Identification and Physiological Characters of Intestinal Bacteria of the Black Soldier Fly, Hermetia illucens

Abstract

The black soldier fly, Hermetia illucens, larvae may depend on indigenous bacteria in the intestine to feed and digest diverse food sources. To prove this hypothesis, we isolated and identified the intestinal bacteria of the black soldier fly for their digestive and antimicrobial abilities. The last instar larvae had long digestive tracts, which were about seven times longer than its body length. An individual of H. illucens larvae possessed a total of 5.0 x 10⁶ bacteria in the whole intestine, of which more than 98% bacteria were located in the hindgut. Three different bacterial isolates cultured on nutrient agar (NA) medium were detected in the intestine and identified as Morganella morganii, Providencia rettgeri and Bacillus halodurans by Biolog microbial identification system. Analysis of 16S rDNA sequences of the intestinal bacteria detected the additional bacteria of Proteus mirabilis, Providencia alcalifaciens, and Providencia sp. These intestinal bacteria cultured on NA medium exhibited high resistance to 4 antibiotics and inhibited growth of other microbes which are mainly plant pathogens. Also, these bacteria exhibited catalytic activities to degrade cellulose, lipid, proteins, and carbohydrates. These results suggest that H. illucens larvae possess intestinal bacteria that may play crucial roles in their digestive physiology.

Rearing substrate impacts growth and macronutrient composition of Hermetia illucens (L.) (Diptera: Stratiomyidae) larvae produced at an industrial scale

“…BSF larvae are able to grow on diets with low protein content, although with a prolonged time of feeding to reach their final weight, compared to larvae fed on diets richer in proteins 35,40 . The high fibre content of apples and bananas did not appear to impact the ability of larvae to digest these diets, which could be in part due to gut bacteria able to digest cellulose 48 . The fast growth rate and high larval biomass observed in SG larvae and, above all, on diets containing SG mixed with fruit, could be attributed to a more balanced ratio between proteins and carbohydrates 26,35 .…”

Effect of rearing substrate on growth performance, waste reduction efficiency and chemical composition of black soldier fly (Hermetia illucens) larvae

“…BRE larvae showed very good performance despite the high structural carbohydrate content of the relative rearing substrate (NDF: 447 g kg −1 DM; ADF: 225 g kg −1 DM). Such a result clearly demonstrates that BSF larvae are also able to efficiently bioconvert wastes and by‐products characterized by high fiber content, thanks to the presence, in the digestive tract of the insect, of intestinal bacteria able to degrade cellulose . The amino acid composition of the rearing substrates was not analyzed in our trials, and little literature is available concerning the effects of dietary amino acids on development and nutritional composition of BSF larvae .…”

“…Such a result clearly demonstrates that BSF larvae are also able to efficiently bioconvert wastes and by-products characterized by high fiber content, thanks to the presence, in the digestive tract of the insect, of intestinal bacteria able to degrade cellulose. 31 The amino acid composition of the rearing substrates was not analyzed in our trials, and little literature is available concerning the effects of dietary amino acids on development and nutritional composition of BSF larvae. 32,33 Studying the nutritional composition of BSF prepupae reared on different organic waste substrates, Spranghers et al 32 showed that the amino acid content of the prepupae had narrow ranges, particularly when compared to the noticeable differences found in the amino acid composition of the rearing substrates.…”

Review of insect pathogen risks for the black soldier fly (Hermetia illucens) and guidelines for reliable production

“…Studies investigating the internal and external microbiome of healthy insects and their substrate showed strong links between the diversity of bacterial species in the insects and the type of substrate used. Most research focuses on the use of molecular methods, such as 16S rRNA gene sequencing and pyrosequencing, to detect and identify the bacteria present (Forster et al, 2007; Jeon et al, 2011; Zheng et al, 2013a; Kim et al, 2014; De Smet et al, 2018; Wynants et al, 2019). Zheng et al (2013b) found many potentially pathogenic bacteria in all BSF stages, such as Xanthomonadales.…”