Cottonseed Press Cake as a Potential Diet for Industrially Farmed Black Soldier Fly Larvae Triggers Adaptations of Their Bacterial and Fungal Gut Microbiota.

Dorothee Tegtmeier,Philipp Heise,Patrick Klüber,Karina Brinkrolf,Andreas Vilcinskas,Sabine Hurka

doi:10.3389/fmicb.2021.634503

Abstract

Black soldier fly larvae (Hermetia illucens, Diptera: Stratiomyidae) are used for the bioconversion of organic side products into valuable compounds such as proteins, lipids and chitin. However, the economic competitiveness of farmed insects compared to conventional protein production systems in agriculture and aquaculture depends on the availability of large quantities of inexpensive insect feed. Cottonseed press cake (CPC) is a side-stream of cotton production that is rich in proteins and lipids but unsuitable as feed for several farmed animals, except ruminants, due to the presence of the anti-nutritional sesquiterpenoid gossypol. Here, we tested CPC as a feed for black soldier fly larvae and studied the impact of this diet on the gut microbiome. Larvae reared on CPC developed normally and even showed a shorter life-cycle, but were smaller at the end of larval development than control larvae reared on chicken feed. The adaptability of the larvae to different diets is mediated by their versatile gut microbiome, which facilitates digestion and detoxification. We therefore used amplicon sequencing to analyze the bacterial and fungal communities associated with larvae reared on each diet, revealing differences between the larval guts and frass (residual feed substrate) as well as differences between the two diet groups. For example, Actinomycetaceae and Aspergillaceae were significantly enriched in guts of the CPC diet group and may help to metabolize compounds such as gossypol. Potentially probiotic yeasts and beneficial Enterobacteriaceae, which presumably belong to the core microbiota, were detected in high relative abundance in the gut and frass, indicating a functional role of these microbes, especially the protection against pathogens. We conclude that CPC may be suitable as an inexpensive and environmentally sustainable feed for the industrial rearing of black soldier flies.

Highlights

The larvae of the black soldier fly (Hermetia illucens) are economically the most important farmed insects used for the bioconversion of organic waste into valuable compounds such as proteins, lipids and chitin
The life cycle of black soldier flies reared on Cottonseed press cake (CPC) showed many similarities to that of the flies raised on chicken feed, but the total developmental cycle was significantly (p < 0.001; df = 4; t = 2.13) shorter on the CPC diet (43.4 ± 1.8 days) compared to the chicken feed diet (47.3 ± 3.5 days)
Larval development and the transition from prepupa to pupa were similar on both diets, whereas intrapuparial metamorphosis was significantly (p < 0.001; df = 4; t = 2.13) faster in the CPC diet group

Summary

Introduction

The larvae of the black soldier fly (Hermetia illucens) are economically the most important farmed insects used for the bioconversion of organic waste into valuable compounds such as proteins, lipids and chitin (van Huis, 2013; Müller et al, 2017). These fast-growing insects can recycle large amounts of organic carbon into edible proteins and oils rather than breaking it down into CO2 and methane (Perednia et al, 2017). The BSFL microbiome is shaped by diet and other biotic and abiotic factors, explaining substantial differences between the microbiomes of larvae reared in different locations (Wynants et al, 2019)

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