No abstract

Ticks can significantly affect the health and fitness of the host. Seasonal population dynamics of ticks play a vital role in disease transmission and the shaping of life-history traits of both tick and host. In this study, we examine the seasonal population dynamics of Ixodes hirsti in South Australia. For 2 years, we measured the prevalence and intensity of I. hirsti on passerines on Kangaroo Island. Ticks were present on birds from April to November and absent from December to March, with a peak in tick prevalence between June and September. The peak in tick abundance coincided with the host breeding season. Across the year, the most prominent fluctuations in tick abundance occurred in birds that were previously characterized as having high tick prevalence. Tick abundance on passerines fluctuated with host availability and climatic conditions: more ticks were present in months with high humidity and rainfall and low temperature. However, the relative influences of climate and host availability on tick presence were hard to separate.

Ticks are extremely susceptible to desiccation when not on a host. Even though Ixodid ticks are capable of surviving extreme conditions, it is in the best interest of the tick to locate a host quickly. The aim of this study was to determine the host stimuli used by larval Ixodes hirsti for location of their passerine host. Additionally, we recorded the average questing height of larval ticks. We found that I. hirsti larvae were attracted to shade and heat, while they were unresponsive to host odor and CO2. The average questing height was 12.4 cm. Sensitivity to both shade and heat will aid larval I. hirsti in their ambush strategy to find a host. Preference for shaded environments and a low questing height favors the occurrence of larvae in high humidity environments. Such moist environments indirectly increase lifespan duration because of reduced movement for water sorption, and increase tick questing which is limited by vertical mobility. Additionally, larval ticks with a low questing height have a higher chance of encountering a ground foraging passerine host.

Ticks reduce the fitness of their host by increasing mortality rate and reducing reproductive success. Understanding the distribution of ticks is therefore crucial in assessing the vulnerability of host populations. The distribution of ticks is dependent on the dispersal capabilities of their hosts as well as the suitability of the new habitat. In this study, we examine the spatial distribution of Ixodes hirsti in South Australia and investigate the influence of vegetation characteristics on the presence of ticks. Additionally, we conducted a preliminary investigation into the effects of vegetation characteristics on the microclimate experienced by questing ticks. Ticks were present in six of the nine study sites. We found that the number of shrubs and the percentage of ground covered by shrubs were significant predictors of the presence of ticks: ticks were present only at sites with a dense cover of shrubs. Additionally, our preliminary data showed that dense understorey was associated with a low saturation deficit and, as such, provided a suitable microclimate for tick survival.

In 2006, we examined Kangaroo Island kangaroos, Macropusfuliginosusfuliginosus, for ticks. We collected three tick species: Ixodes hirsti Hassall, Hemaphysalis bancrofti Nuttall & Warburton, and Bothriocroton concolor (Neumann). Surprisingly, the specimens included eight females and one nymph of B. concolor, which had previously been considered strictly host specific to the echidna (Tachyglossus sp.). This is the first record of B. concolor on the Kangaroo Island kangaroo.