Host identification in unfed ticks from stable isotope compositions (δ13 C and δ15 N).

Determination of the ratios of natural stable isotopes (13 C/12 C and 15 N/14 N) in unfed Ixodes ricinus nymphs and adults, which, in their previous stage, fed on captive wild rodents (Apodemus sylvaticus and Myodes glareolus), wild birds (Parus major and Cyanistes caeruleus) or domestic ruminants (Ovis aries and Bos taurus), demonstrated that it is possible to identify each host category with confidence. First, the tick-blood spacing, which is the difference between values obtained from ticks and the blood of hosts that they had fed on in the previous stage, was consistent (152 spacings investigated from 15 host individuals in total). Second, potential confounding factors (tick age and sex) did not affect the discriminatory power of the isotope patterns, nor did different rearing conditions (room temperature vs. 4 °C) or the duration of development (maximum of 430 days). The findings that the tick-blood isotope spacings, across a diverse range of hosts, were similar and predictable, and that confounders had little or no effect on this, strongly support the usage of the isotope approach. Because each of the host categories has a different role in the population dynamics of I. ricinus and in tick-borne pathogen ecology, the method described here has great potential for the clarification of tick and tick-borne pathogen ecology in the field.

[The ecology of ticks, tick-borne diseases and biological tick control in Baden-Württemberg]. / Ökologie von Zecken als Überträger von Krankheitserregern in Baden-Württemberg und biologische Zeckenbekämpfung.

Ticks and tick-borne diseases are of great significance for the health of humans and animals. However, the factors influencing their distribution and dynamics are inadequately known. In a project financed by the Baden-Württemberg Ministry of the Environment, Climate and Energy Industry, as part of the program BWPLUS, interdisciplinary specialists work together to determine the influence of weather, (micro)climate, habitat, land use, human activities, and the population dynamics of host animals on the distribution and abundance of ticks and the diseases that they transmit in Baden-Württemberg. The project comprises four modules: the large-scale distribution of ticks in Baden-Württemberg (module 1), detailed studies of host-tick-pathogen interaction in relation to the microclimate (module 2), and the spatial occurrence of important tick-borne pathogens (module 3). The fourth module involves the comprehensive analysis and synthesis of all data in order to determine the relative importance of the factors studied and to develop a risk model. Recently, intensive investigations into tick control have been undertaken using various entomopathogenic fungi and nematodes as well as a parasitoid wasp. Our aim was to determine whether these natural enemies could be used to effectively reduce the number of free-living ticks.

The influence of physiological age of Argas reflexus larvae (Acari: Argasidae) and of temperature and photoperiod on induction and duration of diapause.

The occurrence of diapause and quiescence was investigated in Argas reflexus engorged larvae, nymphs I and nymphs II. For diapause experiments, larvae were maintained at five different locations: at constant 20°C long day (LD; 17 h light:7 h dark) or short day (SD; 10 h light:14 h dark), at two locations with natural photoperiod and temperature and at one location with natural photoperiod but constant 15°C. At 20°C, diapause incidence was low in physiologically young larvae, increased with larval age, and then decreased to zero in specimens of increased physiological age. This pattern, observed both at constant LD and SD, suggests that the propensity to diapause changes with the physiological age of the unfed larva. The duration of diapause decreased with increasing larval physiological age at all locations, resulting in a seasonally synchronized moulting pattern. The results suggest that A. reflexus larvae are photoperiodically sensitive both before and after feeding and that decreasing daylengths may be particularly strong inductive stimuli. The developmental zero and thermal constant of the larvae were determined as 13.24°C and 220 degree-days, respectively. Degree-day measurements revealed that larval A. reflexus may enter a diapause of different length when fed between August and December and kept at natural daylength. Development of engorged nymphs I and nymphs II, but not of larvae, was ultimatively restricted at a temperature of 37.5°C, but immediately resumed at 25°C, demonstrating the occurrence of quiescence at high temperatures. Similarly, at a low temperature of 15°C, many nymphs I and II did not develop within 58 months, but did so successfully after transfer to 25°C, without additional food intake.

Seasonal oviposition and temperature requirements of eggs may limit northern distribution of European Argas reflexus (Acari: Argasidae).

Seasonal reproduction and embryonic development was investigated in Argas reflexus (F.) throughout a 5-yr period. Ticks were kept in desiccators at approximately 76% RH at 2 experimental sites--an attic and an outdoor aviary--that provided a natural photoperiod and temperature. Tick oviposition was limited to the summer months (June through August) regardless of the year of investigation and of the seasonal time of tick feeding. Engorged female ticks entered diapause between late July and late August. Ticks that had already started oviposition, stopped at that time and continued in the following year without requiring another blood meal. In the laboratory, A. reflexus eggs exhibited an upper lethal temperature (ULT50: 1-h exposure) of 44.1 degrees C (95% CL: 43.7-45.5 degrees C), which is in accordance with the increased egg mortality observed in the attic, where temperatures reached > or = 45 degrees C. A. reflexus eggs showed a low level of cold tolerance. Despite a supercooling point of approximately -25 degrees C, their lower lethal temperature (LLT50: 24-h exposure) was only -12.3 degrees C. Even at a typical winter temperature of 3 degrees C and 76% RH, 50% egg mortality occurred after only approximately 34 d. In the attic and the aviary, none of the A. reflexus eggs were able to overwinter successfully during any of the investigated winters, including comparatively mild ones. The results strongly suggest that the temperature sum available for embryonic development in summer/autumn limits the northern distribution of A. reflexus.

Effects of climate change on ticks and tick-borne diseases in europe.

Zoonotic tick-borne diseases are an increasing health burden in Europe and there is speculation that this is partly due to climate change affecting vector biology and disease transmission. Data on the vector tick Ixodes ricinus suggest that an extension of its northern and altitude range has been accompanied by an increased prevalence of tick-borne encephalitis. Climate change may also be partly responsible for the change in distribution of Dermacentor reticulatus. Increased winter activity of I. ricinus is probably due to warmer winters and a retrospective study suggests that hotter summers will change the dynamics and pattern of seasonal activity, resulting in the bulk of the tick population becoming active in the latter part of the year. Climate suitability models predict that eight important tick species are likely to establish more northern permanent populations in a climate-warming scenario. However, the complex ecology and epidemiology of such tick-borne diseases as Lyme borreliosis and tick-borne encephalitis make it difficult to implicate climate change as the main cause of their increasing prevalence. Climate change models are required that take account of the dynamic biological processes involved in vector abundance and pathogen transmission in order to predict future tick-borne disease scenarios.

Water loss and metabolic water in starving Argas reflexus nymphs (Acari: Argasidae).

Basic components of the water balance were determined in A. reflexus unfed second instar nymphs kept at 30 degrees C and different relative humidities in darkness. At 2.5% and 32.5% RH, A. reflexus survived for 170+/-60 and 246+/-71 days, respectively. At 56%, 75.5% and 96.5% RH, the experiment was terminated after 168 days without any mortality. The initial water content of hydrated A. reflexus kept at 85% RH was 70.3+/-1.8% while the water content was close to 50% in ticks dehydrated at /=56% suggesting that A. reflexus increased its oxidative metabolism under dehydrating conditions and thus delayed lethal dehydration. Interestingly, the dry mass of dead ticks was almost identical irrespective of whether the ticks had previously been kept at 2.5% and 32.5% RH, i.e. irrespective of their different survival periods. This raises the question whether the ticks had died by dehydration or by exhaustion of energy reserves.

The supercooling ability of ticks (Acari, Ixodoidea).

The supercooling capacity of nine laboratory-held species of ticks originating from different geographical areas, as well as five field-collected species from Germany, was investigated. All but one tick species showed mean supercooling points between about -17 and -23 degrees C, suggesting that the capacity to supercool to temperatures of < or = -17 degrees C might be an inherent property of many tick species unrelated to their geographic origin. Photoperiod did not influence the mean supercooling point in any of the species and there was also no distinct seasonal pattern of supercooling in seasonally acclimatized Dermacentor marginatus. Thus, the supercooling ability was independent of the presence/absence of diapause. The finding of thermal hysteresis in D. marginatus hemolymph raises the question of whether or not anti-freeze proteins are involved in the supercooling capacity of that species. An interspecies comparison revealed a weak negative correlation between relative water content and supercooling point of the ticks and an even weaker correlation between body mass or body water mass and the supercooling point. Since the ticks exhibited low supercooling points both before and shortly after feeding, the blood used as food should lack potent ice nucleators.

Cold hardiness, supercooling ability and causes of low-temperature mortality in the soft tick, Argas reflexus, and the hard tick, Ixodes ricinus (Acari: Ixodoidea) from Central Europe.

Seasonal supercooling points (SCPs=temperature of crystallization) and cold hardiness were investigated in the indigenous hard tick, I. ricinus, and in A. reflexus, a soft tick introduced to Central Europe from the South. Both species proved to be freeze-susceptible as well as highly susceptible to inoculative freezing. None of the postembryonic developmental stages of either species showed any distinct seasonal pattern of SCP. Unexpectedly, the introduced A. reflexus exhibited a distinctly higher degree of cold hardiness in terms of lower lethal temperature (LT(50): 24h exposure) as well as lethal time (T(50): time of survival at -10.1 degrees C) than I. ricinus. Engorged I. ricinus larvae as well as engorged summer acclimatized A. reflexus larvae showed some mortality at temperatures well above the SCP. This mortality was generally expressed as a failure of the following stage to eclose properly. A 10-day cold acclimation at +3 degrees C eliminated that kind of mortality in summer acclimatized A. reflexus larvae, but not in I. ricinus larvae. It was frequently observed that freezing of ticks resulted-possibly via leakage from the midgut-in a subsequent reddish brown discoloration of the ticks after thawing. Taking into account that discoloration was an indication of previous freezing, it was concluded, that after long-term exposure (for >/=30 days) at -10.1 degrees C, a temperature well above the SCP, some tick mortality could be observed that was not caused by previous freezing. Weighing experiments clearly demonstrated, that the level of dehydration was not critical for survival of A. reflexus during long-term cold exposure, even at low RH. This indicates, that cold-related factors other than freezing and dehydration were detrimental to this species.

The pigeon tick (Argas reflexus): its biology, ecology, and epidemiological aspects.

The European pigeon tick, Argas reflexus (F.), is in central Europe predominantly an urban pest parasitizing wild and domesticated pigeons, Columba livia. Under certain circumstances, however, it also bites humans, occasionally causing an IgE-mediated type-I allergy. Control of A. reflexus is very difficult because of a number of remarkable morphological, physiological, and behavioural features of the tick. The present study aimed at elucidating the distribution and the frequency of occurrence of A. reflexus in Berlin and its possible vector role for Borrelia burgdorferi sensu lato (s. l.). Buildings reported by occupiers to be infested with A. reflexus were personally examined. In addition, the carrier status of this soft tick for B. burgdorferi (s. l.) was investigated in three German towns by an indirect immunofluorescence assay. A total of 188 Berlin buildings was found to be infested with A. reflexus between 1989 and 1998. Infestations were found in 17 out of the 21 districts, clustering in the inner city. There was only a single Borrelia-positive tick out of 800 sampled in Berlin, Leipzig, and Hannover using the genus specific antibody H9724. The same tick was PCR-negative for B. burgdorferi outer surface protein A. Neither these results nor those of other studies on the occurrence of antibodies against B. burgdorferi in pigeons suggest that field populations of A. reflexus and/or pigeons in central Europe harbour the causative agent of Lyme borreliosis.