Expression of T. castaneum odorant receptors (ORs). Heat map showing the expression levels of the 337 analyzed ORs as log2[RPKM + 1] with a maximum of 8.1 (Orco has a value of 11.1 in antenna) in different tissues [adult antennae, head (missing antennae but including mouthparts), mouthparts, legs, and body]. The candidates are ordered according to their chromosomal localization (Additional file 13: Figure S9c). Horizontal brackets above indicate clustering in the genome, and the arrowheads represent the orientation of the open reading frame. ORs that are member of clades four, five, and six [115] are written in grey letters. The line labeled with Adult and Larva refers to data from [115]. The character H (respectively B) indicates that the corresponding OR was detected in head or body cDNA samples by reverse PCR of the labeled developmental stage. A black letter indicates that an amplicon was detected in the majority of replicates, a grey letter means only in a few replicates, a dash indicates no PCR product and no character means no data available. A comparison of the number of expressed genes is summarized in Additional file 13: Figure S9b. The expression levels are represented by a greyscale with highest shown expression levels (3 RPKM or higher) labeled black to make sure that also low level expression is identifiably presented. The asterisks mark statistically significantly differentially expressed genes compared to body (based on biological replicates of five antennal, two head, three mouthpart, two leg, and two body samples). The red asterisks represent up- and the blue down-regulation (p values adjusted are * < 0.05, ** < 0.01, and *** < 0.001). B body, H head, OR odorant receptor, RPKM reads per kilobase per million