Identification of potential volatiles as indicators of stress by black soldier fly larvae

There is a clear need to develop diagnostics to ensure optimal conditions while minimizing stress as related to animal welfare with the black soldier fly (BSF, Hermetia illucens (L.)). For ensuring the well-being of traditionally farmed animals, the application of the “5 freedom of Brambell Report” is in use. The animal should be free from hunger and thirst (1); discomfort (2); pain, injury, and disease (3); to express normal behavior (4); and from fear and distress (5). Considering the insects, it is important to develop tailored techniques for appropriate stress evaluation since they should be managed as sentient creatures, and their productive sector is forecast to grow strongly in the next few years. Volatile organic compounds (VOCs) released by insects could serve such a purpose. This research focused on BSF larvae given their global value to the insects as feed industry. The objective of the current study was to examine VOC emissions from larvae after harvest and during a 24 h starvation (i.e., finishing step) period under low and high stress conditions. This finishing step allows the larvae to evacuate their gut prior to the ‘kill step’ but unfortunately, it can often be performed under conditions that may cause stress to the insects. We focused on VOC emissions during the finishing step under different light (e.g., light v no light) and temperature conditions (25ºC v 40ºC). As for farmed animal stress is defined as “reflex reaction that occurs when animals are exposed to negative environmental conditions, causing unfavorable consequences, from discomfort to death”, any changes in insects’ VOCs emission in terms of quantity and quality of compounds during the starvation reflect their biological response to challenging parameters. Identification of indicator volatiles could be developed into real-time methods for monitoring BSF for stress responses. When detected at a threshold indicating stress, system adjustments can quickly be made to alleviate stress while increasing survival and larval chemical quality, optimizing their final use in the feed sector.