Inbreeding without consequences? Limited effects of inbreeding on life-history and performance traits in Hermetia illucens

Abstract Background The black soldier fly ( Hermetia illucens ) is key to the circular bioeconomy, but intensive mass-rearing risks genetic drift and inbreeding depression. While early domestication causes rapid genetic erosion, long-term colonies often persist without collapsing, potentially due to the purging of deleterious alleles. Whether highly domesticated strains retain susceptibility to residual inbreeding depression remains unclear. This study evaluated how acute full-sib mating impacts life-history, physiological, and reproductive traits in a laboratory strain colonized for over 64 generations. Results Full-sib mating triggered no severe phenotypic declines or compromise growth curves. Developmental durations differed significantly across most ontogenetic stages, but absolute variations were marginal and remained within 1.2 days. Inbred larvae exhibited higher substrate reduction and lower feed conversion efficiency (ECI), indicating elevated metabolic costs. Final larval and adult weights were reduced in the inbred group, although natural sexual dimorphism remained the primary driver of body weight variance. Reproductive parameters and fecundity did not exhibit significant differences between groups. Clutch sizes and oviposition patterns only differed descriptively. In contrast, adult survival was severely impacted; inbred flies showed reduced lifespans and an earlier median lethal time (LT 50 ) in females. Conclusions Acute inbreeding does not cause an immediate production collapse in long-term domesticated strains, demonstrating phenotypic resilience that is highly valuable for managing sudden population bottlenecks. Nevertheless, metabolic inefficiencies and reduced adult longevity indicate that residual inbreeding depression persists and can compromise survival and resource utilization. These findings provide a foundational population biology perspective for optimizing the genetic management and long-term stabilization of industrial insect rearing systems.