A comparison of Ixodes rubicundus (Acari: Ixodidae) infestations on Friesian and Bonsmara cattle in South Africa

This study was conducted to compare the relative resistance of crossbred Bos indicus X B. taurus Bonsmara and B. taurus Friesian cattle to Ixodes rubicundus (Karoo paralysis tick) infestations. During periods of peak abundance of the ticks, Friesian oxen harboured almost twice or more than twice as many ticks as either Bonsmara oxen or cows. During periods of low tick abundance tick burdens on both cattle breeds were closely similar. It is envisaged that cattle can play an important role in an integrated control strategy against the Karro paralysis tick.     

Interspecific variations in attachment sites and density assessment in femaleIxodes rubicundus (Acari: Ixodidae) on domestic and natural hosts

The attachment sites of female Karoo paralysis ticks (Ixodes rubicundus) and equations to assess tick burdens on domestic (sheep and goats) and natural (mountain reedbuck) hosts were determined. No intraspecific differences in attachment sites for Merino sheep and Angora goats could be observed, but interspecific differences were evident.Ixodes rubicundus in general attaches on the ventral aspects of the host. More than 50% of these ticks attached to the fron quarters of the body of the domestic host, and 60% to the hindquarters of the natural host. The length of Merino sheep wool had no affect on either the attachment site or number of attached ticks. In general, more ticks were found attached to the woollen than non-woollen body areas. Equations are provided which can estimate tick burdens on hosts by counting the ticks on two or three selected body areas of the host. To facilitate sampling procedures, approximate sample sizes for the various hosts needed to estimate average tick burdens have been provided. Depending on the level of precision required (with bounds on the error of estimation equal to 1, 2 or 5 ticks), the number of animals in a flock of 200 Angora goats that must be examined varied from 26 to 85.     

The distribution of ticks (Acari: Ixodidae) of domestic livestock in Portugal

This paper introduces the first countrywide faunistic study of the tick parasites on ruminants in Portugal. The aim of this study was to map accurately the distribution of the ticks Dermacentor marginatus, Rhipicephalus (Boophilus) annulatus, R. bursa, Hyalomma m. marginatum, H. lusitanicum and Ixodes ricinus in Portugal. Additional information about the abiotic preferences of these species has been obtained through the use of abiotic (temperature- and vegetation-derived) variables have been recorded from remotely sensed information at a nominal resolution of 1.1 km². A further aim was the development of predictive models of distribution using Classification and Regression Trees (CART) methodologies. Four species (R. annulatus, R. bursa, D. marginatus and H. m. marginatum) are mostly restricted to south-eastern parts of the country, under hot and dry climate conditions of Mediterranean type. H. lusitanicum has been collected almost only in the southern half of Portugal. I. ricinus has a very patchy distribution and is mainly associated with vegetation of Quercus spp., found in southern zones of the country, but it is present also in the more humid western part. A variable number of abiotic variables, mainly temperature derived, are able to describe the preferences of the tick species. It is remarkable that variables derived from maximum values of the Normalized Derived Vegetation Index (yearly or summer-derived) only apply to discriminate areas where I. ricinus has been collected. CART models are able to map the distribution of these ticks with accuracy ranging within 75.3 and 96.4% of actual positive sites.     

Differential distribution of immature Ixodes dammini (Acari: Ixodidae) on rodent hosts

Ectoparasites such as ixodid ticks that remain attached to hosts for several days while feeding on blood are able to overcome the inflammatory and immune responses of some hosts and not others. The immature stages of the deer tick Ixodes dammini are found more frequently on the white-footed mouse, Peromyscus leucopus, than on other rodents. We propose that P. leucopus is more tolerant to I. dammini than is a less common host, the meadow vole, Microtus pennsylvanicus. To test this hypothesis, the distribution patterns and engorgement indices were determined for larval and nymphal I. dammini collected from wild-caught P. leucopus and M. pennsylvanicus. There were more immature ticks, which were more fully engorged, on P. leucopus than on M. pennsylvanicus. There were more and better engorged ticks on male than on female hosts. Laboratory studies on the number and weights of larval I. dammini collected off naive and previously exposed P. leucopus and M. pennsylvanicus support the results of the field study. Fewer larval ticks were recovered from previously exposed M. pennsylvanicus than P. leucopus, and the ticks weighed less. Larval and nymphal ticks aggregated among hosts in the study grid, and higher densities per male P. leucopus were correlated with higher engorgement indices, suggesting that immature I. dammini feed better at higher densities. The feeding success of I. dammini on its preferred host species might be due to its adaptation to the immune and inflammatory reactions of the host.     

Cold-hardiness of Dermacentor marginatus (Acari: Ixodidae)

The cold-hardiness of Dermacentor marginatus using laboratory-reared offspring of ticks collected in Germany was characterized. Investigations of unfed stages revealed that adult ticks suffered 50% mortality at –10°C after 4–5 months, but larvae and nymphs suffered mortality within few days, whereas –15°C was lethal for all stages within a very short period. Larval hatch and moulting of engorged larvae and nymphs did not occur at 10°C. Embryonic development of eggs with larval hatch was considerably reduced by exposure of eggs to 10°C. Engorged females did not lay eggs at 10°C, the oviposition capability, however, persisted over 6 months at 10°C, 5 months at 5°C, 3 months at 0°C and 2 months at –10°C without substantial decrease of the oviposition capacity or reduction of viable eggs. These results present evidence that unfed adult ticks are the ecoepidemiologically most effective stages, which are capable to tolerate long and extremely cold winters without substantial impairment of the population density. It is also considered that engorged females interrupt their oviposition at low and subzero temperatures delaying it for months and so contribute in bypassing winter conditions. None of the stages survived supercooling indicating that D. marginatus is freeze intolerant. Mean supercooling point (SCP) ranged between –26°C in eggs and –12, 6°C in engorged females. Compared with eggs, the SCP of the other stages was significantly higher. In conclusion, the SCP is considered to have no predictive value in the context with cold-hardiness.     

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.     

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.     

Concerning the problem of the northern limit of Ixodes persulcatus (Acari: Ixodidae) distribution in Karelia

The influence of changes in climate conditions on the abundance and formation of the northern limit of Ixodes persulcatus distribution in Karelia has been studied. It has been demonstrated that the territory in which the heat provision is sufficient for the development of ixodid ticks significantly increased during 2000–2007. Thus, it favored an increase in the abundance and enhanced distribution of I. persulcatus.     

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.     

Ticks (Acari: Ixodidae) within various phytophysiognomies of a Cerrado reserve in Uberlandia, Minas Gerais, Brazil

Cerrado biome, the South American savannah, covers about 2 million km² and is very rich in endemic species but threatened by agriculture. In this report free-living tick species are presented, and their seasonal and relative distribution within the various phytophysiognomies in a small Cerrado reserve in Minas Gerais State, Brazil. Overall 2,694 free-living ticks were found during a 2 years sampling period with CO₂ traps and cloth dragging. Of these, 73.5% were Amblyomma cajennense and 0.6% Amblyomma dubitatum. All other ticks (25.9%) were retained as Amblyomma spp. Adults of A. cajennense peaked in spring, the nymphs in winter of both years. Amblyomma larval clusters were found in autumn and winter. Adult ticks (46.7%) and nymphs (39.5%) were most often found in woodlands, whereas most larval clusters were found in valley-side marshes (39%). Amblyomma cajennense, Anocentor nitens, Rhipicephalus (Boophilus) microplusand Rhipicephalus sanguineus ticks were found on domestic animals from neighboring properties. Search for Rickettsia in the hemolymph of 497 A. cajennense and one A. dubitatum ticks yielded negative results. Results confirmed earlier reports on the overwhelming prevalence of A. cajennense ticks in the Cerrado biome of Brazil and added information to habitat preferences of this tick species, a major vector in Brazil of the Rocky Mountain spotted fever.