Black soldier fly transcriptome analysis related to the identification of candidate chemoreceptive proteins for the detection of egg VOCs

In insects, the recognition of volatile organic compounds (VOCs), involved in the processes of feeding, mating and escaping from predators, is mediated by proteins belonging to the families of Odorant Binding Proteins (OBPs), Olfactory Receptors (ORs), Ionotropic Receptors (IRs) and Chemosensory Proteins (CSPs). In order to select optimal oviposition sites, adult black soldier flies, Hermetia illucens (L.) (Diptera: Stratiomyidae), are attracted not only to organic materials but also to the presence of eggs laid by conspecific females. To identify chemoreception candidate transcripts, RNA-seq was performed on Hermetia illucens antennae and whole body of male and female adults. The de novo transcriptome assembly resulted in 78,763 contigs and functional annotation using Blast2GO identified 59 putative OBPs, 186 ORs, 56 IRs, 7 CSPs. VOCs sampling was conducted in order to identify volatile organic compounds emitted by black soldier fly eggs. These were collected about six hours after oviposition; approximately 3 g of eggs were partitioned into equal units and subsequently into equal replicates. VOCs sampling, through a Closed Loop Stripping Analysis (CLSA) method, was performed on each unit and replicates directly at initiation (Day0) and 24h (Day1), 48h (Day2), 72h (Day3) after oviposition, respectively. The identification of attractive volatile organic compounds (VOCs), linked to the functional characterization of proteins involved in chemoreception, will allow the understanding about molecules perceived by females in the oviposition process and provide indications and guidelines for designing and screening new attractive substances, analogous to the identified compounds, with the aim to improve insect mass production.