Does What You Eat Affect How You Mate? Disentangling the Interactions Between Diet-Induced Phenotypic Plasticity and Adult Reproductive Strategies in Black Soldier Flies

Phenotypic plasticity enables organisms to response to environmental variations by generating a range of phenotypes from a single genotype. In holometabolous insects, traits that influence larval plasticity may hold relevance for adult life history strategies. We present a comprehensive investigation into phenotypic plasticity in black soldier flies, a species known for its efficient waste-to-biomass conversion in the larval stage. Here, we document adult sex-specific plastic responses and reproductive strategies shaped by larval diets. We examined traits including adult body size, reproductive organ development, sperm length, mating behaviours, egg production and other life history parameters across different treatments. Our findings reveal notable sex-specific differences in phenotypic plasticity, with females showing increased plasticity in reproductive investment. Furthermore, males and females differed starkly in allometric growth and weight ratio of reproductive organs. Diets that facilitated longer male lifespans also prompted earlier male emergence suggesting an interplay between lifespan and degree of protandry. This maximizes the overlap of male and female lifespans, thereby enhancing mating success in diverse environmental conditions. Our results reveal plastic responses in mating behaviours, where diets producing smaller adults, smaller reproductive organs, and shorter sperm correlated with significantly enhanced mating effort and performance. This study highlights the complex interactions between nutrition, development, and reproductive strategies, and has significant implications for the insect bioconversion industries.