The most important proteins involved in olfaction include odorant binding protein (OBP), chemosensory protein (CSP), olfactory receptor (OR), and gustatory receptor (GR). Despite that the exhaustive genomic analysis has revealed a large number of olfactory genes in a number of model insects, it is still poorly understood for most nonmodel species. This is mostly due to the reason that the small antenna is challenging for collection. We can generally isolate one or few genes at a time by means of the traditional method. Here, we present the large-scale identifying members of the main olfactory genes from the head of Tomicus yunnanensis using Illumina sequencing. In a single run, we obtained over 51.8 million raw reads. These reads were assembled into 57,142 unigenes. Nearly 29,384 of them were functionally annotated in the NCBI nonredundant database. By depth analysis of the data, 11？OBPs, 8？CSPs, 18？ORs, and 8？GRs were retrieved. Sequences encoding full length proteins were further characterised for one OBP and two CSPs. The obtained olfactory genes provide a major resource in further unraveling the molecular mechanisms of T. yunnanensis chemoperception. This study indicates that the next generation sequencing is an attractive approach for efficient identification of olfactory genes from insects, for which the genome sequence is unavailable. 1. Introduction Olfaction plays a role in almost every aspect of insect life, which represents one of the key interfaces between insects and the environment. It is used by insects to recognize a huge variety of airborne molecules for providing them with information about food, predators, and potential mates [1]. Olfaction is a complex process requiring the interaction of numerous proteins to generate a neuronal signal. The first step in the recognition of chemical signals is the odorants that enter the insects’ antennae and other sensory organs via pores and travel across the hydrophobic space to the chemosensory receptors, where the response of the insect to the signal is initiated [2]. Chemoreceptor of insects is mainly formed by the olfactory receptors (ORs) and gustatory receptors (GRs), which are located in the dendritic membrane of neurons [3, 4]. As common odorants are hydrophobic molecules [5], it is difficult for them passing the aqueous barrier of the sensillar lymph surrounding the dendrites of neuronal cells [6]. During the passing process, odorants are thought to be translocated from the air to the chemoreceptors by a variety of protein mainly existing in the sensillar lymph, including odorant-binding
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