Mineral composition in black soldier fly (Hermetia illucens) larvae and resulting frass from fruit and their peels

Farming black soldier fly (Hermetia illucens) larvae (BSFL) leads to two products; BSFL as high quality protein/lipid and leftover `frass' as an organic fertiliser. Little information exists on the influence of different substrates on the mineral composition of these products. In this study, orange or banana peels, fruit and in their combination were fed to BSFL for two weeks. BSFL survival was high (95-100%) and not significantly different among treatments. Peels of either fruit led to significantly shorter and lighter BSFL. However, banana peels significantly increased P, K, Ca, Na, Mn and Mg in BSFL compared to all others. In the frass, the P content was unaffected by treatment while K was significantly highest and lowest when banana and orange peels were composted with BSFL, respectively. Meanwhile, Cu and Zn, which are often limiting nutrients, were significantly highest and lowest in the orange peel/fruit treatment and banana treatment, respectively. In all cases, the tested minerals in BSFL were substantially higher than the initial substrate, especially for Fe, and the mineral levels generally reflected those in the substrate. Although fruits and their peels are not recommended as the only food source for BSFL and provided little Fe, Ni or Cu, the peels could be viewed as valuable supplements to enhance the P, K, Ca, and Mg content in BSFL and frass.