Hatching Methods of Black Soldier Fly Eggs: Implications for Industrial Rearing Efficiency

The black soldier fly (BSF) is a key species in circular economy models, where early developmental stages strongly influence production efficiency. Although most rearing protocols rely on moist substrates for egg hatching, BSF eggs can hatch without nutritive support. This study compared two hatching methods under controlled conditions to optimize egg-to-larvae conversion at industrial scale. Eggs (<24 h old) from an in-house colony were collected using standardized 3D-printed oviposition devices (Kinsect S.r.l), weighed, and incubated in plastic containers (20 × 30 cm) using either "wet hatching" (WH; Gainesville diet, 70% water) or "dry hatching" (DH; non-nutritive support). Experiments were conducted at 27 °C and 70% relative humidity with ten replicates per treatment. In WH, containers with fresh wet substrate beneath the oviposition platforms were replaced daily from first hatch to day 5, and larvae dropping into the substrate were counted daily. In DH, neonates dropping onto the container surface were collected daily, weighed, and transferred to WH substrate to estimate larval counts. Day-specific counts reflected larval recovery integrating hatching timing with early survival and handling effects rather than representing pure hatching rates. Larval output was expressed per gram of eggs, and survival was calculated using a literature-based egg weight (0.028 mg). Total larval output, survival and day- specific counts were compared between treatments using independent samples t-tests Total larval output and survival did not differ significantly (WH: 20,075 ± 4,531 larvae g−1 eggs, 56 ± 13%; DH: 18,053 ± 4,301 larvae g−1 eggs, 51 ± 11%). Temporal patterns differed: WH showed earlier larval recovery on day 3 (7,783 ± 3,289 larvae), whereas DH had no larvae. By day 4, DH surpassed WH in larval recovery (16,844 ± 4,356 vs. 11,920 ± 5,710 larvae), and on day 5, DH still yielded higher counts (1,208 ± 583 vs. 372 ± 316 larvae), with no larvae observed thereafter. Although cumulative output was similar, dry hatching concentrated larval emergence, reduced contamination risk, and allowed flexible handling. These results suggest that dry hatching can be implemented in industrial BSF production to synchronize larval availability and improve operational efficiency, while minimizing challenges related to early larval mortality, uneven distribution, and substrate contamination.