Neurophysiological and Behavioral Responses ofIxodes scapularisto host odors

The black-legged tick,Ixodes scapularis(Ixodida, Ixodidae), is one of the major disease vectors in the United States and due to multiple human impact factors, such as decreasing forest size for land development and climate change, it has expanded its range and established across the United States. Throughout the life cycle, ticks locate hosts for their blood-meal and although the ecologies of this tick and their hosts have been studied in depth, the sensory physiology behind host location largely remains unexplored. Here we report establishing a robust paradigm to isolate and identify odors from the natural milieu forI. scapularis. We performed single sensillum recordings (SSR) from the olfactory sensilla on the tick tarsi, and used the SSR system as biological detector to isolate natural compounds that elicited biological activity. The SSR setup was further tested in tandem with gas chromatography (GC) wherein the ticks’ olfactory sensillum activity served as a biological detector. The GC-SSR recordings from the wall pore sensilla in the Haller’s organ, and further identification of the biologically active deer glad constituents by GC-mass spectrometry (GC-MS) revealed methyl substituted phenols as strong chemostimuli, as compared to ethyl or propyl substitutions. Strongest electrophysiological activity was elicited bymeta-cresolfollowed bypara-cresol. Ethyl- and propylphenols with any of the three,ortho, metaorparasubstitutions, did not induce any neurophysiological activity. Finally, a behavioral analysis in a dual-choice olfactometer of all these phenols at three different doses revealed no significant behavioral response, except forp-cresol at −3 dilution Overall, this study contributes to our understanding ofI. scapularistick’s neurophysiology and provides a robust platform to isolate and identify natural attractants and repellents.