Effects of Bacterial Supplementation on Black Soldier Fly Growth and Development at Benchtop and Industrial Scale

Abstract

Historically, research examining the use of microbes as a means to optimize black soldier fly (BSF) growth has explored few taxa. Furthermore, previous research has been done at the benchtop scale, and extrapolating these numbers to industrial scale is questionable. The objectives of this study were to explore the impact of microbes as supplements in larval diets on growth and production of the BSF. Three experiments were conducted to measure the impact of the following on BSF life-history traits on (1) Arthrobacter AK19 supplementation at benchtop scale, (2) Bifidobacterium breve supplementation at benchtop scale, and (3) Arthrobacter AK19 and Rhodococcus rhodochrous 21198 as separate supplements at an industrial scale. Maximum weight, time to maximum weight, growth rate, conversion level of diet to insect biomass, and associated microbial community structure and function were assessed for treatments in comparison to a control. Supplementation with Arthrobacter AK19 at benchtop scale enhanced growth rate by double at select time points and waste conversion by approximately 25–30% with no impact on the microbial community. Predicted gene expression in microbes from Arthrobacter AK19 treatment was enriched for functions involved in protein digestion and absorption. Bifidobacterium breve, on the other hand, had the inverse effect with larvae being 50% less in final weight, experiencing 20% less conversion, and experienced suppression of microbial community diversity. For those tested at the industrial scale, Arthrobacter AK19 and R. rhodochrous 21198 did not impact larval growth differently as both resulted in approximately 22% or more greater growth than those in the control. Waste conversion with the bacteria was similar to that recorded for the control. Diets treated with the supplemental bacteria showed increased percent difference in predicted genes compared to control samples for functions involved in nutritional assimilation (e.g., protein digestion and absorption, energy metabolism, lipid metabolism). Through these studies, it was demonstrated that benchtop and industrial scale results can differ. Furthermore, select microbes can be used at an industrial scale for optimizing BSF larval production and waste conversion, while others cannot. Thus, targeted microbes for such practices should be evaluated prior to implementation.

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

“…Our method of incorporating the residue-derived inoculums back into the substrate did not improve the rearing performance. This is in contrast with previous studies that showed clear improvement in rearing efficiencies with the addition of pure-culture bacteria or defined bacterial mixtures (Kooienga et al, 2020;Rehman et al, 2019;Somroo et al, 2019;Xiao et al, 2018;Yu et al, 2011), and even the rudimentary use of fermentate is ubiquitous in accelerating the fermentation of foods. A possible explanation for this result is that the residues did not include probiotic bacteria.…”

“…isolated intestinal bacteria and showed a positive influence on the larval growth after the addition of Escherichia coli and Bacillus licheniformis to the substrate, but not Stenotrophomonas maltophilia. Similarly,Kooienga et al (2020) observed that the growth rate increased with Arthrobacter AK19 and Rhodococcus rhodochrous 21198, but the addition of Bifidobacterium breve to the substrate had adverse effects. Similarly,Mazza et al (2020) inoculated chicken manure with pure-culture bacteria and bacterial mixtures isolated from eggs and digestive tracts.…”

“…Rearing performance has also been improved by inoculating substrates with pure-culture bacteria (Kooienga et al, 2020;Rehman et al, 2019;Somroo et al, 2019;Yu et al, 2011) or defined bacterial mixtures (Callegari et al, 2020;Mazza et al, 2020). Certain fly-, soil-, or manure-associated bacteria (e.g.…”

“…Several questions remain regarding how the inoculation of substrates can reliably improve the rearing performance; however, variable results can be partially explained by the different digestive/metabolic capacities of microbes and variable nutritional requirements of BSFL depending on the operational rearing parameters. It remains to be confirmed as to which of the added bacteria colonise the residue or digestive tract, and whether viable bacteria are responsible for the reported improvements Kooienga et al (2020). recently showed that despite the growth improvements by R. rhodochrous 21198 and Arthrobacter AK19, only the latter colonised the larval digestive tract.Our study was the first to use sterile inoculums instead of sterile water as a negative control.…”

The connection between the gut mycobiome community of natural black soldier fly populations and their environment

“…As their metabolic complexity and ability is intense, they have the potential to dramatically affect the physiological condition of the insect. Revealing these metabolic interactions may help to increase the rearing efficiency of insects, such as the BSF, which is currently being reared at large scales as an alternative protein source (25).…”