Identification and preliminary characterization of chemosensory-related proteins in the gall fly, Procecidochares utilis by transcriptomic analysis

Chemoreception is critical for insect behaviors such as foraging, host searching and oviposition. The process of chemoreception is mediated by a series of proteins, including odorant-binding proteins (OBPs), gustatory receptors (GRs), odorant receptors (ORs), ionotropic receptors (IRs), chemosensory proteins (CSPs) and sensory neuron membrane proteins (SNMPs). The tephritid stem gall fly, Procecidochares utilis Stone, is a type of egg parasitic insect, which is an effective biological control agent for the invasive weed Ageratina adenophora in many countries. However, the study of molecular components related to the olfactory system of P. utilis has not been investigated. Here, we conducted the developmental transcriptome (egg, first-third instar larva, pupa, female and male adult) of P. utilis using next-generation sequencing technology and identified a total of 133 chemosensory genes, including 40 OBPs, 29 GRs, 24 ORs, 28 IRs, 6 CSPs, and 6 SNMPs. The sequences of these candidate chemosensory genes were confirmed by BLAST, and phylogenetic analysis was performed. Quantitative real-time PCR (qRT-PCR) confirmed that the expression levels of the candidate OBPs varied at the different developmental stages of P. utilis with most OBPs expressed mainly in the pupae, female and male adults but scarcely in eggs and larvae, which was consistent with the differentially expressed genes (DEGs) analysis using the fragments per kilobase per million fragments (FPKM) value. Our results provide a significant contribution towards the knowledge of the set of chemosensory proteins and help advance the use of P. utilis as biological control agents.