Effect of Bokashi fermentation on Hermetia illucens (Diptera: Stratiomyidae) development and microbiome.

Fermentation technology can enhance the digestibility of the substrate for insects used to digest biowaste such as the black soldier fly (BSF) Hermetia illucens (Diptera: Striatomidae) and lead to improved performance and higher protein yields, as shown recently for some bacteria evaluated singly, with other bacteria instead having a mostly detrimental effect. The Bokashi technology is a method for treating biowaste using controlled lactic acid fermentation under anaerobic conditions. So called “effective microorganisms” (EM) consist of a mixed culture of microorganisms such as lactobacilli, yeasts and Actinomycetes. When substrates are inoculated with EM the microbial equilibrium shifts to create an improved microbiome, with secondary metabolites produced by the modified microbiome that can perform beneficial functions, including breaking down harmful chemicals and immobilizing heavy metals. Using a commercially available Bokashi starter, we anaerobically digested two organic substrates, fresh oranges and brewery’s spent grains, with the Gainesville diet used a control, with the goal of assessing the impact of the fermented solid fraction on BSF development (weight, growth rate, developmental time from larvae to prepupae), on BSF protein content, on substrate bioconversion efficiency and on microbiome composition of both BSF larvae and substrates (before and after BSF digestion) at the industrial scale. Bokashi fermentation resulted in higher larval weight and reduced developmental time for BSF larvae that fed on Bokashi-fermented substrates. The effect was particularly remarkable on fresh oranges, showing the capability of Bokashi fermentation to increase the digestibility of an otherwise poor substrate. The effects of Bokashi fermentation on the microbiome composition of both BSF larvae and frass will also be presented.