Nutritional content and bioconversion efficiency of Hermetia illucens (Diptera: Stratiomyidae) : harvest as larvae or prepupae?

Abstract

Most research on nutritional composition that relates to use of fly larvae as an alternative ingredient in animal feed has focused on the prepupal stage of Hermetia illucens. However, crude protein and lipid content of H. illucens larvae vary dramatically during larval development, and little evidence has been presented to support use of prepupae for animal feed. The aim of this study was to establish the nutritional value of larvae and prepupae of H. illucens reared on organic waste streams for use in animal feed. The effect of harvesting of either larvae or prepupae on waste reduction was also measured. Freshly hatched neonates (90 mg) were placed on 12 kg of mixed pre-consumer waste and held at 28°C. Moisture content, crude protein, crude lipid, ash, fibre, survival, total biomass, individual larval biomass, waste reduction and bioconversion on a dry matter basis were determined and compared between larvae harvested on Day 15 and prepupae harvested on Day 20. Prepupae had higher fibre content than larvae, while moisture content, crude protein, crude lipid and ash did not differ between the two groups. Total biomass was higher in larvae than in prepupae due to mortality between the two stages. Size of individual larvae was very similar between the two groups. In terms of nutritional content or biomass production, it is not detrimental to harvest larvae early or to harvest a mixture of larvae and prepupae or prepupae only. However, harvesting later, when larvae have become prepupae, would lead to a reduction in potential harvest and total biomass output, especially as survival declines over time. Bioconversion and waste reduction did not differ between Day 15 and Day 20, indicating that nutrient recovery from waste was not improved by harvesting at the prepupal stage.