Identification of VOCs from substrates colonized by black soldier fly larvae

The molecular perception of volatile organic compounds (VOCs), linked to the processes of feeding, mating and escape from predators, is related to molecules belonging to chemoreceptive gene families, namely Odorant Binding Proteins (OBPs), Olfactory Receptors (ORs), Ionotropic Receptors (IRs), Chemosensory Proteins (CSPs). Larval black soldier flies, Hermetia illucens L. (Diptera: Stratiomyidae), are able to decompose large amounts of different organic materials and waste products. Larvae have a highly sensitive chemoreceptive system, specialized in perceiving molecules linked to the decomposition of organic waste. In order to test different food waste in relation to the emission of different volatile organic compounds, larvae were fed on six different substrates: 1) apple, 2) banana, 3) spent grain deriving from brewery waste, 4) apple and banana mixed in 1:1 ratio, 5) apple and spent grain mixed in 1:1 ratio, 6) banana and spent grain mixed in 1:1 ratio. VOCs sampling, through a Closed Loop Stripping Analysis (CLSA) method, was conducted two times on each substrate: at the beginning of the larval feeding process (ti) and at the end of the larval feeding process (tf). The end of the process was determined when, following daily measures, no increase or a decrease in larval weight could be registered. A VOC trap containing Hayesep Q porous polymer was connected to a vacuum pump and placed in the container with diet and larvae. Volatiles were collected for 1h at 1 l/min flow rate. At the end of the process, VOC traps were removed and the content was eluted with dichlorometane (DCM) in GC vials. The identification of volatile organic compounds (VOCs) emitted by different substrates colonized with black soldier fly larvae, linked to the functional characterization of proteins involved in chemoreception, will allow the selection of the most attractive compounds useful to study strategies to increase insect fitness.