Next-generation sequencing of sensory structures of the American dog tick, Dermacentor variabilis

The American dog tick, Dermancentor variabilis (Acari: Ixodidae), is the primary vector for transmitting Rickettsia rickettssii with expanding populations present in the eastern and central portions of the U.S.  Pathogen transmission occurs during feeding, allowing for growth, sexual maturation and mating.  Olfactory stimuli that induce tick host-seeking and feeding behavior convey information about host species, proximity and directionality.  Additionally, physical contact with host dermal secretions and blood confirm host type and identity, allowing for successful feeding.  The main external apparatus responsible for olfaction is the Haller’s organ.  The Haller’s organ, located on the first tarsus of the first pair of legs, uses putative odorant-binding proteins to bind chemicals that travel through the porous regions of the sensilla cuticle and transports them to the receptors on the sensillum cell wall.  Despite the vital role of the Haller’s organ, little is known about the genetic structure, protein construction or exact functioning of stimuli perception.  Through next-generation sequencing technology and analyses we have identified transcripts exclusive to the Haller’s organ with possible roles in olfaction.  The location and function of identified transcripts has been verified through comparative alignments with known olfactory proteins and receptors identified in other insect species and using PCR studies to confirm transcript expression only in the Haller’s organ.  Identification of putative messages in the Haller’s organ will allow for a more complete understanding of the olfactory mechanism in ticks and provide alternative targets for population control.