PROJECT SUMMARY Blacklegged ticks are the primary vector of Borrelia burgdorferi, the causative agent of Lyme disease. A basic understanding of tick host selection has been neglected. The major goal of this exploratory project is to better understand the process of host selection from tick host choice to successful parasitism, and identify candidate volatile organic compounds (VOC’s) that may influence host attraction. Previous analyses and our own data have documented increased tick burdens on specific host species and not others, even when sharing an overlapping niche suggesting host roles in tick burdens. Conspecific tick burdens may also play a role in tick host acceptance. Understanding the influences on tick host selection and associated volatile compounds, will provide important foundation and insight for the development of novel tick control methods, driving preventative management and improve human health by reducing the risk of tick-borne disease transmission. To accomplish this goal, we will use a combination of live rodent hosts in host behavior analysis and olfactometer studies to determine influences on tick attraction, and then will identify candidate compounds using gas chromatography (GC) and EI and CI GC-mass spectrometry. The specific aims are: • Specific aim 1 – Attraction to live hosts: To determine if host choice by I. scapularis is a deliberate or random response to live hosts, and if successful parasitism is affected by host behavior and/or species differences. • Objective 1.1. Determine differences of I. scapularis host choice between live red-backed voles and white- footed mice. • Objective 1.2. Determine differences of I. scapularis host choice between live red-backed voles and white- footed mice with conspecific tick parasitism. • Objective 1.3. Determine host behavioral factors influencing successful parasitism of I. scapularis between red-backed voles and white-footed mice. • Specific aim 2 – Attraction to odors: To determine if odors of hosts with and without conspecific tick burdens attract I. scapularis. • Objective 2.1. Determine attraction of I. scapularis to odors from red-backed voles and white-footed mice • Objective 2.2. Determine attraction of I. scapularis to odors from groups of conspecific ticks. • Objective 2.3. Determine attraction of I. scapularis to odors from red-backed voles and white-footed mice with conspecific parasitism. • Specific aim 3. To assess and identify candidate volatile compounds expressed by I. scapularis, red-backed voles, and white-footed mice influencing I. scapularis attraction.