In some industrial post-harvest processing systems of black soldier fly (BSF) (Hermetia illucens), the larvae are minced and homogenized for protein and fat extraction. The quality of the resulting products can be affected by the gastrointestinal content of the insect. This content is poor in nutrients and rich in microbes and digestive enzymes. Post-harvest starvation has been suggested as a gastrointestinal evacuation (GE) method for BSF larvae, however, no direct evidence is available for GE and improvement of the quality of larvae after starvation. In the present study, we determined the GE dynamics through dissection of BSF larvae kept for 72 h under different temperature and substrate conditions after harvest. Different GE patterns were observed, depending on the environmental condition after harvest. At low temperature (10 °C), GE was not completed (> 90%). The most complete GE was observed after 6 h in water and after 48 h under fasting. Shortening the pre-slaughter period is important to avoid the decline of nutritional and microbial qualities of larvae. Interestingly, further investigations indicated improvements in the nutritional, color, and microbial qualities of the larvae after specific GE treatments. These larvae showed higher crude protein and fat, reduced microbial counts, lower wet weight, lighter puree color, and no change in their dry weight, ash, and fibre contents compared to larvae after conventional fasting. Broadly, results indicate that it may be beneficial to add an optimized degutting method after harvest to improve the quality of larvae for processing.

Black soldier fly larvae (BSF, Hermetia illucens) has gained much attention in the last few years for its use as biowast recycler as well as a new source of animal proteins. An increased interest has been shown toward the microbiota associated with BSF for the roles the microorganisms have in host development, behaviour, metabolism and immune system. However, the functions and dynamics of the microbiota, the effect they have on insect health and growth performance remain vastly unknown. This study endeavours to clarify the role of the microbiota on BSF ontogeny by exploring genomic expression during larval development in axenic conditions (i.e., absence of microorganisms). We hypothesized that the absence of the microbiota will be associated with reduced expression of genes linked to digestion, growth and immunity. During transcriptome analysis, we looked at differentially expressed transcripts using DESeq2 to compare conventional and axenic larvae (reared on BHI culture growth media, 28C, 70%RH and 12L:12D photoperiod) at day 4, 8 and 10 post-hatching (sample n=6/replica, each condition = 6 replica). To produce axenic larvae, eggs were dipped in 2.5% active chlorine, then in 70% EtOH followed by in PBS 1X (3min/solution) and hatched in sterile ventilated flask. Larval length (± 0.5 mm) revealed that the rearing substrate resulted in poor growth (axenic = 1.5 ± 0.5 mm; conventional = 2 ± 0.5 mm at day 10) compared to the usual Gainesville substrate (control = 18 ± 1.5 mm). No significant difference was observed between the axenic and conventional groups. Gene expression is currently being analysed with RSEM and annotated to characterise variation in time and underline the implicated gene functions and involved pathways in BSF development in presence vs in absence of microbiota. This study explores the effect of microbiota on host expression during development and is paving the way to future researches aiming to modulate BSF microbiota for rearing optimization, thus facilitating industrial production.

Black soldier fly (Hermetia illucens) larvae (BSFL) are increasingly used for waste management purposes because of their extraordinary ability to feed on a variety of waste organic matter and convert this material into valuable products. Although nutrient composition of the rearing substrate can affect larval performances and the bioconversion process, the astonishing adaptability of this insect to dietary substrates, without any dramatic impact on its development, strongly suggests that BSFL can finely and profitably regulate nutrient intake and post-ingestion processes to match their nutritional requirements. In the present study we investigated if and how the midgut of BSFL, which is involved in the digestion and absorption of nutrients, sets in motion post-ingestion responses to compensate variations in nutrient composition of the rearing substrate. To this purpose, we compared insects grown on a nutritionally balanced diet for dipteran larvae and a nutritionally poor diet that mimics fruit and vegetable waste composition, a substrate produced in large amount worldwide, whose use is allowed in the European Union for the mass rearing of insects that are used for the production of fish feed. Our morphofunctional characterization of the midgut responses, supported by a transcriptomic analysis, shows a diet-dependent adaptation process of the midgut that allows the larva to fully exploit the unbalanced diet, with minor effects on the growth performance. Besides differences in cell morphology, activity of digestive enzymes, and accumulation of long-term storage molecules, midgut cells of larvae grown on fruit and vegetable waste show differential expression of genes coding for digestive enzymes, transport proteins, and immune factors. Our data demonstrate that the functional plasticity of the midgut has a key role in the ability of BSF larvae to grow and develop on substrates with low nutrient content.

In this industrial scale set-up, several agri-food side-streams are investigated for use as substrate for lesser mealworms. Both the effect of feed composition on performance of larvae and on nutritional compositon of larvae is examined.