Chemical ecology of ticks: olfaction, behaviour, chemistry and control

蜱是所有食血节肢动物中最广泛的致病生物体，在传播对人类和兽医健康具有重要意义的疾病媒介方面，其能力仅次于蚊子。蜱虫几乎是完全看不见的，它们依靠化学感觉来识别和定位宿主，从而成功地吃到血。与昆虫相比，蜱虫的化学感觉系统代表了一个新的前沿。触角的缺失，嗅觉感受器的稀少，用于检测挥发性物质的特殊器官（哈勒氏）的发育，以及位于口腔部位的感受器的多模态作用，使蜱虫成为了解蜱虫如何检测化学物质的理想系统。主要的化学感觉器官由哈勒氏器官代表，它位于第一对腿的前肢上。除了检测宿主激素外，哈勒器官化学感受器还被认为参与检测信息素、聚集化学物质和环境线索。尽管哈勒氏器官在蜱的外周感觉系统中起着关键作用，但人们对其在化学感觉中的作用知之甚少。以前的研究证实了它在嗅觉中的作用，而不是味觉，直到最近才有报道称，须肢也参与了挥发性物质的检测。这是很重要的，因为大多数对蜱虫的驱避试验并没有区分嗅觉驱避和触觉化学感受/味觉驱避。嗅觉感受器能够探测到挥发性分子，有证据表明，嗅觉至少在一定程度上参与了蜱虫对驱虫剂的反应。我的研究计划的长期目标是解决我们对蜱虫宿主选择/接受的理解中的关键空白，揭示化学线索感知背后的机制，提供预防蜱虫叮咬的方法，从而预防人类和动物的感染。我们将通过研究蜱嗅觉的神经感觉生理学和化学生态学作为阐明宿主接受/拒绝化学的基础来实现这一目标。我的研究项目将通过将气味和化学线索引发的神经生理反应与蜱虫相应的诱导和观察行为联系起来，揭示人类/动物-蜱虫相互作用背后的动力学。刺激物将包括宿主挥发物和天然驱虫产品，包括精油和其他行为活性化合物，以确定宿主附着和驱虫的相关性。我的研究计划将提供关于蜱虫嗅觉敏感性的关键信息，它们敏感的气味库，以及特定天然化合物的驱避活性的行为调查。了解蜱虫化学感觉的基本生物学对加拿大和全球都很重要，因为它为最终设计避免传播莱姆病等病媒病原体的机制提供了必要的平台。

Ticks vector the widest array of disease-causing organisms of all hematophagous arthropods and are second only to mosquitoes in their capacity to transmit disease agents of importance to human and veterinary health. Being almost totally blind, ticks rely on chemosensation to identify and locate hosts for a successful blood meal, and the tick chemosensory system represents a new frontier compared with that of insects. The lack of antennae, the presence of very few olfactory sensilla, the development of a distinctive organ (Haller's) used for volatile detection, the multimodal role of sensilla located on mouth parts, make ticks an ideal system for understanding how acarines detect chemicals. The main chemosensory organ is represented by the Haller's organ, located on the foretarsus of the first pair of legs. Other than detecting host kairomones, Haller's organ chemoreceptors are suggested to be involved in the detection of pheromones, aggregation chemicals, and environmental cues. Despite the pivotal role of the Haller's organ in the tick peripheral sensory system, little is known about its function in chemosensation. Previous studies confirmed its role in olfaction but not gustation, and only recently pedipalps have been reported to be involved in volatile detection as well. This is significant because most repellency assays for ticks do not discriminate between repellency due to olfaction versus that from tactile chemoreception/gustation. Olfactory sensilla are able to detect volatile molecules, and evidence suggests that olfaction is involved at least, in part, in tick responses to repellents. The long-term objective of my research program is to address critical gaps in our understanding of tick host selection/acceptance, unveiling the mechanisms behind chemical cue perception, providing means to prevent tick bites and thus infections in humans and animals. We will achieve this by studying the neuro-sensory physiology and chemical ecology of tick olfaction as a basis for elucidating the chemistry of host acceptance/rejection. My research program will unveil the dynamics behind human/animal-tick interactions by linking the neurophysiological response elicited by odorants and chemical cues with the corresponding induced and observed behaviour in ticks. Stimuli will include volatiles of hosts and natural repellent products including essential oils, and other behaviourally-active compounds, to determine relevance in host attachment and tick repellency. My research program will provide critical information regarding olfactory sensitivity in ticks, the odorant repertoire to which they are sensitive, and behavioural investigations of the repellent activity of specific natural compounds. Understanding the fundamental biology of tick chemosensation is important to Canada and globally as it forms the necessary platform to ultimately devise mechanisms to avoid the transmission of pathogens that vector diseases, like Lyme disease.