The gut and feed residue microbiota changing during the rearing of Hermetia illucens larvae.

Larvae of Hermetia illucens, commonly known as black soldier fly, efficiently convert organic waste into nutrient-rich supplements for different applications. Here we performed a preliminary experiment to investigate the dynamics of the H. illucens gut microbiota and changes in the composition of the bacterial community in the residue of the larval feed during rearing. We furthermore quantified the presence of antibiotic resistance and disinfectant genes in the gut and feed microbiota during the rearing process to elucidate if rearing leads to a reduction, increase, and/or transfer of resistance genes from the feed to larvae and vice versa. We found that the gut and feed residue bacterial communities were distinct throughout the rearing process. The gut microbiome remained more stable compared to the feed residue microbiome varying in both bacterial abundance and community structure during rearing. Antibiotic-resistance genes were present in both, gut and feed residues, with a significant increase in pupae and residue samples taken at the end of the rearing process. Disinfectant-resistance genes were present in the feed residue and even increased during the rearing process but were not transferred to the gut microbiome. We conclude that H. illucens larvae have a stable gut microbiome that does not change significantly over the course of larval development, whereas bacterial communities in the feed residue are strongly affected by rearing. If the presence of antibiotics and disinfectants during rearing, can promote the spread of antibiotic/disinfectant-resistance genes among feed and larvae needs to be evaluated in further experiments.