Variation in strain performance and estimates of heritability of body size indicate considerable potential for genetic improvement of the black soldier fly (Hermetia illucens)

The black soldier fly (Hermetia illucens L., Diptera: Stratiomyidae) has emerged as a key species in the sustainable protein industry. Whilst genetic variation in performance has been suggested, the extent of heritability and genotype-by-environment (G × E) interactions in this species remains relatively unexplored. This study used a standardised split-brood design and linear mixed effect models to evaluate genetic effects at the between- and within-strain levels across diets as environments. In the first experiment, three strains were tested across three diets to identify strain × diet interactions. Significant interactions were observed for larval weights, development, family viability and protein content, indicating differential adaptability of strains to specific dietary substrates. The second experiment expanded on these results by testing two strains across three diets, but with a larger number of families (n = 23) and individual-level phenotyping of body size using 4018 individuals. Moreover, crude estimates of narrow-sense heritability (h²) were obtained using a full-sibling design. Heritability estimates for larval and prepupal body size were high: h² = 0.67 and 0.78, respectively, although the estimates will be upwardly biased if there is substantial non-additive genetic variation. Together, our results highlight the potential for selective breeding to optimise black soldier fly strains for industrial applications, supporting the growth of this novel industry.