Perspectives on microbial community changes produced by Hermitia illucens frass and their impact on soil suppression against Fusarium oxysporum f. sp. lactucae

BACKGROUNDOrganic soil amendments rich in chitin have demonstrated significant potential promoting suppressive soils. Suppressive soils inhibit the growth and activity of soilborne pathogens, being a sustainable alternative to chemical fumigation. The aim of this study was to determine the ability of frass produced from black soldier fly larva (BSFL), a novel chitin‐rich soil amendment, and other amendments enriched in chitin to promote suppressive soils against Fusarium oxysporum f. sp. lactucae (Fol) and to assess the role of the microbial community on suppressiveness.BSFL frass, compost, chitin and a mixture of compost and chitin were mixed with soil. Some soil mixes were incubated for 4 months to promote further changes in the microbial community structure. Then, incubated and non‐incubated soil mixes were inoculated with Fol to study the reduction of disease severity caused by Fol on lettuce and the evolution of soil microbial communities.RESULTSSoils that were incubated with chitin or BSFL frass showed a significant decrease in Fol population density and disease severity compared to the unamended and non‐incubated soils (P < 0.05). Analyses of microbial community of soils incubated with chitin and BSFL frass were compared to the non‐amended soil, they were enriched on fungal and bacterial OTUs of microorganisms known as biocontrol agents such as Mortierellales, Trichoderma spp., Chaetomium globosum, Streptomyces, Bacillus and Sphingomonas.CONCLUSIONSoil incubated with chitin and BSFL frass seem to promote suppressiveness against Fol. Further studies on chitin or BSFL frass concentration, incubation period or amendment rate are needed to improve soil suppressiveness. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.