Project summary Transfer RNAs (tRNA) represent one of the most abundant forms of RNA and are required for protein synthesis. Chemically modified ribonucleosides in tRNAs play critical roles in aspects that range from decoding codons to stress tolerance. Limited studies for metazoans, specifically in blood feeding arthropods, have been conducted on tRNAs and their modifications. The goal of these studies is to provide a characterization of the tRNA pool and modifications in blood feeding insects. These changes will be examined during blood feeding, reproduction, and mating at the whole organism and tissue levels. Our studies are supported by the following: 1) preliminary results from limited samples, which identified and quantified tRNA modifications, that suggest there are differences between blood feeding and sexes; and 2) Re-analysis of previously published data sets indicate expression patterns of genes associated with tRNA modification vary following a blood meal and between sexes. This study has two specific aims: Specific Aim 1. Characterize transfer RNA modifications in insects between sexes and during blood feeding. Specific Aim 2. Investigate the role of transfer RNA modifications during blood feeding and reproduction. Upon completion of this proposed research, we will establish tRNA expression and modification profiles for multiple blood feeding species in relation to reproduction and blood feeding. The role of several modifications will be elucidated by the use of targeted reduction of specific tRNA modifying enzymes. These proposed studies will be the first to extensively examine tRNA expression and modification patterns in blood feeding insects. Our results will provide the groundwork for future, novel tRNA-based studies of blood feeding insects such as identifying tRNA modifications critical to vector survival as climate change progresses and the dynamics between tRNA expression and modifications during pathogen transmission.