A biochemical analysis of Black Soldier fly (Hermetia illucens) larval frass plant growth promoting activity

Abstract

Black Soldier fly (Hermetia illucens) larval (BSFL) frass separated from BSFL processed catering waste, and that recovered directly from larvae, was examined for its nitrogen, phosphate and potassium (N:P205:K2O), phytohormone and biogenic amine content, its plant growth promoting activity, and screened to test the hypothesis that bacteria characteristic of the genus Enterococcus, present in the biome of decaying catering waste and the larval gut, pass freely through the gut and are excreted in viable form into their frass. Its plant growth promoting activity was measured by comparing the growth of winter wheat berry (Triticum aestivum) grown in frass treated soil relative to that measured in untreated (control) soil. Its N:P205:K2O, biogenic amine and phytohormone composition were determined by standard soil analysis, HPLC and HPLC/GC-MS methodologies, respectively, and found to be too low to account for its plant growth promoting activity which induced a 11% increase in arial mass and shoot length in treated plants over controls. Colonies of Enterococci grew out on streaking frass collected directly from larvae on standard bile-esculin azide agar culture plates, confirming the hypothesis that viable Enteroccoci are excreted in their frass. Since Enterococci are capable of colonizing the rhizosphere and boosting the growth of plants on amendment into soil, these findings lend further insight into the underlying mechanism(s) accounting for the increased growth of plants growing in frass treated soils.