Jiogue, J.; Merle, M.; Konde, M.; Foughar, M.; Genevey, C.; Permana, A.; Maquart, P.-O.; Filee, J.

The black soldier fly, Hermetia illucens, is increasingly valued in applied entomology due to its remarkable capacity to upcycle organic waste and for high nutritional value of its larvae. As a result of global expansion and domestication, the species now displays substantial genetic diversity, yet performance differences between strains remain poorly documented. This study aimed to better understand the relationship between genotype and phenotype, as well as their interaction, to support the improvement of its domestication. Five distinct strains collected from the wild by artisanal farmers or obtained from industrial farms were genetically characterized using whole genome sequencing. These analyses revealed high genetic divergence based on mitochondrial genome and SNP nuclear genome phylogeny. To assess phenotypic performance, the strains were reared on three diets differing in nutritional value: poor (alfalfa meal), intermediate (wheat bran) and rich (chicken feed) and their growth rate was assessed. At harvest, we evaluated different life history traits including survival rate, average larval mass, feed conversion ratio, substrate reduction and bioconversion rate. Statistical analyses revealed strong effects of both diet and strain (p < 0.001), but the key result was the pronounced strain by diet interaction. Performance varied drastically depending on substrate quality: some strains showed high versatility across all diets, while others performed mainly on nutrient-rich substrates or excelled in substrate degradation. In contrast, other strains displayed more specialized profiles, with marked sensitivity to fibrous diets. These contrasted reaction norms highlight that diet performance cannot be interpreted independently of the strain genetics. Overall, these findings underscore the value of preserving diverse local genetic resources and the need for improved molecular tools to guide strain selection.