Morphological and molecular study of larval and adult Hermetia illucens L. (Diptera: Stratiomyidae) olfactory system

Insects use chemical perception to interact with other insects and with the environment. The perception of volatile substances, linked to the processes of feeding, mating, escaping from predators and searching for oviposition sites is mediated, among the others, by Odorant Binding Proteins (OBPs). In order to select optimal oviposition sites, adult black soldier flies Hermetia illucens L. (Diptera: Stratiomyidae) are attracted to molecules deriving from organic material. Similarly, the larval stages of the black soldier fly have a highly sensitive olfactory system, able to perceive molecules coming from organic substrates. To identify chemoreception candidate transcripts, RNA-seq was performed on Hermetia illucens antennae and whole body of male and female adults as well as on H. illucens whole larvae. The de novo transcriptome assembly resulted in 78,763 contigs in adult transcriptomes and 25,197 contigs in larval transcriptome. Functional annotation using Blast2GO software and following analysis identified 60 putative OBPs in adult transcriptomes and 18 putative OBPs in larval transcriptome. All the 18 larval OBPs were compared with all the 60 adult OBPs and a high level of similarity, and in some cases a perfect identity, was found in terms of aminoacid sequence. This result confirms that OBPs play a key role in Hermetia illucens olfactory perception. Moreover, the identification of volatile organic compounds (VOCs) emitted by different substrates colonized with black soldier fly larvae was conducted. A parallel investigation by scanning electron microscopy (SEM) was performed on Hermetia illucens larvae and adults to identify structures possibly related to the olfactory perception.