Mealworm Frass as a Potential Organic Fertilizer in Synergy with PGP-Based Biostimulant for Lettuce Plants

This study evaluates frass, a byproduct of mealworm rearing, as an organic fertilizer for lettuce. Experiments tested different frass doses, with and without a Bacillus-based biostimulant. Frass improved biomass and nutrient supply, but medium–high doses harmed root development. The biostimulant counteracted these negative effects, boosting growth and plant quality. Together, frass and biostimulants show strong potential for sustainable fertilization strategies.