Seasonal patterns of abundance and host relationships of the Australian paralysis tick,Ixodes holocyclus Neumann (Acarina: Ixodidae), in southeastern Queensland

Estimates of seasonal abundance of larvae, nymphs and females of the paralysis tick, Ixodes holocyclus, were obtained by collecting ticks that engorged on small mammals and birds trapped in two localities in southeastern Queensland: Brisbane (wet sclerophyll forest) and Tamborine Mountain (cleared rain forest). The long-tailed short-nosed bandicoot, Isoodon macrourus, was the most common mammal trapped but small numbers of other marsupials, rodents and ground frequenting birds were also captured. Small numbers of five other tick species were also collected. In both habitats there was clearly one dominant generation of I. holocyclus;7er year, although the presence of all stages at most times of the year indicated overlapping of smaller cohorts. Females were most abundant in spring and early summer, larvae in summer-autumn, and nymphs in autumn-winter. I. holocyclus was abundant on I. macrourus and rare on most other mammals and birds captured. At the peak of abundance of each instar, each bandicoot dropped from 500 to 2000 engorged larvae, 100 to 200 engorged nymphs, and four to six engorged females. Life tables were compiled for the tick in both habitats and these indicate that there was relatively high survival from engorged larva to engorged nymph and thence to engorged female and that most mortality occurred between detaching of the engorged female and the detaching of the engorged larva. The tick was more abundant on bandicoots from cleared rain forest and rain forest edge, than on those from sclerophyll woodland. The survival of engorged larvae and nymphs of I. holocyclus and the larval productivity of engorged females were examined in a warm moist climate where the tick was abundant (Tamborine Mountain) and in a hotter dryer climate where the tick was rare or absent (Amberley). In both localities engorged larvae and nymphs survived to the next instar in all seasons of the year. On most occasions engorged females produced eggs which hatched. Mature bandicoots from tick infested areas showed little or no resistance to infestation with larvae or nymphs of I. holocyclus, whereas other small mammals from the same area showed an appreciable degree of resistance to the immature stages of the tick. Feeding larvae and nymphs exposed to normal light-dark cycles in the laboratory detached during the afternoon and early evening. This behaviour and host resistance are discussed in relation to the daily activity cycles of host species, their habitat preferences, and their role as hosts for I. holocyclus.     

Drop off rhythm and survival periods of <Emphasis Type="Italic">Amblyomma lepidum</Emphasis> (Acari: Ixodidae) under field conditions

In this study, engorged Amblyomma lepidum ticks were found to drop off in two peaks, one in the morning and one in the evening. Most larvae and females engorged during the morning hours between 06.00 h and 10.00 h with a peak around 08.00 h, whereas the majority of the nymphs dropped in the evening between 18.00 h and 24.00 h with the peak around 22.00 h. Although the effect of time on drop-off patterns of the ticks was statistically significant (p≤ 0.001), there were no significant seasonal influences. Survival of unfed stages of A. lepidum was also studied and was found to increase from larvae to adult ticks. The longest survival periods of 10, 11 and 14 weeks were recorded during the wet season for larvae, nymphs and adults, respectively. It is concluded that environmental conditions required for survival of A. lepidum are optimal only during the wet season and that during other seasons the tick depends primarily on prevailing micro-climatic conditions for its survival.     

Gene silencing of the tick protective antigens, Bm86, Bm91 and subolesin, in the one-host tick Boophilus microplus by RNA interference

The use of RNA interference (RNAi) to assess gene function has been demonstrated in several three-host tick species but adaptation of RNAi to the one-host tick, Boophilus microplus, has not been reported. We evaluated the application of RNAi in B. microplus and the effect of gene silencing on three tick-protective antigens: Bm86, Bm91 and subolesin. Gene-specific double-stranded (dsRNA) was injected into two tick stages, freshly molted unfed and engorged females, and specific gene silencing was confirmed by real time PCR. Gene silencing occurred in injected unfed females after they were allowed to feed. Injection of dsRNA into engorged females caused gene silencing in the subsequently oviposited eggs and larvae that hatched from these eggs, but not in adults that developed from these larvae. dsRNA injected into engorged females could be detected by quantitative real-time RT-PCR in eggs 14 days from the beginning of oviposition, demonstrating that unprocessed dsRNA was incorporated in the eggs. Eggs produced by engorged females injected with subolesin dsRNA were abnormal, suggesting that subolesin may play a role in embryonic development. The injection of dsRNA into engorged females to obtain gene-specific silencing in eggs and larvae is a novel method which can be used to study gene function in tick embryogenesis.     

Role of Rusa deer Cervus timorensis russa in the cycle of the cattle tick Boophilus microplus in New Caledonia

Two field experiments were conducted to evaluate the efficiency of Rusa deer in the development of the cattle tick Boophilus microplus in comparison with that of steers in the same pastures and under the same conditions of infestation. No difference was noted between a mixed steer/deer herd and a pure steer or pure deer herd in the infestation pattern of each host, suggesting that attachment to the alternative host is mechanical and not affected by the simultaneous presence of the primary host on the pasture. Deer are capable of producing engorged viable females, with weight and reproductive performances similar to or even better than females fed on steers. For moderate levels (1 million larvae per hectare) and high levels (32 million larvae per hectare) of pasture infestation, tick burdens on steers were not very different (e.g. average 1911 and 2681ticks per m² skin, respectively, on day 24). This may be because of saturation of steer skin sites at the moderate larval dose. Deer harboured 2.7–33 times fewer ticks than steers and produce no engorged females at the moderate larval level and 32 times fewer engorged females than steers at the high larval level. Infestation of deer was dosedependent with averages of 12 and 399ticks per m² skin on day 25 at the moderate and high larval levels, respectively. At a high infestation level of the environment, Rusa deer may contribute, but to a limited extent, to infestation of pastures and, consequently, of cattle. However, their role in sustaining a viable tick population requires further investigation.     

Staphylococcus saprophyticus is a pathogen of the cattle tick Rhipicephalus (Boophilus) microplus

During experimental Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) infestation on cattle, approximately 5% of engorged female ticks showed symptoms of bacterial infection. The affected ticks were unable to oviposit, secreted a distinctive yellow exudate through the genital orifice and eventually died. Microscopic analysis of tick exudate showed abundant clusters of Gram-positive cocci bacteria that were isolated and cultured on bacteriological medium. Biochemical phenotyping and 16S rRNA ribotyping analysis on cultured bacteria identified it as Staphylococcus saprophyticus. This species was also isolated from healthy tick larvae, indicating that S. saprophyticus is commonly found in ticks during different developmental stages. However, conspicuous symptoms are only found on fully engorged females. Cultured S. saprophyticus induced identical pathological symptoms when the bacteria were experimentally inoculated into healthy ticks, demonstrating it to be the causative agent of the R. microplus infectious lethal disease described in this work.     

Instar development and disengagement rate of engorged female winter ticks,Dermacentor albipictus (Acari: Ixodidae), following single- and trickle-exposure of moose (Alces alces)

Seven hand-reared moose (Alces alces) calves and one yearling were infested with 30 000 larvae each of the winter tick,Dermacentor albipictus, either by single- or trickle-exposure (1000/day). They were examined weekly for instar changes from September/October until late May. By 2 and 3 weeks post-exposure, most larvae on single- and trickle-infested moose, respectively, had fed and molted to nymphs. Thereafter, tick development was similar between both infestation techniques. Nymphs dominated the tick population from October to mid-February, and adults from mid-February to May. The peak of host disengagement by engorged females was late March in both years. Weights of engorged females from calf moose declined over time during the disengagement period.     

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.     

Development, survival, and oviposition of the rabbit tick, Haemaphysalis leporispalustris (Packard) (Acari: Ixodidae), at constant temperatures

The relationship between development, survival, and oviposition rates, and five constant temperatures is described for the developing and reproductive life stages of the rabbit tick, Haemaphysalis leporispalustris (Packard). Development was most rapid at 29.7 C for egg and larvae, and 35.6 C for nymphs. Survival was greatest between 14.7 and 29.7 C, but was reduced at 35.6 C for eggs and larvae. Oviposition was optimal between 19.9 and 29.7 C with a maximum mean daily oviposition of 253 eggs/female/day on the third day of oviposition at 29.7 C. Maximum mean total eggs per female produced was 1,157 with a range of 277 to 3,327. The total number of eggs produced per female correlated with the weight of the engorged female. Both linear and sigmoid curve equations were used to approximate the relationship between the temperature and development rates of eggs, larvae, and nymphs. The nymphs had the highest heat requirements of the 3 development stages. Comparisons with field host-parasite data indicate that the rabbit tick has a 2-yr life cycle in southwestern Nova Scotia.     

Feeding performance ofAmblyomma variegatum (Acarina: Ixodidae) fed repeatedly on rabbits

Rabbits infested with different stages ofAmblyomma variegatum Fabricius, 1794 became resistant to subsequent infestations by the same tick. Resistance was manifested by a reduction of 73.6% in the mean engorged weight of female ticks by the 3rd infestation. By the 5th infestation, only 70% of the nymphs engorged and their mean engorged weight was 57.7% of that of nymphs fed on tick-naive control rabbits. In the case of larvae, there was a 22.8% reduction in their mean engorged weight by the 6th infestation. Based on increases in body length while feeding on tick-naive rabbits, the nymphs could be divided into four feeding categories, i.e. Nl (unfed), N2, N3 and N4 (increasing states of engorgement). While 92–96% of ticks which dropped from susceptible rabbits fitted into feeding category N4, only 28% of those that dropped from tick-resistant rabbits fitted into that category. The remainder of the ticks fitted into categories N3 (60%) and N2 (12%). The majority of those ticks with reduced weight developed into adults which had an atypical scutal ornamentation pattern, in that an additional pair of lateral spots was regularly observed on the males. The females of such ticks deposited small numbers of eggs from which no larvae hatched.     

Development and biological characteristics of <Emphasis Type="Italic">Haemaphysalis longicornis</Emphasis> (Acari: Ixodidae) under field conditions

The development and biological characteristics of Haemaphysalis longicornis were investigated under field conditions in Xiaowutai National Natural Reserve Area, North China. Unfed larvae, nymphs and adults were fed on rabbits and exposed to daylight. Three free-living stages were allowed to develop in field plot selected in a tick natural habitat. The host seeking behavior and seasonal occurrence were observed. Haemaphysalis longicornis were active from mid March to mid October. The premoult period of nymphs and preoviposition of females were regulating phases of their life cycle. The developmental durations of eggs, larvae and adults were constant under field conditions regardless when the development started. The oviposition periods in May and June were statistically shorter than those in July and August. The daily oviposition patterns of females engorged in May and June demonstrated unobvious peak, which differed from those engorged in July and August. The daily oviposition peak of the latter occurred on the 4th day of oviposition. Moreover, a positive correlation was found between the mass of the laid egg and the body weight of engorged females (r = 0.62, P < 0.001). The female reproductive efficiency indices were 2.9, 6.1, 10.5 and 9.0 in May, June, July and August, respectively. The mean weight (3.33 mg) of engorged nymphs molting to females was significantly higher than that (2.35 mg) of those molting to males (P < 0.001), but the body weights of both sexes were overlapping.     

Redescription of the larva,and description of the nymphal and adult stages of Ornithodoros peruvianus Kohls,Clifford & Jones, 1969 (Acari: Argasidae)

The soft tick Ornithodoros peruvianus Kohls, Clifford & Jones, 1969 was described as a parasite of bats in Peru upon the examination of engorged larvae only. Recently, larvae of this tick species were reported on bats from northern Chile. However, the adult and nymphal stages of O. peruvianus have remained undescribed. This study aimed to redescribe the larva of O. peruvianus based on unfed specimens, and to describe nymphs, the male and the female of this species. Ticks were collected on the walls inside three caves in northern Chile. Two females laid eggs in the laboratory. Part of the unfed larvae was separated for morphological and morphometrical analyses, and the remaining specimens were fed upon laboratory mice in order to obtain subsequent nymphal and adult stages. The first nymphal stage (N1) moulted either to male or to a second nymphal stage (N2) without feeding. Obtained N2 moulted either to male or female after one meal. PCR amplification of tick mitochondrial 16S rRNA of specimens from the three caves revealed almost identical sequences. The unfed larva of O. peruvianus has an elongated idiosoma, and fringed setae cover the ventral surfaces of coxae, palps and tarsi. Nymph 1 has a thin integument covered by incipient mammillae and barely noticeable dorsal disks; it lacks cheeks and possesses few short setae on the basis capitulum. Nymph 2 has a pair of small cheeks and resembles adult stages in its tegumentary traits and capitulum. Adult stages exhibit developed cheeks (larger in females) without the capacity to completely cover the capitulum. Very small and low mammillae cover the surface of the dorsal idiosoma in adults. As this feature also occurs in other bat-associated soft ticks, regardless of their phylogenetic relatedness, small mammillae in bat soft ticks are suggestive of convergent evolution.

     

Blood feeding of Ornithodoros turicata larvae using an artificial membrane system

An artificial membrane system was adapted to feed Ornithodoros turicata (Ixodida: Argasidae) larvae from a laboratory colony using defibrinated swine blood. Aspects related to larval feeding and moulting to the first nymphal instar were evaluated. A total of 55.6% of all larvae exposed to the artificial membrane in two experimental groups fed to repletion and 98.0% of all fed larvae moulted. Mortality rates of first instar nymphs differed significantly depending on the sorting tools used to handle engorged larvae (χ² = 35.578, P < 0.0001): engorged larvae handled with featherweight forceps showed significantly higher mortality (odds ratio = 4.441) than those handled with a camel‐hair brush. Differences in the physical properties of the forceps and camel‐hair brush may affect the viability of fragile soft tick larvae even when care and the same technique are used to sort them during experimental manipulations. The current results represent those of the first study to quantify successful feeding to repletion, moulting and post‐moulting mortality rates in O. turicata larvae using an artificial membrane feeding system. Applications of the artificial membrane feeding system to fill gaps in current knowledge of soft tick biology and the study of soft tick–pathogen interactions are discussed.     

Growth of Haemaphysalis (Kaiseriana) longicornis on cattle.

Increases were recorded of lengths of larvae, nymphs and females of the tick, Haemaphysalis (Kaiseriana) longicornis during feeding on cattle, so that categories could be established for estimating the ages of ticks in natural populations. Most larvae and nymphs engorged in 4 days and females in 5 or 6 days. Four age categories were defined for larvae and 3 for nymphs. The growth of females was variable but 4 stages of physiological development were defined based on changes in their lengths. The lengths were determined of each instar 24 h before detachment to enable estimation of the numbers maturing each day on cattle in the field.     

Development, survival, fecundity and behaviour of Haemaphysalis (Kaiseriana) longicornis (Ixodidae) at two locations in southeast Queensland.

The free-living stages of the tick Haemaphysalis (Kaiseriana) longicornis were studied at Mt Tamborine (526 m altitude) and Amberley (25 m altitude) in southeast Queensland between 1971 and 1980. Data are presented on the number of eggs and larvae produced, the moulting success of engorged larvae and nymphs and the survival and behaviour of unfed larvae, nymphs and adult females. Temperature, moisture, daylength, grass length and age of unfed ticks were investigated as sources of variation in development rates, fecundity or survival. At Mt Tamborine the life cycle was well synchronized with the seasons to produce one generation per year. At Amberley higher temperatures accelerated development rates and would have delayed diapause, so disrupting the life cycle.     

Susceptibility of the cattle tick Boophilus microplus (Acari: Ixodidae) to isolates of the fungus Beauveria bassiana

The susceptibility of the tick Boophilus microplus to Beauveria bassiana was evaluated by inoculating eggs, larvae and engorged females of the tick with five fungal isolates at concentrations of 10⁶, 10⁷ and 10⁸ conidia/ml. Tick eggs (0.25 g) were immersed in 1 ml of a suspension of the different conidial concentrations for 1 min. Similar exposure was performed by immersion of 2000 larvae and homogeneous groups of nine engorged females in 2 and 20 ml of conidial suspension, respectively. Treated eggs, larvae and adults were placed in an incubator at 27 ± 1 °C and relative humidity above 80% for evaluation of the fungal action. All fungal isolates applied at all conidial concentrations reduced the hatching rate of larvae from treated eggs by 1.36–65.58% and increased the mortality rate of inoculated larvae by 0.8–70.49%. In the bioassay with engorged females, oviposition period was reduced by 9.69–47.80%, egg mass weight by 4.71–53.87%, estimated reproduction by 8.3–60.62%, egg production index by 5.03–54.20%, percent larval hatching by 0.27–13.96%, and the mortality rate of treated females was increased by 96.60–100%. The reduction of the estimated reproduction obtained for the treated groups ranged from 8.37 to 64.52%. The sporulation of the pathogen on dead females ranged from 3.70 to 88.88% depending on the isolate and concentration used. Isolates AM 09, CB 7 and JAB 07 were the most effective and effectiveness increased with increasing concentrations of conidia in the suspensions.     

Partial strategic tick control within a herd of European breed cattle in the state of Rio Grande do Sul,southern Brazil

A trial is described, in the state of Rio Grande do Sul, southern Brazil, as one of a series suggested to investigate the effects of strategic but selective acaricide treatments of cattle within herds against Boophilus microplus. They are aimed at considering the repercussions of farmer attempts at immediate reductions in acaricide costs and the potential for creation of ‘refugia’ of untreated ticks. Half (Group 1) of a small experimental herd of European breed heifers were treated strategically against ticks, three times during the late spring–early summer and twice during autumn (southern hemisphere), with an injectable avermectin endectocide, designed to act directly against the first and third generations of parasitic B. microplus per ‘cattle tick year’ at this site, respectively. The consequent levels of infestations on all of the member cattle in their common pasture were monitored. Group 1 showed low to zero tick counts during the 28-day treatment interval periods and up to ca. 14 days after the last of such a series. Treated cattle, however, became re-infested outside of these periods and to levels that would be considered as unacceptable by farmers in the state. The untreated cattle (Group 2) showed infestations at generally higher levels, than their contemporaries, within and outside of the treatment periods. There were thus ample sources of larvae in the pasture, derived principally from falling, untreated engorged female ticks, re-infesting both the treated and untreated cattle. Advantages of maintaining chemically untreated cattle ticks within a herd, compared to their disadvantages as contaminants to classical strategic control procedures, merit re-evaluation, especially in relation to the recent, world-wide resurgence of acaricide resistance in B. microplus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ecology and phenology of cattle ticks in Zambia: Development and survival of free-living stages

A study on development and survival of free-living stages of three important cattle ticks in Zambia,Amblyomma variegatum Fabricus,Boophilus decoloratus Koch, andRhipicephalus appendiculatus Neumann, was carried out to complement studies on seasonal dynamics of parasitic stages.Different instars of engorged ticks were exposed under quasi-natural conditions according to the season in which they occur naturally. Generally, development rates of all stages of the three species were related to temperature, whilst the duration of survival was influenced mainly by rainfall and consequent relative humidity.Observations on the effect of age and climate on the behaviour of ticks on pastures were also made. BothA. variegatum andR. appendiculatus completed only one generation per year. InA. variegatum, engorged females detaching early in the adult season (August to October) undergo morphogenetic diapause. Adults ofR. appendiculatus emerging between August and October enter a period of behavioural diapause before becoming active in December. These mechanisms effectively synchronize the life-cycles of these two univoltine species. The one-host tick,B. decoloratus, is able to complete three to five generations each year with no indication of seasonal synchronization.     

Comparison of the effects of Altozar and DDT on females ofIxodes persulcatus Sch. during and after feeding

Ixodes persulcatus females were treated with Altozar and DDT at one of six consecutive time-points during the period beginning with attachments and ending with the commencement of oviposition.The moment of tick attachment (point 1) appeared to be the most sensitive time for the action of Altozar; a delay of detachment of some of the engorged females was observed, as well as a decrease in their mean weight and the non-detachment of a considerable number of the females over a long period. Similar effects were observed when Altozar was applied on the first and third days after attachments (points 2 and 3) although in the first case they were less pronounced. Altozar treatments on the fifth day of feeding, shortly before oviposition, and especially immediately after detachment (points 4,5 and 6, respectively) mainly resulted in non-viability of the eggs.DDT was ineffective when it was applied at point 1. DDT treatments of ticks at points 3 and 5 were highly effective; this was expresseds by a reduction in weight of the engorged females and a suppression of their fecundity at point 3, and death of all the larvae at different times after hatching at point 5. Many larvae also perished when the ticks were treated with DDT at point 6. Ticks were quite tolerant to DDT action when they were treated at points 2 and 4.The action of both compounds ultimately resulted in the inhibition of tick reproduction, but the rate and method depended on the compound applied as well as on the time of treatment. Altozar effects after treatment at points 1–3 may be considered to be hormonal.     

The role of medium-sized mammals as reservoirs of Borrelia burgdorferi in southern New York

The ability of raccoons (Procyon lotor), striped skunks (Mephitis mephitis) and opossums (Didelphis virginiana) to serve as reservoirs of Borrelia burgdorferi, the spirochetal agent of Lyme disease, was compared with that of white-footed mice (Peromyscus leucopus). Twenty-eight (28) medium-sized mammals and 34 white-footed mice were captured in Westchester County, New York (USA) in summer 1986. Animals were caged over pans of water for 1 to 2 days to recover engorged tick larvae (Ixodes dammini) that detached from the hosts after feeding. With the exception of mice, numbers of engorged tick larvae recovered exceeded those counted during initial examinations of the hosts by 30% (opossums) to nearly 90% (raccoons). Newly-molted nymphal ticks derived from the engorged larvae were examined for the presence of spirochetes by darkfield microscopy. Percentage infection was 5% (n = 22) for ticks from skunks and 14% (n = 191) for ticks from raccoons. None of 24 nymphs from larvae that fed on opossums survived long enough for spirochete examination. By comparison, 40% (n = 72) of nymphs from larvae which fed on white-footed mice were infected. Of the individual hosts from which molted nymphs had fed as larvae, 67% of mice, 33% of skunks, and 55% of raccoons produced spirochete-positive ticks.     

Entomopathogenic fungi associated with Ixodes ricinus ticks

The objective of this study was to demonstrate the occurrence of entomopathogenic fungi on Ixodes ricinus ticks in relation to the tick stage, engorgement and season. Ticks were collected from the vegetation, from small rodents and from deer. All entomopathogenic fungi found belonged to the Hyphomycetes. Paecilomyces farinosus and Verticillium lecanii were the predominant species. Other species, found only on engorged females were: Beauveria bassiana, B. brongniartii, P. fumosoroseus and V. aranearum. Eight out of 1833 ticks collected from the vegetation and three out of 269 engorged nymphs were infected with fungi. Thirty-three out of 149 engorged females were infected, whereas males and engorged larvae were not infected. Throughout the season, a significantly higher proportion of ticks collected in autumn were infected. Entomopathogenic fungi may have a significant impact on the size of the I. ricinus population, since females were the most frequently infected stage.