Effect of diet composition on growth and temperature development in black soldier fly (Hermetia illucens) larvae rearing

Black soldier fly (BSF) larvae can use food by-products or residues as a substrate for growth, and these larvae can be used as a protein source for farmed animals. Therefore, their use in animal feeding is considered a strategic solution to improve the sustainability and efficiency of animal production. Insects must be farmed under strict environmental conditions: temperature, humidity, light, and aeration are important factors affecting larvae welfare and the efficiency of their bioconversion. Diets (i.e., substrates) should be formulated carefully since they have a direct effect on microclimatic conditions and larval development. The goal of this trial was to test four different diets: control (poultry feed), vegetable (carrots, potatoes, and brewer’s spent grain: 1:1:1), carnivorous (ground epiglottis and cod waste; 1:1), omnivorous (vegetable: carnivorous; 1:1) and assess their effect on larval growth performance, chemical composition, and substrate temperature. BSF Larvae (6-day-old) were randomly chosen and allocated to the 4 diets (4 plastic containers, i.e. replicates, per substrate, each measuring 32 x 23 x 12 cm, containing 2000 larvae and approximately 2 kg of substrate). The environmental conditions were kept at 27±1°C and 65±5% RH, with photoperiod of 12L:12D. The temperature of each container was measured twice daily (morning and afternoon) for the entire experimental period (7 days) using a thermal imaging camera. Each container was aerated daily to ensure that the substrate was thoroughly moisturized and rotated. The preliminary results showed that the carnivorous diet resulted in significantly lower growth performances (-30% larval biomass at the end of the trial compared to the average of the other three groups; P<0.01). The chemical analysis revealed that these larvae had a significantly higher dry matter content (DM; about 44%) than the other groups (P<0.01), implying a high larvae meal yield. The vegetarian diet had the lowest DM (about 22%); which was significantly lower than the other diets (P<0.01). In terms of substrate temperatures, the control diet showed considerably lower average temperatures (P<0.01) compared to the omnivorous and vegetable diets. However, this did not seem to affect larvae growth in this substrate. These preliminary findings showed an effect of the diets on substrate temperature and larvae growth; however, the chemical analyses currently in progress will provide further insights on larvae composition.