Insect Frass as an Agricultural Resource Against Abiotic and Biotic Crop Stresses: Mechanisms of Action and Possible Negative Effects

The relentless growth of the global population, coupled with increasing biotic and abiotic stresses on crops, poses a major challenge: enhancing agricultural productivity while mitigating these stresses and reducing chemical inputs. Insect farming has led to the large-scale production of insect frass, a nutrient-rich by-product with biofertilizer and biostimulant potential. This review examines the effects of frass on plant stress responses, including its mechanisms of action and possible negative effects. Regarding abiotic stress, frass from certain insects improves plant resilience to drought, waterlogging and salinity, while facilitating heavy metal sorption and complexation in contaminated soils. For biotic stress, frass contains antifungal, antibacterial, and nematicide compounds, as well as entomopathogenic fungi, all of which can reduce pest survival. Additionally, frass activates plant defense mechanisms, such as the increased expression of the defense-related genes involved in stress signaling and immune activation. However, some studies report negative effects, including pathogen dispersion, pest attraction, and the inhibition of beneficial microorganisms commonly used as biopesticides. Despite these risks, frass is a promising alternative for sustainable agriculture, reducing chemical dependency while improving plant resilience. Nevertheless, further research is needed to mitigate its potential risks and optimize its agricultural application.