Impact of bokashi fermentation on life-history traits of black soldier flyHermetia illucens (Diptera: Stratiomyidae) larvae at an industrial scale

Abstract

Larvae of the black soldier flyHermetia illucens (Diptera: Stratiomyidae) (BSFL) are increasingly used in a circular economy context for industrial production of protein, oil, and frass, while serving as a sustainable method for managing numerous types of organic waste. On both fronts, there are ongoing efforts to optimise feedstocks for increased larval performance, yields of protein and/or oil, and efficiency of volumetric reduction of waste. Fermentation of organic waste prior to providing it to BSFL can help accomplish both goals. A few studies have individually evaluated fermenting agents such as lactic acid bacteria, yeasts, and fungi, showing that they can improve BSFL digestion of biowaste. However, the potential of co-fermentation by multiple microbes to improve waste digestion by BSFL has not been well explored. Here we tested a type of anaerobic fermentation, known as bokashi, that simultaneously uses lactic acid bacteria, yeasts, and fungi, on a common nutritious industrial feedstock (brewery’s spent grains) and on a nutritionally poor agricultural waste (unharvested oranges) on resulting life-history traits of BSFL. We show that bokashi-fermented substrates increased BSFL biomass and growth rate on both feeding substrates and dramatically reduced BSFL development duration on the nutritionally challenging oranges. Besides this, BSFL reared on fermented industrial feedstock reached the peak weight a day earlier, on average, than those feeding on the same unfermented substrate. Collectively, these effects would be beneficial for industrial BSF farming. We also highlight research areas to be tackled before bokashi fermentation can become widely adopted by the BSF farming sector.