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

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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.