The larvae of Hermetia illucens are known to successfully bio‐convert a vast range of organic substrates into high protein and fat biomass, but little is known about the larval instars. During this research, larval head capsules and biomass growth were measured daily and the specific metabolic rate of larger instars were considered. The head capsule measurements revealed that H. illucens pass through 6 actively feeding larval stadia before entering the last nonfeeding but migrating 7th stadium. Larval growth follows a sigmoid curve with slowly accelerating growth in the earlier stadia and decelerating growth in the latest stadia. In contrast, development was fast until reaching stadium 6 and then slowed down. Accordingly, the specific metabolic rate was high in instars 3, 4 and 5 and reduced in instars 6 and 7.
Bio-conversion of different organic waste streams in Hermetia illucens larval biomass suitable for animal feed is a promising sustainable solution across different sectors. However, environmental factors can affect the allocation of energy to fitness, survival and growth of insects in complex ways and can therefore impact the optimal functionality of bio-conversion systems. This study investigated the influence of temperature and diet quality differences on the metabolic rate (MR), development, growth, food intake, and body nutrient composition of H. illucens larvae. The fifth instar larvae were reared on three artificial diets (unbalanced diets: Protein and Carbohydrate, and control diet: Gainesville) and exposed to two constant temperatures (20 and 27 °C), until they reached the prepupa stage. The MR was measured in the sixth instar larvae and the body nutrient composition was measured in the prepupa larvae. The MR of H. illucens larvae was found to increase with temperature, leading to a higher food intake and faster growth rate. When reared on unbalanced diets, the larvae were found to experience metabolic costs and to consequently increase larval development time and decrease food intake. There was a significant temperature × diet interaction across the investigated parameters, indicating that larvae of H. illucens can prioritise energy allocation and adjust their metabolism in order to ensure further development. The nutrient composition reveals that larval nutrient profile can be enhanced through diets. Nonetheless, caution should be taken when exploring this procedure, as it could be associated with an extra metabolic cost.
The feed sector requires new sustainable sources of protein, and at the same time better waste management practices are required to decrease and upcycle post-consumers’ food waste (catering and organic household waste), which is currently used for energy production or discharged as waste. The production of Hermetia illucens larvae (L.) (BSFL) was conducted in 15 batches at pilot scale. Furthermore, a feeding strategy experiment was conducted to optimize feedings and decrease handling, followed by a digestibility study for assessing the applicability of BSFL as a feed ingredient. About 190 kg of food waste was used to produce 79 kg of BSFL. The bioconversion of food waste into BSFL was found to be highly efficient, with feed conversion rate (FCR) values ranging between 1.7 and 3.6, when assessed on dry matter. The feeding experiment showed similar BSFL and insect frass production as well as similar FCR, revealing that a decrease in handling can be obtained if two feeding episodes are used. The digestibility of protein and fat was high at 86.2 and 90.4% and revealed that BSFL meal can be successfully used as a protein and fat source in feed for carnivore animals outside the food chain (e.g., pet food).
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