Methods for estimating the demographic structure of the taiga tick (Ixodidae) based on results of standard parasitological observations

A retrospective estimation of the abundance dynamics of the taiga tick Ixodes persulcatus in mixed coniferous and leaf-bearing forests of the Udmurtia Republic in the period 1957-1986 was carried out. A possibility to estimate the absolute number of all stages of I. persulcatus based on relative indices. Females of I. persulcatus lay 20,250 eggs per 1 hectare, and this number of eggs gives birth to 15,000 larvae. From this number, 7870 larvae hibernate and 6550 individuals became fed. The number of nymphs is 5930, among which 5110 individuals live up to spring, and 1390 became fed. The number of adult mites in autumn is 1250; in subsequent spring this number decreases to 780. The mean number of engorged females is 8. The mortality rate of ticks caused by the deficit of hosts increases from preimaginal stages to adults; for larvae, nymphs and imago this index is 16.6, 72.8, and 97.9%, respectively. Quotas of individuals with 3-, 4- and 5-year life cycle among the unfed imago are 70.4, 28.0, and 1.6%, respectively.     

Variability of the life cycle duration in the taiga tick from mixed coniferous-broad-leaved forests of the Udmurt Republic

Seasonal cohorts of the unfed Ixodes persulcatus imago in the study area were found to consist of the ticks passed through three-, four-, and five-year life cycles, in the ratio 72.6, 26.4, and 2.0% respectively, on the base of mean long-term values. Such ratio is established if 91.7% of larvae and 79.9% of nymphs develop without diapause, while the rest of larvae and nymphs develop with diapause. Mean duration of the tick generation is 3.3 years, with the fluctuations in certain of the years within the limits of 3.15-3.36 years.     

The infection of ixodid ticks collected from humans with the tick-borne encephalitis virus in Tomsk city and its suburbs

The ticks Ixodes persulcatus and I. pavlovskyi collected from people visited gardens and suburban forests have been examined by the IFA methods on the presence of tick-borne encephalitis virus (TEV). It was established, that the most part of ticks collected from humans belongs to I. persulcatus, despite the fact that I. pavlovskyi dominates on the territory of the city and its suburbs. TEV infection was registered more often in fed ticks, in comparison with those without signs of preceding feeding. Infected specimens constituted 9.4% of 53 I. persulcatus individuals examined. In I. pavlovskyi 3.7% of 27 examined specimens were infected. In fed ticks (41 specimens of I. persulcatus and 20 I. pavlovskvi) the rates of infected specimens were higher and constituted 48.8 and 35%, respectively. In suburban forests, as well as in the city, I. persulcatus was found to attack humans more often than I. pavlovskyi. TEV infection was recorded in 12.7% of 220 unfed I. persulcatus specimens examined and in 41.6% of 142 fed individuals. In I. pavlovskyi, 6.6% of unfed and 25% of fed specimens was infected (33 unfed and 24 fed specimens were examined). Thus, in all territories examined, percent of infected specimens was significantly lower in I. pavlovskyi, and in fed ticks of both species, TEV was recorded more often.     

Transovarial and transphasic transmissions of Borrelia by the taiga tick Ixodes persulcatus (Ixodidae)

Three generations of the taiga tick Ixodes persulcatus, the descendants from naturally infected females, have been examined by means of dark field and phase contrast microscopies and indirect immunofluorescent reactions with monoclonal antibodies. Location of borreliae in oocytes was examined by means of electron microscopy. The examined ticks derived from 9 females collected in the Novgorod Province, from 6 females of 1st laboratory generation and 5 females of the 2nd generation. In total, 250 larvae, 178 nymphs, 59 females and 70 males of three consequent generation have been examined. Almost 100% of descendants of naturally infected females were infected with Borrelia burgdorferi s. l. and similar infection rate was observed in unfed tick larvae collected in field conditions. The borreliae received transovarially to larvae of the 1st generation then were transmitted to 100% nymphs and imago of this generation and two next generations.     

Sex ratio in ixodid tick collections from Leningrad Province

The analysis of results of many-year regular collections of ixodid ticks has shown that females (56%) were dominant in I. persulcatus while in I. ricinus were dominant males (52%). The ratio between sexes in both species changed noticeably as in individual years so during the imago activity season. In summer collections of I. lividus females were dominant every year, the share of which accounted on the average for 70% and varied from 69 to 75% within different seasons and from 60 to 83% within imago activity season. During hibernation and in spring the share of males and females was nearly adequate.     

Demography and population models of ticks of the genus Ixodes with long-term life cycles

The most important parameters necessary for the creation of population models for threehost species with long-term life cycles are discussed with an example of ticks Ixodes persulcatus and I. ricinus. In these species, specimens of the same biological age may belong to different age cohorts and their calendar age may differ by several months or even years. Accurate estimation of the calendar age of separate individuals is dofficult; it is based on the extrapolation by its possible biological age and by belonging to the certain age cohort of a natural population. Population models that can predict simultaneous abundance of activated hungry specimens of all the three developmental stages and probability of host-finding in hyngry ticks during questing period possess the prognostic value. Daily mortality of ticks of different developmental stages and phases of each stage (questing, feeding, preparation for molting, and diapause) must also be known. The abundance of questing hungry ticks in the ecosystem is determined by the balance between recruitment of the population with new individuals, their selection by hosts, dying of ticks from starvation, and consumption of ticks by predators. At present, unfortunately, only some of these parameters are known rather sufficiently.     

Long-term dynamics of the epizootic process in natural foci of ixodid tick borreliosis in mountain taiga forests of the Middle Ural

During eleven spring-summer seasons (1992-2002), the dynamics of the epizootic process in natural foci of ixodid tick-borne borrelioses (ITBB) were studied in taiga forests of the Middle Ural (Perm Province, Russia). In these foci, Borrelia garinii and B. afzelii circulate, and their main vector is the Ixodes persulcatus tick. Main parameters of the epizootic process were calculated for each season. In four seasons (1993, 1996, 1999 and 2002), the parameters characterizing the abundance of unfed nymphs and adult ticks, as well as the prevalence of Borrelia in them, density of infected ticks, and approximate total number of Borrelia in them proved to increase essentially and simultaneously. These seasons were preceded by the years of population peaks in forest small mammals (1992, 1995, 1998 and 2001), especially in the Clethrionomys glareolus vole, the dominant species in the local fauna of these mammals and the main reservoir host of Borrelia. Apparently, the possibility of horizontal transmission of the ITBB agents sharply increased in such years, and this resulted in the intensification of their dissemination.     

Comparative evaluation of the efficacy of Borrelia indication in ixodes ticks (Ixodidae) using dark field microscopy and polymerase chain reaction (PCR)

Indication of Borrelia (B. burgdorferi sensu lato) in 205 adult unfed I. persulcatus ticks from a natural focus was carried out simultaneously by methods of PCR and dark-field microscopy of vital preparations. PCR method revealed Borrelia prevalence in considerable number of ticks, in which Borrelia were not found by microscopy of 250 microscopic fields in a preparation from each individual tick. At the same time, PCR method didn't give positive results for approximately 8% of ticks, which contained rather high concentration of Borrelia (more than 10 per 100 microscopic fields). In general, PCR method doesn't have advantages in comparison with a microscopy of vital preparations for study the Borrelia prevalence in ticks.     

Mixed infection by tick-borne encephalitis virus and Borrelia in ticks

To investigate the relationships between tick-borne encephalitis (TBE) virus and the bacterial spirochaete Borrelia burgdorferi sensu lato in vectors with mixed infections, unfed adult Ixodes persulcatus ticks were collected by flagging from vegetation in southern-taiga forests of the Pre-Urals region of Russia where both infections circulate sympatrically. Prevalences of TBE and Borrelia infections in a total of 4234 ticks were compared over 5 years. No significant differences were revealed between the prevalence of Borrelia infection in ticks with and without TBE virus (29.4+/-7.8% vs 23+/-3.6%), or between the prevalence of TBE virus infection in ticks with and without Borrelia (24.0+/-6.6% vs 18.4+/-3.4%). In ticks with mixed infection (40/689 = 5.8%), concentrations of TBE virus and Borrelia were not significantly correlated with one another. Field observations showed parallel trends in the prevalence of these pathogens in tick populations from year to year (1993-1997) indicating that, in I. persulcatus with mixed infection, Borrelia and TBE virus do not seem to interfere with each other and are apparently not involved in any antagonistic relationships.     

Pathogenicity of entomopathogenic fungi to different developmental stages of Rhipicephalus sanguineus (Acari: Ixodidae).

The pathogenicity of 4 species of entomopathogenic fungi (Hyphomycetes species: Beauveria bassiana, Metarhizium anisopliae, Metarhizium flavoviride, and Paecilomyces fumosoroseus) to various developmental stages of Rhipicephalus sanguineus (Acari: Ixodidae) ticks was compared under laboratory conditions. The most virulent isolate, M. anisopliae-108, caused 92-96% mortality to unfed larvae and nymphs on day 7 postinfection (PI) and 100% mortality to unfed adults and engorged females on day 21 PI. The pathogenicity of M. anisopliae-108 to engorged larvae and nymphs was lower--82.6 and 60%, respectively. All tested B. bassiana, M. flavoviride, and P. fumosoroseus isolates were significantly less virulent (P < 0.05) or avirulent toward most life stages of R. sanguineus. The M. anisopliae and M. flavoviride isolates also prevented or reduced the ability of the ticks to lay eggs several days before their deaths. Female ticks infected by the fungi achieved only 11.3-60.8% of their egg-laying capacity compared with the controls.     

Seasonal changes in antioxidant defence systems in seminal plasma and fluids of the boar reproductive tract

This study aimed to analyze seasonal variations in the antioxidant defence systems of the seminal plasma and fluids of the cauda epididymis and vesicular glands of the boar. The analyzed antioxidants included superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and total L-glutathione (GSH+GSSG). Seasonal changes in total protein content and total antioxidant status (TAS) of the seminal plasma and reproductive fluids were also analyzed. Compared with the spring-summer period, total protein content in the seminal plasma was significantly higher during the autumn-winter period. Among the antioxidants analyzed, only SOD activity showed marked seasonal variations, being significantly higher during the spring-summer period. Likewise, the fluid of the cauda epididymis exhibited greater SOD and CAT activity during the spring-summer period, whereas TAS levels were markedly higher during the autumn-winter period. Neither GPx activity nor total GSH+GSSG content in the cauda epididymal fluid was significantly affected by the seasonal periods. The vesicular gland fluid exhibited an approximately 4-fold greater level of SOD activity during the autumn-winter period, as compared with the spring-summer period. By contrast, greater CAT and GPx activity, and a higher level of total GSH+GSSG were observed in the vesicular gland fluid during the spring-summer period. In conclusion, the findings of this study indicate that seasonal variations could have varying effects on the antioxidant defence systems in the seminal plasma and fluids of the boar reproductive tract.     

Increased expression of ATG genes during nonfeeding periods in the tick Haemaphysalis longicornis

Ticks are long-lived hematophagous arthropods and have tolerance to starvation. They can survive without food during the host-seeking period for several months to years. To understand how ticks obtain energy over a long period of non-feeding (starvation), we focused on autophagy, a crucial proteolysis system via the lysosomes for various cellular processes that is induced during starvation in eukaryotes. In the present study, EST databases for several organs of the tick Haemaphysalis longicornis led to the identification of HlATG3, HlATG4 and HlATG8, homologues of 3 autophagy-related (ATG) genes, ATG3, ATG4 and ATG8/LC3/GABARAP, respectively, which are essential for the Atg8 conjugation system in model animals. Real-time PCR results revealed that the expression of HlATG3, HlATG4 and HlATG8 in the tick showed higher levels during the non-feeding period than the feeding period, suggesting that the Atg8 conjugation system is at work in unfed ticks. Notably, their expression levels were higher in the midgut, a digestive organ, of unfed than fed adults. Histological analysis demonstrated that lipids and glycogen accumulated within the epithelial cells of the midgut in unfed ticks, implying that the midgut of unfed ticks serves as storage of those components as nutrients during non-feeding. Furthermore, autophagic organelles were found in the midgut undifferentiated cells of unfed ticks. The starved condition appears to be associated with the increased expression of HlATG genes in the midgut of unfed ticks. Tick autophagy might help compensate for the loss of nutrients derived from host blood components during the non-feeding period.     

Susceptibility of <Emphasis Type="Italic">Amblyomma variegatum</Emphasis> ticks to acaricides in Ghana

The susceptibility of unfed and fed stages of larvae, nymphs and adult females of Amblyomma variegatum ticks were tested using Shaws filter paper dip method against four acaricides; chlorfenvinphos and dioxathion, chlorfenvinphos, gamma benzene hexachloride and amitraz at four different concentrations including the recommended dose rates. Based on their lethal concentrations (LC₅₀ & LC₉₀) chlorfenvinphos and dioxathion combined and chlorfenvinphos alone placed first and second, respectively, in all stages except at the unfed nymphal stage where gamma benzene hexachloride topped with a LC₅₀ of 0.001629, while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone had LC₅₀ of 0.001794 and 0.002258, respectively. Amitraz appeared to have a quick knock-down effect on larvae and nymphs but at the recommended dose rate, showed no mortality of the ticks at that stage. However, at a concentration of 0.040%, amitraz showed a 100% inhibition of oviposition and hatching of laid eggs. Gamma benzene hexachloride produced only 66% inhibition of oviposition while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone produced 100% inhibition of oviposition at their recommended dose rates. Fed nymphs were more susceptible than the unfed nymphs. Eggs laid by engorged female ovipositing ticks, applied with gamma benzene hexachloride, hatched.This revised version was published online in May 2005 with a corrected cover date.     

Protection of Metarhizium anisopliae conidia from ultra-violet radiation and their pathogenicity to Rhipicephalus evertsi evertsi ticks

Metarhizium anisopliae conidia were formulated in water or in olive oil containing 3% commercial sunscreens (Everysun or E45 Sun Block 50) and exposed to an artificial UV source for up to 5 hours. Survival of conidia after 5 h of exposure to UV in oil formulation was 29% when protected with Everysun, 40% when protected with E45, and 4% in control. In comparison, survival of conidia formulated in water was 13% when protected with Everysun, 24% when protected with E45, and 0% in control. Furthermore, the influence of sunscreens on conidia viability and virulence to Rhipicephalus evertsi evertsi larvae and unfed adult ticks was evaluated. Adding these compounds to the conidial formulations did not reduce the viability of the conidia. Larval mortality was 95 and 100%, while unfed adult mortality was 90 and 97% after being exposed to unprotected conidia formulated in water or in oil, respectively. Conidia protected by Everysun or E45 formulated in water, induced 88 and 83% mortality in larvae, and 92 and 90% mortality in unfed adults, respectively. Conidia suspended in oil and protected by Everysun or E45 induced 94 and 91% mortality in larvae, and 83 and 81% in unfed adults, respectively. These observations indicate that olive oil and the two sunscreens confer protection to conidia against damages by UV radiation without interfering with their pathogenicity to ticks.     

昆虫病原线虫斯氏线虫和异小杆线虫对长角血蜱雌蜱的致病力

用昆虫病原线虫小卷蛾斯氏线虫（Sc BJ）、夜蛾斯氏线虫（Sf Otio）、拟双角斯氏线虫（Sc D43）、格氏斯氏线虫（Sg NC32）和嗜菌异小杆线虫（Hb E-6-7）对长角血蜱雌蜱进行感染试验,所用线虫剂量为4 000 Ijs/dish。结果表明,5种线虫均对长角血蜱雌蜱有致死效应。Hb E-6-7和Sc BJ两种线虫对雌蜱各发育期致病力最强,导致雌蜱的累积死亡率和半致死时间分别为饥饿雌蜱82.5%,9.0天和75.0%,8.8天;吸血雌蜱90.0%,8.0天和82.5%,8.0天;饱血雌蜱93.3%,7.3天和86.7%,7.3天。Sc D43对饱血雌蜱有较高的致死效应,为80.0%,但半致死时间较长,为11.7天。Sf Otio和Sg NC32对长角血蜱雌蜱的致死效应较低。饱血雌蜱较饥饿雌蜱和吸血雌蜱更易被线虫感染。     

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.     

Autophagy-related genes from a tick, Haemaphysalis longicornis

Ticks are gorging-fasting organisms;(1) their life cycle is characterized by alternate off-host (starvation) and on-host (meal) conditions. Their generation time is estimated in several years and many ticks spend more than 95% of their life off the host. They seem to have a unique strategy to endure the off-host state for a long period. Thus, we focused on autophagy, which is induced by starvation and is essential for extension of the lifespan,(2-4) and hypothesized that ticks also have a system of autophagy to overcome the starved condition. Recently, we showed the existence of a homologue of an ATG gene, ATG12, and its expression pattern from nymphal to adult stages in a three-host tick, Haemaphysalis longicornis. The expression level of HlATG12 was downregulated at the beginning of feeding and was highest at 3 months after engorgement. In addition, the HlAtg12 protein was localized to the region around granule-like structures within midgut cells of unfed adults. These results indicate that HlATG12 functions during unfed stages. Here, a potential role of autophagy in unfed ticks is discussed with regard to reports in other animals, such as yeast, mammal, and fruit fly.     

Ticks collected from selected mammalian hosts surveyed in the Republic of Korea during 2008-2009

A tick survey was conducted to determine the relative abundance and distribution of ticks associated with selected mammals in the Republic of Korea (ROK) during 2008-2009. A total of 918 ticks were collected from 76 mammals (6 families, 9 species) captured at 6 provinces and 3 Metropolitan Cities in ROK. Haemaphysalis longicornis (54.4%) was the most frequently collected tick, followed by Haemaphysalis flava (28.5%), Ixodes nipponensis (7.6%), Ixodes pomerantzevi (4.8%), Ixodes persulcatus (4.6%), and Haemaphysalis japonica (0.1%). Adults (57.0%) and nymphs (28.7%) of Ixodes and Haemaphysalis spp. were collected most frequently from medium or large mammals in this survey, while few larvae (14.3%) were collected. Hydropotes inermis was the most frequently captured mammal (52.6%), with a 16.4 tick index and 5 of 6 species of ticks collected during this survey. H. longicornis (69.7%) was the predominant tick collected from H. inermis, followed by H. flava (22.2%), I. persulcatus (6.1%), I. nipponensis (1.8%), and H. japonica (0.2%).     

Survival of six species of African ticks in relation to saturation deficits

The survival of unfed males and females of six species of African ticks was monitored at five different saturation deficits at constant temperature (25°C). The survivorship curves for each species comprised a pre-mortality period, prior to when ticks started to die and a mortality period corresponding to a rapid increase in the mortality rate. Longevity was defined as pre-mortality plus mortality. A negative correlation between the longevity of the ticks and the saturation deficits was found with ticks surviving longer at lower deficits. The survival of males and females was similar. At low saturation deficits (2–4 mmHg) Amblyomma hebraeum survived the longest periods (74 weeks). Some correlation was found between the tick survival under dehydrating conditions and habitat associations. Rhipicephalus appendiculatus and Haemaphysalis leachii, the most mesic in distribution, had the shortest longevity (21 and 13 weeks, respectively) at high saturation deficits (7–21 mmHg). Hyalomma marginatum rufipes, the most xerophilic in distribution, had the longest survival (39.3±10.5 weeks) at high saturation deficits. Other factors apart from the adult survival should be taken into account when accounting for the tick distribution, in particular the tolerance of earlier developmental stages to desiccation.