Yoder J A, Benoit J B, Rellinger E J, Tank J L
Department of Biology, Wittenberg University, Springfield, Ohio 45501, USA.
Med Vet Entomol. 2006 Dec;20(4):365-72. doi: 10.1111/j.1365-2915.2006.00642.x.
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.
最近的报告表明，常见的棕色犬蜱，即犬蜱，血红扇头蜱（拉特雷尔）（蜱螨目：硬蜱科）是美国落基山斑疹热的有效传播媒介。由于这种蜱与人类接触频繁，且具有在人类家中生存的独特能力，因此它受到了公共卫生领域的关注。为了评估其生存所需的水分条件，我们测定了从卵到成虫各个发育阶段的水平衡特征。这是首次在蜱的整个生命周期中评估其水分关系。值得注意的是，血红扇头蜱对干旱环境具有不同程度的适应性，其特点是每个阶段都有独特的低失水率，这使其与其他蜱类有所区别。对其脱水耐受极限和身体含水量百分比的分析表明，没有证据表明该蜱的各个阶段在含水量较低时能更有效地发挥功能，这表明该物种是为了保存水分而进化，而非适应干旱耐受性。除了卵之外，所有阶段都能从空气中吸收水汽，并能饮用自由水来补充水分储备。在发育过程中，水分平衡策略会发生转变，从幼虫阶段强调水分获取（从较干燥的空气中吸收水汽），转变为成虫阶段强调水分保留（低失水率）。这些关于血红扇头蜱嗜干性的研究结果表明，水分过多是主要的水分胁迫因素，这表明这种蜱在生存中对富含水分的栖息地依赖性较小，这与其对干旱环境的偏好相匹配。我们认为，家庭和犬舍中受控制的、局限于宿主的环境通过创造孤立的干旱环境，使这种蜱能够在不利于维持水分平衡的地区生存，从而在促进血红扇头蜱的广泛分布方面发挥了关键作用。
