Identification and Expression Analysis of Chemosensory Receptor Genes in Bradysia odoriphaga (Diptera: Sciaridae)

The chive midge, Bradysia odoriphaga, is a major insect pest affecting Chinese chive production in China. Its adult life stage is nonfeeding and has a short life span. Hence, the perception of chemical stimuli is important for its adult behavior and reproductive success. To better understand its chemosensory process at the molecular level, chemosensory receptor genes were identified based on transcriptomes of B. odoriphaga. In total, 101 chemosensory genes were identified from the antenna and body transcriptomes, including 71 odorant receptors (ORs), 18 ionotropic receptors (IRs), 5 gustatory receptors (GRs), and 7 sensory neuron membrane proteins (SNMPs). Phylogenetic analysis indicated that most of these genes have homologs among other Dipteran insects. A transcript abundance comparison based on FPKM values was conducted to analyze the sex- and tissue-specific expression profiles of these chemosensory genes. Moreover, quantitative real-time PCR of OR transcripts was performed on different tissues (female antennae, male antennae, heads, and legs) to verify the transcriptional expression levels of ORs in the transcriptomes. This analysis suggested that 44 ORs showed significantly higher expression in the female antennae, while 16 OR transcripts were most highly expressed in the male antennae and may play significant roles in sex pheromone detection. In addition, some IRs and GRs might be involved in CO2 and sugar detection and temperature sensing. In the present study, 101 chemosensory genes were identified, and their putative functions were predicted. This work could provide a basis to facilitate functional clarification of these chemosensory genes at the molecular level.