Productive performance of Tenebrio molitor larvae in response to the protein level in the substrate

Insect production for animal feeding is receiving increasing interest worldwide. The dietary protein level is a key factor influencing overall production and feeding costs. Thus, a growth performance trial was conducted with Tenebrio molitor larvae for 28 days using substrate feeds based on wheat grain and barley straw with increasing levels of soybean meal to reach 100 (10P), 120 (12P), 140 (14P) and 160 (16P) g crude protein (CP) per kg dry matter (DM). Four trays per treatment, with 40 larvae and 24 g substrate, were set up. Average mortality was 0.142 and did not differ among treatments. Feed intake decreased linearly (L, P <0.001) and quadratically (Q, P <0.01) and larval growth (mg/d per larvae) tended to decrease (Q, P =0.065) as the dietary CP increased from 100 to 160 g/kg DM. Protein intake, however, increased (L, P <0.001) with the CP content of the diet. Feed to gain ratio decreased (L, P <0.01) as the dietary CP level increased but total production per tray of DM, CP or ether extract, was not affected. In conclusion, an increase in the dietary CP content over 100 g/kg DM by including soybean meal in the substrate might not be needed to optimise larval growth. A CP content in the diet of 100 g/kg might improve the economic results because of lower feeding costs.