Valorization of residual substrate from the rearing of black soldier fly (Hermetia illucens) in plant cultivation: microbiological and chemical quality and impact on plant growth

Insects are produced on an industrial scale for applications in food, feed, pet food and for the extraction of biochemicals. By far the most widely reared insects are the larvae of the black soldier fly (Hermetia illucens), which can be produced on a wide range of organic streams (substrates). When the larvae are harvested at the end of a cycle, a residual product called 'residue' or 'frass' remains. This residue consists of larval faeces, unconsumed substrate and molt skins. Evidence exists in literature that this material can be meaningfully used as a soil improver or fertilizer in plant cultivation, but there are still many questions on that application. The residue has to be subjected to a hygienic step. Heating for 1h at 70°C is suggested as a reference treatment. Alternative treatments are also possible. In the first place, the impact of such treatments on the microbiological and chemical quality (with a focus on the chitin content) of the residue will be studied. Secondly, the effect of the use of the treated or untreated residue on the growth of bean plants (Phaseolus vulgaris) will be investigated. The effect of the residue on the growth of the plants in normal conditions and when they are subject to drought stress will be examined, both at the physiological and biochemical level. In a last part of the PhD useful bacteria in the residue will be searched for and isolated, with the aim to use them as biostimulants.