Microbial community dynamics during decomposition of insect exuviae and frass in soil

As the mass-rearing industry of insects for food and feed is expected to grow, residual streams associated with this activity will become increasingly available. Before these residues can be used as organic amendments, more knowledge on the decomposition and dynamics of the involved microbial communities is needed. This study investigated decomposition, N-mineralization, and fungal/bacterial community composition during 16 weeks of incubation of exuviae and frass of black soldier fly, mealworm, and house cricket in arable soil. Decomposition of insect residues in litterbags was rapid, with more than 50% weight loss in 2 weeks. Accumulation of mineral-N from insect materials distributed in the soil was also highest during the first 2 weeks, but it was more profound for exuviae than their frass counterparts. Soil amendment with insect residues enriched soil microbial inhabitants belonging to Gammaproteobacteria, Bacilli, Actinobacteria, and Mortierellomycetes. Comparison of microbial community composition in soil amended with sterilized and nonsterilized mealworm exuviae indicated that the presence of microbial propagules in the exuviae had no significant influence on the composition of bacterial decomposers and a minor, but significant impact on fungal community composition. Overall, our results reveal a good prospect of using insect residual streams as soil amendment.