The black soldier fly, Hermetia illucens (L. 1758), is an omnivorous saprophagous insect with a high potential for valorizing organic by-products rich in carbohydrates. Among carbohydrates, H. illucens relies on soluble sugars for the growth and storage lipid synthesis. This study aimed to assess the impact of common soluble sugars on the development, survival, and fatty acid composition of H. illucens. Monosaccharides and disaccharides were individually incorporated into a chicken feed diet. Cellulose was used as a control. Larvae fed glucose, fructose, sucrose, and maltose grew faster than control larvae. In contrast, lactose exhibited anti-nutritional effects on larvae, slowing down growth and reducing final individual weight. However, all soluble sugars produced larvae fatter than the control diet. Notably, the tested sugars shaped the fatty acid profile. Maltose and sucrose increased saturated fatty acid content compared to cellulose. Conversely, lactose increased the bioaccumulation of dietary unsaturated fatty acids. This study is the first to demonstrate the effect of soluble sugars on the fatty acid profile of H. illucens larvae. Our findings highlight that the tested carbohydrates have significant effects on black soldier fly fatty acid composition and can thus determine their final applications.

The interest in edible insects’ mass rearing has grown considerably in recent years, thereby highlighting the challenges of domesticating new animal species. Insects are being considered for use in the management of organic by-products from the agro-industry, synthetic by-products from the plastics industry including particular detoxification processes. The processes depend on the insect’s digestive system which is based on two components: an enzymatic intrinsic cargo to the insect species and another extrinsic cargo provided by the microbial community colonizing—associated with the insect host. Advances have been made in the identification of the origin of the digestive functions observed in the midgut. It is now evident that the community of microorganisms can adapt, improve, and extend the insect’s ability to digest and detoxify its food. Nevertheless, edible insect species such as Hermetia illucens and Tenebrio molitor are surprisingly autonomous, and no obligatory symbiosis with a microorganism has yet been uncovered for digestion. Conversely, the intestinal microbiota of a given species can take on different forms, which are largely influenced by the host’s environment and diet. This flexibility offers the potential for the development of novel associations between insects and microorganisms, which could result in the creation of synergies that would optimize or expand value chains for agro-industrial by-products, as well as for contaminants.

Bruchids are the most important pests of leguminous seeds in the world. In this study, the focus was done on Callosobruchus maculatus, a serious pest of Vigna unguiculata seeds. As no efficient control methods preventing collateral effects on beneficials currently exist, this study investigated whether RNA interference (RNAi) could provide a new biotechnological and selective tool for bruchids control. Three principal objectives were followed including (i) the identification of all RNAi machinery core components and a key protein to silence in C. maculatus genome (c.f., dicer-2, argonaute-2, R2D2, and laccase 1), (ii) the identification of suitable reference gene for RT-qPCR analyses, and (iii) the micro-injection of dsRNA coding for laccase 1 to adults of C. maculatus to assess gene expression levels by RT-qPCR and potentially related mortalities. Phylogenetical analyses performed from transcriptomic information successfully identified all necessary proteins in the RNAi mechanism and also the open reading frame of laccase 1 in C. maculatus. A new reference gene was identified (i.e., alpha-tubuline 1) and coupled with glutiathone S transferase for RT-qPCR analyses. Double-stranded RNAs coding for laccase 1 and green fluorescent protein (control) were produced and 400 ng of each dsRNA were micro-injected into C. maculatus adults. RT-qPCR analyses revealed a stable significant decrease in laccase 1 expression in about 80% of adults treated with laccase 1 dsRNA after three days post-injection. No significant mortalities were observed which is probably related to the non-exposure of adults to anti-nutritional factors that are usually regulated by laccase. Further research should focus either on the feeding larval stage which is directly exposed to anti-nutritional factors, or on other target genes to induce dead phenotypes. This study is the first gene silencing report on a bruchid species and supports RNAi as a potential future method of control.

Due to its high bioconversion efficiency and nutritional value, the black soldier fly (Hermetia illucens L. 1758) is a promising insect species for sustainable animal feed production. However, concerns remain regarding microbial safety when larvae are reared on substrates contaminated by pathogenic or spoilage bacteria. This study investigated the effects of substrate inoculation with Bacillus subtilis 168 or Pseudomonas putida KT2440 on larval performance and gut microbiota composition. Larvae reared on contaminated diets showed no significant differences in survival or development time compared to controls. However, a short-term reduction in growth was observed in the Bacillus-exposed group. qPCR analyses confirmed the temporary presence of Bacillus taxa in larval guts, while Pseudomonas taxa were effectively excluded. Amplicon sequencing of the 16S rRNA gene revealed that the contamination did not affect gut bacterial microbiota richness and composition. Instead, the bacterial communities evolved naturally with Lactobacillales-related bacteria dominating early stages and Morganellaceae taxa becoming more abundant in prepupae. Our findings demonstrate the stability and resilience of H. illucens gut bacterial microbiota, reinforcing the safety and suitability of H. illucens as a feed ingredient, even when reared under challenging microbial conditions.

The conversion of agro-industrial co-products and unsold organic plant-based residues into black soldier fly (BSF; Hermetia illucens (L. 1758)) proteins was assessed for use in organic post-weaning piglet diets in Belgium. A total of 72 crossbred female piglets (Landrace × Pietrain) were enrolled in a 5-week feeding trial. Experimental diets consisted of a common energy core (81.2% of the feed) and a protein core (18.8%) composed of organic soybean meal, pea meal, and potato protein, partially replaced by defatted BSF meal at inclusion levels of 15%, 25%, and 35%. All diets were formulated to be isoenergetic and isonitrogenous, with standardized ileal digestibility values for lysine, methionine, threonine, and tryptophan held constant. Incorporating 15% defatted BSF meal can substitute conventional organic protein sources without compromising growth performance in post-weaning piglets. However, economic modelling based on a cumulative feed conversion ratio expressed on a dry matter (DM) basis showed that break-even prices for organic BSF meal remained well below the price of the control protein nucleus (€1039·t⁻¹, excluding VAT), indicating that economic parity could not be achieved at typical market prices under the observed feed efficiency.

The black soldier fly ( Hermetia illucens L. 1758) is increasingly used for waste bioconversion due to its remarkable nutritional and metabolic plasticity. While substrate composition strongly influences larval lipid content and fatty acid (FA) profiles, the specific role of dietary carbohydrates remains unclear. This study examined the effects of maltose and lactose on lipid recruitment and storage in BSF larvae. Ten isolipidic and isoglucidic diets were formulated using chicken feed as a basal substrate, supplemented with 2% peanut or rapeseed oil and either 4% or 8% maltose or lactose. Larval lipid content increased with sugar inclusion, independently of sugar type. Maltose enhanced lauric acid (C12:0) accumulation. By contrast, lactose-fed larvae displayed similar FA profiles across inclusion levels. Nevertheless, net lipid removal from the substrate was lower in lactose-fed treatments, as reflected by the higher frass lipid content at the end of the experiment. Both sugars activated fatty acid synthesis, yet lactose appeared to additionally elicit delta-9 desaturase activity, increasing oleic acid (C18:1n9) levels. These results highlight how the type of carbohydrate modulates lipid deposition in BSF larvae. Manipulating dietary sugars could be a strategy to optimise larval lipid profiles for industrial applications. The study also outlines new hypotheses regarding carbohydrate-specific metabolic regulation in this species.