Use of the black soldier fly as a bioconversion tool at the industrial scale

The larval stage of the black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), are extremely voracious and able to consume a wide range of organic materials, ranging from fruits and vegetables to animal remains and manure. This ethological characteristic is particularly interesting for waste management at an industrial scale. The extraordinary ability to accumulate high levels of proteins and lipids, allows the use of resulting larvae as animal feed. Vegetables and fruit by-products are promising rearing substrates for insects produced for this purpose. In order to examine the effect of different diets on insect growth, lipids and larval proteins content and to evaluate pH values changes in diets used, approximately 10,000 larvae/unit were reared on six substrates: 1) apple, 2) banana, 3) spent grain from brewery waste, 4) apple and banana, 5) apple and spent grain, 6) banana and spent grain. High growth rate was observed in all the tested diets with differences among larvae final weights. Larvae fed with the apples and spent grain mix reached the highest final weight (1653 g ± 354.9366 g), the highest percentage of crude proteins (48.01% ± 3.7%) and showed the highest amount of diet bioconversion, while larvae fed with spent grain showed the highest growth rate, reaching their maximum weight in only six days (1.75 g ± 0.22 g/10 larvae). Although the initial pH value was dependent on the six different substrates, all tested diets reached a basic pH value at the end of the trial. This study shows that waste management through black soldier fly bioconversion processes represents a new economically important resource and opens new perspective of a sustainable environmental friendly industrial development. Moreover, the study demonstrates that the choice of the substrate has a direct influence on larval macronutrient composition and therefore on the biological market value.