The temperature and humidity preferences of Haemaphysalis longicornis, Ixodes Holocyclus and Rhipicephalus sanguineus (Ixodidae): studies on eggs

Surveillance and detection of Haemaphysalis longicornis (Acari: Ixodidae) in protected areas from Georgia, USA

The invasion of the Asian longhorned tick, Haemaphysalis longicornis Neumann, into the United States poses a significant ecological, veterinarian, and public health threat. We conducted a comprehensive tick survey using standard tick flagging protocol for collection over 3 field seasons, March-August, and 56 surveyed sites to identify the presence of H. longicornis in the native ecosystem and prove its establishment according to USDA criteria. Of the total 56 state parks and wildlife management areas (WMA) surveyed, only one was found to be invaded by H. longicornis; detection of H. longicornis occurred at Buck Shoals Wildlife Management area in White County, GA. This site is maintained by the state of Georgia, has no agricultural animals present, and hosts a large white-tailed deer population. After the initial detection of H. longicornis in 2022, an additional field season occurred in 2023, where H. longicornis was confirmed as established based on USDA criteria. The increase in H. longicornis populations from 2021 to 2023 at Buck Shoals WMA points to the rapid spread of this tick within the environment. Our findings provide evidence of the rapid establishment of H. longicornis in the southern edge of suitability for this tick and within the native ecosystem beyond farmlands and private land.

Seasonal distribution of Haemaphysalis longicornis (Acari: Ixodidae) and detection of SFTS virus in Gyeongbuk Province, Republic of Korea, 2018

The seasonal distribution of hard ticks was investigated in 2018 in Gyeongbuk Province, Republic of Korea. Ticks were assayed for severe fever with thrombocytopenia syndrome virus (SFTSV). Ticks were collected monthly using CO₂-baited traps from April to November in four habitats (grasslands, grave sites, hiking trails, and mixed forests). Based on morphological and molecular identification, Haemaphysalis longicornis was the most commonly collected species, followed by H. flava and Ixodes nipponensis. Ticks were more commonly collected in grassland habitats, followed by the grave sites, hiking trails, and mixed forests. Peak numbers of nymphs and adults of H. longicornis occurred in May and June, respectively, and Haemaphysalis larvae were collected from August to October. A total of 9/187 (4.8%) pools were positive for SFTSV between June and October in 2018. Phylogenetic analysis of partial fragments of the SFTSV obtained in this study showed that all positive virus samples clustered into genotype B.

Climatic suitability of the eastern paralysis tick, Ixodes holocyclus, and its likely geographic distribution in the year 2050

The eastern paralysis tick, Ixodes holocyclus is one of two ticks that cause potentially fatal tick paralysis in Australia, and yet information on the full extent of its present or potential future spatial distribution is not known. Occurrence data for this tick species collected over the past two decades, and gridded environmental variables at 1 km² resolution representing climate conditions, were used to derive correlative ecological niche models to predict the current and future potential distribution. Several hundreds of candidate models were constructed with varying combinations of model parameters, and the best-fitting model was chosen based on statistical significance, omission rate, and Akaike Information Criterion (AICc). The best-fitting model matches the currently known distribution but also extends through most of the coastal areas in the south, and up to the Kimbolton peninsula in Western Australia in the north. Highly suitable areas are present around south of Perth, extending towards Albany, Western Australia. Most areas in Tasmania, where the species is not currently present, are also highly suitable. Future spatial distribution of this tick in the year 2050 indicates moderate increase in climatic suitability from the present-day prediction but noticeably also moderate to low loss of climatically suitable areas elsewhere.

Differential expression of heat shock protein genes in Rhipicephalus sanguineus (Acari: Ixodidae) exposed to temperature and humidity variations

The brown dog tick (Rhipicephalus sanguineus), a well-recognized parasite that is an important vector of many pathogens, widely distributed in the world, can be found in dogs and many other host animals, including humans. However, the response of this species to climate changes is not fully understood yet. Therefore, this study aimed to analyze the expression of the genes encoding for hsp20 and hsp70 of nymphs and eggs of R. sanguineus in response to different relative humidity and temperature. While no significant differences were observed in hsp70 levels in nymphs, striking variations were found for hsp20. On the contrary, significant differences were found on the expression levels of both HSPs when exposed at different treatments. Expression of hsp20 was more affected by relative humidity than by temperature, which could imply that hsp20 may have a more critical protective role during vulnerable developmental stages of the tick than hsp70.

Seasonal Activity of Haemaphysalis longicornis (Acari: Ixodidae) in Southern New York State

The Asian longhorned tick, Haemaphysalis longicornis Neumann, is a species native to eastern Asia that has recently been discovered in the United States. In its native range, H. longicornis transmits pathogens that cause disease in humans and livestock. It is currently unknown whether H. longicornis will act as a vector in the United States. Understanding its seasonal activity patterns will be important in identifying which times of the year represent greatest potential risk to humans and livestock should this species become a threat to animal or public health. A study site was established in Yonkers, NY near the residence associated with the first reported human bite from H. longicornis in the United States. Ticks were collected once each week from July 2018 to November 2019. Haemaphysalis longicornis larvae were most active from August to November, nymphs from April to July, and adult females from June to September. This pattern of activity suggests that H. longicornis is capable of completing a generation within a single year and matches the patterns observed in its other ranges in the northern hemisphere. The data presented here contribute to a growing database for H. longicornis phenology in the northeastern United States. Potential implications of the short life cycle for the tick's vectorial capacity are discussed.

Aspects of the development of Ixodes anatis under different environmental conditions in the laboratory and in the field

BACKGROUND

Numerous laboratory and fewer field-based studies have found that ixodid ticks develop more quickly and survive better at temperatures between 18 °C and 26 °C and relative humidity (RH) between 75 and 94%. Ixodes anatis Chilton, 1904, is an endophilic, nidicolous species endemic to North Island brown kiwi (Apteryx mantelli) (NIBK) and the tokoeka (Apteryx australis), and little is known about the environmental conditions required for its development. The aims of this study were to determine and compare the conditions of temperature and RH that ensure the best survival of the kiwi tick and the shortest interstadial periods, in laboratory conditions and outdoors inside artificial kiwi burrows.

METHODS

Free-walking engorged ticks were collected off wild kiwi hosts and placed in the laboratory under various fixed temperature and humidity regimes. In addition, sets of the collected ticks at different developmental stages were placed in artificial kiwi burrows. In both settings, we recorded the times taken for the ticks to moult to the next stage.

RESULTS

Larvae and nymphs both showed optimum development at between 10 °C and 20 °C, which is lower than the optimum temperature for development in many other species of ixodid ticks. However, larvae moulted quicker and survived better when saturation deficits were < 1-2 mmHg (RH > 94%); in comparison, the optimum saturation deficits for nymph development were 1-10 mmHg.

CONCLUSIONS

Our results suggest that the kiwi tick has adapted to the stable, but relatively cool and humid conditions in kiwi burrows, reflecting the evolutionary consequences of its association with the kiwi.

Protecting dogs and cats against the Australian paralysis tick, Ixodes holocyclus (Acari: Ixodidae): A review of the Australian acaricide registration process

Tick control is mainly achieved through the use of effective ectoparasiticides that can be either dermally or systemically distributed in/on the host. Before any acaricide can be legally made available to veterinarians and pet owners, it must demonstrate efficacy in a series of well-designed dose confirmation studies. The data generated during these studies are then reviewed by government regulators and used for the registration of the acaricide. In Australia, the most significant tick species is the Australian paralysis tick, Ixodes holocyclus. This three-host tick produces a potent neurotoxin (holocyclotoxin) that induces a rapidly ascending flaccid paralysis that can be fatal to companion animals and larger mammals such as cattle and horses. The Australian Pesticides and Veterinary Medicines Authority (APVMA) is the national Australian regulator which sets the data requirements for the registration of acaricides. This paper reviews the requirements set by the APVMA and puts them in direct context with the biology, distribution and reported acaricide susceptibility of I. holocyclus. An overview of acaricides currently registered in Australia for the control of I. holocyclus in dogs and cats, their reported efficacy data and the conduct of I. holocyclus efficacy trials are also provided.

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A review of the requirements for the conduct of acaricide efficacy trials for Ixodes holocyclus was undertaken.

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The requirements of the Australian government regulator were put in direct context with the biology of the species.

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The need for the inclusion of Far North Queensland ticks into tick studies needs to be further assessed.

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At present, there is no evidence of acaricide resistance in Ixodes holocyclus.

Interactions Between Ticks and Lyme Disease Spirochetes

Borrelia burgdorferi sensu lato causes Lyme borreliosis in a variety of animals and humans. These atypical bacterial pathogens are maintained in a complex enzootic life cycle that primarily involves a vertebrate host and Ixodes spp. ticks. In the Northeastern United States, I. scapularis is the main vector, while wild rodents serve as the mammalian reservoir host. As B. burgdorferi is transmitted only by I. scapularis and closely related ticks, the spirochete-tick interactions are thought to be highly specific. Various borrelial and arthropod proteins that directly or indirectly contribute to the natural cycle of B. burgdorferi infection have been identified. Discrete molecular interactions between spirochetes and tick components also have been discovered, which often play critical roles in pathogen persistence and transmission by the arthropod vector. This review will focus on the past discoveries and future challenges that are relevant to our understanding of the molecular interactions between B. burgdorferi and Ixodes ticks. This information will not only impact scientific advancements in the research of tick- transmitted infections but will also contribute to the development of novel preventive measures that interfere with the B. burgdorferi life cycle.

Climate change and its potential for altering the phenology and ecology of some common and widespread arthropod parasites in New Zealand

Climate change, in the form of global warming, is a current concern and because farming systems, livestock parasites and their hosts are influenced by the weather, it is possible to predict (albeit with some uncertainty) changes in these in some broadly descriptive fashion, as climate changes. This review examines the on- and off-host responses to potential changes in temperature and humidity of a representative selection of arthropod ectoparasites (sheep chewing louse, Bovicola ovis; sheep blowflies, Lucilla spp., Calliphora stygia, and Chrysomya rufifacies; cattle tick, Haemaphysalis longicornis; scrotal mange mite, Chorioptes bovis; cat flea, Ctenocephalides felis; and dog flea, Ctenocephalides canis) that occur in New Zealand and in many other countries, and how these environmental factors can be perturbed by host manipulation. The bioclimatic preferences of the parasites are examined in relation to future broad climate parameters and how parasite life cycles, seasonality and population dynamics may be influenced. Likely adaptations of farming systems to meet climate change imperatives are briefly discussed. Collectively it is estimated that regions of New Zealand faced with warmer, wetter conditions under climate change may see an increase in flystrike and cattle tick prevalence, and perhaps an increase in the biting louse, but fewer chorioptic mange and flea infestations. In contrast, drier, warmer regions will possibly experience fewer ectoparasites of all types with the exception of flea infestations. Economic effects of increases in ectoparasite prevalence, using approximate dipping costs as a model are examined, and risks posed to New Zealand by some exotic arthropod parasites with the potential to invade under climate change, are briefly outlined.

Predicting the potential distribution of Amblyomma americanum (Acari: Ixodidae) infestation in New Zealand, using maximum entropy-based ecological niche modelling

Although currently exotic to New Zealand, the potential geographic distribution of Amblyomma americanum (L.), the lone star tick, was modelled using maximum entropy (MaxEnt). The MaxEnt model was calibrated across the native range of A. americanum in North America using present-day climatic conditions and occurrence data from museum collections. The resulting model was then projected onto New Zealand using both present-day and future climates modelled under two greenhouse gas emission scenarios, representative concentration pathways (RCP) 4.5 (low) and RCP 8.5 (high). Three sets of WorldClim bioclimatic variables were chosen using the jackknife method and tested in MaxEnt using different combinations of model feature class functions and regularization multiplier values. The preferred model was selected based on partial receiver operating characteristic tests, the omission rate and the lowest Akaike information criterion. The final model had four bioclimatic variables, Annual Mean Temperature (BIO₁), Annual Precipitation (BIO₁₂), Precipitation Seasonality (BIO₁₅) and Precipitation of Driest Quarter (BIO₁₇), and the projected New Zealand distribution was broadly similar to that of Haemaphysalis longicornis Neumann, New Zealand's only livestock tick, but with a more extensive predicted suitability. The climate change predictions for the year 2050 under both low and high RCP scenarios projected only moderate increases in habitat suitability along the mountain valleys in the South Island. In conclusion, this analysis shows that given the opportunity and license A. americanum could and would successfully establish in New Zealand and could provide another vector for theileriosis organisms.

Haemaphysalis longicornis: the life-cycle on dogs and cattle, with confirmation of its vector status for Theileria orientalis in Australia

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Conditions for the optimal generation interval for the “bush tick”, Haemaphysalis longicornis, in Australia have been determined.

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Stabilates containing infective sporozoites of Theileria orientalis ikeda were produced from ground-up ticks (GUTS) and salivary glands of H.longicornis.

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Sporozoites of Theileria orientalis required around 3–5 days of tick feeding to mature in salivary glands before transmission occurred (like T.parva).

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GUTS and salivary gland stabilates produced detectable infections with T.orientalis in naive calves around 3–4 weeks after inoculation.

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This study confirms the final host status of H.longicornis for T.orientalis in Australia, facilitating research for prophylaxis and vector control.

The intracellular protozoal parasite Theileria orientalis ikeda has rapidly spread across South-eastern Australia since 2006, causing deaths and production losses in cattle. The 3-host “bush tick” Haemaphysalis longicornis (Neumann) appears the principal biological vector in the endemic regions. To generate sufficient numbers of ticks to produce stabilate for infection to confirm vector competency and for acaricide trials, the optimal conditions and stage-specific intervals for the generational life-cycle of H.longicornis was defined on two dogs and two steers. To determine whether H.longicornis was a definitive host for Theileria orientalis, nymphal stages were fed on a steer infected with T.orientalis and moulted adults were permitted to feed for 3 days on an uninfected calf prior to harvest. Subsequent detection of infection after inoculation of four naïve calves with stabilate produced from ground-up adult ticks or dissected salivary glands confirmed H.longicornis as one final (definitive) host for T.orientalis in Australia.

Determining Effects of Winter Weather Conditions on Adult Amblyomma americanum (Acari: Ixodidae) Survival in Connecticut and Maine, USA

The lone star tick (Amblyomma americanum L.) is native to the United States, with its primary range encompassing the Southeast and portions of the Midwest. It is an aggressive ectoparasite that actively seeks out hosts through detection of carbon dioxide and vibrations and can transfer ehrlichiosis-causing bacteria as well as a carbohydrate that causes alpha-gal syndrome (red meat allergy) in humans. It has become of increasing concern as its range has recently expanded into coastal regions of the Northeast. Historically, harsh northeastern winter weather conditions made these areas inhospitable for A. americanum survival, but a warming climate coupled with increased host availability seem to have facilitated their range expansion. We developed a study to observe the effects of weather conditions on adult A. americanum overwintering survival. The study was conducted over three years in Connecticut and Maine. Ground-level conditions were manipulated to determine the effects of differing combinations of natural insulative barriers (leaf litter and snow accumulation) on adult A. americanum survival. We determined that there was a significant difference in survival between the two states, between years in Maine, and between sexes within Connecticut. However, presence or absence of snow and/or leaf litter had no impact on survival. Overall, we found a positive correlation between mean hourly temperature and adult survival in Maine, where temperatures were consistently below freezing. The results of this study can be included in an adaptive, predictive analytic model to accommodate the expected fluctuations and range expansion of A. americanum that will most likely accompany an increase in temperatures throughout the Northeast.

Discovery of Haemaphysalis longicornis (Ixodida: Ixodidae) Parasitizing a Sheep in New Jersey, United States

We report the discovery of large numbers of Haemaphysalis longicornis Neumann (Ixodida: Ixodidae) infesting a sheep in Hunterdon County, New Jersey, United States. All life stages were found on the sheep, which had no history of travel outside the country. H. longicornis is native to East Asia, and there are invasive populations in Australia, New Zealand and several Pacific islands, where this tick is a major livestock pest. It is currently unknown whether the New Jersey collections represent a limited or established population, but because this species could present a significant threat to human and animal health in the United States, vigilance is encouraged.

Are recreational areas a risk factor for tick paralysis in urban environments?

In Australia, tick paralysis in dogs (caused by a toxin in the saliva of Ixodes species during feeding) is a serious, distressing condition, and untreated it is often fatal. The aim of this study was to quantify the association between parkland (recreational or natural) in an urban area and the occurrence of canine tick paralysis. Brisbane, as a large urban centre located within the zone of paralysis tick habitat along the east coast of Australia, was selected as the study area. Postcodes selected for inclusion were those defined as being of an urban character (Australian Bureau of Statistics). The number of natural and recreational parkland polygons and total land area per postcode were derived. Tick paralysis case data for the selected postcodes were extracted from a national companion animal disease surveillance database. Between October 2010 and January 2017, 1650 cases of tick paralysis in dogs were reported and included in this study. Significant correlations were found between the number of reported cases per postcode and parklands: natural counts, 0.584 (P < 0.0001); natural area, 0.293 (P = 0.0075); recreational counts, 0.297 (P = 0.0151); and recreational area, 0.241 (P = 0.0286). Four disease clusters were also detected within the study area. All of these were located on the edges of the study area - either coastal or on the urban fringe; no clusters were identified within the core urban zone of the study area. Of the disease cases included in this study, strong seasonality was evidence: 68% of all cases were identified in spring. Within urban environments, areas of natural vegetation in particular appear to pose a risk for tick paralysis in dogs. This evidence can be used by veterinarians and dog owners to reduce the impact of tick paralysis by raising awareness of risk areas so as to enhance prevention via chemoprophylaxis and targeted searches of pet dogs for attached ticks.

Using a rule-based envelope model to predict the expansion of habitat suitability within New Zealand for the tick Haemaphysalis longicornis, with future projections based on two climate change scenarios

Haemaphysalis longicornis is the only species of tick present in New Zealand which infests livestock and is also the only competent vector for Theileria orientalis. Since 2012, New Zealand has suffered from an epidemic of infectious bovine anaemia associated with T. orientalis, an obligate intracellular protozoan parasite of cattle and buffaloes. The aim of this study was to predict the spatial distribution of habitat suitability of New Zealand for the tick H. longicornis using a simple rule-based climate envelope model, to validate the model against published data and use the validated model to project an expansion in habitat suitability for H. longicornis under two alternative climate change scenarios for the periods 2046-2065 and 2081-2100, relative to the climate of 1981-2010. A rule-based climate envelope model was developed based on the environmental requirements for off-host tick survival. The resulting model was validated against a maximum entropy environmental niche model of environmental suitability for T. orientalis transmission and against a H. longicornis occurrence map. Validation was completed using the I-similarity statistic and by linear regression. The H. longicornis climate envelope model predicted that 75% of cattle farms in the North Island, 3% of cattle farms in the South Island and 54% of cattle farms in New Zealand overall have habitats potentially suitable for the establishment of H. longicornis. The validation methods showed an acceptable level of agreement between the envelope model and published data. Both of the climate change scenarios, for each of the time periods, projected only slight to moderate increases in the average farm habitat suitability scores for all the South Island regions. However, only for the West Coast, Marlborough, Tasman, and Nelson regions did these increases in environmental suitability translate into an increased proportion of cattle farms with low or high H. longicornis habitat suitability. These results will have important implications for the geographical progression of Theileria-associated bovine anaemia (TABA) in New Zealand and will also be of interest to Haemaphysalis longicornis researchers in Australia, Japan, Korea and New Zealand.

Predicting the potential environmental suitability for Theileria orientalis transmission in New Zealand cattle using maximum entropy niche modelling

The tick-borne haemoparasite Theileria orientalis is the most important infectious cause of anaemia in New Zealand cattle. Since 2012 a previously unrecorded type, T. orientalis type 2 (Ikeda), has been associated with disease outbreaks of anaemia, lethargy, jaundice and deaths on over 1000 New Zealand cattle farms, with most of the affected farms found in the upper North Island. The aim of this study was to model the relative environmental suitability for T. orientalis transmission throughout New Zealand, to predict the proportion of cattle farms potentially suitable for active T. orientalis infection by region, island and the whole of New Zealand and to estimate the average relative environmental suitability per farm by region, island and the whole of New Zealand. The relative environmental suitability for T. orientalis transmission was estimated using the Maxent (maximum entropy) modelling program. The Maxent model predicted that 99% of North Island cattle farms (n=36,257), 64% South Island cattle farms (n=15,542) and 89% of New Zealand cattle farms overall (n=51,799) could potentially be suitable for T. orientalis transmission. The average relative environmental suitability of T. orientalis transmission at the farm level was 0.34 in the North Island, 0.02 in the South Island and 0.24 overall. The study showed that the potential spatial distribution of T. orientalis environmental suitability was much greater than presumed in the early part of the Theileria associated bovine anaemia (TABA) epidemic. Maximum entropy offers a computer efficient method of modelling the probability of habitat suitability for an arthropod vectored disease. This model could help estimate the boundaries of the endemically stable and endemically unstable areas for T. orientalis transmission within New Zealand and be of considerable value in informing practitioner and farmer biosecurity decisions in these respective areas.

Biology, ecology and distribution of the tick, Haemaphysalis longicornis Neumann (Acari: Ixodidae) in New Zealand

Haemaphysalis longicornis is the only tick in New Zealand that infests livestock. Throughout its range H. longicornis is exposed to and exhibits tolerance to a wide range of environmental conditions, although it flourishes more in moist, warm-temperate environments. This review examines aspects of the biology, physiology and ecology of H. longicornis that determine its distribution and seasonal activity in New Zealand, based on laboratory and field studies. Examples are also drawn from studies outside New Zealand for comparative purposes, especially in the context of seasonal activity as seen in less temperate latitudes. The tick is able to withstand a wide range of temperature, from its developmental threshold of ∼12°C to nearly 40°C at its lethal limit, but its tolerance of dehydration is less wide, especially in the larva and adult, the former especially being the stage that largely determines suitable biotopes for the tick and its present distributional limits. The importance of H. longicornis to the New Zealand livestock industry has recently increased through the establishment and spread of Theileria orientalis Ikeda among dairy and beef cattle, although the tick has always posed production-limiting problems for cattle, deer and to a lesser extent, sheep. The tick's role as a vector of theileriosis and how aspects of the tick's biology affect the spread and maintenance of this disease are discussed. It is proposed that, of available wildlife hosts, the brown hare with its wide-ranging habits, is an important disseminator of ticks. Currently control of ticks is difficult partly because of their wide host range, overlapping activity periods of stadia, and also because the greater part of their annual cycle is spent on pasture. This means that acaricides alone do not satisfactorily reduce tick populations or provide comprehensive protection to stock, so integrated management combining pasture management with good husbandry and chemical prophylaxis is advocated.

The relationship between the Southern Oscillation Index, rainfall and the occurrence of canine tick paralysis, feline tick paralysis and canine parvovirus in Australia

The aim of this study was to describe the association between climate, weather and the occurrence of canine tick paralysis, feline tick paralysis and canine parvovirus in Australia. The Southern Oscillation Index (SOI) and monthly average rainfall (mm) data were used as indices for climate and weather, respectively. Case data were extracted from a voluntary national companion animal disease surveillance resource. Climate and weather data were obtained from the Australian Government Bureau of Meteorology. During the 4-year study period (January 2010-December 2013), a total of 4742 canine parvovirus cases and 8417 tick paralysis cases were reported. No significant (P ≥ 0.05) correlations were found between the SOI and parvovirus, canine tick paralysis or feline tick paralysis. A significant (P < 0.05) positive cross-correlation was found between parvovirus occurrence and rainfall in the same month (0.28), and significant negative cross-correlations (-0.26 to -0.36) between parvovirus occurrence and rainfall 4-6 months previously. Significant (P < 0.05) negative cross-correlations (-0.34 to -0.39) were found between canine tick paralysis occurrence and rainfall 1-3 months previously, and significant positive cross-correlations (0.29-0.47) between canine tick paralysis occurrence and rainfall 7-10 months previously. Significant positive cross-correlations (0.37-0.68) were found between cases of feline tick paralysis and rainfall 6-10 months previously. These findings may offer a useful tool for the management and prevention of tick paralysis and canine parvovirus, by providing an evidence base supporting the recommendations of veterinarians to clients thus reducing the impact of these diseases.

Development and biological characteristics of Haemaphysalis longicornis (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.

The influence of temperature and humidity on oviposition and hatchability of Amblyomma lepidum (Dönitz, 1808) (Acarina: Ixodidae) under laboratory conditions

The effect of temperature and humidity on the oviposition and hatchability of Ablyomma lepidum was studied. Above 90% of adult ticks applied on calves succeeded to attach and feed through 6-13 days. The development process was studied under three levels of temperature: 27, 35 and 40 degrees C, each level with five sets of humidity. Temperature rather than humidity affected all developmental parameters. It was found that high temperature of 40 degrees C, even at high humidity 75.5-97.8% significantly affected pre-oviposition, oviposition, pre-hatching periods, egg mass weight and egg conversion ratio (p<or=0.0001), hatching period and hatchability (p<or=0.05). The effect of humidity on the pre-hatching period and hatchability was highly significant (p<or=0.0001), while it was less significant on pre-oviposition and hatching periods (p<or=0.05). It could be concluded that the development process is influenced by the interaction of both temperature and humidity. However, humidity above 90% and temperature range of 27-35 degrees C seem to be the optimum requirements for ideal development of A. lepidum.

Developmental profiles in tick water balance with a focus on the new Rocky Mountain spotted fever vector, Rhipicephalus sanguineus

Recent reports indicate that the common brown dog tick, or kennel tick, Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) is a competent vector of Rocky Mountain spotted fever in the U.S.A. This tick is of concern to public health because of its high frequency of contact, as it has a unique ability to thrive within human homes. To assess the moisture requirements necessary for survival, water balance characteristics were determined for each developmental stage, from egg to adult. This is the first time that water relations in ticks have been assessed throughout the complete lifecycle. Notably, R. sanguineus is differentially adapted for life in a dry environment, as characterized by a suppressed water loss rate distinctive for each stage that distinguishes it from other ticks. Analysis of its dehydration tolerance limit and percentage body water content provides no evidence to suggest that the various stages of this tick can function more effectively containing less water, indicating that this species is modified for water conservation, not desiccation hardiness. All stages, eggs excepted, absorb water vapour from the air and can drink free water to replenish water stores. Developmentally, a shift in water balance strategies occurs in the transition from the larva, where the emphasis is on water gain (water vapour absorption from drier air), to the adult, where the emphasis is on water retention (low water loss rate). These results on the xerophilic-nature of R. sanguineus identify overhydration as the primary water stress, indicating that this tick is less dependent upon a moisture-rich habitat for survival, which matches its preference for a dry environment. We suggest that the controlled, host-confined conditions of homes and kennels have played a key role in promoting the ubiquitous distribution of R. sanguineus by creating isolated arid environments that enable this tick to establish within regions that are unfavourable for maintaining water balance.

Habitat requirements of the seabird tick, Ixodes uriae (Acari: Ixodidae), from the Antarctic Peninsula in relation to water balance characteristics of eggs, nonfed and engorged stages

The seabird tick Ixodes uriae is exposed to extreme environmental conditions during the off-host phase of its life cycle on the Antarctic Peninsula. To investigate how this tick resists desiccation, water requirements of each developmental stage were determined. Features of I. uriae water balance include a high percentage body water content, low dehydration tolerance limit, and a high water loss rate, which are characteristics that classify this tick as hydrophilic. Like other ticks, I. uriae relies on water vapor uptake as an unfed larva and enhanced water retention in the adult, while nymphs are intermediate and exploit both strategies. Stages that do not absorb water vapor, eggs, fed larvae and fed nymphs, rely on water conservation. Other noteworthy features include heat sensitivity that promotes water loss in eggs and unfed larvae, an inability to drink free water from droplets, and behavioral regulation of water loss by formation of clusters. We conclude that I. uriae is adapted for life in a moisture-rich environment, and this requirement is met by clustering in moist, hydrating, microhabitats under rocks and debris that contain moisture levels that are higher than the tick's critical equilibrium activity.

The effect of desiccation and low temperature on the viability of eggs and emerging larvae of the tick, Rhipicephalus (Boophilus) microplus (Canestrini) (Ixodidae)

Process-based population models need sound and comprehensive data on an animal's response to climatic factors if they are to function reliably under a wide range of climatic conditions. To this end, different aged egg masses of the livestock tick, Rhipicephalus (Boophilus) microplus, were either desiccated in atmospheres with saturation deficits of 5, 10, 15 or 20 mmHg at 20 or 26 degrees C, or chilled at temperatures of 5, 10 or 14 degrees C with a saturation deficit of 1 mmHg for varying periods. The survival rate of the eggs through to hatching was related to the initial age of the eggs, the severity of the treatments and the duration of exposure. We established a relationship between desiccation and weight loss of eggs and, secondarily between weight loss and mortality. Mortality increased with weight loss until it reached 100% when the weight loss was about 35%. Low temperatures were increasingly detrimental to eggs as they reduced from 14 to 5 degrees C. Freshly laid eggs were more susceptible to both low temperatures and desiccation than were older eggs. Larvae emerging from eggs that were stressed by either cold or desiccation lived for a shorter time under optimal conditions than did larvae from eggs incubated under optimal conditions. Larvae from eggs with the same hatching rate had the same viability, whether the stress was induced by desiccation or low temperatures. Models were developed to describe the dynamics of weight loss of eggs with desiccation, the accumulation of cold stress of the eggs, and their effects on egg survival and larval viability. These data provide a sound basis for the development of predictive models for use under field conditions, although the response of different aged eggs to low temperatures was too variable to allow us to develop an accurate model to describe that relationship. Field models will also need to take diurnal temperature fluctuations into account.

Influência da temperatura sobre os tipos celulares presentes na hemolinfa de larvas e ninfas de Rhipicephalus sanguineus

Este trabalho foi realizado com o intuito de se verificar a influência de três temperaturas (18, 27 e 32°C) sobre os tipos celulares presentes na hemolinfa de larvas e ninfas de Rhipicephalus sanguineus (Latreille, 1806). Seis tipos celulares básicos foram encontrados na hemolinfa: prohemócitos (PR), plasmatócitos (PL), granulócitos (GR), esferulócitos (ES), adipohemócitos (AD) e oenocitóides (OE). Os ES foram divididos em dois subtipos (ES I e ES II), devido às variações morfológicas encontradas. O efeito da temperatura foi mais acentuado sobre o estádio de larva. Ocorreu queda acentuada de GR e aumento de ES II na temperatura de 18°C, enquanto que à 27 e 32°C, os valores foram semelhantes. GR foi o tipo celular mais abundante, indicando o seu envolvimento no metabolismo. Para ninfas este também foi o tipo celular mais abundante, porém não ocorreram variações acentuadas segundo a temperatura, indicando que cada estádio de desenvolvimento apresenta determinada necessidade metabólica que se expressa nos tipos celulares presentes na hemolinfa.

Experimental teratogeny in the tick Hyalomma marginatum marginatum (Acari: Ixodida: Ixodidae): effect of high humidity on embryonic development

The effect of 90% RH on the embryonic development of Hyalomma marginatum marginatum Koch was investigated at 25 degrees C. Under the influence of this factor, 2.1% dead eggs, 13.0% dead embryos, 6.9% abnormally hatched larvae, 0.2% larvae with malformations, and 77.8% normal larvae appeared. The embryos died during the cleavage of nuclei, the formation of the blastoderm, the formation of the germ band and its metamerization, and the differentiation of the leg anlagen. Egg hatch was also inhibited in various phases. Various kinds of anomalies were observed in larvae of Hyalomma m. marginatum. Most teratological changes (70.8%) occurred within the idiosoma. They were hetromorphose (32.6%), oligomely (15.4%), heterosymely (12.3%), symely (1.5%), atrophy (6.1%), and ectomely (3.1%). Anomalies within the gnathosoma occurred rarely (3.1%). As many as 26.2% larvae had composite anomalies (oligomely, heterosymely, atrophy) together. They contained various structures of the gnathosoma or idiosoma. These anomalies decreased the survival rate of the larvae. The investigations showed that during the formation of the blastoderm, the formation of the germ band and its metamerization the embryos have the largest susceptibility of being affected by high humidity. Some anomalies in specimens collected from nature may develop under influence of unfavorable humidity levels.

Influence of temperature and relative humidity on the moulting success of Amblyomma limbatum and Aponomma hydrosauri (Acari: Ixodidae) larvae and nymphs

This study compared the duration of the moulting periods of engorged larvae and nymphs of the ixodid ticks, Amblyomma limbatum and Aponomma hydrosauri, at different temperature/relative humidity regimes, and examined the relationships between the engorged weight of ticks and their weights after moulting. The results showed that for each species, there was a significant relationship between the weights of unfed nymphs and engorged larvae, and the weights of unfed adults and engorged nymphs. The weight of engorged nymphs was also a good indicator of their sex, with female ticks having heavier weights as engorged nymphs. Temperature and relative humidity had a marked effect on the moulting success of engorged ticks of both species. Aponomma hydrosauri larvae and nymphs were able to moult at lower temperatures than Amb. limbatum but most ticks, except Ap. hydrosauri larvae, failed to moult at 13 degrees C. Additionally, there was a marked decrease in the pre-moult times of ticks at higher temperatures, with larvae taking less time to moult than nymphs. At temperatures greater than 21 degrees C, Amb. limbatum took less time to moult than Ap. hydrosauri but this interspecific difference was less marked for nymphs. The interspecific differences in the responses of engorged larvae and nymphs to different temperatures and relative humidities correlated with interspecific differences in off-host behaviour and with the different climates the two species experience throughout most of their distributional range.

Reproductive bionomics of the soft tick, Ornithodoros turicata (Acari: Argasidae)

The effects of different temperatures and relative humidities (RHs) were tested on various reproductive parameters of Ornithodoros turicata, an argasid tick that inhabits gopher tortoise burrows in Florida, USA. The pre-oviposition, oviposition and incubation periods of the ticks decreased as temperature increased. These periods were also affected by the RH. The number of eggs oviposited was affected significantly by the combined effect of temperature and RH. Fewer eggs were laid by ticks in the 24 degrees C regimes and the 27 degrees C/95% RH regime compared to those in the other temperature/RH groups. There was an inverse relationship between the number of eggs oviposited and the percentage of hatched larvae that was correlated with the temperature and RH. Ticks reared at 27 degrees C/90% RH and 30 degrees C/90% RH laid more eggs than those reared in the other combinations of temperature and humidity but fewer larvae hatched from these eggs. The reproductive fitness index (RFI) values were highest in females held in the 24 degrees C groups and the 30 degrees C/95% RH group, although significantly more larvae hatched at the lower temperatures. The optimum reproductive conditions for O. turicata under laboratory conditions appear to be 24 degrees C and 90-95% RH. While mating occurred at all temperatures, none of the females laid eggs at 22 degrees C. The ticks may move preferentially to low temperatures when not feeding to remain above the critical equilibrium humidity and/or below the critical metabolic level necessary for prolonged survival. However, most female ticks oviposited after 45 days when moved to 27 degrees C/95% RH. Ornithodoros turicata females may have a limited capability to delay oviposition until an optimal microenvironment for egg deposition can be located in the burrow.

The life-cycle of Amblyomma variegatum (Acari: Ixodidae): a literature synthesis with a view to modelling

All available information on the life-cycle of Amblyomma variegatum is collated. Data for each parameter are analysed to derive mathematical descriptions, which may now be used to construct a model of the life-cycle of this tick. Areas for future research are identified. These include the collection of data for most parameters around threshold conditions to clarify discrepancies reported in the literature and to better quantify the relationships described, examination of the effects of photoperiod and host type on various parameters, and assessment of feeding success of each instar on natural hosts.

Influence of environmental factors on oviposition and egg development in Amblyomma limbatum and Aponomma hydrosauri (Acari: Ixodidae)

This study examined the influence of temperature and light on the length of the pre-oviposition period of engorged females of two Australian ixodid ticks, Amblyomma limbatum and Aponomma hydrosauri. The hatching success and development time of eggs of both species were also compared at different temperatures and relative humidities. Darkness was found to have no effect on the duration of the pre-oviposition time or reproductive output of females of either species. In contrast, the preoviposition period of females of both species decreased with increasing temperature. Amb. limbatum females had shorter pre-oviposition periods than Ap. hydrosauri at all temperatures examined. Temperature and relative humidity had a marked effect on the hatching success of eggs. Eggs of both species had reduced hatching success at low relative humidities. Eggs failed to hatch at temperatures below 21 degrees C. Ap. hydrosauri eggs also failed to hatch at 34 degrees C while Amb. limbatum eggs failed to hatch at 36 degrees C. Within the range of temperatures suitable for egg development, the hatching times of eggs of both species decreased with increasing temperature. Amb. limbatum eggs developed faster than Ap. hydrosauri eggs at temperatures greater than 25 degrees C, but slower at cooler temperatures. These differences in the duration of their preoviposition period, and the responses of females and their eggs to different temperatures and relative humidities correlate with the different climates the two species experience throughout most of their distributional range.

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.