• bioconversion
• Black Soldier Fly
• chitosan production
• intestinal microbiota
• organic waste
• plastivorous activity

Edible insects not only represent a sustainable protein source with significant potential for advancing alternative food and feed, but they are also recognised for their efficiency in converting food and waste, reducing greenhouse gas emissions, and having a low overall environmental impact. Among these, Hermetia illucens (Diptera Stratiomyidae), commonly known as the Black Soldier Fly (BSF), is one of the most studied species, thanks to its exceptional properties and applications. While widely recognised for its role in animal feed production, BSF demonstrated success in various applications, including the degradation of several organic waste, converting them into valuable resources such as food, feed, biofuels, fertilisers, proteins, lipids, and biopolymers. In particular, BSF larvae, through the consumption of organic waste, generate a chitin-rich biomass useful for chitosan production, a natural biopolymer with numerous applications. Several research indicates BSF larvae's ability to decompose contaminants, including antibiotics, mycotoxins, and pesticides. Moreover, recent studies demonstrated their capability to consume certain synthetic polymers, offering new possibilities for global plastic waste management. Although Tenebrio molitor (Coleoptera Tenebrionidae), Galleria mellonella (Lepidoptera Pyralidae), and Zophobas (Zophobas) atratus (Coleoptera Tenebrionidae) are the most studied species for plastic biodegradation, BSF could be a promising candidate with analogue potentials.
The current PhD thesis focused on rearing H. illucens to assess the larval bioconversion of different organic waste for chitin extraction and chitosan production (a), and the larval polystyrene biodegradation ability, introducing new possibilities for plastic waste management (b).
(a) As the EU regulations (No. 2017/893) restrict the use of certain organic waste types for edible insect rearing, BSF larvae were reared on various organic substrates, including legally permitted (standard, fruit, and vegetable diets) and not permitted, containing meat (meat and mixed diets). Larval performances (weight, length, feed conversion rate, and survival rate) were assessed for the different rearing substrates and BSF prepupae were used for chitin extraction and chitosan production. Chitosan, according to the FEDKITO PRIMA project, would contribute to producing sustainable packaging for protecting fresh food from fungal and insect attacks. The synergy of BSF, organic waste bioconversion, and chitosan production for biodegradable film represents an innovative and sustainable circular economy approach, transforming waste into useful and eco-friendly resources. The results highlighted efficient conversion of the vegetable and fruit waste-based diet to body weight, resulting in suitable for high-performance mass production of BSF prepupae. However, meat and mixed diets (not permitted in the EU), for their higher protein content, adversely affected the growth and development of BSF larvae. After demineralisation, deproteinisation, deacetylation, and discolouration of BSF prepupae reared on the five diets, chitin and chitosan were obtained. Interestingly, from the results obtained the yield of chitin and chitosan was not influenced by the diet, contrary to the mineral and protein percentages and chitin acetylation, which suggests modulating possibilities. This approach aligns with circular economy principles by efficiently recycling various food waste, such as vegetables and fruits, to produce multifunctional chitin and chitosan polymers.
(b) BSF larvae were reared on a diet contaminated with fluorescent polystyrene (PS) microparticles to investigate their plastivorous activity. A multidisciplinary approach was employed to explore various aspects. The evaluation of growth performance (weight and length) and survival rate between larvae reared on the PS-contaminated and control diets did not reveal significant differences. This emphasised the larvae's ability to thrive in PS-rich substrates, suggesting the utilisation of the synthetic polymer as a carbon source. Furthermore, microscopic analysis using Confocal Laser Scanning Microscopy (CLSM) revealed the abundant presence of PS fluorescent particles in the foregut and midgut, and minimally in the hindgut. The fluorescence was also observed within the midgut epithelium cells, indicating potential midgut microorganism degradation of PS microparticles and byproducts translocation in epithelium cells. Transmission Electron Microscopy (TEM) observations confirmed the presence of dense formations in midgut epithelium cells attributable to PS biodegradation products. Gas Chromatography-Mass Spectrometry (GC-MS) revealed the presence of styrene, a monomer of PS, after 1 and 3 days in the intestine of larvae fed on the PS diet. Contrarily, after 7 days, the presence of styrene was below the detection limit, indicating degradation and transformation into other byproducts involved in the PS biodegradation process. Lastly, the analysis of the intestinal microbiota of BSF larvae showed significant differences in beta diversity between the bacterial communities of control and PS diets. The presence of the Corynebacterium genus, which is involved in the aerobic PS degradation pathway, as well as the abundance of Enterococcus, Enterobacteriaceae, Enterobacter, and Escherichia-Shigella, also found in the microbiota of other plastivorous species when exposed to polystyrene, supported the hypothesis that BSF larvae are involved in plastivorous activity. This investigation not only strengthens existing hypotheses regarding the BSF larvae's ability to consume plastic waste but also unveils some mechanisms in the degradation process.
The results obtained in this thesis underscore the ability of both BSF larvae and their intestinal microbiota to biodegrade and valorise not only organic waste but also synthetic polymers. Particularly, BSF can be considered an essential species for integrated waste management techniques. The bioconversion of organic substrates yields high-value products, such as chitosan, while the biodegradation of polystyrene contributes to sustainable solutions for plastic waste management.