Selenium and Zinc Biofortification in Black Soldier Fly Larvae

Insects are natural bio-accumulators of different micro nutrients and minerals. Minerals such as selenium (Se) and zinc (Zn) are essential for both animals and humans. Therefore, the aim of this study was to examine the Zn and/ or Se bioaccumulation potential of black soldier fly larvae (BSFL) reared on fortified substrates. To study this, BSFL were reared on five distinct substrates: I) control substrate (CTR) of plant-ingredients (Gainesville diet); 2) Okara and potato waste-based substrate (OP); 3) OP fortified with 150 mg/kg of Zn (Zn); 4) OP-Se fortified with 0.3 mg/kg of Se (Se); and V) OP fortified with 150 mg/kg of Zn + 0.3 mg/kg of Se (SeZn). Each treatment had five replicates. Se was fortified in the inorganic form of sodium selenate, while Zn was administered in the form of zinc sulfate monohydrate. All experiments were conducted under conditions of darkness (26°C, 60% relative humidity), and the growth performance of the larvae was observed. The analysis found that the mean larval weight was unaffected by the treatments. However, the CTR group exhibited significantly higher total weight at the end of the trial (P<0.05). The survival rate was not affected by the treatment. The nutritional composition of the larva was affected by the type of substrate and not the fortification of Se and Zn. Larvae reared on OP substrates had elevated levels of lipids (P<0.05) and reduced ash content (P<0.05) compared with the other groups. Furthermore, the fortification of Se and/or Zn affected their bioaccumulation in the harvested larvae. The results confirm that OP, when supplemented with Zn and Se, is a suitable substrate for BSFL, resulting in “fortified” larvae characterised by a favourable nutrient profile. However, it is imperative to consider the content of lipids, Zn and Se when utilising BSFL for feed production. Nevertheless, further research is required to ascertain the unintended effects of these substrates on BSFL metabolism.