Spatial distribution of the Karoo paralysis tickIxodes rubicundus (Acari: Ixodidae) within a false upper Karoo veld type

Spatial distribution of the Karoo paralysis tick (Ixodes rubicundus) has been studied in a paralysis enzootic area of the southwestern Orange Free state. Significantly more females than males were collected from the vegetation. Most ticks (99%) used grass as questing sites at a height of approximately 45 cm (range 10–97 cm), which correlates with the size of host animals. No significant differences between the questing height of male and fermale ticks were evident. The ticks were found on most of the grass species present and, except for the genusEragrostis no specific preference was evident. When questing, the capitulum ofI. rubicundus is usually (90%) directed towards the ground. Seventy-eight percent of the ticks occurred singly on a specific grassblade or flowerhead. In those cases where two ticks occurred together, no sexual aggregation was evident. Most ticks occurred under or close ( =62 cm) to the corwn cover of specific shrub or tree species. These plant species were characterized by a dense crown cover with a mat of decaying leaf litter underneath. The preference of the tick for wild olive trees (Olea europaea fricana) suggests that except for the physical characteristics of this tree species, host factors may also be important. Significantly more ticks were distributed on the cooler, more protected southern sides of vegetation in comparison to the northern sides.     

Control of Karoo paralysis ticks through vegetation management

Abstract. Karoo paralysis, caused by feeding Ixodes rubicundus females, is a major disease of small stock in South Africa. Control methods currently practised are almost exclusively chemical based. To limit overdependance on chemicals, vegetation management was investigated as a possible method for control, to be incorporated in an integrated tick management system. Laboratory and field experiments were conducted to determine, firstly, the extent of vertical migration and survival of ticks on long and short copper rods which simulated grasses as questing substrates; secondly, the infestation burdens of sheep exposed to similar tick challenges in pens with long and short grass; and thirdly, the effect of trimming the lower crown line of wild olive trees, simulating the browsing effect of goats, on tick density in the immediate environment of the trees. When ticks were exposed to optimal (>45 cm) and sub-optimal (<10 cm) length rods on which to quest, the extent of vertical migration over extended periods of time (up to 87 days) was significantly higher ( P < 0.001) for the ticks exposed to long rods. Also, almost 3 times as many ticks exposed to long rods survived compared to those exposed to short rods. Sheep exposed to long grass were infested by twice as many ticks compared to those exposed to short grass. Tick density at modified wild olive trees ( Olea europaea africana ) (0.027 ticks/m²) differed significantly ( P < 0.05) from that at control trees (0.088 ticks/m²). It is recommended that coarse grazers such as cattle and horses should be used to graze down long grasses before sheep are introduced into camps known to be infested with I. rubicundus. Similarly, domestic goats can, through their browsing effect on shrubs and trees, modify the vegetation and as such play an important role in an integrated tick management system.     

Investigation into the critical equilibrium humidity,active atmospheric water absorption and water content ofRhipicephalus evertsi mimeticus

The critical equilibrium humidity for fully engorged nymphs ofRhipicephalus evertsi mimeticus was shown to be between 91% and 93.5% r.h., and for adult male and female ticks to be between 82% and 84.5% r.h. Studies on gnathosoma and idiosoma by selective exposure to differing relative humidities have shown that dehydrated adult male and female ticks are capable of active uptake of atmospheric water vapor only through their mouthparts. The percentage of water content of unfed adult male and female ticks previously dehydrated was not influenced by subsequent exposure to different relative humidities, varying similarly in both sexes, male imagines between 59.6% and 63.7%, female imagines between 59.6% and 64.4%. Analogous values (62.3% and 61.1%) were obtained for the water content of male and female imagines not previously dehydrated, which were incubated at 30°C and 100% r.h. for 7 days.     

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.     

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.     

Hyalomma truncatum (Acari; Ixodidae): investigations into the scototaxis of unfed adult ticks

Under controlled test conditions, unfed male and female Hyalomma truncatum ticks exhibited a positive scototaxis to stationary, two-dimensional targets. Upright-positioned rectangles were the most attractive targets. The attractiveness of these targets increased with their size. Significantly more ticks responded scototactically positively to the targets under a luminance contrast ratio of 5:1, as compared with other luminance contrast ratios. Targets with an elevation angle of 13° were occupied more frequently than objects with higher elevation angles. Scototaxis was the same towards a stationary and a sinusoid oscillating target. When an upright-positioned rectangle was combined with a CO₂ gradient, the number of ticks that migrated into the CO₂ gradient and contacted the target did not increase significantly. The interval between exposure and first locomotion of the ticks, however, was significantly shorter under the influence of a CO₂ gradient than in all other experiments without a CO₂ gradient. A temperature gradient simulating a natural host (cattle) did not alter the scototaxis. The results of these investigations suggest that the positive scototaxis exhibited by adult H. truncatum ticks is not likely to be part of their appetence behaviour but rather searching behaviour to find adequate protection from harsh climatic conditions.     

Activity periods and questing behavior of the seabird tick Ixodes uriae (Acari: Ixodidae) on Gull Island, Newfoundland: the role of puffin chicks

Questing behavior of Ixodes uriae and their associated seasonal, host-feeding patterns are crucial to our understanding of tick life history strategies and the ecology of diseases that they transmit. Consequently, we quantified questing behavior of nymphs and adult female I. uriae ticks at Gull Island, a seabird colony in Newfoundland, Canada, to examine seasonal variation of off-host and on-host tick activity. We sampled a total of 133 adult Atlantic puffins (Fratercula arctica), 152 puffin chicks, and 145 herring gull (Larus argentatus) chicks for ticks during the breeding seasons of 2004 and 2005. Questing ticks were sampled by dragging a white flannel cloth across the grassy breeding areas during the mo of May, June, July, and August. Nymph questing activity reached a peak during mid-July (79 and 110 individuals/hr in 2004 and 2005, respectively). The prevalence of nymphs and adult female ticks on different seabird hosts varied between years and during the seasons. Puffin chicks had the highest prevalence (above 70% in July) of nymphs in both years and this was correlated with questing activity. Female ticks rarely fed on puffin chicks, but were prevalent on adult puffins and gulls, although prevalence and questing of ticks were not correlated in these hosts. These patterns of off-host and on-host tick activity suggests that I. uriae ticks likely use a combination of questing and passive waiting, e.g., in puffin burrows, to detect hosts, depending on the tick stage and the host species.     

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.     

Density of Ixodes scapularis ticks on Monhegan Island after complete deer removal: A question of avian importation?

Questing adult blacklegged tick (Ixodes scapularis Say) abundance declined markedly three years after the 1999 removal of white‐tailed deer (Odocoileus virginianus Zimmermann) from Monhegan Island, ME. Since 2000, subadult ticks have not been found on Norway rats (Rattus norvegicus Berkenhout); questing nymphs have not been found since 2002. This suggested I. scapularis was reintroduced annually via bird importation of subadult ticks, but unable to complete its two‐year life cycle on the island due to lack of deer. To investigate this, we used uncertainty analysis to estimate 1) questing adult ticks/ha that would result from avian importation of nymphs, and 2) questing adult ticks/ha on Monhegan Island, using bird capture and tick burden data from Appledore Island, ME, flagged tick data from Monhegan Island, and ten uncertain parameters. During the deer‐fed period (1990–2001), estimated tick density on Monhegan Island was 18 times greater than that of imported ticks. During the post‐deer‐fed period (2002–2008), Monhegan Island tick density was equivalent to imported tick density. This supported the premise that all I. scapularis ticks on Monhegan Island have been bird‐derived since 2002.     

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     

Respiratory metabolism of the soft tick,Ornithodoros turicata (Dugès)

The rate of oxygen consumption was investigated in fed larval, nymphal and adult Ornithodoros turicata ticks and in starved nymphal and adult ticks. Oxygen consumption rate of fed adult ticks increased with increasing temperature. The metabolic rate of adult ticks was affected by starvation whereby starved adult ticks showed a significantly lower oxygen consumption than their fed counterparts. The oxygen consumption rate of fed female ticks was significantly higher than that of fed males but, there was no significant difference between the oxygen consumption rates of starved female versus starved male ticks. Oxygen consumption of fed larvae was significantly greater than those of fed first through third instar nymphs. Fed and starved nymphal ticks as well as fed adult ticks ventilated continuously. In contrast, starved adults ventilated discontinuously. The ability to reduce metabolic rate, plus the capability to ventilate discontinuously allow O. turicata adults to cope with prolonged starvation.     

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.     

Composition and seasonal variation of Rhipicephalus turanicus and Rhipicephalus sanguineus bacterial communities

A 16S rRNA gene approach, including 454 pyrosequencing and quantitative PCR (qPCR), was used to describe the bacterial community in Rhipicephalus turanicus and to evaluate the dynamics of key bacterial tenants of adult ticks during the active questing season. The bacterial community structure of Rh. turanicus was characterized by high dominance of Coxiella and Rickettsia and extremely low taxonomic diversity. Parallel diagnostic PCR further revealed a novel Coxiella species which was present and numerically dominant in all individual ticks tested (n = 187). Coxiella sp. densities were significantly higher in female versus male ticks and were overall stable throughout the questing season. In addition, we revealed the presence of the novel Coxiella sp. in Rh. sanguineus adult ticks, eggs, and hatched larvae, indicating its vertical transmission. The presence of both spotted fever group Rickettsia spp. (SFGR) and non-SFGR was verified in the various individual ticks. The prevalence and density of Rickettsia spp. were very low compared to those of Coxiella sp. Furthermore, Rickettsia sp. densities were similar in males and females and significantly declined toward the end of the questing season. No correlation was found between Coxiella sp. and Rickettsia sp. densities. These results suggest different control mechanisms in the tick over its different bacterial populations and point to an obligatory and facultative association between the two tick species and Coxiella sp. and Rickettsia spp., respectively.     

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.     

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.     

Lethal Effect of Rickettsia rickettsii on Its Tick Vector (Dermacentor andersoni)

Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, was lethal for the majority of experimentally and transovarially infected Rocky Mountain wood ticks (Dermacentor andersoni). Overall, 94.1% of nymphs infected as larvae by feeding on rickettsemic guinea pigs died during the molt into adults and 88.3% of adult female ticks infected as nymphs died prior to feeding. In contrast, only 2.8% of uninfected larvae failed to develop into adults over two generations. Infected female ticks incubated at 4°C had a lower mortality (80.9%) than did those held at 21°C (96.8%). Rickettsiae were vertically transmitted to 39.0% of offspring, and significantly fewer larvae developed from infected ticks. The lethal effect of R. rickettsii may explain the low prevalence of infected ticks in nature and affect its enzootic maintenance.     

Hyalomma truncatum and Rhipicephalus evertsi mimeticus (Ixodoidea,Ixodidae): reactions of adult ticks to vertically incident narrow- and wideband optical radiation with and without the influence of a CO2 gradient

Investigations concerning the reactions of unfed Hyalomma truncatum and Rhipicephalus evertsi mimeticus female and male ticks to vertically incident narrow- and wideband optical radiation at irradiances of 0.115 mWcm^-2 and 0.98 mWcm^-2, respectively, revealed that, independent of sex, adults of the two species are capable of perceiving a wide range of wavelengths. Considering the migration into the entry area of the optical radiation at the test chamber's ceiling as a positive phototaxis, H. truncatum always reacted with higher percentages than R. e. mimeticus. Compared to the controls, R. e. mimeticus ticks occupied the entry area of the optical radiation significantly more frequently only in the wavelength ranges of 415–474 nm, 529–628 nm, 611–707 nm and 190–2,600 nm, but always with low rates. High percentages of H. truncatum ticks, however, consistently reacted with a positive phototaxis in all the offered monochromatic sectors between 292–707 nm and also in the wide spectral range of 190–2,600 nm, particularly in the range of 470–520 nm. When ticks of both species were additionally confronted with a stable CO₂ gradient, continuously increasing from 0.18 vol% at the bottom to 0.90 vol% at a height of 40 cm in the test chamber, they moved less frequently to the entry area of the optical radiation, compared to ticks tested without CO₂, regardless of their exposure to darkness or to narrow- and wideband radiation. The percentages of ticks, however, that moved in a vertical direction, but did not reach the chamber's ceiling were always higher, with the exception of R. e. mimeticus at the wavelength range of 415–474 nm. A total of 30 unfed male and 30 unfed female adult ticks of both tick species were investigated at each combination of a narrow- and wideband spectral range, with and without the influence of a CO₂ gradient. Considering moving ticks only, the interval between exposure and first movement of ticks was shorter under the influence of an additional CO₂ gradient. The average delay in reaction with and without the stimulus of the CO₂ gradient was 156.2 s and 195.6 s, respectively, for H. truncatum and 126.6 and 226.3 s, respectively, for R. e. mimeticus.     

The role of host behaviour in tick-host interactions: a domestic host-paralysis tick model

The aim of this study was to quantify the infestation densities of Karoo and brown paralysis ticks on sheep and goats and explain it in terms of the etho-ecology of these ticks and their domestic hosts. The Karoo paralysis tick usually quests from a vantage point on the vegetation whereas the brown paralysis tick displays an appetence response from the ground and mainly engages hosts that are prostrate. Both tick species are confined chiefly to hilly areas. Temporal differences in the infestation densities of the hosts within and between tick species were evident. These differences were related to disparities in the spatial distribution of the hosts, their activity patterns and the specific appetence responses of the two tick species. Differential climatological conditions affected the quality of forage in areas with a varied topography and the feeding preferences of hosts influenced tick-host sympatry and hence infestation densities.     

Temperature effects on sex differentiation of two South American atherinids, Odontesthes argentinensis and Patagonina hatcheri

Synopsis The present study investigated the effects of water temperature (18, 21, and 25 °C) on the histological process of gonadal sex differentiation of two commercially important atherinid fishes from South America, Odontesthes argentinensis (sea pejerrey) and Patagonina hatcheri (Patagonian freshwater pejerrey). In both species, female gonadal sex differentiation began with the formation of lateral stromal cell outgrowths and the appearance of meiotic oocytes. The male gonads remained quiescent for about twice as long as the female gonads, with differentiation becoming evident by the formation of the main sperm duct and of cysts of germ cells at the periphery of the gonads. Meiosis in males occurred relatively long after somatic differentiation of the testis. The ovaries of O. argentinensis differentiated at 28 days (20.3 mm) at 25 °C, 42 days (24.0 mm) at 21 °C, and 56 days (23.8 mm) at 18 °C. In the males, differentiation was observed at 98 days at 25 and 21 °C (39.4 mm and 40.4 mm, respectively), but at 112 days under 18 °C (40.7 mm). In P. hatcheri, differentiation of females occurred at 21 days (17.8 mm) at 25 °C, 28 days (20.8 mm) at 21 °C, and 35 days (23.2 mm) at 18 °C. Male differentiation became evident at 56 days under 25 and 21 °C (30.8 and 32.7 mm, respectively), and at 70 days (37.7 mm) at 18 °C. The sex-ratios of O. argentinensis reared at 18 or 21 °C were female-biased whereas those at 25 °C were not; groups reared at 18 °C had significantly more females than groups from the same progeny reared at 25 °C. In contrast, the sex-ratios in all groups of P. hatcheri did not differ significantly from 1:1 and no significant differences were found between groups of the same progeny reared at different temperatures. These results suggest the occurrence of thermolabile sex determination (TSD) in O. argentinensis whereas in P. hatcheri gonadal sex appears to be strongly genetically determined.