Performance of larvae of different black soldier fly genotypes on different feed substrates – a first step towards genotype-specific feeding recommendations

Insects are considered as promising future dietary protein source for poultry and aquaculture feeding. The most wide-spread source are black soldier fly (BSF) larvae. Literature indicates that life history performance and body composition of BSF larvae are extremely variable. This restricts the prediction of the nutritional quality of insect-based feeds and economic performance in general. Feed substrate for BSF larvae is one major driver for the observed variation, as documented in a number of reports. Yet, pronounced differences were still found for comparable feed substrates across studies. These have mostly been attributed to different experimental settings whereas potential influences of BSF genetics have largely been neglected, also because appropriate monitoring tools were lacking. In a fully crossed factorial design we compared the performance of four genetically distinct BSF strains (inferred from newly developed polymorphic nuclear genetic markers) grown on three feed substrates with six replicates each. Various growth and compositional traits were determined. Both factors, feed substrate and BSF genetics, as well as the interaction between the two, were found to have a highly significant impact on virtually all investigated life history traits (mortality, growth dynamics, average larval weight) and body compositional characteristics (dry matter, organic matter, crude protein, ether extract) of harvested larvae. The same applied for feed conversion ratio, nitrogen efficiency, degradation of fibre in the digestive tract as well as nitrogen and carbon emissions. Frequently detected stronger differences between genotypes within feed substrates than within genotypes across feed substrates show that BSF genetics is key for interpreting and triggering outcomes. However, the findings also indicate that larvae of different genetic origin have different nutritional requirements, further suggesting that optimal feeds may vary across BSF strains, or vice versa, that based on the choice of the latter, different available rearing substrates may be exploited with different success. Our results imply that efficiency and sustainability of BSF productions may be substantially increased by considering BSF genetics and interactions with feed substrate composition. They provide ideas for targeted objectives to be implemented in efficient BSF larvae production. Ample indication for BSF genotypespecific effects also provides valuable insights for pinpointed BSF breeding strategies.