The bacterial communities of black soldier fly larvae (Hermetia illucens) during consecutive, industrial rearing cycles

In recent years, the (gut) microbiota of black soldier fly larvae (BSFL, Hermetia illucens) has been the focus of several studies that try to elucidate its composition, its interaction with rearing parameters (like the substrate used) and its impact on rearing performance. While these studies have improved our understanding, conclusions from these studies are often based on only one or a few (mostly laboratory) rearing cycles. This leaves the questions whether such results are impacted by variability in between rearing cycles and whether sampling the microbiota, under the same rearing parameters, would yield repeatable results. To obtain insight in the overall variability in the microbiota, the bacterial community compositions of BSFL as well as the feeding substrates were investigated at two different time points during six consecutive rearing cycles in three BSFL-producing companies. This was done by sequencing the partial 16S ribosomal RNA gene amplicons. Based on the results, two main observations were done: (1) there was a clear resemblance over the different cycles at each time point for each individual company, and (2) a clear shift in the community for larvae as well as substrates occurred between the two time points within one production cycle. Additionally, when comparing production sites, an Enterococcus sp. was found at each time point for each company. Other species, such as Corynebacterium sp. and Providencia sp., were commonly found in all companies as well. To conclude, our study reveals that there is a low inter-cycle variability in the larval bacterial community over consecutive rearing cycles within a single company, when they operate using a standardised rearing protocol.