Growth performance of the black soldier fly (Hermetia illucens) on by-products from brewing production

Hermetia illucens (Diptera: Stratiomyidae), also known as the black soldier fly, is considered an interesting candidate as alternative source of protein for livestock. Larvae of this species are able to efficiently bio-convert organic waste material into insect biomass. In addition, larvae can consume twice of their weight per day of waste, accumulating high amounts of protein and fat. The choice of the correct rearing substrate is essential in order to contribute to the disposal of waste or by-products obtained from the various stages of the industrial food production, that could hardly find other utilization, and to maximize the production of black soldier fly prepupae. Moreover, it is important to identify a lowcost diet with no competition with animal or human consumption. Among numerous by-products of vegetal origin, in this study black soldier fly larvae were reared on the following substrates originating from the brewing production: brewer’s spent grain, trub, and a mix of the two by-products (50 and 50%). The influence of the rearing substrates of the different life-history traits was observed. In particular, we considered the survivorship of the different developmental stages, the larval final weight, the duration of the larval period and the emergence of adults. Larvae could complete their development on the three substrates tested. Nevertheless, some differences were observed on the different parameters. In particular, the mixture of the two by-products resulted in a faster growth of the larvae that took less days to reach prepupal stage than the ones grown on the single by-product. The same trend was noticed on the final larval weight. The mortality of the larvae was significantly higher on those grown on brewer’s spent grain, while no differences were noticed among the other substrates. This study showed the possibility to rear the black soldier fly on different byproducts coming from the brewing production industry, that can therefore represent an interesting rearing substrate for the insect. More research is needed to optimize the diet for a possible use in mass rearing system.