Effects of rearing system and microbial inoculation on black soldier fly larvae growth and microbiota when reared on agri-food by-products

Abstract

Black soldier fly larvae (BSFL) are widely used in recycling and upcycling of nutrients in agri-food by-products, but low and inconsistent BSFL rearing performance (i.e. larval growth, bioconversion rate, and substrate reduction) has been identified as a key challenge. The aims of this research were two-fold: (1) validate an existing closed rearing system design; and (2) assess whether a microbial inoculum derived from the rearing residue increases rearing performance. In controlled bench-scale experiments, BSFL were reared on tomato pomace (TP) and white wine pomace (WWP), along with food waste as control substrate. The two aims were assessed based on the following response variables: larval mass, substrate reduction, residue properties (i.e. pH, temperature, moisture content), and larval intestinal and residue microbiota. Higher BSFL mass (by 5.1 mg dry mass) at harvest on WWP and substrate reduction on TP (by 11.7% dry mass) in the closed system compared to the open system confirmed the potential of closed systems for rearing performance improvements of agri-food by-products. The rearing system also affected the residual moisture content and temperature, but only had a small effect on microbiota. Performance improvements by the closed rearing system design may be outweighed by insufficient aeration with pasty substrates and higher operational efforts for aeration and larval separation from the high-moisture residues. In contrast to the rearing system design, addition of the residue-derived microbial inoculum did not result in improved performance, nor did it alter intestinal and residue microbiota. Missing performance improvements could have been due to absent or low numbers of probiotic bacteria. The success of microbial substrate supplementation could be improved by studying effects of larval-associated microbes and developing cultivation methods that selectively amplify the beneficial (yet unknown) members of the microbial community. Our investigations aimed to increase the valorisation of low-value agri-food by-products in BSFL rearing.

Genotype-by-Diet Interactions for Larval Performance and Body Composition Traits in the Black Soldier Fly, Hermetia illucens

“…Identifying beneficial cultivable or transmittable microbial candidates depends on their characteristics and the nature of their host association. Specific microbial inoculations may positively influence production efficiency [ 107 , 108 , 109 , 110 ]. Yet, despite no clear evidence for vertical maternal imprinting for the time being [ 111 ], the BSF may possess such specific symbioses known from other insect systems (e.g., [ 112 , 113 ]), which thus may be amenable to fostering alternative inheritable solutions.…”

Upgrading ammonia-nitrogen from manure into body proteins in black soldier fly larvae

“…Unlike the larval transamination pathway, the microbial biomass pathway could reduce manure NH 3 emissions if NH 3 -N assimilation in larvae is maximized via rearing conditions. For instance, substrates inoculated with microbes can increase both bioconversion and larval weights (Mazza et al, 2020;Wong et al, 2021;Xiao et al, 2018), although this is not always the case (Gold et al, 2021;Hasnol et al, 2020). Future assessments should elucidate if increased bioconversion due to specific microbial inocula is correlated with larger NH 3 -N assimilation in manure-based diets.…”

Food industry waste - An opportunity for black soldier fly larvae protein production in Tanzania

“…While the larvae can consume many different types of biowaste, the nutritional composition of the substrate has a great impact on BSFL composting efficiency, measured as e.g., waste-to-biomass conversion efficiency (BCE), final larval weight, waste reduction efficiency, and larval survival during composting (Kawasaki et al, 2019;Lalander et al, 2019;Gold et al, 2020). To achieve high BCE (≥12 % dry matter (DM)) and high final larval weight (≥200 mg larva −1 ), the substrate needs to have a sufficiently high protein content (≥15% DM ) (Lalander et al, 2019;Gold et al, 2020) and a balanced protein to carbohydrate ratio (~1:1) (Cammack and Tomberlin, 2017;Gold et al, 2020), while the fiber and lipid content should not be too high (Gold et al, 2021;Lopes et al, 2020;Rehman et al, 2017). For example, low BCE (<12% DM ) has been reported when treating vegetable and fruit waste with a low protein content (≤13% DM ) (Isibika et al, 2019;Jucker et al, 2017;Lalander et al, 2019;Nyakeri et al, 2017) and no BSFL survival has been reported when composting pure fish waste with a high fat content (>50% DM ) (Lopes et al, 2020;Isibika et al, 2021).…”